Table of contents

The passive diffusion of drugs through the epithelial surfaces of an eye (the most widespread method for medical treatment of various diseases) is considered. The permeability of water and drugs through rabbit cornea was measured in the isolated cornea (separate from an eye) and in the whole cornea. The permeability coefficients of water and dexamethasone were estimated by the method of optical coherence tomography (OCT). Because multiple photon scattering introduces noise and distortions to the OCT signal, measurements were performed at depths up to 500 μm where most likely single scattering of light occurs in cornea. It is shown that the permeability coefficients in the isolated and whole cornea strongly differ from each other. For example, the water permeability in the isolated and whole cornea is (7.09±0.12)×10^-5 and (1.71±0.51)×10^-5 cm s^-1, respectively.

The problem of opto-acoustic (AO) diagnostics of light scattering and absorption in biological media is considered. The objects under study were milk, bovine and porcine liver, and bovine muscle tissue. The forward and backward schemes for recording acoustic signals were used in experiments. The spatial distribution of the light intensity was measured for each biological medium from the temporal profile of the excited OA pulse and the absorption coefficient and reduced scattering coefficient were determined. Opto-acoustic signals were excited by a 1064-nm pulsed Nd:YAG laser and a tunable Ti:sapphire laser at 779 nm. It is shown that the proposed method can be used for obtaining a priori information on a biological medium in problems of optical and AO tomography.

The possibility of using the opto-acoustic (OA) method for monitoring high-intensity ultrasonic therapy is studied. The optical properties of raw and boiled liver samples used as the undamaged model tissue and tissue destroyed by ultrasound, respectively, are measured. Experiments are performed with samples consisting of several alternating layers of raw and boiled liver of different thickness. The position and transverse size of the thermal lesion were determined from the temporal shape of the OA signals. The results of measurements are compared with the real size and position of the thermal lesion determined from the subsequent cuts of the sample. It is shown that the OA method permits the diagnostics of variations in biological tissues upon ultrasonic therapy.

The application of backward diffuse reflection (BDR) spectroscopy for in vivo monitoring the degree of haemoglobin oxygenation and concentration of photosensitisers in tissues subjected to photodynamic therapy is demonstrated. A simple experimental technique is proposed for measuring diffuse reflection spectra. The measurements are made under steady-state conditions using a fibreoptic probe with one transmitting and one receiving fibre separated by a fixed distance. Although this approach does not ensure the separation of contributions of scattering and absorption to the spectra being measured, it can be used for estimating the degree of haemoglobin oxygenation and concentration of photosensitisers in the tissues. Simple expressions for estimating the concentration of photosensitisers from the BDR spectra are presented and the accuracy of this approach is analysed. The results of application of BDR spectroscopy for monitoring various photosensitisers are considered.

Based on the digital image analysis and inverse Monte-Carlo method, the proximate analysis method is deve-loped and the optical properties of hairs of different types are estimated in three spectral ranges corresponding to three colour components. The scattering and absorption properties of hairs are separated for the first time by using the inverse Monte-Carlo method. The content of different types of melanin in hairs is estimated from the absorption coefficient. It is shown that the dominating type of melanin in dark hairs is eumelanin, whereas in light hairs pheomelanin dominates.

Changes in the optical properties of the eye sclera of a laboratory animal (rabbit) caused by the noninvasive administration of an immersion agent (aqueous glucose solution) into sclera are studied experimentally in vivo by the method of reflection spectroscopy and simulated numerically. The diffusion coefficients of glucose and water in sclera are estimated from simulations of optical clearing within the framework of the developed model as h(5.4±0.1)×10^-7 and (5.8±0.2)×10^-7 cm² s^-1, respectively. Experiments showed that the application of the glucose solution on the sclera allows the efficient control of its optical properties, which makes it possible to deliver the laser energy to internal eye tissues without considerable attenuation and distortions of its spatial distribution in laser diagnostics and therapy.

The possibility of using spatially resolved reflectometry (SRR) at a wavelength of 820 nm to detect changes in the optical properties of a highly scattering layered random medium simulating a biological tissue caused by changes in the glucose level is analysed. Model signals from a three-layer biological tissue phantom consisting of two skin layers and a blood layer located between them are obtained by the Monte-Carlo method. It was assumed that variations in the glucose level induce variations in the optical parameters of the blood layer and the bottom skin layer. To analyse the trajectories of photons forming the SRR signal, their scattering maps are obtained. The ratio of the photon path in layers sensitive to the glucose level to the total path in the medium was used as a parameter characterising these trajectories. The relative change in the reflected signal caused by a change in the glucose concentration is analysed depending on the distance between a probe radiation source and a detector. It is shown that the maximum relative change in the signal (about 7%) takes place for the source — detector separation in the range from 0.3 to 0.5 mm depending on the model parameters.

A review of experimental and theoretical studies on radiative processes induced by a bichromatic (two-frequency) laser radiation in atoms, molecules, and solids is presented. The optical excitation of matter is considered at transitions of different types: bound—bound, bound—free, and free—free. A special attention is devoted to the possibility of the coherent control of the basic characteristics of radiative phenomena by varying the relative phase of monochromatic components of radiation. It is shown that this method opens up new possibilities for controlling photoinduced processes.

A new combined cw single-frequency dye/Ti:sapphire laser with a ring resonator located in the horizontal plane and improved radiation frequency stability is developed. The short-term radiation linewidth does not exceed 10 kHz for the Ti:sapphire laser and is smaller than 100 kHz for the dye laser. The drift velocity of the emission line does not exceed 25 MHz h^-1. The scheme and design of the developed laser are presented which allow convenient switching of the laser between its solid-state and dye configurations.

It is shown that the efficiency of a pulsed e-beam sustained discharge overtone CO laser in the multiline regime achieves 16% and in the single-line regime its efficiency is 0.75%. The theoretical and experimental data are in good agreement taking into account the local specific energy input.

The energy parameters of an HF laser operating by using a new method for oxidising-gas production, which is based on the principle of two-region mixing, are optimised. The total amount of the inert diluent (helium) supplied to the laser was varied during experiments by varying its relative fraction only in the second mixing region. For an optimal relative fraction of the diluent in the second mixing zone and for an optimal position of the optical axis of the cavity under a constant pressure in the gas generator, the laser radiation power and the specific power output could be increased by 50% and 60%, respectively, compared to the laser operation regime realised in our previous experiments. In this case, the inert diluent amount decreased by 35% and the length of the generation region increased by 20%.

A model of a multimode bipolarisation solid-state laser with intracavity frequency doubling is developed. The interaction of different longitudinal modes is described within the framework of rate-equation approximation while the interaction of each pair of orthogonally polarised modes with identical longitudinal indices is described taking into account the phase-sensitive interaction of these modes. Comparison with the experimental data is performed.

The scheme of a magnetic calorimeter for recording extremely low energy releases is developed. The calorimeter is activated by the method of adiabatic demagnetisation and its response to the energy release is measured with a superconducting quantum interference device (SQUID). The estimate of the ultimate sensitivity of the calorimeter with the SQUID demonstrates the possibilities of its application for detecting ultralow radiation intensity, recording single X-ray quanta in the proportional regime and other events with ultralow energy releases. The scheme of the calorimeter with the SQUID on matter waves in superfluid ⁴He is proposed.

It was shown earlier that the ionisation propagation in a gas at about the atmospheric pressure may proceed due to the multiplication of the existing electrons with a low background density rather than the transfer of electrons or photons. We consider the feasibility of using the plasma produced in the afterglow of this background-electron multiplication wave for pumping plasma lasers (in particular, Xe₂* xenon excimer lasers) as well as excilamps. Simulations show that it is possible to achieve the laser effect at λ≈172 nm as well as to substantially improve the peak specific power of the spontaneous radiation of xenon lamps.