Table of contents

Although the roots of this scientific field go back to the end of the nineteenth century when A G Bell discovered the photoacoustic effect generated by the absorption of modulated light in a sample, major and rapid progress only occurred since the mid-1970's when the photoacoustic effect in condensed matter was put on a firm theoretical basis by A Rosencwaig and A Gersho. Since that time the fields of photoacoustics and the related fields of photothermal phenomena and laser ultrasonics have grown enormously. A multitude of ways of generating the effects has emerged using all kinds of radiation. Likewise, the diversity in methods for the detection of the generated thermal and acoustic waves has increased dramatically. One of the reasons for the popularity of the photoacoustic and photothermal field is the wide applicability of these techniques for fundamental and applied research. At this moment, the field has become really multidisciplinary and it is safe to say that it has reached a mature state with an established position in measurement technology and materials characterization. This conference as well as the ones before reflected this large diversity in the program topics and the research disciplines of the participants.

This 15th International Conference on Photoacoustic and Photothermal Phenomena was held on a campus of the Catholic University of Leuven in Belgium in the week of 19–23 July 2009. During the conference 15 tutorial lectures, 8 plenary lectures, 36 invited talks, 120 oral and 172 poster communications were presented. The conference was attended by 252 participants from 38 countries from all over the world. During a special session award lectures were presented by winners of the prizes of the International Photoacoustic and Photothermal Association (IPPA). Winners of the senior prize were A Mandelis, D Fournier and A C Boccara. The winner of the junior prize was T W Murray.

The editors of the proceedings of this conference believe that the published papers provide significant contributions to the field of photoacoustic and phothermal phenomena and can serve as a good introduction to scientists outside of the field.

C Glorieux J Thoen Editors

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The technique of Deep Level Photo-Thermal Spectroscopy (DLPTS) is extended to the low temperature region in order to cover several defect states in semi-insulating GaAs. Measurements are taken at three different modes, temperature-scanned, pulse-rate-scanned, and time-scanned DLPTS. It is demonstrated that each mode provides unique information about the defect configuration, and the combination of the different modes offers a powerful tool for DLPTS studies of physical optoelectronic processes in SI-GaAs. The non-exponentiality/broadening of experimental data is extensively studied using the two prevalent broadening theories: the stretched exponential and the Gaussian distribution of activation energies. A hierarchical carrier emission model has been proposed for the stretched exponential behavior. Simulations indicate that the two broadening theories exhibit roughly similar broadening effects and good fits to the experimental data. The origin of this similarity indicates an ergodic equivalence of random energy distribution and the constrained hierarchical emission process.

To achieve a spatially resolved measurement of magnetic properties two different pho-tothermal approaches are used which rely on heat dissipated by magnetic resonance absorption or thermal modulation of the magnetic properties, respectively. The heat produced by modulated microwave absorption is detected by the classical photothermal methods such as photoacoustic effect and mirage effect. Examples comprise depth resolution of the magnetization of layered tapes and visualisation of magnetic excitations in ferrites. The second photothermal technique relies on the local modulation of magnetic properties by a thermal wave generated with an intensity modulated laser beam incident on the sample. This technique has a higher spatial resolution and sensitivity and has been used to characterize lateral magnetic properties of multilayers and spintronic media. To extend the lateral resolution of the ferromagnetic resonance detection into the nm-range techniques have been developed which are based on the detection of the modulated thermal microwave response by the thermal probe of an atomic force microscope (AFM) or by detection the thermal expansion of the magnetic sample in the course of the resonant microwave absorption with an AFM or tunnelling microscope. These thermal near field based techniques in ferromagnetic resonance have been successfully applied to image magnetic inhomogeneities around nano-structures and to measure the ferromagnetic resonance from magnetic nano-dots.

This thermal wave conference dates back to 1979 when it was held for the first time in Ames/Iowa. All participants have this area still in mind, maybe not only due to the landscape but also to the cheerleader courses held parallel to our sessions on the same campus. So after 30 years time has come to review some thermal wave developments that started back in 1979 and to see how they affected other fields, e.g. NDE. This paper traces the origin of lock-in thermography back to the roots which is essentially to show how initially two different areas (thermal waves and thermography) merged partially together to become a powerful tool for modern NDE.

Several instrumental methods used to obtain photoacoustic (PA) infrared spectra of solids are discussed in this article. We describe modulation frequency effects, synchrotron infrared PA spectroscopy, amplitude and phase modulation, and the use of infrared lasers. These techniques allow the spectroscopist to acquire information that is often not obtainable using more traditional methods.

The salient features of periodically modulated photoacoustic (PA), photothermal radiometry (PTR) and photopyroelectric (PPE) methods are reviewed with emphasis on their use for characterization of layered samples. Using a general one-dimensional (1-D) heat diffusion model, explicit solutions for up to six layers are given in terms of thermal impedances. Two typical model configurations can be transformed and combined using symmetry properties in order to match a particular excitation/cell configuration couple. Different special cases allow for simultaneous measurement of two thermal parameters. For temperature-dependent investigations the direct temperature-conversion feature of the PPE method is advantageous. We show results on the temperature calibration of LiTaO₃ and PVDF pyroelectric sensors.

One of the ever present problems in laser ultrasonic techniques is the relatively poor signal to noise ratio, which means that in many cases the data acquisition rates are unacceptably slow or the necessary laser power can damage the sample. Here we present our approach to parallelising the detection process which can greatly speed up measurement times. We describe results using both a commercial detector array and custom arrays designed in house. The approach we have taken is generally applicable for a range of pump probe experiments and we give examples where applicable

Pulsed photothermal profiling involves reconstruction of temperature depth profile induced in a layered sample by single-pulse laser exposure, based on transient change in mid-infrared (IR) emission from its surface. Earlier studies have indicated that in watery tissues, featuring a pronounced spectral variation of mid-IR absorption coefficient, analysis of broadband radiometric signals within the customary monochromatic approximation adversely affects profiling accuracy. We present here an experimental comparison of pulsed photothermal profiling in layered agar gel samples utilizing a spectrally composite kernel matrix vs. the customary approach. By utilizing a custom reconstruction code, the augmented approach reduces broadening of individual temperature peaks to 14% of the absorber depth, in contrast to 21% obtained with the customary approach.

We have developed a new method for in-vivo human nail characterization by using opto-thermal transient emission radiometry (OTTER) and condenser-chamber TEWL (trans-dermal water loss) method – AquaFlux. With OTTER, we can measure nail water content, nail water concentration depth profiles, as well as topically applied solvent penetration through nail. With AquaFlux, we can measure nail transonychial water loss (TOWL). Combining the water content results with TOWL results, we can get the water diffusion coefficient of nail. Measuring the water diffusion coefficients of nail at different nail water concentration levels can also yield information on how nail diffusion coefficients change with water content. We will present the theoretical background, and experimental results on water concentration depth profile in nail, as well as topically applied solvent penetration through nail.

Photoacoustic Imaging (also known as thermoacoustic or optoacoustic imaging) is a novel imaging method which combines the advantages of Diffuse Optical Imaging (high contrast) and Ultrasonic Imaging (high spatial resolution). In photoacoustic imaging, a short laser pulse excites the sample. The absorbed energy causes a thermoelastic expansion and thereby launches a broadband ultrasonic wave (photoacoustic signal). This way one can measure the optical contrast of a sample with ultrasonic resolution. For collecting photoacoustic signals our group introduced so called integrating detectors a few years ago. Such integrating detectors integrate the pressure in one or two dimensions (line or plane detectors). Thereby the three dimensional imaging problem is reduced to a two or a one dimensional problem for the pressure projections for line or plane detectors, respectively. Several reconstruction methods like Fourier or F-SAFT reconstruction or back projection are used for the two dimensional first step, but the model-based time reversal method shows a significant advantage: acoustical heterogeneity and attenuation, which both cause blurring of reconstructions, can be directly implemented in the reconstruction method. The integrating detectors are mainly optical detectors and thus can provide a high bandwidth up to several 100 MHz. Using these detectors the resolution is often limited by the acoustic attenuation in the sample itself, because attenuation increases with higher frequencies. For thin layers, small cylinders, and small spherical inclusions the effect of attenuation in human fat is simulated and the influence of dispersion on image reconstruction is shown.

We report on calorimetric measurements carried out in an upgraded photopyroelectric setup enabling the determination of the frequency dependence of the specific heat and of the latent heat exchanged over first order transitions as well as the simultaneously determined nematic correlation length obtained from light scattering measurements. It has been applied to the study of the Nematic-Isotropic transition of 8CB liquid crystal confined in a silica nanoparticle network, where the specific heat shows a double peak structure.

Aerosols are particles in the size range of nanometers to some micrometers, suspended in air or other gases. Their characterization and separation according to different physical and chemical properties is of great interest for environmental analysis and certain industrial applications. Photo-thermophoresis is an optothermal effect, which occurs when aerosol particles are illuminated by intense light. Locally inhomogeneous heating, resulting in locally increased impingement rates of the gas molecules, generates driving forces. These photophoretic forces can move fine particles either towards or away from the light source. We employ this effect for characterization and separation according to optical and thermal properties of aerosols. We hope to establish this new approach as a helpful supplement to the existing separation methods based on electrical, thermal or flow field forces.

Coherent phononic oscillations in Bi and Ag nanowires were studied with a femtosecond pump-probe technique. In Bi nanowires laser pulses of 50 fs excited simultaneously acoustic oscillations at a frequency of about 9.5 GHz and optical phonons in the THz range. The transmission of nanowires on a glass substrate and the light scattered from free standing nanowires were measured. In Ag nanowires laser-induced acoustic oscillations at different excitation levels were studied. The observed reduction of the oscillation frequency at higher pump energy was related to a transient softening of the material. This was directly confirmed for optical phonons by experiments with a pre-pump pulse of variable energy, producing different excitation densities.

Spatially resolved photo-carrier techniques, in which a modulated and tightly focused laser beam with photon energy larger than the band gap of the semiconductor material under investigation is employed to generate free carriers, are applied to the simultaneous determination of the electronic transport properties of semiconductor wafers, that is, the carrier lifetime, the carrier diffusivity, and the front surface recombination velocity. The simultaneous determination is fulfilled by measuring and multi-parameter fitting the modulation-frequency-dependent three-dimensional distribution of photo-generated free carriers in a semiconductor wafer to a rigorous three-dimensional theoretical model. The uncertainties of the fitted parameter values are analyzed by investigating the dependence of a mean square variance including both amplitude and phase errors on the corresponding transport parameters and compared to that obtained by the conventional frequency-scan approach, in which only the frequency dependence of the amplitude and phase of the photo-carrier signals are recorded at the excitation spot. Both theoretical simulations and experimental results show that the accuracy of the simultaneous multi-parameter determination is greatly improved by the spatially resolved information of the photo-generated free-carrier diffusion in the semiconductor wafers.

In this work, we present a short review of the recent development of the theoretical models for top-hat cw laser induced spectroscopies of thermal lens and thermal mirror. With the same probe and top-hat excitation lasers, an apparatus is set up to concurrently measure both thermal lens and thermal mirror effects of transparent samples. With the theoretical models and the experimental apparatus, not only optical and thermal properties are measured, but also the fluorescence quantum coefficient and the temperature coefficient of the optical path length of a fluorescent sample are simultaneously determined with no need of any reference sample. Mechanical properties also could be measured. Opaque samples are also studied using top-hat cw laser thermal mirror and top-hat photothermal deflection techniques to determine thermal properties (e.g., thermal conductivity and unit volume specific heat). This work shows that the combined top-hat cw laser photothermal techniques are useful for nondestructive evaluation of both transparent and opaque samples with a less expensive non-TEM₀₀ Gaussian laser.

A measurement system for quantitative registration of transient and irreversible lens effects in DUV optics induced by absorbed UV laser radiation was developed. It is based on a strongly improved Hartmann-Shack wavefront sensor with an extreme sensitivity of ~λ/10,000 rms @ 193nm, accomplishing precise on-line monitoring of wavefront deformations of a collimated test laser beam transmitted through the laser-irradiated site of a sample. Caused by the temperature dependence of the refractive index as well as thermal expansion, the initially plane wavefront of the test laser is distorted into a convex or concave lens, dependent on sign and magnitude of index change and expansion. The observed wavefront distortion yields a quantitative measure of the absorption losses in the sample. Results for fused silica and CaF₂ are presented.

The mode-mismatched thermal lens technique(TL) has been used to study many semitransparent materials. Its theoretical development considers weakly absorbing materials, which introduce restrictions on the sample's optical thickness. However, the same equipment required by TL can be used to perform the thermal mirror (TM) experiment, which is useful to characterize materials with any optical absorption coefficient. In this work, we investigate a simple correction to be used in the TL model, making it possible to apply TL to a wide range of materials. Using TL and TM, we have determined the temperature coefficient of the optical path length (ds/dT) of a glass.

The photoacoustic (PA) effect is observed when modulated (or pulsed) light is absorbed by a sample inside a closed chamber and converted in heat, generating acoustic waves; PA measurements have been employed to evaluate transdermal penetration of topically applied drugs. Phonophoresis is the utilization of ultrasonic (US) energy to enhance absorption of drugs across the epidermal barrier, and its usefulness has been shown by PA measurements. The aim of the present work was to determine the characteristic absorption times of the anti-inflammatory Nimesulid (gel) in human skin, with and without help of therapeutic phonophoresis. After local cleaning, measurements were performed in the forearm of each volunteer before Nimesulid application and for different times after application through massage with the US equipment head; the protocol was repeated for the opposite forearm, but without US emission. Curves of the PA signal level as a function of time were adjusted by a Boltzmann equation, leading to the determination of the characteristic absorption time (about 12 minutes). No significant gain was observed in Nimesulid absorption with the utilization of US radiation, indicating that topic application of Nimesulid does not require the use of phonophoresis, due to the natural fast penetration of the Nimesulid gel.

Cystic fibrosis (CF) is an autosomal recessive inherited disease that increases viscoelasticity of pulmonary secretions. Affected patients are required to use therapeutic aerosols continuously. The expression of ABH glycoconjugates in exocrine secretions determines the nature of part of the carbohydrates present in these secretions, allowing the classification of individuals into the so-called "secretor" and "non secretor" phenotypes. The aim of this work was to employ photoacoustic (PA) measurements to monitor the solubilization kinetics of pulmonary secretions from CF patients, analyzing the influence of the secretor status in the solubilization kinetics of samples nebulized with different therapeutic aerosols. Sputum samples were obtained by spontaneous expectoration from positive and negative secretor CF patients. Each sample was nebulized with i) tobramycin, ii) alpha dornase, and iii) N-acetylcysteine in a PA cell; fitting of the data with the Boltzmann equation led to the determination of t₀ (typical interaction time) and Δt (solubilization interval) for each curve. Differences between the secretor and non-secretor phenotypes were statistically significant in the groups for tobramycin and alpha dornase, but not for N-acetylcysteine. Results show that the secretor status influences the solubilization of pulmonary mucus of CF patients nebulized with tobramycin and alpha dornase.

Accidental presence of small quantities of different allergens such as beta-lactoglobulin in food products is a problem for unaware allergic consumers. Therefore, sensitive methods are needed for detection of trace quantities of allergens. By implementing TLS detection into a FIA system, the sensitivity of beta-lactoglobulin detection was improved. The use of different solvents in the FIA system, however, causes perturbations in the TLS signals. The aim of this research was to reduce the influence of spurious signals and to improve the detection limits of the analytical assay. The optimal performance of the FIA-TLS system for beta-lactoglobulin determination was achieved by using PBS buffer solutions (pH 7.5), which resulted in lowest limits of detection of 2 pM BLG and the total assay time of 10 min.

Photoacoustic spectroscopy was applied to study the physiological behavior of passion fruit when coated with edible films. The results have shown a reduction of the ethylene emission rate. Weight loss monitoring has not shown any significant differences between the coated and uncoated passion fruit. On the other hand, slower color changes of coated samples suggest a slowdown of the ripening process in coated passion fruit.

The combined use of a high power light emitting diode (LED) and the compact photoacoustic (PA) detector offers the possibility for a rapid (no extraction needed), accurate (precision 1.5%) and inexpensive quantification of lycopene in different products derived from the thermally processed tomatoes. The concentration of lycopene in selected products ranges from a few mg to several tens mg per 100 g fresh weight. The HPLC was used as the well established reference method.

The photoacoustic (PA) technique has been increasingly employed in biomedical studies, allowing in vivo skin measurements not easily performed with other techniques. It is possible to use PA measurements to evaluate transdermal delivery of products topically applied through manual massage or phonophoresis, that is the utilization of ultrasound waves to enhance drug absorption. The aim of this study was to analyze the influence of the period of phonophoresis application in the transdermal penetration of piroxicam gel. In vivo PA measurements employed a tungsten lamp as light source and a thin aluminum foil closing the PA chamber. The PA signals of the arm (i) clean; and (ii) after phonophoresis were utilized to estimate the concentration of piroxicam into skin. For all (4) volunteers, drug concentration in skin after phonophoresis application was the same for the different application times employed; in this way, phonophoresis for one minute seemed to be sufficient to enhance piroxicam penetration into skin. The actual amount of drug delivered into tissue depends on the person, suggesting a dependency with the skin type, which affects the PA signal level [2]. We conclude that drug delivery depends not only on the application method, but also on the specific skin type.

Since 1999, our group at the CADIFT, University of Toronto, has developed the application of Frequency Domain Photothermal Radiometry (PTR) and Luminescence (LUM) to dental caries detection. Various cases including artificial caries detection have been studied and some of the inherent advantages of the adaptation of this technique to dental diagnostics in conjunction with modulated luminescence as a dual-probe technique have been reported. Based on these studies, a portable, compact diagnostic instrument for dental clinic use has been designed, assembled and tested. A semiconductor laser, optical fibers, a thermoelectric cooled mid-IR detector, and a USB connected data acquisition card were used. Software lock-in amplifier techniques were developed to compute amplitude and phase of PTR and LUM signals. In order to achieve fast measurement and acceptable signal-to-noise ratio (SNR) for clinical application, swept sine waveforms were used. As a result sampling and stabilization time for each measurement point was reduced to a few seconds. A sophisticated software interface was designed to simultaneously record intra-oral camera images with PTR and LUM responses. Preliminary results using this instrument during clinical trials in a dental clinic showed this instrument could detect early caries both from PTR and LUM signals.

Dental caries involves continuous challenges of acid-induced mineral loss and a counteracting process of mineral recovery. As an emerging non-destructive methodology, photothermal radiometry and modulated luminescence (PTR-LUM) has shown promise in measuring changes in tooth mineral content. Human molars (n=37) were subjected to demineralization in acid gel (pH 4.5, 10 days), followed by incubation in remineralisation solutions (pH 6.7, 4 weeks) without or with fluoride (1 or 1000 ppm). PTR-LUM frequency scans (1 Hz – 1 kHz) were performed prior to and during demineralization and remineralization treatments. Transverse Micro-Radiography (TMR) analysis followed at treatment conclusion. The non-fluoridated group exhibited opposite amplitude and phase trends to those of the highly fluoridated group: smaller phase lag and larger amplitude. These results point to a complex interplay between surface and subsurface processes during remineralization, confining the thermal-wave centroid toward the dominating layer.

A Wavelength-Modulated Differential Laser Photothermal Radiometer (WM-DPTR) technique was used for non-invasive blood glucose monitoring in the mid-IR range, where the prominent absorption peak is glucose specific and isolated from other interfering peaks in human blood. The WM-DPTR method consists of the out-of-phase modulated excitation at two discrete wavelengths 9.5 μm and 10.4 μm (near the peak and the baseline of glucose absorption), generated from two quantum cascade lasers (QCL) and the differential emission detection through a thermal-wave upconversion process via a HgCdZnTe (MCZT) detector (2-5 μm). The differential method suppresses the background signal and reduces source-detection interference, thus enhancing glucose detection sensitivity. The results from aqueous glucose phantom (0–440 mg/dl) measurements demonstrate that both amplitude and phase of the WM-DPTR signal can be used for glucose detection. The dynamic range and the sensitivity of the glucose detection are influenced greatly by the laser intensity ratio and modulation frequency. The optimal intensity ratio for high sensitivity is ~1. Other laser intensity ratios increase dynamic range but reduce sensitivity. Sensitivity increases with frequency.

We compared five different skin hydration measurement techniques, namely OTTER, Fingerprint sensors, Corneometer, Nova, and Moisture Checker, in order to understand the correlations between different skin hydration measurement techniques and to understand the repeatability of each technique. The measurements are performed on different in-vivo skin sites from different volunteers and at different hydration levels. The repeatability of different techniques is achieved by measuring the same skin site repeatedly. The correlations between different skin hydration measurement techniques are achieved by plotting results from different techniques against each other. The different skin hydration levels are achieved through the recovery period after a skin immersive hydration.

We present our latest study on the thermal diffusivity effect in opto-thermal skin measurements. We discuss how thermal diffusivity affects the shape of opto-thermal signal, and how to measure thermal diffusivity in opto-thermal measurements of arbitrary sample surfaces. We also present a mathematical model for a thermally gradient material, and its corresponding opto-thermal signal. Finally, we show some of our latest experimental results of this thermal diffusivity effect study.

To date, most Photoacoustic (PA) imaging results have been from soft biotissues. In this study, a PA imaging system with a near-infrared pulsed laser source has been applied to obtain 2-D and 3-D images from both soft tissue and post-mortem dental samples. Imaging results showed that the PA technique has the potential to image human oral disease, such as early-stage teeth decay. For non-invasive photoacoustic imaging, the induced temperature and pressure rises within biotissues should not cause physical damage to the tissue. Several simulations based on the thermoelastic effect have been applied to predict initial temperature and pressure fields within a tooth sample. Predicted initial temperature and pressure rises are below corresponding safety limits.

Unlike other research groups we use so called integrating detectors which integrate the pressure along the detector. Such integrating line detectors can be realised by interferometers. We developed fiber-based integrating detectors for photoacoustic imaging which are easy to handle and are more convenient for clinical use. Now we present first 3D photoacoustic measurements on simple objects using a glass fiber Fabry-Perot detector as integrating line detector

We have developed a low cost, low power, photo-acoustic cell using a light emitting diode (LED) light source with monotone modulation for the purpose of measuring concentrations of aqueous liquid solutions in a non-invasive manner. The apparatus is smaller and cheaper than a conventional instrument such as a photo-acoustic cell in conjunction with a spectrometer.

A high resolution ac photopyroelectric calorimeter has been used to provide qualitative information on latent heat exchange and so establish the character of phase transitions in solids. Antiferromagnetic to paramagnetic transition in CoO is shown to present a small heat exchange characteristic of a weak first order transition. Well known first and second order transitions in KFeF₄ and NiO, respectively, are studied as a contrast method.

We present heterodyne detected transient grating measurements on water filled Vycor glass in the range of temperature 20-90 °C at the wave vector q = 1 μm^-1. The data have been analyzed with the model of Pecker and Deresiewicz, which enables a consistent physical description of the measured complex dynamics. Our experimental results confirm that the system is well described by hydrodynamic laws in spite of nano-metric dimension of the pores.

Three different picosecond ultrasonic techniques for longitudinal and transverse acoustic pulse generation have been combined with Impulsive Stimulated Thermal Scattering (ISTS) to probe structural relaxation dynamics in glycerol and DC704 (tetramethyl tetraphenyl trisiloxane) at megahertz and gigahertz frequencies (~ 50 MHz – 100 GHz) from below their respective glass transition temperatures up to 370 K.

Crosslinked poly (N-isopropylacrylamide) (PNIPAAm) is a temperature-sensitive hydrogel with approximately 32 ⁰C lower critical solution temperature (LCST) in pure water. The PNIPAAm chains hydrate to form extended structures in water when the latter is below LCST. However, when heated to above LCST, they become compacted by dehydration. In this work, we have used the PNIPAAm- polyacrylamide (PAAm) mixtures with varying molar percentages of PNIPAAm and PAAm that were prepared by free radical crosslinking copolymerization.

N' -N'methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) were used as crosslinker and an initiator, respectively. A photopyroelectric technique was applied to test the universality of the sol- gel transition as a function of polymer concentration ratios and to determine thermal effusivity of PNIPAAm- PAAm mixtures. The effects of varying PAAm concentrations on the LCST were studied by determining the temperature dependence of the thermal effusivity, with emphasis is on the influence on the properties and formation on the LCST of PNIPAAm- PAAm mixtures of the acrylamide concentration.

We have carried out a theoretical analysis of the dependence of the particle mass fraction on the thermal diffusivity of dilute suspensions of nanoparticles in liquids (dilute nanofluids). The analysis takes in to account adsorption of an ordered layer of solvent molecules around the nanoparticles. It is found that thermal diffusivity decreases with mass fraction for sufficiently small particle sizes. Beyond a critical particle size thermal diffusivity begins to increase with mass fraction for the same system. The results have been verified experimentally by measuring the thermal diffusivity of dilute suspensions of TiO₂ nanoparticles dispersed in polyvinyl alcohol (PVA) medium. The effect is attributed to Kapitza resistance of thermal waves in the medium.

Using a mathematical model on photoacoustics that includes both temperature and pressure effects explicitly, we analyze the behaviour of resonances of a cylindrical photoacoustic cell consisting of two buffer volumes and a resonator. We excite the cell at a certain frequency and find the ratio of resonator versus buffer diameter needed to obtain resonance. The results show that the resonance ratio depends on the absolute cell size. Also the amplitude of the acoustic signal measured in the middle of the resonator does not necessarily decrease when the total cell volume is increased. If the resonator diameter is sufficiently small, decreasing its diameter will increase the acoustic signal, although the total cell volume has to be increased to obtain resonance. This gives the advantage of being able to obtain a comparably large signal and at the same time use large buffer diameters to suppress window absorption signals. Finally we also compare the quality of the above-mentioned model and the lossy Helmholtz equation. We find that there is a shift in resonance ratio and the signal damping differs slightly. Albeit these differences are not large, and in many cases negligible, the model can be easily coupled with a solid absorption model in order to investigate the importance of thermal and pressure coupling between two acoustic media subject to heat absorption.

We will report here on the design and realization of an optoacoustic sensor for the detection of formaldehyde. The sensor consists of a commercial QCL and a resonant PA cell. Two different cell configurations have been investigated: a "standard" H cell and an innovative T-cell with an optical fiber directly inserted into. Two different type of sound detector have been employed: electret microphones and optical MEMS-based microphone. As possible applications, we will describe the results obtained in the detection of formaldehyde (CH₂O), a gas of great interest for industrial processes and environmental monitoring.

We present typical device characteristics of novel DFB laser diodes which are employed in various sensing applications including high resolution photoacoustic spectroscopy. The laser diodes discussed are based on a genuine fabrication technology which allows for the production of ultra stable devices within a broad spectral range from 760 nm up to 3000 nm wavelength. The devices exhibit narrow linewidths down to <1 MHz which makes them ideally suited for all photoacoustic sensing applications where a high spectral purity is required. As an example we will focus on a typical medical application where these diodes are used for breath analysis using photoacoustic spectroscopy.

This article proposes an optical fiber hydrogen (H₂) sensor based on photothermal reflectance [hereinafter modulated optical reflectance (MOR)] technique. Our H₂ sensor is based on a technique that detects the changes of MOR signals in palladium film, which is widely known to absorb H₂ gas. The sensor element is a palladium film deposited on a 2.5-mm-diameter FC-ferrule made from zirconium to realize the optical fiber sensor. Our recently developed "laptop" MOR instrument assembled with optical fiber components is applied to this technique. Thus, an extremely compact photothermal H₂ gas sensor system can be constructed. We certified that our technique has hypersensitive less than 1% with a concentration of H₂ gas and also demonstrated that the response time is approximately 5 seconds when the sensor head is filled with H₂ gas.

Nowadays, air pollution is presented as a serious threat to the planet. The concentration of gases from anthropogenic activities, such as transport, cause consequences ranging from local to global scale, affecting the climate, the environment and the human health. It is necessary to detect and monitor of a large number of gas species emitted by these sources of pollutants. The photothermal techniques, specially photoacoustic spectroscopy, allow the detection of many gaseous species. In this work, it is presented a new detection limit for a photoacoustic spectrometer composed of a CO₂ Laser and a Photoacoustic Resonant Cell. Analyses of many gas samples collected in the exhaust of urban buses in the city were performed. Ethylene was detected with the help of the CO₂ Laser photoacoustic spectroscopy and concentrations of CO, CO₂ and NO were obtained through a commercial infrared photoacoustic analyzer called URAS.

We present a simple resonant photoacoustic (PA) setup based on a modulated CW CO₂ laser and a synchronic detection system that acquires the signal and the reference through the sound card of a PC. The precise phase reading of this system allows detecting the delay of the signal coming from the excited CO₂ molecules immersed in air and, with an adequate processing, the environmental abundance of this gas, closely related to global warming, can be determined.

Lamb waves propagating in plate like structures, have been investigated to characterise a silicon wafer in a non destructive way. A laser ultrasonic technique was first used for the generation and the detection of these guided acoustic waves. A two-dimensional Fourier transform was next performed on the whole experimental data to obtain the dispersion curves, revealing the propagation of symmetric and antisymmetric modes. The sample characterisation was carried out in an original way, directly comparing the experimental results to theoretical ones. A feedforward neural network, specifically trained to recognize the same propagation behaviours, achieved to fit the experimental dispersion curves with a theoretical anisotropic model. Knowing the wafer thickness and density, the elastic constants were then determined without any user intervention. This non contact method showed very good agreement with the results obtained in the literature, and was found to be prompt and easy to automate.

Resonant acoustic spectroscopy is applied for determination of KTP crystal optical absorption coefficient α at the λ=1.064 μm. Kinetics of the KTP crystal different resonant acoustical modes under high-power laser radiation influence were measured. We suppose that the discrepancy α values obtained is due to acoustical resonances sensitivity to inhomogeneous heating. Resonant acoustic spectroscopy can probably enable a determination of the inhomogeneous crystal temperature distribution.

In this paper, the transient displacement excited by a laser line source is calculated for a bi-layer cylinder made of homogeneous and isotropic materials. A sample made by welding tin in a copper tube and a sample of cooper rod are considered. Experimental displacements are observed by the laser ultrasonic technique, and corresponding theoretical waveforms are calculated. Good agreement is found in the arrival time, shape and relative amplitude of various longitudinal and shear bulk waves propagating through the sample or reflected by the interface.

The laser-based modal resonant ultrasound spectroscopy is modified for measurements of thin surface layers on a substrate. This paper describes determination of all in-plane elastic properties of thin layers from small resonant frequency shifts of substrate induced by deposition of the layer.

A semi-analytical model is developed to calculate the elastic response of a gold submicronic particle embedded in a silica thin film, following a subpicosecond optical excitation. Real and imaginary parts of the transient reflectivity are then derived, accounting for elasto-optic contribution in the particle and in the matrix, as well as particle and film surface motion. The major contribution comes from the particle surface displacement. Picosecond ultrasonics measurements in a reflection configuration on a single 430 nm diameter gold particle confirm the conclusions of the model and demonstrates the suitability of this technique to investigate the opto-acoustic response of such submicronic particles.

Experimental results about light-to-sound transduction with semiconductor superlattices are presented. Picosecond ultrasonics with pump and probe incident on opposite sides of the substrate allows a full decoupling between generation and detection processes. Associating a metallic transducer, we show that superlattices generate quasi-monochromatic wave packets which can propagate over macroscopic distances in the underlying substrate but are also very selective and sensitive detectors. At the end, using two superlattices simultaneously as phonons generator and detector we evidence that these new transducers allow to perform acoustic experiments at the challenging frequency of 1THz.

We report on the first experimental evidence of negative refraction of surface acoustic waves, through a prism-shaped 2D phononic crystal having a solid matrix. The sample is constituted by a periodic array of air holes drilled in a Si substrate. The experiments are performed using a laser-ultrasonic technique.

The ultrashort laser pulse photoacoustic method has been used to characterise the physical properties of spin-coated PMMA layers onto Si wafers with thicknesses from 586 to 13 nm, . Acoustic speeds of polymer films were derived from the measured time of flight of acoustic waves in polymers and from their calculated visco-elastic properties. A 12% increase, in comparison to the PMMA bulk value, of the acoustic speeds was measured for polymer films with thicknesses below 80 nm, which corresponds to an increase in Young's modulus of 26%. In addition, we found that adding a hexamethyldisilazane primer monolayer between the polymer film and the Si substrate lessen the increase in Young's modulus, suggesting that the nanoscale changes are due to interface effects.

The theory of sound generation by nanoparticles under ultrashort laser pulse irradiation has been developed. Metal nanoparticles in an oxide matrix were considered. This case is of practical importance for composite coatings under transient thermal loads. The time dependence of matrix displacement generated by impact of electron pressure under a laser pulse was derived for a 2-D array of nanoparticles.

Using a Green's function method, we present a theoretical analysis of the propagation of acoustic waves in multilayer structures. The structure studied consists of a finite superlattice (SL) made of a periodic repetition of N unit cells deposited on a substrate. Such a structure exhibits extended modes constituting the allowed bands separated by forbidden bands where localized modes associated to free surfaces, defect layers, ... may exist. These modes can be observed either by Raman scattering when an incident light is launched from vacuum towards the multilayer, or by the reflection delay time when an incident acoustic wave is launched from the substrate. Specific applications of our results are given for some available experiments in the literature (e.g., Si/Ge_xSi_1-x, GaSb-AlSb) and a good agreement has been obtained between our theoretical results and the experimental data.

The thermo-physical properties of sulfosalt SnSb₂S₄ thin films deposited at two different glass substrate temperatures by Thermal Evaporation were investigated using the Photothermal Deflection method in its uniform heating case instead of traditionally a non uniform heating one. The advantage of applying this method in this way lies in its simplicity and its sensitivity to both thermal conductivity and thermal diffusivity. These films undergo abrupt changes in thermal properties on both sides of the transition temperature of 140°C which may be show the influence of the substrate temperature on thermal properties of the material.

The heat transfer in copper-carbon flat model systems was studied by frequency dependent photothermal radiometry. A novel approach which relies on the frequency dependence of the photothermal signal phase and amplitude at intermediate frequencies was introduced to determine the thermal interface resistance between the Cu-film and the substrate. The frequency dependent amplitude and phase of the photothermal signals were analyzed in the frame of a model of a one- dimensional heat flow perpendicular to the film plane. The interface resistance of the investigated CuC-sample with a Ti-bonding layer was found to increase by a factor two on heat treatment.

In the present work we propose the laser optoacoustic (OA) method for nondestructive measurement of the thickness of damaged layer in a machine cut silicon wafer. It is based on different mechanisms of laser excitation of ultrasound in monocrystalline silicon – the concentration-deformation mechanism and in a damaged layer – the thermoelastic one by absorption of Q-switched Nd:YAG laser pulse at the fundamental harmonic. Due to the uniform heating of a damaged layer during the laser pulse action the amplitude of the compression phase of the excited OA signal is proportional to the layer thickness. The rarefaction phase of OA signal arises by absorption of the rest of laser energy in monocrystalline silicon beneath the damaged layer. Comparison of the ratio of phase amplitudes with the scanning electron microscopy measurement of damaged layer thickness has shown it linear dependence vs. thickness within the variation of thickness and the corresponding spread of OA signal amplitudes. This provides the possibility of non-destructive laser optoacoustic measurement of the thickness of the damaged layer in silicon wafers. The minimum detectable value of the damaged layer thickness is of the order of 0.15-0.2 micron.

This article proposes an in-situ measurement method of the thermal diffusivity and the thermal conductivity of thin film during deposition inside the vacuum chamber based on a photothermal reflectance technique. Our new technique is simple and reasonable, although no adequate conventional instrument exists. A 2.5-mm-diameter FC-ferrule made from zirconium is contained in a vacuum and used to measure the thermoproperties of the thin film deposited on the end surface of the ferrule. The dependence of the thermal diffusivity and the thermal conductivity of the palladium film on the film thickness are demonstrated. These values are shown to be asymptotically adjacent to those of the bulk since the film is thicker. It is also described that the measurement error is increased, since the optical transmissivity of the thin film becomes to be high when the film is too thin.

An alternative photopyroelectric (PPE) technique that combines the front detection configuration (FPPE) with the thermal-wave-resonator-cavity (TWRC) method is proposed for direct measurement of thermal effusivity of solid materials inserted as backings in the FPPE detection cell. The method uses the scan of the normalized PPE phase as a function of sample's thickness, in the thermally thin regime for the sensor and liquid layer, and thermally thick regime for the backing material. The value of backing's thermal effusivity results from the optimization of the fit of the phase of the signal, performed with sample's thickness and backing's thermal effusivity as fitting parameters. The paper presents experimental results on several solid materials (inserted as backing in the cell), with different values of thermal effusivity (brass, steel, wood) and two liquids (ethylene glycol, water) largely used in the FPPE-TWRC cells. The paper stresses mainly on the sensitivity of the technique to different liquid/backing effusivity ratios. It seems that the method is suitable especially when investigating solids with values of thermal effusivity close to the effusivity of the liquid layer.

The effect of curved surface of both cylindrical and spherical samples with continuous gradient structure (e.g., case hardened surface) on the photothermal radiometric signal(PTR) are investigated. Using an appropriate signal processing, it is found theoretically that the curvature effect of both cylindrical and spherical samples can be, or partially can be suppressed under certain conditions and the PTR signal from the curved composite sample can be equivalent to that of a flat surface with the same structure.

The photoacoustic signal generated by a 2 MHz ultrasound transducer has been detected at 500 Hz modulation frequency by an attached photoacoustic cell. A dominant mechanism for signal generation is the ultrasound absorption in the gas of the cell, where strong acoustic resonances are excited. The periodic heating by ultrasound absorption in the transducer buffer rod and subsequent thermal diffusion into the gas is a second mechanism. Experiment and theory are in reasonable accordance.

A photoacoustic (PA) setup is presented, based on diode laser excitation in the infrared (5 mW, 1728 nm).The sensor being developed is designed to detect spurious amounts of gaseous contaminants like oil vapour in a highly perturbing environment (high flow, high pressure) via excitation of molecular vibrations of C-H bonds. An acoustic oscillator is driven at resonance to amplify the photoacoustic signal. The measurement cell is designed for optimum quality factor (Q) and setup constant [C_n(ω_n)].

Photoacoustic (PA) technique has important applications for material characterization and nondestructive evaluation of opaque solid materials. PA microscopy allows the acquisition of information of samples with inhomogeneous structures as agricultural seeds. A determining factor for seed safe storage is their moisture content. Seeds stored at high moisture content exhibit increased respiration, heating, and fungal invasion resulting in poor seed vigor and viability. Low moisture content, in the seed to be stored, is the best prevention for these problems. In this study, Photoacoustic Microscopy (PAM) was used to characterize seeds with different moisture content. In the PAM experimental setup the photoacoustic cell and its sensor, an electret microphone, are mounted on an x-y stage of mobile axes, with spatial resolution of 70 μm. The excitation light source is a fiber coupled laser diode, at 650 nm wavelength, modulated in intensity at 1 Hz of frequency, by the reference oscillator of a lock-in amplifier. By using a microscope objective the laser beam was focused on the seed surface. The resolution was enough to obtain differences in the obtained images, which are dependent on the moisture content. This method, to study differences in the seed moisture content, is nondestructive and could be useful for a sustainable Agriculture.

The application of photoacoustic (PA) phenomena to medical imaging has been investigated for more than a decade. To implement this modality, one may choose between two types of laser sources, pulsed or continuous wave (CW). This selection will affect all features of the imaging technique. Nowadays pulsed lasers are the state-of-the-art technique in the PTA research. In this work we report frequency-domain photothermoacoustic imaging using linear and non-linear frequency chirps with a CW laser. The images produced using turbid tissue phantoms with subsurface inclusions were compared according to their contrast and depth resolution of absorbing lesions. In the CW method, in addition to the image produced by the amplitude of the cross-correlation between input and output signals, another image which is generated by the phase of the correlation signal is also available. The application of nonlinear frequency modulation instead of the standard linear frequency chirps introduced in our laboratory is demonstrated. These features are additional degrees of freedom uniquely available to the CW (but not to the pulsed laser) method.

Photothermal beam deflection (PDS) has been applied to obtain information regarding the penetration of methylorange (MO) and ditranol (DI) into artificial membranes. The measurable depth range is 56 μm. Photothermal beam deflection allows on the one hand depth resolved investigations by the use of a frequency modulation of the excitation beam to reach deeper regions even in opaque sample, and on the other hand lateral imaging. To explore the potential use of a novel photothermal double beam laser scanning system, measurements in drug delivery analysis have been used for depth profiling and imaging into an artificial membrane, which represents stratum corneum or bovine hoof, appropriately.

Every nonlinear optical laser frequency conversion process is accompanied by the crystal heating due to the absorption of some part of the radiation energy. Optical absorption coefficients and internal crystal temperature distribution during interaction with the high-power laser radiation are directly determined from modelling the experimentally obtained stationary and kinetics data of the radiation-induced frequency shifts of the crystal piezoelectric resonances.

Resonant acoustic spectroscopy technique gives the opportunity to measure the crystal temperature during linear and nonlinear interaction of the laser radiation with crystals. It is based on the registration of the crystal piezoelectric or acoustical resonance frequency change caused by the interaction of the laser radiation with crystals. Piezoelectric resonance is observed by measuring the dependence of the sample electrical impedance on the external electric field frequency. It is shown that inhomogeneous crystal heating can be characterized by the equivalent crystal temperature depending on the influence laser power. Equivalent crystal temperature can be directly determined from the measured piezoelectric resonance frequency.

The aim of this work is to approach in an experimental way, the possibilities of diffusivity thermal measurement, under less energy constraints, offered by front face random photothermal radiometry associated to a parametric analysis. First, we present the principle of the random method. Then, we present the experimental device SAMMIR used in our study. In a third stage, we present the studied sample, the experimental conditions selected and the model developed for the study. We show finally, using the experimental study of a sample of nylon 6.6 that the photothermal method allows, in a particular case, a good approximation of the thermal diffusivity parameter.

The optical fibre thermal wave resonator cavity (OF-TWRC) technique was used to measure thermal diffusivity of a two-layer sample; air-liquid. The thermal waves were generated by transmitting the modulated laser beam through one end of optical fibre and illuminating the other fibre end surface that metalised with silver paint. The cavity length scan was done by moving the fibre end surface towards the pyroelectric detector continuously through air and then into the liquid. A good linear relationship of pyroelectric amplitude with respect to cavity length was obtained in thermally thick region in both media; air and liquid. The thermal diffusivity of air, glycerol and water obtained were closed to the literature values.

High detection sensitivity and spectral selectivity is important for gas analysers to identify the measured compound and to detect low concentrations. We investigated three different modulation methods – pulse gate modulation, pulse frequency modulation and chopper modulation – for a new pulsed quantum cascade laser based photoacoustic sensor. The spectral selectivity and the detection limit for the three modulation methods are compared by measuring nitric oxide absorption lines and different concentrations. The highest detection sensitivity of 70 ppb was achieved with pulse gate modulation but at the lowest spectral resolution. The highest spectral resolution was achieved with chopper modulation but at the lowest detection sensitivity. It is demonstrated that for the three modulation methods a compromise has to be made between selectivity and sensitivity for each measuring task.

This paper presents various examples of assistance to the restoration of mural paintings by infra-red photothermal radiometry. First, we present the experimental device implemented for the study. Then, we show the possibility to detect separation or air voids by this technique in various works of art as the Saint Christopher of the Campanna collection of Louvre, in the painted ceilings of the abbey of Savin Saint sur Gartempe (classified with the world heritage of UNESCO) and finally in the Cocteau frescoes of the vault Saint Pierre of Villefranche sur mer.

This paper is the presentation of photothermal piezoelectric studies of the optical properties performed on a series of AII-BVI mixed crystals. This approach enables not only determination of the basic optical parameters of mixed crystals such as the energy gap value or Urbach edge parameters but it also turned out to be a useful tool for investigations of the surface quality of the samples.

Lockin-thermography has become a valuable tool for non-destructive testing (NDE) of materials since it provides in a short time phase images of hidden defects. However, besides finding defects it is important to derive more information to characterise them. We present an innovative way to combine phase images obtained at different lockin-frequencies by using scatter plots. Besides defect depths this method of data fusion allows for feature extraction like thermal wave reflection coefficient, local planarity, and edge effects due to the lateral heat flow caused by them. The extracted features can be traced back to the original image.

The nondestructive testing (NDT) of honeycomb sandwich structures has been the subject of several studies. Classical techniques such as ultrasound testing and x-rays are commonly used to inspect these structures. Holographic interferometry (HI) and infrared thermography (IT) have shown to be interesting alternatives. Holography has been successfully used to detect debonding between the skin and the honeycomb core on honeycomb panels under a controlled environment. Active thermography has proven to effectively identify the most common types of defects (water ingress, debonding, crushed core, surface impacts) normally present in aeronautical honeycomb parts while inspecting large surfaces in a fast manner. This is very attractive for both the inspection during the manufacturing process and for in situ regular NDT assessment. A comparative experimental investigation is discussed herein to evaluate the performance of HI and IT for the NDT on a honeycomb panel with fabricated defects. The main advantages and limitations of both techniques are enumerated and discussed.

A surface crack close to a spot heated by a laser beam impedes lateral heat flow and produces alterations to the shape of the thermal image of the spot that can be monitored by thermography. A full 3D simulation has been developed to simulate heat flow from a laser heated spot in the proximity of a crack. The modelling provided an understanding of the ways that different parameters affect the thermal images of laser heated spots. It also assisted in the development of an efficient image processing strategy for extracting the scanned cracks. Experimental results show that scanning pulsed laser spot thermography has considerable potential as a remote, non-contact crack imaging technique.

Thermography is used to detect corrosion on a aluminum specimen. Two identical aluminum plates are extracted from the same base material. One of them is machined on one side, in such a way to simulate a material loss. Both the sound and damaged plate are heated on the undamaged side by a sine modulated heating source. A thermographic camera records a sequence of images of the temperature surface of both the sound and damaged sample on the heated (undamaged) sides. Several sequences are recorded with different modulation periods. By a suitable data reduction procedure, the thermographic sequence is reduced to a couple of images representing amplitude and phase of the oscillating temperature field. A perturbative method is used to solve iteratively the direct problem in the corroded domain that is confronted with the experimental data until an optimum matching is reached.

A theoretical model for evaluating 2-layer solid spherical samples that are heated by a modulated light is presented using the Green function method. The specific Green's function corresponding to the composite structure has been derived. The characteristics of the thermal-wave field with respect to the thermophysical properties of the material and the geometrical factors are presented. Experimental results obtained with laser infrared photothermal radiometry show the capability of the model for characterizing the spherical layered structures.

This paper presents results of both theoretical and experimental studies of the characteristics – phase differences of the photoacoustic (PA) signals versus the frequency of modulation and for the purpose of comparison of characteristics – phase of the photocurrent (PC) signal versus the frequency of modulation. If the life time of excess carriers is the main goal of investigations the PC rather than the PA method should be applied wherever it is possible. The paper shows what advantages and disadvantages of both methods are from the point of view of determination of the life time of excess carriers. Finally the paper presents comparison of the phase PA and PC characteristics and life times extracted from both experiments for the series of silicon samples.

A non-contact and non-intrusive method of revealing crack presence in un-sintered (green) automotive transmission parts (sprockets), manufactured by means of a powder metallurgy technology based on analysis of photo-thermal radiometric (PTR) signals and their statistical analysis was developed. The inspection methodology relies on the interaction of a modulated laser generated thermal wave with the potential crack and the resulting change in amplitude and phase of the detected signal [1-5]. The crack existence at points in high stress regions of a group of green (unsintered) sprockets was evaluated through frequency scans. The results were validated by independent destructive cross-sectioning of the sprockets following sintering and polishing. Examination of the sectioned sprockets under a microscope at the locations where signal changes was used for correlation with the PTR signals. Statistical analysis confirmed the capabilities of the method to detect the presence of hairline cracks (~5 − 10 μm size) with excellent sensitivity (91%) and good accuracy (78%) and specificity (61%). This measurement technique and the associated statistical analysis can be used as a simple and reliable on-line inspection methodology of industrial powder metallurgy manufactured steel products for non-destructive quality and feedback control of the parts forming process.

Thermal diffusivities of Al-Mg based metallic matrix composite reinforced with ceramic particles of Al₂O₃ are reported in this article. The samples were produced by rheocasting and the studied operational condition in this case is the shear rate: 800, 1400 and 2000 rpm. Additionally, the AlMg base alloy was tested. Measurements of thermal diffusivity were performed at room temperature by using photoacoustic technique.

Measurements of surface cleanliness and dirt characterization are important problems in a wide range of processes in industry and production. Standard methods are in most cases cumbersome laboratory procedures that must be performed out of the production lines. Instruments and methods for cleanliness determination and dirt characterization require reference standards for calibration. For that purpose we built a possible dirt reference standard (DRS) made by films of graphite grease subjected to heat treatment for mechanical stabilization. The DRS characterization was performed by Laser Ablation Induced Photoacoustics (LAIP). The measurement of the thickness of the films was made by low-coherence interferometry.

Vibrothermography has proven to be a useful technique for the detection of buried defects, which reveal themselves as heat sources when mechanically excited with ultrasounds. In this work we present a method to evaluate the depth of delaminations in opaque samples, from lock-in vibrothermography measurements. It is theoretically demonstrated that the phase and the natural logarithm of the surface temperature above the delamination behaves linearly as a function of the square root frequency. The slope of this linear relation is directly proportional to the delamination depth. Measurements performed on composite plates with calibrated delaminations confirm the validity of the method, provided the width of the delamination is higher than the thermal diffusion length.

To meet the industrial demand for on-line steel hardness inspection and quality control, a non-contact, non-destructive laser photothermal radiometric instrument (HD-PTR) was developed. The instrument is equipped with a non-liquid-nitrogen-cooled HgCdZnTe (MCZT) detector, a National Instruments data acquisition card with a Dynamic System Analysis (DSA) module, and control software. A series of industrial steel samples which included automotive screws and aircraft gears (flat or curvilinear) were examined. The effective hardness case depths of these samples ranged from 0.21 mm to 1.78 mm. The results demonstrated that three measurement parameters (metrics) can be extracted when using a fast swept-sine photothermal method. These parameters include the phase minimum (or peak) frequency, f_min, the half width, W, and the area, S. It was found that they are complementary for evaluating widely different ranges of hardness case depths. f_minis most suitable for large case depths, and W and S for shallower case depths.

The thickness of coatings can be determined using the data measured by Modulated IR Radiometry for sets of coatings, produced under specific controlled conditions: – Keeping constant all deposition parameters except the deposition time, coatings of approximately constant thermal transport properties, but different thickness are produced. The modulated IR phase lag signals measured for the coatings are calibrated with the help of signals obtained for homogeneous opaque reference samples of smooth surface. Quantitative results for the thermal transport properties are obtained using the inverse solution of the 2-layer thermal wave problem by which direct relations are established between the relative extrema of the inverse calibrated thermal wave phase signals measured as a function of the heating modulation frequency and the thermal coating parameters, the ratio of the effusivities coating-to-substrate, the coating's thermal diffusion time, and the coating thickness. The coating thickness values obtained by Modulated IR Radiometry are compared with the values measured by standard microscopic methods, and relative errors of 3 – 4% have been found for the coating thickness of a set of TiCO coatings on steel, presented here as an example.

The non-contact and non-destructive photothermal beam deflection (PBD) method has been used for the characterization of the thermal properties of Alumina (Al₂O₃), Mullite (3Al₂O₃·2SiO₂) and Oxidic-Bonded Silicon Carbide (OBSiC) samples often used in chemical engineering. Measurements of thermal diffusivity κ have been performed. One obtains for Alumina, for Mullite and for OBSiC.

We have employed spectroscopic ellipsometry (SE) in 0.27-30μm covering spectrum from near ultraviolet to far infrared to investigate the ion-implanted silicon wafers used in IC manufacturing, which were oxidized on the surface before ion implantation and rapid thermally annealed after implantation. It was found that the SE parameters are most sensitive to the implantation dose in the far infrared range with wavelength longer than 10μm. For implantation dose measurement of oxidized and annealed wafers the infrared SE has a high resolution in a wide dose range of 10¹³ – 10¹⁶cm⁻².

A three-dimensional modulated free carrier absorption (MFCA) model taking into account the size of a Gaussian-profile probe beam, referred as the accurate model, is developed to describe the influence of the probe beam size on signal analysis of the MFCA technique. Numerical simulations are presented to investigate the influences of different probe beam radii on the amplitude and phase of the laterally resolved MFCA (LR-MFCA) signal at 2kHz and 200kHz, respectively. The MFCA signals obtained by this accurate model are compared to those obtained by a model assuming a point detection (referred as the point model). The conditions that the probe beam size can be neglected are given.

The photothermal beam deflection (PDS) technique was tested for low thermal diffusivity materials. The effect of using different liquids as surrounding media was studied in a systematic way. The fundamental experimental parameters, like the pump beam power and the modulation frequency were also studied in order to find out the best combination that still allows us to get good signals.

Due to the complexity of the optical alignment required, the usual mirage setup was adapted in order to allow the decoupling of the alignment of the cell containing the liquid and the sample holder.

Simple, straightforward methods (like e.g. the phase method) were used for the thermal diffusivity determination of solids once the thermal diffusivity of the liquids used is always much lower than that of solids.

The obtained values for the thermal diffusivity of test samples allow us to conclude that besides being possible to use any of the studied liquids as surrounding medium, ethanol is clearly the best choice, avoiding health problems related to CCl₄, which is the standard choice for PDS and PDS spectroscopy experiments, and technical/physical problems related to water and acetone. Modulation frequencies around 8 Hz combined with a pump beam power below 15 mW were proved to be the ideal conditions for this kind of experiment. The very low pump beam power required is also an important issue when talking about non-destructive analysis.

In this study, the nondestructive testing (NDT) of tilted subsurface defects with a concave cross section was performed using a photoacoustic microscope (PAM). The tilted subsurface defects were formed in a metal plane specimen by mechanical processing. The obtained signal distribution was affected by the tilt angle of the subsurface defects, and the relationship between the gradient ratio and the tilt angle value exhibited a good correlation.

A method of retrieving thermophysical depth profiles of continuously inhomogeneous materials is presented both theoretically and experimentally using the three-dimensional (3-D) photothermal radiometry. A 3-D theoretical model suitable for characterizing solids with arbitrary continuously varying thermophysical property depth profiles and finite (collimated or focused) laser beam spotsize is developed. A numerical fitting algorithm to retrieve the thermophysical profile was demonstrated with three case hardened steel samples. The reconstructed thermal conductivity depth profiles were found to be well anti-correlated with microhardness profiles obtained with the conventional indenter method.

Using matched-filtering principles and linear frequency modulation a powerful photothermal depth-profilometry method is introduced. Unlike FD-PTR, in thermal-wave radar (TWR) the frequency of the optical excitation increases linearly within the chirp period, enabling the method to scan a depth range in a single iteration. Simulations and experimental results suggest a significant improvement in the dynamic range when using TWR instead of conventional PTR. Analytical solutions to the TWR heat diffusion problem for both opaque and transparent solids are provided.

Distinctive hot spot phenomena caused by electrical shunts in thin-film modules are analyzed by infrared thermography. Modelling the shunt current by an equivalent circuit and considering lateral heat transport, the detected phenomena are discussed. Defects show a characteristic intense temperature rise (>12mK) in the center and an extended sphere of influence with reduced temperature rise.

We report about a technique where we transferred the Lockin-principle from Lockin-thermography to interferometry to perform thermal wave lockin-interferometry. This technique is based on speckle-interferometric imaging of periodical height changes going along with the temperature modulation in a thermal wave. We used both electronic speckle pattern interferometry and shearography setups and operated them with low frequency periodical heat deposition while a stack of interferometric fringe patterns was recorded. After unwrapping, each pixel of the stack was Fourier-analysed at the Lockin-frequency, giving an amplitude image and phase image of low frequency thermal deformation. Though this is very much like Lockin-thermography, the image generating mechanism is substantially different: The thermal wave generates periodical thermal expansion correlated with an overall deformation where the depth integral of the thermal wave is involved. At such a low frequency (below 1 Hz), deformation occurs simultaneously everywhere except in areas where thermal wave propagation is modified e.g. by boundaries, which affect the phase of deformation. Depth range is adjusted via modulation frequency as in lockin thermography.

We report on a new method which allows extracting thermoelastic images by full-field method using in-plane measurement. The aim of this work is to show that it is possible to extract the in-plane thermoelastic field. Recently, a vibrometric measurement method has been developed at FEMTO-ST Institute for measuring in-plane displacement with nanometer and sub nanometer resolutions. The use of this method with thermography imaging allowed us to extract thermal expansion of micro samples heated by photothermal or thermoelectrical excitation. In this paper, we present an innovating technique to image thermoelastic field of these investigated samples. This technique is based on a CCD (charge-coupled device) camera which has been optimized for the previously presented applications.

The photothermally modulated magnetic resonance (PM-MR) technique was used to study thin films of Gd grown on fused quartz substrates. With this technique it was possible to observe the magnetic phase transitions for samples with different thickness and thermal treatments. Results were correlated with both magnetization and ESR measurements. The effect of the stress induced by the substrate was clearly observed through peak of the PM-MR signal.

The article deals with the retrieval of the depths and sizes of defects situated in carbon fibers reinforced polymer material from optical lockin thermography phase images. A model that describes the images formation process in anisotropic, homogeneous material is presented. It is used to retrieve the depth and shape of the defects.

In this paper we present, in an experimental way, the possibilities of front face photothermal radiometry to measure, in situ, the longitudinal thermal diffusivity of mural paintings. First, we present the principle of the method of measurement. Then, we present the experimental device implemented for the study. Finally, we show, using the experimental study of a plaster sample, the photothermal method allows in a particular case, a good approximation of the parameter longitudinal thermal diffusivity.

Spectrally resolved active thermography by flash pulse excitation was performed in four sub-bands of a mid-wave infrared camera using spectral filtering and in the full long-wave band of a second infrared camera. On zirconia thermal barrier coatings on steel and PVC blocks, spectrally dependent decay rates of the thermal contrast were found. The observed behaviour can be explained by the infrared spectra of the specimens.

The time-domain response of the temperature of solid specimen surface illuminated by a linearly-focused laser beam scanning over a solid specimen surface was theoretically formulated. The waveform is composed of surface diffusion and reflection components, both of which are represented by incomplete Gamma functions. Experimental results show photothermal radiometric signal increase caused by the reflection of heat flow at the internal defect boundary and agreed with calculated data qualitatively.

The depth of curing due to photopolymerization in a commercial dental resin is studied using photothermal radiometry. The sample consists of a thick layer of resin on which a thin metallic layer is deposited guaranteeing full opacity of the sample. In this case, purely thermal-wave inverse problem techniques without the interference of optical profiles can be used. Thermal profiles are obtained by heating the coating with a modulated laser beam and performing a modulation frequency scan. Before each frequency scan, photopolymerization was induced using a high power blue LED. However due to the fact that dental resins are highly light dispersive materials, the polymerization process depends strongly on the optical absorption coefficient inducing a depth dependent thermal diffusion in the sample. It is shown that using a robust depth profilometric inverse method one can reconstruct the thermal diffusivity profile of the photopolymerized resin.

By scanning thermal microscopy, we study the behavior of nanostructured metallic microstripes heated by Joule effect. Regularly spaced indentations have been made along the thin film stripe in order to create hot spots. For the designed stripe geometry, we observe that heat remains confined in the wire and in particular at shrinkage points within ~1μm². Thermal maps have been obtained with a good lateral resolution (< 300nm) and a good temperature sensitivity (~1K).

In this work we have studied the nitriding effect for the 42CrMo4 steel on the evolution of their thermal and mechanical properties. The thermal properties are determined by the "Photothermal Deflection technique" method. It was shown that the thermal conductivity as well as the thermal diffusivity decreases if the nitrogen fraction in steel increases conversely the microhardness increases with the growth of the nitrogen rate. After, we have correlated the thermal and mechanical properties with an empirical equation that permits to determine the microhardness without its measure.

Photomodulation Raman spectroscopy (PM-RS) has been employed to study the surface depletion electric field Es and to monitor the change in surface charge density in n-type GaAs, using the forbidden LO phonon scattering for low doping samples and coupled plasmon–LO phonon modes for high doping samples. In PM-RS, the photomodulating pumping beam (PB) is incident on the sample while the Raman measurements are in progress hence PM-RS can be viewed as a pump-probe technique. The photogenerated carriers partly neutralize the surface charges. Two different GaAs surfaces (011) with low and moderate doping density and (001) with high doping density were used. The total surface charge density has been obtained as a function of the PB intensity considering a constant depletion electric field for the lower doping sample of (011) surface and using the dependence of the unscreened LO phonon on the depletion width for the higher doping samples of (001) surface. The minority carrier's lifetime was also determined through dynamical measurements for the PM-RS of the low doping sample as ≈ 21 s, in a good agreement with other techniques

If an absorbing medium is constructed so that its sound speed varies periodically in space, the photoacoustic effect takes on a different character than when it is generated in a homogeneous medium. The case considered here is where either the density or the compressibility of the medium varies sinusoidally in space. The wave equation for pressure is shown to reduce to an inhomogeneous Mathieu equation. The properties of the waves generated by heat deposition in such a structure are investigated. Theoretical results are shown for a finite layer excited by a sinusoidal heating source that is a delta function in space.

The thermal conductivity of Ge₂Sb₂Te₅ (GST) layers, as well as the thermal boundary resistance at the interface between the GST and amorphous SiO₂, were measured using a PhotoThermal Radiometry experiment. The two phase-changes of the Ge₂Sb₂Te₅ were retrieved, starting from the amorphous and sweeping to the fcc crystalline state at 130 °C and then to the hcp crystalline state at 310 °C. The thermal conductivity resulted to be constant in the amorphous phase, whereas it evolved between the two crystalline states. The thermal boundary resistance at the GST-SiO₂ interface was estimated to be higher for the hcp phase than for the amorphous and fcc ones.

In this paper we demonstrate an optically powered ultrasonic t ransducer. It has a high efficiency and was designed and fabricated using MEMS (microelectromechanical system) techniques. It can generate narrowband ultrasound from broadband laser excitation. It is a simple two-mask-level MEMS device with a micro-disc seated on a micro-stem. As a laser pulse is incident on the disc centre, the disc is excited into a 'flapping' motion because of the thermomechanical interaction between the absorbing and non-absorbing parts of the disc. This flapping motion is dominated by one of the resonances of the disc, coupling a narrowband longitudinal bulk wave propagating along the axis of the micro-stem into the sample. Experiments with these transducers have shown that narrowband ultrasonic waves with a high SNR (signal to noise ratio) were generated successfully. The device is simple to excite optically and generates higher amplitudes than by normal thermoelastic generation. No physical contact is required to excite the transducer, making it suitable for remote non-contact ultrasonic applications.

The plasma wave (carrier-density wave) and thermal wave in an optically opaque semiconducting cantilever (3D geometry), photogenerated by a tightly focused and intensity-modulated laser beam, were analyzed. The theoretical model for the carrier-density and temperature distribution by using the Green function method and Hankel transformation was given. The amplitude and phase of the carrier-density and temperature space and frequency distribution in the cantilever are calculated, including the thermalization and surface and volume recombination heat processes. These investigations are important for many practical experimental situation (atomic force microscopy, thermal microscopy, thermoelastic microscopy, etc) and sensors and actuators based on cantilevers.

The various types of micromechanical structures (the cantilevers, membranes and plates) were studied by the photothermal elastic vibration method. The amplitude and phase of the photothermal elastic vibration spectra (the elastic displacements vs. the frequency of modulation of the laser beam) were measured. The analysis of these spectra showed that the different characteristics of the micromechanical structures can be obtained. The photothermal elastic vibration spectra, for example, can be used to analyze how the technological processes change the characteristics of the micromechanical structures.

A system of coupled plasma and elastic waves (the plasmaelastic waves) equations are analyzed. The treatment considers a semiconductor elastic plate with isotropic and homogeneous plasma and elastic properties. The solution of the coupled system of plasma and elastic equations are given for a typical photothermal configuration including the carrier surface and volume recombination processes. The analysis of the plasma density and elastic fields shows that the coupling plasmaelastic effects show the attenuation and disperse phenomena.

Photo-Carrier Radiometry has been applied to semi-insulating (SI) GaAs wafers. Due to the ultrafast free carrier lifetime, the conventional diffusion based PCR theory was modified to reflect defect induced carrier radiometry. Modulated and spectrally-gated defect luminescence was measured and analyzed using rate-window detection, in both temperature and frequency domain. Five defect levels were identified through multi-parameter fitting of PCR theory to the experimental data.

The heat propagation at room temperature in the heterostructure – polycrystalline diamond film deposited on a silicon substrate has been investigated by the pulse photothermal method. A thin In film evaporated onto the diamond was used as a thermometer. The experimental response was compared to that calculated by the solution of the heat propagation problem in the three-layer axial-symmetric structure with definite thermal boundary resistance on the interfaces. This analysis permitted the determination of both the thermal conductivity of the diamond film and the thermal resistance of the diamond/Si and In/diamond interfaces.

This paper presents the influence of the composition of several mixed A2B6 crystals on the broadening of the optical absorption coefficient spectra. This broadening is observed as the change of the piezoelectric spectra associated with the change oft he Urbach tail. This effect is interpreted as a result of the increase of the compositional disorder of the crystal lattice.

In this study we will describe and compare different methods based on the Photothermal Deflection Technique (PTD) which permits the determination of thermal diffusivity for bulk semiconductors. The two first methods proposed here consist in drawing the experimental amplitude and phase variation of the photothermal signal versus square root modulation frequency. The sample placed in air is heated thanks to a modulated uniform light beam. The difference between these two methods is that in the second one the sample is covered by a thin graphite layer. We notice that the first method is only sensitive to the thermal diffusivity however the second method is sensitive for both thermal diffusivity and thermal conductivity. Finally the third method which is a spectroscopic one and where the sample is immersed in a CCl₄ filled cell consists to draw the phase variation of the photothermal signal versus wavelength at a fixed modulation frequency. The phase difference between the two saturated zone (high and low absorption coefficient) is sensitive to the thermal diffusivity.

Laser-induced infrared photocarrier radiometry (PCR) was used to characterize industrial polycrystalline silicon solar cells. The ac photovoltage was measured simultaneously with the PCR signal. The PCR and ac photovoltage signals were investigated as functions of modulation frequency, excitation intensity, external dc illumination and load resistance. The interrelation and interpretation of PCR signal, ac photovoltage and static (dc) electrical parameters of solar cells are discussed.

Owing to its novel physical properties, as well as its technological implication in many fields, the thermal and optical properties of WO₃ thin films are studied here. These thin films are prepared from Ammonium Tungstate and deposited on a glass substrate at 400°C by the Spray Pyrolysis Technique. The thermal properties (Thermal conductivity and thermal diffusivity) were studied by the Photothermal Deflection method in its uniform heating case instead of traditionally a non uniform heating one by comparing the experimental amplitude and phase variations versus square root modulation frequency to the corresponding theoretical ones. The best coincidence between theory and experience is obtained for well-defined values of thermal conductivity and thermal diffusivity. The optical properties (optical absorption spectrum and gap energy) were measured using the Photothermal Deflection Spectroscopy (PDS) by drawing the amplitude and phase variation versus wavelength in experimental way and versus absorption coefficient in theoretical one at a fixed modulation frequency. By comparing point by point the normalised experimental and corresponding theoretical amplitude variation, one can deduce the optical absorption spectrum. Using the Tauc law for energies above the gap we can deduce the gap energy. We notice that these films show low thermal conductivity and high transparency in the visible range.

The theoretical models of optically induced elastic bending for a semiconductor circular plate (clamped and simply supported) was derived including both plasmaelastic (PE) and thermoelastic (TE) wave influences. The PE and TE effects versus the modulation frequency of focused laser excitation were analyzed. Obtained results were compared with the optically excited elastic bending produced by homogeneous surface heat source and with experimental measurements.

Photocarrier radiometry (PCR) signal is a monotonic function of the implantation dose if the wafers are not annealed, because the signal is determined by the crystalline damage in the semiconductor induced by implantation. When the wafers are annealed at high temperature with most of the damages recovered, however, the PCR signal is no longer monotonic to the implantation dose. In this work, we obtained the PCR signals of the implanted and non-implanted regions from the same pieces of annealed sample. By subtracting the signals from the non-implanted regions, the influence of doped impurities on PCR signals is investigated. The different response at low implantation dose caused by B⁺ and P⁺ ions is analyzed.

The analytical expression is derived to describe the photocarrier radiometric (PCR) signal for a semi-infinite semiconductor wafer excited by a square-wave modulated laser. For comparative study, the PCR signals are calculated by the semi-infinite model and the finite thickness model with several thicknesses. The fitted errors of the electronic transport properties by semi-infinite model are analyzed. From these results it is evident that for thick samples or at high modulation frequency, the semiconductor can be considered as semi-infinite.

Based on a three-dimensional modulated free carrier absorption (MFCA) model, theoretical analysis is performed to investigate the dependences of MFCA amplitude and phase on the electronic transport properties (the carrier lifetime, the carrier diffusivity, and the front surface recombination velocity) at different pump-to-probe separations and different modulation frequencies. The sensitivity of the multi-parameter estimate employing the dependences of the MFCA amplitude and phase on the modulation frequency at several pump-to-probe separations is theoretically compared with that employing the dependences on the pump-to-probe separation measured at several modulation frequencies. Simulation results show that the two approaches have comparable sensitivities to the electronic transport properties of silicon wafers. As for the MFCA experiments, the frequency scan data measured at different pump-to-probe separations have higher signal-to-noise ratios and therefore should be preferable to the simultaneous determination of the multiple transport properties.

Experimental results for photothermal lens measurements are compared to finite elemental analysis models for commercial colored glass filters. Finite elemental analysis software is used to model the photothermal effect by simulating the coupling of heat both within the sample and out to the surroundings. Modeling shows that heat transfer between the glass surface and the air coupling fluid has a significant effect on the predicted time dependent photothermal lens signals. For comparison with experimental signals, a simple equation based on the finite element analysis result is proposed for accounting for the variance of experimental data where this type of heat coupling situation occurs. The colored glass filters are found to have positive thermo-optical coefficient. Finite element analysis modeling results are also used to correlate experimental measurements of different sample geometries. In particular, the glass samples are compared to ethanol solutions of iron (II) dicyclopentadiene in a sample cuvette even though heat transfer is different for these two samples.

A novel spectroelectrochemical method based on the thermal-lens effect from electrolyte solution using regular Joule heat generation by current focussing in a small-sized channel is under development. Numerical calculations using finite-element modelling were used for a thorough estimation of experimental conditions (cell and electrode shape and size). The major interferring effects were estimated. A change in the analyte concentration near electrodes due to electrolysis is significant and is overcome by large-radius ring elctrodes and AC current. The calculations were confirmed by experiments. An advanced cell design with good reproducibility and the sensitivity of measurements down to 10^-6 M is proposed.

In this work flow injection analysis coupled to collinear dual beam thermal lens spectrometric UV detection was used for determination of silver in water. The detection is based on the increase in absorbance resulting from the formation of colloidal elemental silver due to reduction of Ag⁺ after reaction with BH₄^-. The optimal performance of the experimental setup was achieved with 500 μL sample injection loops or larger and the flow rate of 0.6 mL/min. The estimated limit of detection (LOD) for silver in water was 0.01 mg/L what compares favorably with the maximum contaminant level (MCL) for silver in drinking water.

In this paper performance enhancement in PA measurements through optical pulse shaping is explored and demonstrated. A recently introduced setup, which is based on a CW tunable laser source operating in the optical communications band (1510-1620nm) and an electro-optic modulator, offers exceptional flexibility in controlling the temporal and spectral characteristics of the excitation waveform. Despite its being remarkably simple to construct and to operate, the unique optical configuration of this setup opens the possibility for a range of attractive applications which cannot be implemented by the commonly used pulsed lasers: responsivity and sensitivity optimization through pulse-shaping, enhancement of spatial resolution through pulse compression and simple implementation of high-resolution quantitative spectroscopy.

The photothermal deflection technique, also known as "mirage effect", is a nondestructive method of evaluating thermal properties of solid, liquid or gaseous species. This technique will be used to detect pollutant absorption. As the deflection is stronger in liquids than gases, we will first consider the deflection in paraffin oil. We consider a medium that is heated by a modulated laser diode beam, and we measure the deflection of the probe beam passing through the heated region as a function of the distance between the axes of the beams. After some theoretical considerations and numerical simulations, we present the application of this method to the experimental determination of the thermal diffusivity of a liquid sample in excellent agreement with previously known values.

Thermal lensing (TL) permits ultrasensitive measurements of optical absorption of analytes in very small volumes. Separation-detection conditions of non-labeled amino acids with micro-HPLC/UV absorption detector are optimized, and direct determination of non-labeled amino acids by micro-HPLC/UV-excitation TL detection in a gradient elution is successfully demonstrated. Non-labeled amol-level amino acids is detectable with the TL detection system, which has thousand times better sensitivity than a conventional UV detector.

We measured terahertz reflection responses utilizing a propagating phonon polariton wave, which was generated and detected by two different methods: the near-field heterodyne transient grating and the continuously variable spatial frequency transient grating method. The obtained results were compared for the purpose of clarifying which of both methods is better for measurements of terahertz reflection responses. The phonon polariton wave is propagated and reflected at a ferroelectric crystal edge. From the viewpoint of the separation between the excited and reflected phonon polariton waves, the latter method is better for measurements of reflection responses.

Pulsed photoacoustics should fulfil some of the requirements to be a powerful and precise trace gas detection technique. Beside the high sensitivity and selectivity, large dynamic range and good temporal resolution, pulsed photoacoustics has the potential to measure numerous parameters of the laser beam spatial and temporal characteristics with one or no additional instruments. The different numerical methods can be distinguished for this purpose with respect to the measuring procedure and result analysis. In the following article the numerical method for the laser beam spatial profile determination will be presented. Simultaneously this method allows calculation of the molecular vibrational to translational relaxation time in different gas mixtures.

Considering the time dependence of the absorption coefficient due to the photo-induced chemical reaction (PCR) and species diffusion, we calculate the temperature rise in the thermal lens (TL) effect and the TL signal at the detector plane. This theoretical approach removes the restriction that the PCR time constant is much greater than the characteristic TL time constant, which was assumed in a previously published model. Aqueous Cr(VI)-diphenylcarbazide solution is investigated, and quantitative experimental results for the thermal, optical and PCR properties of the sample are obtained. The relative difference between the parameters extracted from the same experimental data of the Cr(VI) solution using the previous and present models is found to be less than 5%, showing the present model can be used to study the PCR. Moreover the present model is more general than the previous one.

This work considers the application of thermal-lens spectrometry to the monitoring of the crystallization processes in aqueous solutions. Formation of a crystalline germ in a previously homogeneous medium drastically changes the heat and mass transfer along the laser beam path; thus, affecting both equilibrium and time-resolved thermal-lens phenomena. It is shown that long-term oscillations of the steady-state thermal-lens signal could be associated with the formation and growth of the crystal germ. The preliminary estimation of the minimal germ size detectable from this data gives the limit at the level of 300 nm.

The thin Sn₂Sb₂S₅ films which are new absorber material useful for photovoltaic cells are studied in this paper by the photothermal deflection spectroscopic method. Our study consists to draw the experimental normalized amplitude and phase of the photothermal signal versus wavelength at a fixed modulated monochromatic light pump beam frequency. The phase curves are independent of wavelength which is predicted theoretically. However the amplitude ones show saturated regions for high and low absorption coefficient and great variations in the vicinity of the energy gap. These curves show two energy gaps which may be explained by the coexistence of two phases. By comparison of the experimental and theoretical normalized amplitude of the PDS signal one can deduce the optical absorption coefficient and then the energy gaps. The obtained values of the energy gaps are in good agreement with those obtained by reflectivity and transmission measurements.

The optical properties of Tin sulphide thin films grown on a glass substrate by chemical bath deposition were investigated by the Photothermal Deflection Spectroscopy. The experimental normalised amplitude curves of the photothermal signal versus wavelength are compared to the corresponding theoretical ones versus optical absorption coefficient in order to determine the optical absorption spectrum. Then using the Tauc law, one can deduce the energy gap. The influence of the triethanolamine concentration (TEA) in the solution bath on the optical properties was successfully studied.

This study elucidates the potential use of photothermal deflection spectroscopy (PDS), FTIR photoacoustic (FTIR-PAS), FT Raman, and FTIR-attenuated total reflection (FTIR-ATR) spectroscopy as analytical tools for investigating the drug content in semisolid formulations. Regarding the analytical parameters, this study demonstrates the photothermal beam deflection to be definitely comparable to well established spectroscopic methods for this purpose. The correlation coefficients range from 0.990 to 0.999. Likewise, repeatability and limit of detection are comparable.

Photoacoustic (PA) spectra were obtained for CdSe nanorods (NRs) of different aspect ratios, prepared via the organometallic synthesis. The second derivative spectra were used to have an accurate determination of the different excitonic transitions. Using the lowest transition energy (band gap) 1S(e)-1S1/2(h) and applying the effective mass model, the NRs diameters were determined. The obtained diameters were then compared to direct measurements of scanning tunneling microscopy (STM) and XRD. It is observed that the band gap depends on the diameter of the rods due to quantum confinement effect, since diameters are of the order of the bulk CdSe Bohr radius. The second derivative of the PA spectra for CdSe NRs also shows clearly a second excitonic transition1P(e)-1P1/2(h) in contrast to UV-Vis absorption spectra carried out for colloidal samples. The thermal parameters for samples were also measured and compared to the bulk values.

Photoacoustic (PA) technique has been used to study the optical and thermal properties of core/shell (Ag/CdSe) nanostructure. Core shell Ag/CdSe nanostructure particles were prepared using organometalic method, having a core of (12 -14 nm) and CdSe shell thickness ranging from (2.59 nm to 5 nm) as determined by TEM. The PA spectra were compared with regular UV-Vis absorption which gave comparable results, though the UV-Vis is for colloidal form and the PA spectra is for powder form. The obtained spectra are combination of the surface plasmon (SP) absorption bands of the Ag core and the band gap of CdSe shell. Second derivative fitting method and Gaussian peak fitting were used to determine precise absorption peaks and band of the PA spectra. The SP bands of the Ag core show a decrease in amplitude, broadening of the width and red shift as the CdSe shell thickness increases. The CdSe absorption band edge also shows an increasing red shift from (517 nm to 604) nm with the increases in the thickness. The thermal diffusivity of the Ag/CdSe core shell samples increase by an order of magnitude larger than the CdSe bulk value which is caused by Ag core.

In this study the photoacoustic spectroscopy was used to investigate the interaction between colloidal suspended nanosized maghemite particles and molecules present in mamona oil (ricinus communis L.). Maghemite nanoparticles were used to produce a magnetic fluid sample dispersed in mamona oil (MF-Mamona oil). In the L-band region (600 to 900 nm) of the photoacoustic spectra we found the photoacustic signal of sample MF-Mamona oil enhanced with respect to the signal of the purified mamona oil. This finding is claimed to be the signature of the strong interaction between the mamona oil's molecules and the solid surface provided by the suspended nanosized maghemite particles.

The magnetite (Fe₃O₄) nanoparticles (7 nm average diameter) have been synthesized and stably-suspended in a natural copaiba oil. The morphological and structural characteristics of the nanosized magnetite and the colloidal stability of the as-produced magnetic fluid sample were investigated using transmission electron microscopy, X-ray diffraction, photoacoustic spectroscopy and Mössbauer spectroscopy.

Thermal diffusivity of particle pyrolytic carbon layers deposited on 500 μm diameter spherical particle before irradiation has been measured using photoreflectance microscopy (PM). This technique is used to characterize of such small constituents at a microscopic scale and temperature controlled up to 1000 °C. Nevertheless, one of the layers – buffer layer – needs a particular analysis due to its porous structure. Indeed, measurements by PM on this material only permit to obtain the thermal diffusivity of the solid skeleton. These require the use of a numerical homogenization technique to estimate an effective thermal conductivity. The effect of temperature is discussed. Mapping of the thermal diffusivity of coated fuel particles provides useful data for modelling fuel performance during the nuclear reactors operation.

Recently we reported on simultaneous thermal conductivity k and thermal diffusivity a measurement of liquids and in particular of nanofluids in a configuration using an ac excited hot wire combined with lock-in detection of the third harmonic (3ω method) [1]. The conductive wire is used as both heater and sensor. The requirements for the asymptotic validity of the line heat source model are fulfilled at low modulation frequencies below a few Hz. The study of the relative sensitivity of signal amplitude and phase to changes in k and a indicates that there is an optimum frequency range for accurate and stable results. We extend by up to two decades the feasible frequency range for 3ω measurements by considering various more elaborate models for the heat transfer between the wire and the fluid. Finally we show that the same ac hot wire method can be applied to soft solid, composite materials. We measured the k enhancement of a poly(ethylene vinyl acetate) EVA polymer matrix charged with various fractions of graphite.

Photoacoustic (PA) technique has been applied to measure the effective thermal diffusivity (α_eff) of hydrating cement pastes with a varying water to -cement ratio (w/c) and for variable duration (d) of hydration. Four samples with w/c = 0.3, 0.4, 0.5 and o.6 were prepared. The frequency variation of the PA signal for each sample was recorded at the begining (0 d), as well as one week and one month of hydration. The effective thermal effusivity (e_eff) was obtained by measuring the variation of the signal with modulation frequency and the corresponding values of the effective thermal conductivity (k_eff) were calculated. The results for k_eff show a decrease at higher w/c (0.6), no change for other samples has been observed. The thickness of the duplex film of Ca(OH)₂ and C-S-H formed on the surface of the samples of w/c = 0.5 were determined using the effective layer model in the 0 d and after one month of hydration; a remarkable increase was observed in the last case.

This paper presents a method for detecting the magnetocaloric effect (MCE), based on the acoustic detection. Small temperature oscillations, due to the application of a modulated magnetic field, are detected by a microphone in a closed cell. The continuous scanning of a superimposed dc magnetic field allows, by numerical calculation, the determination of large temperature variations caused by magnetic field steps from zero to tens of kOe. Measurements were performed in Gd and Gd₅(Si_xGe_1-x)₄ compounds. The obtained results show the efficiency of the technique, which is suitable for the investigation of materials undergoing both purely magnetic phase transitions and magnetic-crystallographic first order ones.

In present work, we propose a new technique based on uniform electrical heating of pyroelectric detector which investigated simultaneous thermal conductivity and diffusivity of samples. A new one-dimensional theoretical model was developed to determinate thermal proprieties of steel alloy. The obtained values of thermal conductivity are 13 Wm⁻¹K⁻¹, 18 Wm⁻¹K⁻¹ and 24 Wm⁻¹K⁻¹ and of thermal diffusivity are 7×10⁻⁶ m²s⁻¹, 15×10⁻⁶ m²s⁻¹ and 8×10⁻⁶ m²s⁻¹ respectively for sheet steel, galvanized steel and stainless steel. These results are given with an uncertainty at the 1σ level.