Table of contents

The statistics of the angles of light deflection during its propagation in a random two-phase medium with randomly oriented phase interfaces is considered within the framework of geometrical optics. The probabilities of finding a randomly walking photon in different phases of the inhomogeneous medium are calculated. Analytic expressions are obtained for the scattering phase function and the scattering phase matrix which relates the Stokes vector of the incident light beam with the Stokes vectors of deflected beams.

A method is proposed for determining effective optical parameters of multiply scattering random media by analysing the angular intensity distribution of coherent backscattering from a finite-thickness medium layer taking into account the reflectivity of its boundaries. The optical parameters of dry paper layers and paper layers saturated with immersion liquids are studied in the visible region by measuring the half-widths of coherent backscattering peaks at 633 and 532 nm and using the diffuse and collimated transmission spectroscopy. It is shown that the scattering of probe radiation in paper layers is isotropic.

The propagation of radiation in different spectral ranges in a superficial skin layer partially filled with titanium dioxide nanoparticles at the volume concentration 0.67%–2.25% is simulated by the Monte-Carlo method. This volume concentration corresponds to the maximum admissible concentrations of particles that most efficiently attenuate radiation in the independent scattering regime. The transmission of radiation at 307, 400, and 500 nm in a 20-μm thick skin layer is simulated and the effect of nanoparticles on the contributions from photons of different scattering orders to transmission is considered. It is shown that the administration of nanoparticles results in the broadening of the scattering-order distribution of photons propagated through the skin layer and the shift of the maximum of this distribution in the direction of a greater number of scattering events at wavelengths 400 and 500 nm, the effect being more pronounced at 400 nm. The increase in the scattering order elongates photon trajectories in the medium and enhances diffusely scattered radiation, thereby reducing transmission.

We analyse the possibilities of simultaneous measuring three optical parameters of scattering media, namely, the scattering and absorption coefficients and the scattering anisotropy parameter by the intensity profile of backscattered radiation by using the neural network inversion method and the method of adaptive-network-based fuzzy inference system. The measurement errors of the absorption and scattering coefficients and the scattering anisotropy parameter are 20%, 5%, and 10%, respectively.

Single crystal and optical ceramic CaF₂ samples are studied by the method of thermally induced depolarisation of laser radiation at 1076 nm. The absorption coefficients of the single crystal and ceramics are estimated as α < 4.5×10^-4 cm^-1 and α < 1.33×10^-3 cm^-1, respectively.

Self-induced transparency is theoretically studied in the system of quantum transitions whose frequencies differ due to the isotope shift caused by differences in the mass, shape, and shell structure of atomic nuclei. In the case of good mutual resolution of the spectral lines of different isotopes, only one component of the mixture is in resonance with the pulse field, while the rest of the components interact with the pulse under quasi-resonance conditions. This circumstance determines the specific features of the effect in heterogeneous media. The conditions for realisation of self-focusing and quasi-channeling are found taking into account transverse perturbations. The latter regime is characterised by a change in the shape of the propagating pulse whose transverse size remains invariable.

Dispersion phase matching curves and spectral distributions of the efficiency of difference frequency generation in the terahertz range are calculated for collinear propagation of interacting waves in zinc blende semiconductor crystals (ZnTe, CdTe, GaP, GaAs). The effect of the pump wavelength, the nonlinear crystal length and absorption in the terahertz range on the spectral distribution of the efficiency of difference frequency generation is analysed.

Various schemes for amplification of Stokes signals are investigated. Some new systems, such as an SBS amplifier in the transient amplification regime and a combined laser amplifier–SBS amplifier, are proposed and realised. Conditions are found under which amplification is accompanied by small distortions of the spatial structure of a signal. A two-pass system for small-signal amplification with phase conjugation is developed by using a PC mirror in the combined amplification system. The gains up to 10¹⁶ were obtained for the phase conjugation quality ∼80%, the output energy ∼1 J, and pulse duration ∼30 ns.

The optimal pressures of the active H₂, HBr impurities and the working substance (copper bromide) for an effective operation of the CuBr laser are determined experimentally. It is shown that to achieve the highest output laser parameters by increasing the voltage across the gas-discharge tube and the pump pulse repetition rate, it is also necessary to increase the amount of the impurity introduced. At the same time, the optimal pressure of copper bromide decreases with increasing the pulse repetition rate.

The technology is developed for manufacturing active polymer optical fibres doped with organic dyes. Stimulated emission and amplification in the long-wavelength part of the visible spectrum is studied for rhodamine 11B, phenalemine 512 and substituted DCM pyran in polymer optical fibres. Lasing was observed upon longitudinal and transverse pumping by the second harmonic of a Nd:YAG laser. The gain in polymer fibres was estimated by measuring the intensity ratio of radiation of a master oscillator (dye laser) propagated through the excited (pumped) and unexcited (not pumped) fibre pieces doped with organic dyes. It is shown that the lasing efficiency of rhodamine 11B in a transversely pumped polymer fibre can achieve 36%. The maximum gain (25 dB m^-1) is obtained in fibres doped with phenalemine 512.

The design of a TEA CO₂ laser with UV preionisation by a surface corona discharge is described and the dependences of its average output energy on the gas-flow rate, discharge voltage and pulse repetition rate are presented. The scheme of the electric circuit and the geometry of the pre-ionisation system are considered. The electric circuit is designed to produce only impulse voltage difference between the laser electrodes. The triggering system of the trigatron is used to prevent the appearance of the arc. The dependences of the current, voltage and average output energy on the gas-mixture composition and applied voltages at a low pulse repetition rate are presented. The central output wavelength of the laser was measured with an IR spectrometer. Lasing at two adjacent vibrational–rotational transitions of the CO₂ molecule was observed, which demonstrates the possibility of simultaneous lasing at several lines.

A method for producing non-Gaussian light beams with a uniform intensity profile is described. The method is based on the use of a combined waveguide quasi-optical resonator containing a generalised confocal resonator with an inhomogeneous mirror with absorbing inhomogeneities discretely located on its surface and a hollow dielectric waveguide whose size satisfies the conditions of self-imaging of a uniform field in it. The existence of quasi-homogeneous beams at the output of an optically pumped 0.1188-mm waveguide CH₃OH laser with a amplitude-stepped mirror is confirmed theoretically and experimentally.

The influence of intense electric and optical fields produced by a streamer discharge in wide-gap semiconductors on their spectroscopic properties is studied. The effect is manifested in the reversible change of the luminescence parameters of the active medium. Methods are proposed for increasing the service life and efficiency of a streamer laser in limiting regimes, which are based on the use of semiconductor protective layers of a certain crystallographic orientation and a crystal microrelief with the size of elements of the order of the wavelength of light. Streamer emission was observed and studied in new promising Eu:CaGa₂S₄ and Eu:Ca₄Ga₂S₇ materials.

The scheme of an active interferometer for amplification of small optical signals for their subsequent photodetection is proposed. The scheme provides a considerable amplification of signals by preserving their quantum-statistical properties (ideal amplification) and also can improve these properties under certain conditions. The two-mode squeezed state of light produced upon four-wave mixing, which is used for signal amplification, can be transformed to the non-classical state of the output field squeezed in the number of photons. The scheme is phase-sensitive upon amplification of the input coherent signal. It is shown that in the case of the incoherent input signal with the average number of photons ⟨n_s⟩∼1, the amplification process introduces no additional quantum noise at signal amplification as large as is wished. A scheme is also proposed for the cascade small-signal amplification (⟨n_s⟩∼1) in the coherent state producing the amplified signal in the squeezed sub-Poisson state, which can be used for the high-resolution detection of weak and ultraweak optical signals.

The minimal coherence length of probe optical radiation sufficient for formation of a homogeneous interference structure is estimated. The estimate is based on the analysis of the interference structure in the intensity distribution of the field scattered by rough surfaces and point objects and also formed in interferometers. Analysis was performed for the field intensity detected for the time T > 10τ_c (under the condition that the coherence time of the probe radiation is τ_c > 3/ω₀, where ω₀ is the central frequency of the emission spectrum). It is shown that the minimal coherence length L_c of the probe radiation, at which the homogeneous stratified interference structure of the scattered field can be still formed, is 8λ (λ is the central wavelength). The possibility of using this result for determining the maximal information content of the method of low-coherence optical tomography is analysed.

The geometrical and wave approaches to the transformation of a family of the illumination distributions, measured at different sections of a laser beam focused by an optical system, to a family of different-aspect projections of the Wigner function of this beam required for the reconstruction of this function by the method of computer tomography are considered from a unified point of view by using the mathematical apparatus of matrix optics.

The laser amorphisation of glass ceramics (LAGC) is studied by optical pyrometry and video recording. The mechanism of local LAGC as a structural phase transition determined by the temperature kinetics in the laser-irradiated region is proposed. The ranges of the power density and exposures to the 10.6-μm IR radiation required for amorphisation of the typical glass ceramics, a SiO₂–Al₂O₃–CaO–MgO–TiO₂ sital are determined. It is shown that LAGC can be used to fabricate a number of miniature optical elements such as lenses, lens rasters, light guides and waveguides, etc.

The possibilities of enhancing the efficiency of laser drilling of micron holes, increasing their depth, and eliminating their conic shape are studied by using a single-mode loop Nd:YAG laser with self-phase conjugation on the gain gratings and passive Q-switching by a scanned gradiently coloured F₂^-:LiF crystal. Holes of diameters 15–150 μm and depth up to 20 mm with the aspect ratio (ratio of the hole depth to its diameter) of 50–155 are drilled in various metals and alloys. It is shown that passive Q-switch scanning during drilling provides the increase in the depth and speed of the laser drilling of superdeep holes by a factor of 1.5–2.

A spark-gap preionisation system is studied in a laser pumped by a generator with an inductive energy storage and a semiconductor current interrupter. This preionisation system was shown to produce, in addition to UV and VUV radiation, soft X-ray pulses with photon energies higher than 5 keV. The X-ray radiation was recorded from the plasma of a volume discharge in nitrogen, helium, and a NF₃–helium mixture. Shortening the rise time of the voltage pulse applied across the spark gaps of the preionisation system and the main gap was demonstrated to increase the radiation pulse duration and to improve the efficiency of exciplex lasers and of several other dense-gas lasers.

The energy and spectral emission characteristics of a barrier discharge are studied in mixtures of inert gases with iodine vapour. The emission spectrum exhibits a strong 342-nm D' → A' molecular band of the I₂^* molecule, the 206.2-nm resonance line of iodine, and a group of emission bands of iodine. Small admixtures of Ne (5%) to the Ar – I₂ mixture increase the emission efficiency and power by a factor of 2–2.5. A sealed off I₂ excilamp with the emission maximum at 342 nm is fabricated.