Table of contents

List of Scope, Invited Speakers, International Programme, Local Organising Committee are available in this pdf.

24^th International Conference on Spectral Line Shapes (ICSLS 2018)

It is commonly accepted that the Europhysics Study Conference on Spectral Line Broadening and Related Topics which was held in Meudon in 1973 was the first in the current series of ICSLS meetings. The ICSLS is a bi-annual conference series and to date has been held at alternating European and North-American conference venues. It is proposed that it move to other continents in future. The most recent venues were Paris, France (2004), Auburn, USA (2006), Valladolid, Spain (2008), St. John's, Canada (2010), St. Petersburg, Russia (2012), Tullahoma, Tennessee, USA (2014) and Torun, Poland (2016). The 2018 (24th) ICSLS conference took place in Dublin during June 17 - 22, 2018.

The ICSLS covers a broad range of topics related to spectral line shape studies, including: line shapes of atomic and molecular transitions in neutral gaseous mixtures, single and multi-photoionisation ionisation processes, high and low temperature plasmas, clusters and helium droplets, nanophotonic processes, spectroscopy of stellar atmospheres and interstellar media, spectroscopy of planetary atmospheres and exoplanets, cold atoms and molecules, collision-induced spectra, processes in laser fields, innovative techniques of line shape applications for diagnostic purposes and fundamental studies with narrow optical resonances along with applications in e.g., industrial, environmental, medical and all other potential domains of interest. The conference includes a mix of invited talks, talks selected from submitted abstracts and poster presentations.

List of Conference Photograph and Sponsors are available in this pdf.

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.

This work elaborates on laboratory measurements of hydrogen Balmer series lines and diatomic molecular species in laser-plasma. Comparisons with astrophysical white dwarf spectra, recorded at various observatories and the Hubble space telescope, point out direct applications of experimental results. The recorded general relativity gravitational- or Einstein-shift of the atomic lines allows one to infer the ratio of mass and radius. The Stark-effect redshifts of hydrogen alpha and hydrogen beta lines investigated with time-resolved emission spectroscopy are usually one order of magnitude larger than the gravitational shift. In view of white dwarf atmospheres dominated by hydrogen and the associated absorption spectra, averaging the laser-induced plasma data reveals spectral line shapes that mask the redshift caused by the Stark effect. The available white dwarf data indicate that the collected radiation propagated through regions of different density in the star's atmosphere. Diatomic spectra are typically recorded as white dwarfs further progress in their transformation.

With relative accuracies reaching 10⁻¹⁸, optical atomic clocks are currently the most sensitive physical instruments known to man. Weakly bound ultracold molecules enable the study of fundamental physics through their sensitivity to e.g. the proton-to-electron mass ratio or hypothetical Yukawa-type fifth forces predicted by several extensions of the Standard Model. These applications, however, require precision measurements of molecular transitions that are beyond current experimental capabilities. Here we propose to construct an 'optical molecular clock' that would solve this problem by bringing the experimental techniques used in optical atomic clocks to the realm of cold molecules. We show that such a clock could utilize ultracold ytterbium molecules and we predict the positions and properties of Yb₂ clock lines. A successful experimental realization of this proposal could pave the way towards sub-Hz level molecular spectroscopy.

We report on complementary theoretical and laboratory investigations of the 2p ion yield cross sections for the molecular-ion series SiH_n⁺ (n = 1, 2, 3), in the 95-108 eV photon energy range, below the L-shell threshold. The experiments used an electron cyclotron resonance (ECR) plasma molecular-ion source coupled with monochromatised synchrotron radiation in a merged-beam configuration. The experimental spectra are compared with total photoabsorption cross-sectional profiles calculated using an ab initio configuration interaction method inclusive of spin-orbit coupling and the vibrational dynamics. The experimental results show vibrationally resolved resonances for SiH₂⁺ in the 98-102 eV range. The calculations indicate twenty four core-excited states below the energy of 102 eV, of which only four contribute significantly to the observed spectrum. These states correspond to the excitation of an atomic-like 2p electron to the SiH₂⁺ (5a₁) valence orbital.

We review our recent studies on the spectral line shapes of H₂, including its isotopologues, self-perturbed or perturbed by helium. Line shape parameters are derived following the generalized Hess method and making use of the close-coupling formalism.

Tungsten ion densities are determined by measuring radial profiles of line emissions in LHD. Zn-(W⁴⁴⁺) and Cu-like (W⁴⁵⁺) ion densities are determined from line emission at 60.9 Å and 127.0 Å, respectively. Ion densities of W²⁴⁺, W²⁵⁺ and W²⁶⁺ are also determined from tungsten pseudo-continuum (a so-called unresolved transition array (UTA)) at 29-33 Å. Observations of magnetic dipole (M1) forbidden lines at 3377Å enable evaluation of the ion density of W²⁷⁺. In EAST tokamak the tungsten concentration is estimated by a combination of the UTA and total radiation loss. In HL-2A the tungsten influx is evaluated from line emission of W⁶⁺ ions at 216.2 Å and 261.4 Å, which are measured during the tungsten reappearance phase after tungsten laser blow-off. All these results demonstrate a good approach towards quantitative tungsten analysis.

We present an analysis of hydrogen Balmer line shapes observed in two white dwarf spectra. One spectrum presents singlet lines while the second one presents lines with a triplet structure. The latter is a feature of the presence of a strong magnetic field. Using both Stark and Zeeman effects, we infer the density and the magnetic field. Our line shape calculations employ a computer simulation technique. The radiative transfer is accounted for through a onedimensional slab model.

Data have been obtained for ejection of valence shell 4p and 3d electrons in krypton and the ¹t₂ and ²a₁ orbitals in methane. Measurements, with kinematics both on and off the Bethe ridge, examine how the spectral shapes change for fixed energies of 1015 eV for the incident electron, 880 eV for scattered and 120 eV for ejected electron and angular momentum changes. The studied interactions are activated by excitation and ionization of inner shell (-d) electrons and concern complex electron correlations. The triple differential cross sections for the Bethe ridge conditions within the experimental accuracy are similar to the values predicted by the Distorted Wave Impulse Approximation and Born Approximation calculations but need further consideration of electron correlation effects.

We have measured sets of mass spectra for positive ions produced by low-energy electron impact on phenanthrene. Ions have been mass resolved using a reflectron time-of-flight mass spectrometer, and the electron impact energy has been varied from 0 to 100 eV in steps of 0.5 eV. Ion yield curves of most of the fragment ions have been determined by fitting groups of adjacent peaks in the mass spectra with sequences of normalized Gaussians. The aim of this paper is to provide a detailed comparison of phenanthrene with its isomer anthracene, for which we have published results in a previous paper [1]. Appearance energies for a selection of fragment ions of phenanthrene have been determined, and are compared with anthracene. The most significant differences are observed in the ion yield curves of the ions containing 12 carbon atoms. The ion yield curves of phenanthrene have higher maximum yields and lower appearance energies compared to anthracene. For the fragments containing 9 and 10 carbon atoms the phenanthrene yields are slightly lower, but the appearance energies are the same as for anthracene. Small differences in yields are also observed for the fragments with 6 and 7 carbon atoms. The double and triple ionization energies of phenanthrene have been determined and are in agreement with anthracene.

We present time resolved, spatially integrated spectra of aluminium II oxide formed from the condensation of an aluminium laser plasma in air. The spectra show a revival of the emission from aluminium oxide molecules at 35µs after the plasma ignition. Thermodynamic calculations, together with temperature measurements, indicates that as the plasma cools, the aluminium oxide molecule forms through two different channels, explaining its increased presence.

The absorption due to H2–H2 complexes is investigated theoretically. The potential and dipole surfaces for the complex are taken from the literature. Quantum dynamical calculations of the roto-translational absorption spectrum are performed. Special attention is paid to the fine features due to hydrogen dimers, (H₂)₂, at the centers of the collision-induced rotational S(0) and S(1) transitions. The computed absorption coefficients are used to analyze the spectra of the four giant planets of our solar system.

We have derived a formula for calculating the polarization state of the Lyman-α line in plasma caused by anisotropy in the electron velocity distribution function. Calculation results under the condition of the magnetically confined fusion plasma show that the longitudinal alignment of 0.01 is caused by approximately 10%–20% difference in the electron temperature in the directions parallel and perpendicular to the magnetic field. It is also found that the polarization decreases with the increasing electron density, n_e, due to the collisional population averaging effect over the magnetic sublevels in the range of n_e > 10¹⁸ m⁻³ and is virtually extinguished at n_e = 10²¹ m⁻³.

This paper presents the experimental Stark-broadening and shifting analysis of 40.68 MHz nitrogen RF-CCPs. The non-thermal plasmas were generated in a cylindrical parallel plate plasma reactor under 0.2-0.8 Torr and 50-200 Watt. The physical and chemical spectral analyses of the system were performed by using the OES method. Many N I and N II lines were detected in the UV-Vis-NIR region. The diagnostic measurements of the plasmas were done according to the Saha relation and the Boltzmann plot method, under the LTE assumption. The calculated T_e, T_gas, n_e and n₀ take values in the range of (10748 ± 742 – 16144 ± 653) K, (690 ± 82 – 833 ± 22) K, (0.598 ± 0.024 – 2.87 ± 0.03) × 10¹⁴ cm⁻³ and (2.32 ± 0.06 – 11.37 ± 1.44) × 10¹⁵ cm⁻³, respectively. The normalized Stark-broadening parameters (ω_e and d_e) of the vacuum visible N II multiplets (653.445, 659.749 and 661.545 nm) were determined for 10.000 and 15.000 K.

Since the invention of the extremely thin cell which sustains prolonged action of hot and dense alkali vapours, a number of spectroscopic problems have been solved with its aid. As the width of the cell is comparable to, or smaller than, the wavelength of the actual atomic transition, The Doppler width of the fluorescence light is reduced due to the cage effect. Stimulated by recent measurements of the fluorescent excitation line shapes in the extremely thin cell we studied the dependence of these line shapes on the cell thickness.

We have analyzed 10 room temperature spectra of the fundamental band of CO and CO-air using the Voigt, speed-dependent Voigt, speed-dependent Rautian line shape models. Line positions, intensities, air- and self-broadening coefficients, pressure induced air- and self-shift coefficients, and line-mixing parameters have been retrieved. The CO- and N₂-broadened carbon monoxide half width coefficients have been calculated using a potential energy surface based on Tipping-Herman intermolecular interaction potential and taking the electrostatic interactions into account.

Doppler free two photon optogalvanic measurements of the Stark splitting of the 2S level of hydrogen are used to determine the local electric field strength (E-field) in the cathode fall region of a hollow cathode discharge operated in pure hydrogen. The aim of these measurements is to study how the cathode fall characteristic depends on cathode material (stainless steel and tungsten) and cathode diameter (10 and 15 mm). The measurements revealed that the cathode diameter has a minor influence whereas the cathode fall characteristics obtained for stainless steel cathodes are remarkably modified due to sputtering.

In this work, measurements of cyanide (CN) molecular spectra following laser-induced optical breakdown are communicated. The recorded time-resolved data are Abel inverted to determine the spatial distributions of the maximum CN signals and to evaluate molecular excitation temperatures. The experiments are conducted in a 1:1 CO₂:N₂ gas mixture contained in a cell kept at atmospheric pressure, and the micro-plasma is generated using 150 mJ, 6 ns Q-switched Nd:YAG laser radiation. The optical emissions from the micro-plasma are dispersed using a 0.64 m spectrometer and are recorded along the wavelength and slit dimensions using an intensified charge-coupled device.

The probabilities of the radiative transitions ν'1(³P₁)–ν''0(¹S₁) and the radiative lifetimes of the resonant ν'1(³P₁) states of the CdAr molecules as functions of the vibrational excitation degree were calculated using the effective Hamiltonian method and the semiempirical method of quasi-molecular term analysis.

Optical transitions between both discrete and continuum states are considered in the frame of the model of two delta potentials. The wave functions of the definite parity are utilized for both discrete and continuum states cases.

We report on the experimental and theoretical study of qusimolecular emission near the forbidden atomic line Hg(6³P₂-6¹S₀) in a mixture of mercury vapor with argon. The experimental profile is a continuous band in the range 2230 - 2275 Å with a maximum at about 2255 Å. By using the semiempirical method of quasimiolecular term analysis and available experimental potential curves the interaction potentials of the excited atoms Hg* + Ar and the probabilities of the radiative transitions are determined. Based on them quasimolecular emission spectra are calculated.

This study is aimed at the explanation of peculiarities in emission spectral profiles obtained by different authors for the excimer band HgXe(A30+) – HgXe(X10+). The calculations of the spectral profiles have been fulfilled for two limiting cases: for the high density and low density of buffer gas atoms. The results obtained lead to the conclusion that the discrepancies can be mainly caused by the recombination and relaxation processes determining the population ro-vibrational states of the HgXe(A30+) excimer. The inverse spectroscopic problem is considered.

We have developed an empirical Barker, Fisher and Watts (BFW) interatomic potential for the Ar–Kr pair along with a dipole moment computed from first principles using Møller–Plesset perturbation theory to second order (MP2). Using these results, we performed molecular dynamics calculations to compute the Ar–Kr collision induced absorption (CIA) spectrum at different temperatures. By comparing them to other calculations using a two body interaction treated with quantum mechanics, we have shown that the difference is due to the dimer's contribution which grows in importance as the temperature is lowered.

Non-LTE modelling requires accurate atomic data e.g. collisional excitation and ionization cross-sections and rate coefficients. In order to improve the modeling of the solar photosphere, as well as to model atmospheres of other similar and cooler stars where the main constituent is also hydrogen, it is necessary to take into account the influence of all the relevant collisional processes on the excited-atom populations in weakly ionized hydrogen plasmas. In this context we present the data needed for the inclusion of the specific atomic collisional processes in the investigation of the optical and kinetic properties of weakly ionized stellar atmospheres layers. The ionization processes in collisions of excited hydrogen atoms with atoms in ground states were considered for the principal quantum numbers 2 ≤ n ≤ 20 and temperatures 4000 K ≤ T ≤ 20000 K.

Making reliable semi-classical calculations using the Modified Complex Robert and Bonamy formalism require an intermolecular potential expanded to a high order. Reduced matrix elements (RMEs) need to be computed for each component of the intermolecular potential using the wavefunctions of the states involved in the transition. Calculations for a number of transitions of 13 vibrational bands were performed using the vibrational dependent RMEs and using the ground state RMEs for both upper and lower states. The calculations show that for transitions that obey the sum rules the spectroscopic effect is small.

The combined relativistic energy approach and relativistic many-body perturbation theory, with a zeroth order approximation density functional theory, are used to calculate the ionisation rates and effective lifetimes values for Rydberg atoms in a black-body radiation field. Calculations for the rubidium atom in Rydberg states with principal quantum number n > 26 are presented and compared with available theoretical and experimental data.

Computing the parity non-conservation (PNC) effect parameters in a few heavy atomic systems has been performed and based on the combined relativistic nuclear mean-field theory and relativistic many-body perturbation theory (PT) formalism with accounting for the interelectron correlation and dominant QED corrections. Results of computing the PNC amplitudes and weak charges for different heavy atoms (caesium, thallium, ytterbium) are presented and compared with available data in the literature.

We review our recent experimental and theoretical studies on the spectral line shapes of D₂ in helium baths. We also provide the most accurate to date experimental line positions of the first pure rotational Stokes lines, S₀(j=0-2), of D₂.

In the chiro-optical phenomenon known as photoelectron circular dichroism, the angular distribution of electrons ionized from chiral molecules by circularly polarized light pulses has been found to be anti-symmetric with respect to the direction of the light propagation. To study this phenomenon, chiral molecules were multiphoton ionized with a femtosecond laser in our laboratory. Using a simple stereo-detection setup, direct measurements of the asymmetry for the exemplar aromatic chiral molecule 1-phenylethanol were made using 260 nm pulses produced at a rate of 1 MHz. It was found that the asymmetry had a linear dependence on Stokes' S₃ parameter indicating that the photoelectron circular dichroism is due to a single photon process from the excited state of the molecule. This is in contrast to previous and new results for camphor where a more complex dependence on S₃ suggested that selective excitation of molecules with certain orientations was influential.

In this work, an ab-initio method is used to study few-photon ionisation of helium with linearly and circularly polarized light. The photoionization cross sections are estimated from the ionization yields calculated by directly propagating the time-dependent Schrödinger equation (TDSE) and are compared with those obtained from the lowest-order (non-vanishing) perturbation theory (LOPT). The results show a clear deviation of the TDSE yields from those of the LOPT as well as the dominance of the linearly-polarized ionization yields over the circularly polarized ones, towards higher field intensities.

In this work, we present measurements of the intensity-dependent photoelectron spectrum of Kr irradiated by the FLASH FEL tuned to a photon energy of 25.8 eV. Intensity dependent photoelectron spectra were obtained with the aid of a Velocity Map Imaging (VMI) spectrometer. As the FEL photon energy is close to threshold, two photon sequential double ionization is favoured. The number of open channels is kept to a minimum and leading to a simple description of the process.

Vacuum ultraviolet laser induced breakdown spectroscopy (VUV-LIBS) experiments were carried out on pharmaceutical samples and machine learning techniques were applied to analyze the samples. The motivation for the application of these machine learning techniques is the classification of analytes, allowing us to distinguish pharmaceuticals from one another based on their spectra. Three machine learning techniques have been compared, self-organizing maps (SOM), support vector machines (SVM) and convolutional neural networks (CNN). For multiclass and 1vs1 testing CNNs appeared to perform the best of the three machine learning techniques on the relatively small number of pharmaceutical LIBS spectra used in this study.

Initial results from time resolved imaging on the formation of a plasma in ambient air, with properties akin to those of the stagnation layer that can be formed at the collision front between two expanding plasmas in vacuo, are reported. Our proposed method for creating stagnation in air at atmospheric pressure is to take a single laser pulse focused into the vertex of a V-shaped channel so the plasma formed on the two surfaces of the V-shaped channel will expand normal to the surface, interact with each-other and potentially stagnate. Time-resolved broadband imaging was used to track the plume expansion and evolution of the plasma.

We report the development of an electrostatic sector analyser (ESA) combined with a time-of-flight (TOF) spectrometer along with some preliminary results from its use in measuring the energies of ions emitted from colliding laser produced plasmas.

The nonlinear coupling of Langmuir, ion sound and electromagnetic waves can create wave collapse conditions in a plasma, and modify the line shapes emitted by hydrogen atoms. Such conditions may appear in the presence of a strong source of energy, and create numerous regions where wave packets localize and the plasma density is decreased. We use a model of envelope solitons for the electric field acting on the emitter, and calculate the dipole autocorrelation function and the line shape with a numerical simulation. We investigate the role of the frequency of wave packets, and propose an approach retaining a dispersion relation ω(k).

The report concentrates on a study of vacuum ultraviolet (VUV) photoabsorption spectroscopy of metal atoms and ions using laser plasma generated continuum radiation. The absorption spectra of lowly charged ions of lead and bismuth have been obtained using the Dual Laser Plasma (DLP) photoaborption technique. While the RTDLDA code of Zangwill provides a good approximation to the overall spectral shape, the Cowan suite of codes, with input parameters tuned by comparison with spectral lines already identified in the literature are needed to identify unknown lines.

Atomic processes and plasma surface interactions play a key role in the physics of the edge, divertor and X-point plasmas. Passive spectroscopy is one of the best methods to characterize tokamak edge plasmas. In this work, we report on synthetic spectra calculations for the characterization of electron density in recombining divertor plasma conditions. It is shown that an analysis of the Stark broadening of Balmer lines with moderate principal quantum number provides the electron density with good accuracy.

A space-resolved VUV spectroscopy using a 3 m normal incidence spectrometer is utilized to measure the impurity emission profile in the edge and divertor plasmas of the Large Helical Device in the wavelength range of 300 - 3200 Å. The ion temperatures derived from the Doppler profile fitting for the spectra of carbon CII 1335.71 × 2 Å, CIII 977.02 × 2 Å, and CIV 1548.20 × 2 Å are comparable to ionization potential for each charge state. The vertical profile of the ion temperature measured from CIV line has higher values in the edge observation chords compared to those in the central chords.

We have investigated the polarization of the Lyman-α line due to anisotropic electron collisions in the Large Helical Device (LHD). Optical components provided by the CLASP (Chromospheric Lyman-αlpha Spectro-Polarimeter) project [Kano R 2017 ApJL 839 L10] team have been incorporated into a VUV spectrometer so that linearly polarized light spectra at different angles can be obtained sequentially. The steady-state phase of an ECH (electron cyclotron heating) discharge has been analyzed, and it is confirmed that the Lyman-α line is polarized. From a temporal variation analysis of the intensity, integrated over the line profile, the polarization degree is evaluated to be 3.4%. A simple theoretical model calculation shows that this polarization degree can be explained by approximately 10% anisotropy in the electron temperature between the parallel and perpendicular directions with respect to the magnetic field.

Spatially-resolved spectral measurement of a hydrogen pellet ablation cloud has been conducted in the Large Helical Device. Least square fittings of one of the obtained spectrum are inconsistent when the complete local thermodynamic equilibrium (CLTE) condition is supposed. A better agreement is found when a more general spectral model is used. The electron density of 1.4 × 10²³ m⁻³ obtained is similar to that obtained in a previous study [M. Goto et al., Plasma Phys. Control. Fusion 49, 1163 (2007)]. The electron temperature of 0.4 eV is however significantly lower than the value of 1 eV derived in the same previous study.

This work identifies analytical lines in laser-induced plasma for chemical analyses of major elements found in surrogate nuclear debris. These lines are evaluated for interferences and signal strength to insure they would be useful to measure relative concentrations. Compact, portable instruments are employed and can be included as part of a mobile nuclear forensics laboratory for field screening of nuclear debris and contamination. The average plasma temperature is measured using the well-established Boltzmann plot technique, and plasma's average electron density is determined using empirical formulae based on Stark broadening of the H-alpha line. These measurements suggest existence of partial local thermal equilibrium.

Balmer line and continuum spectral emission of hydrogen are modeled for detached divertor plasmas (electron density, n_e~10²⁰-10²¹m⁻³ and electron temperature, T_e~1 eV) of Tokamaks. The Stark broadened high-n lines are calculated considering electronic broadening using the impact approximation. Continuum emission is calculated using analytical equations for radiative recombination and bremsstrahlung. Discrete to continuum transition is modeled using a dissolution factor approach.

Ablation of titanium wafers in air is accomplished with 60 µs pulsed, 2.94 µm laser radiation. Titanium monoxide spectra are measured in the wavelength range of 500 nm to 750 nm, and molecular signatures include bands of the C³ Δ → X³ Δ α, B³ Π → X³ Δ γ', and A³ Φ → X³ Δ γ transitions. The spatially and temporally averaged spectra appear to be in qualitative agreement with previous temporally resolved studies that employed shorter wavelengths and shorter pulse durations than utilized in this work. The background signals in the current study are possibly due to particulate content in the plume. A chemical kinetic model of the plume is being developed that will be coupled to a diatomic emission model in order to extract a molecular temperature from the observed spectra.

Laser Induced Breakdown Spectroscopy (LIBS) is an analytical technique used to classify and potentially quantify elements in complex hosts (or matrices) [1,2]. In this study, silicon based aluminium thin films were developed to study the depth profile and ablation rate of the material. Five films with different thicknesses from 1mm to 1.5 micron were used. The experimental setup consisted of s single pulse system with a Nd:YAG laser (1064 nm, up to 450 mJ, pulse duration 6 ns) used to irradiate the samples, an optic fibre spectrometer was used to detect the spectrum. The results show low ablation rate with time integrated method.

In this paper, we present a study of broadening of thallium emission spectral line shapes in the Tl-Hg discharge. The spectral lines were emitted from high frequency electrodeless lamps, containing Tl, Hg, Ar mixtures and measured by means of Fourier transform spectrometer. The deconvolution procedure, by means of ill posed inverse task solution, was performed to obtain the real (without instrumental function) profiles for further analyze. The solution was implemented using Tikhonov regularization algorithm. The Tl 276.8 nm, 351.9 nm, 352.9 nm spectral lines were analyzed in detail in dependence on the discharge power. The additional broadening of Tl 276.8 nm and 351.9 nm lines were observed due to the excitation transfer in collisions of ground state Tl atoms with excited Hg atoms.

In this paper, we present a study of the validation of the deconvolution procedure for multicomponent overlapping spectral line profiles. The solution of the ill-posed inverse task was implemented using the Tikhonov regularization algorithm. For this study, both, theoretically modelled and experimentally measured 253.7 nm mercury spectral line profiles were used, emitted from high-frequency electrodeless lamps.

This work is aimed at the application of wavelength modulation spectroscopy with the second harmonic detection for determination of OH radical concentration in laminar premixed flames of methane-air mixtures. Several hot water lines and two overtone OH transitions were identified in high-resolution absorption spectra measured in our experimental setup. Information on spectral line-shape parameters for selected OH transitions were extracted from the experimental data using relevant methods and approximations. An appropriate line-shape model was finally implemented into an automated least-square fitting procedure in order to quantify the local mole fraction of OH radical in an atmospheric pressure flames.

We report the development of a portable single-shot Fourier transform spectrometer for application in laser induced breakdown spectroscopy (LIBS) with a particular emphasis on remote or standoff LIBS. The device, based on a design by Harvey and Padgett[1], has a number of inherent features that give it performance advantages over a portable grating spectrometer, in particular a gain in signal to noise ratio (SNR). Tests with low-pressure discharge lamps show a gain in SNR of at least five times that of a traditional portable grating spectrometer in stand-off mode. In addition, the instrument has also demonstrated the ability to measure the spectrum from a short or ultrashort pulsed source in a single shot, e.g. a laser produced plasma.

We present a novel InP photonically integrated optically injected device that is gain switched for the generation of an optical frequency comb. Using this technique, an optical frequency comb with a free spectral range of 6.25 GHz and nine spectral lines within a 3 dB spectral window is obtained. Such a device provides tunability of both the free spectral range and the centre emission wavelength, which facilitates the matching of the wavelength to the signature of a target gas. The stable spacing and high phase correlation between the comb lines confirms the potential of the device to be used in various applications such as spectroscopy, telecommunications and gas sensing.