Alexey A. Mishin

Coherent, low-coherent, and polarized light interaction with tissues undergoing refractive-index matching control

It is shown experimentally and theoretically that due to interaction of totally or partially coherent light beams with such tissues as the human eye sclera and skin which undergo the refractive indices matching the collimated and total transmission, diffuse reflection and speckle structure of transmitted beams are changing in accordance with transition from multiple to low-step scattering. The scleral samples in a final stage of tissue optical clearing have the same properties as an optical retarder.

Scleral tissue light scattering and matter diffusion

Theoretical and computer modeling approaches, such as Mie theory, radiative transfer theory, Monte Carlo simulation method were applied for tissue optics analysis in a process of its optical clearing due to refractive indices matching. CW transmittance and forward and backward scattering measurements were used for tissue structural and optical properties monitoring. As a controlled tissue samples of the human sclera were taken. As a chemical applicator-controller osmotically active trazograph solution was used. The scleral absorption and scattering spectra as well as diffusion coefficient describing the samples of the human sclera permeability to trazograph wer experimentally estimated. Presented results are general and can be applicable for description of many other fibrous tissues.

Optical and osmotic properties of human sclera

Theoretical and computer modeling using Mie theory, radiative transfer theory, diffusion wave correlation spectroscopy, Monte Carlo simulation technique were applied for human sclera optics analysis in a process of its optical enlightening caused by osmolitically active chemicals administration.

Control of bovine sclera optical characteristics with various osmolytes

In order to understand the mechanisms of human sclera optical enlightening due to administration of osmolytes in vitro investigations of time-dependent transmittance spectra of bovine sclera were undertaken.

Speckle-imaging methods using focused laser beams in applications to tissue mapping

Correlation analysis of the far-zone speckle intensity has been examined in application to biotissue structure investigation. Asymptotic value of the exponential factor of intensity structure function has been proposed as the informative parameter. Generation of the 2D images of this factor distribution is discussed for different illumination conditions. Mapping of the light-scattering biotissue structure images has been carried out for the samples of normal and psoriatic human epidermal strippings.

Fibrous tissue optical properties control

The changeable scattering properties of fibrous tissue like the human sclera were studied in vitro. The collimated light transmittance, photon-correlation, and polarization measurements were done. The optical characteristics of fibrous tissue were controlled using various osmotically active solutions including glucose. It was shown that refractive indices matching of collagen fibrils and base material of fibrous tissue is responsible for tissue optical enlightening and coherent beam transmittance.

Light source for low-coherence interferometry and imaging

Light emitting module, which consist of superluminescent diodes (SLD) with spectral width approximately 20 nm full width of half maximum (FWHM), simple optical objective and driver for constant output power has been designed. An influence of the length of coherence of the illumination source used on the correlation characteristics of spatial distributions of speckle intensity is investigated.

Coherent-domain methods in biomedical optics

Far-zone speckle patterns formation in the case of non- single scattering of the focused coherent probe beams by tissue samples is experimentally studied. Reversible transition between different scattering regimes stimulated by the application of the certain chemical agents to the human sclera samples had been studied using speckle intensity correlation analysis; corresponding results are presented. Possibilities of the scattering structures imaging using structure function analysis of the far-zone dynamic speckles are shown in in-vitro experiments with samples of the human skin epidermis.

Speckle pattern polarization analysis as an approach to turbid tissue structure monitoring

Depolarization effects accompanying the coherent light multiple scattering by optically inhomogeneous tissues are studied for the certain cases of the light-tissue interaction. Correlation between polarization states of the scattered light fields (speckle patterns) for different stages of the transition from multiple scattering mode to the single scattering one is experimentally analyzed for the case of human sclera enlightenment process. This process can be induced by the application of the special chemical agents (e.g., Trazograph solution). Reversibility of the enlightenment is demonstrated by measuring mean intensities of the scattered light for different polarization states. Some possibilities of the usage of this approach for turbid media structure visualization are discussed.

Correlation dimension of speckle patterns for fractal-like scatterers

Various methods of coherent optical quantification of the structure functions of the boundary field phase distributions in the case of fractal-like scattering objects are considered: (1) by using the analysis of the angular dependence of scattered light mean intensity; (2) by estimating the parameters of the structure function of the far-field intensity fluctuations of scattered light. It has been shown in the second case that the equality of the correlation exponents of the boundary field phase and of the far-field intensity takes place if scattering objects with the Gaussian phase statistics are illuminated by a collimated beam and a great number of statistically independent elementary scatterers within illuminated area is provided. Experiments with rough glass plates illuminated by the Gaussian beams have shown that the values of the correlation exponents of the boundary field phase fluctuations (which have been obtained by means of microinterferometric measurements) are in satisfactory agreement with the corresponding values of the far-field speckle intensity.