Table of contents

Using the method of photon-correlation spectroscopy, the coefficient of translational diffusion D_t and the hydrodynamic radius R of the particles in aqueous solutions of the bovine serum albumin, containing silicon nanoparticles, are determined. The character of the dependence of these parameters on the concentration of the protein indicates the absence of interaction between the studied particles in the chosen range of albumin concentrations 0.2 — 1.0 mg mL^-1.

A new method for delivering nanoparticles into the skin using the fractional laser microablation of its surface and the ultrasonic treatment is proposed. As a result of in vitro and in vivo studies, it is shown that the 290-nm laser pulses with the energy from 0.5 to 3.0 J provide the penetration of nanoparticles of titanium dioxide with the diameter ∼100 nm from the skin surface to the depth, varying from 150 to 400 μm. Histological testing of the skin areas, subjected to the treatment, shows that the particles stay in the dermis at the depth up to 400 μm no less than for three weeks.

The issues of detecting the inhomogeneities are studied aimed at mapping the distribution of absorption and scattering in soft tissues. A modification of the method of diffuse optical tomography is proposed for detecting directly and determining the region of spatial localisation of such absorbing and scattering inhomogeneities as a cyst, a hematoma, a tumour, as well as for measuring the degree of oxygenation or deoxygenation of blood, in which the late arriving photons that diffuse through the scattering object are used.

Investigation of the diffusion of cytamines, a typical representative of which is cortexin, is important for evaluating the drug dose, necessary to provide sufficient concentration of the preparation in the inner tissues of the eye. In the present paper, the cortexin diffusion rate in the eye sclera is measured using the methods of optical coherence tomography (OCT) and reflectance spectroscopy. The technique for determining the diffusion coefficient is based on the registration of temporal dependence of the eye sclera scattering parameters caused by partial replacement of interstitial fluid with the aqueous cortexin solution, which reduces the level of the OCT signal and decreases the reflectance of the sclera. The values of the cortexin diffusion coefficient obtained using two independent optical methods are in good agreement.

We study the possibility of solving the multiparameter inverse problem of nonlinear laser fluorimetry of molecular systems with high local concentration of fluorophores (by the example of chlorophyll α molecules in photosynthetic organisms). The algorithms are proposed that allow determination of up to four photophysical parameters of chlorophyll α from the experimental fluorescence saturation curves. The uniqueness and stability of the inverse problem solution obtained using the proposed algorithms were assessed numerically. The laser spectrometer, designed in the course of carrying out the work and aimed at nonlinear laser fluorimetry in the quasi-stationary and nonstationary excitation regimes is described. The algorithms, proposed in this paper, are tested on pure cultures of microalgae Chlorella pyrenoidosa and Chlamydomonas reinhardtii under different functional conditions.

Lasing at a wavelength of 1.98 μm is obtained for the first time in a diode-pumped (λ = 792 μm) active element made of a Tm³⁺: Sc₂SiO₅ crystal grown by the Czochralski method. The laser slope efficiency reached 18.7% at the output power up to 520 mW.

The operation of single-mode diode lasers with a front mirror passivated by ZnSe films of different thicknesses is studied in the pulsed regime (pulse duration τ = 0.2 – 10 μs). It is found that in the case of short (0.2 μs) pulses, the catastrophic optical damage threshold grows almost linearly as the film thickness on the front mirror increases from 0.1 to 0.5 μm. It is shown that lasers with mirrors passivated by 'thick' (0.4 – 0.6 μm) ZnSe films can operate stably in the case of 'long' (2 – 10 μs) pulses. It is assumed that in this pulsed regime the ZnSe film provides an additional heat removal from the hot zone of the front mirror, and consequently increases the optical damage threshold.

The possibility of operation of a pulsed chemical H₂ – F₂ laser on purely rotational transitions with simultaneous lasing on vibrational – rotational transitions is theoretically investigated. The lasing of a hydrogen—fluorine laser (mixture pressure 1.1 atm) on both v,j – 1 → v – 1,j (j=2 – 20) and v,j → v,j – 1 (j = 12 – 19) transitions has been modelled taking into account the resonant one- and two-quanta vibrational – rotational processes. The calculated specific energy extraction for purely rotational transitions reaches 0.3–0.5 J L^-1 at j=18 and 19 (wavelength 15.5–14 μm) and 0.4–0.7 J L^-1 at j=13 and 14 (wavelength 21–19 μm).

The paper reports the development of a test bed for a chemical oxygen — iodine laser based on a high throughput jet flow singlet oxygen generator (JSOG). The system provides vertical singlet oxygen extraction followed by horizontal orientation of subsequent subsystems. This design enables the study of flow complexities and engineering aspects of a distributed weight system as an input for mobile and other platform-mounted systems developed for large scale power levels. The system under consideration is modular and consists of twin SOGs, plenum and supersonic nozzle modules, with the active medium produced in the laser cavity. The maximal chlorine flow rate for the laser is ∼1.5 mole s^-1 achieving a typical chemical efficiency of about 18%.

Self-heterodyning in dc-discharge-pumped single-mode CO₂ lasers is analysed theoretically and studied experimentally under strong and weak feedback conditions. Relations for the autodyne gain and modulation depth due to the effect of backscattered radiation with a Doppler-shifted frequency are obtained. Nonlinear distortions of the autodyne signal caused by a strong laser — target feedback are studied. It is shown that the autodyne detection of backscattered radiation in CO₂ lasers can be considered linear even in the case of strong laser beam distortions (nonlinear distortions below 5%).

Laser processing of epitaxial PbSe films has been found to produce periodic concentric surface ring structures that extend over several laser spot radii from the exposed zone. The proposed theoretical interpretation of this effect in terms of defect — deformation interactions adequately describes the observed morphology, periodicity and complex (multimode) shape of the ring structures.

The effects of rapid nonuniform heating of electrons on reflection of a p-polarised pulse from the metal are quantitatively described. Under conditions of normal and high-frequency skin effects, the absorption coefficient and phase shift of the reflected wave are calculated numerically upon irradiation of a gold target.

An experimental investigation was made of water removal from a shallow bath under the action of a CO₂-laser radiation pulse focused to a spot of size substantially smaller than the bath length. We showed that the specific expenditure of energy is determined by the intensity of laser radiation at the water surface for different values of the focal spot area and pulse duration. The removal dynamics was studied by single-frame photography technique. It was determined that the water is removed layerwise only from the walls of the cavern, which expands in the horizontal direction upon cessation of the radiation pulse. Two-dimensional numerical simulations were made of the water removal, and a mechanism was proposed to explain the experimentally observed removal pattern.

An experimental investigation was made of optical schemes for the generation of the second Stokes component in the SRS of broadband chirped laser pulses in high-pressure gases. Measurements were made of the energy conversion efficiency and the spatial characteristics of the light beam of the second Stokes component for one- and two-fold focusing of the pump radiation into the gas-filled cell as well as in schemes involving a quartz capillary and two gas-filled cells. The highest energy efficiency of conversion to the second Stokes component was attained in the case of cascade generation in the optical scheme with two pressurised-gas cells. In the SRS in hydrogen in this scheme, the Ti:sapphire laser radiation with a wavelength of 0.79 μm was converted to the 2.3-μm second Stokes component with an efficiency of 8.5%.

Bragg gratings with a second-order resonance wavelength in the near-IR spectral region have been inscribed into single-mode chalcogenide (As₂S₃) glass fibre by a He — Ne laser beam using a configuration typical of Bragg grating fabrication in germanosilicate fibre, with the use of a phase mask that ensures effective diffraction of the writing light into the +1 and -1 orders. The spectra of the inscribed gratings show no resonances due to cladding mode excitation because the cladding material is photosensitive.

The evolution of the phase delay between linearly polarised orthogonal modes in a spun fibre elastically twisted around its axis has been studied experimentally and theoretically using a model for a helical structure of the built-in linear birefringence axes. The phase delay is a sinusoidal function of elastic twist angle, with an amplitude and period dependent on fibre parameters: spin pitch and built-in linear birefringence beat length. It is shown that, at a known spin pitch, phase delay versus elastic twist angle data can be used to determine the beat length of built-in linear birefringence in the range 0.01 to 100 mm. The theoretical analysis results are supported by experimental data for conventional and microstructured spun fibres.

An algorithm of computer-based correction of images of extended objects distorted by turbulent atmosphere is developed. The method of computer correction is used to correct a distorted image of an extended object on a horizontal 2300-m-long observation path. The angular size of the corrected-image region was 15'.

The increase in the absorption of light by a semiconductor (when the light photon energy is somewhat smaller than the semiconductor bandgap or equals it) in the presence of a strong light wave (for which the semiconductor is transparent) has been investigated. The possibility of designing novel light detectors for measuring the energy parameters and spatial and temporal characteristics of high-power IR laser radiation is demonstrated.

It was shown previously that in taking into account only dipole transitions, the crossing of quasi-energy levels is possible in the system if any of the transitions forms a closed loop [1]. It followed herefrom that for the analysis of the crossing conditions, it is necessary to consider a system which has at least four levels. In this paper we show that we can uniquely specify which quasi-energy levels cross at the given values of the parameters of the atomic system and radiation field, without solving an algebraic quartic equation. It was found that the most suitable system for the implementation of the crossing is the group of energy levels ⁵S_1/2, ⁵P_1/2, ⁵P_3/2 and ⁵D_3/2 of a rubidium atom. The performed calculations of the laser field intensity and frequency values at which crossing takes place in this system show that they are easily attainable. It turned out that in this system there occur crossing of quasi-energy levels corresponding to the excited atomic levels.