Valentin M. Grimblatov

Optomechanical effect of tissue blood microcirculation under compression

The changes of diffuse reflected light by tissues with blood pulse circulation as function of external pressure was studied. The experimental measurements were performed with steady state and pulsatile components of the photoplethysmographic signal taken from human finger under compression. Specially designed reflection-mode sensor registered the true waveform of pulse waves. The unexpected change of the pulsatile amplitude from increasing to decreasing with compression was found. To explain this effect a Kubelka-Munk approximation model of a deformable medium with embedded particles of different types and concentrations was developed. On the basis of this model it is shown that the observed optomechanical effect is brought about by a shift of the balance between blood pressure and the external pressure of stressed vessel walls and surrounding media. The results show capability of photoplethysmographic technique to detect very small local tissue stress changes and to measure local vessel wall elasticity.

Diagnostics of lenslike media with small-scale inhomogeneities by method of probing beam intensity moments

The use of Gaussian probing beams for measuring parameters of distributed lenses is well known. But common methods become invalid in widespread cases when investigated media contain additive scattering inhomogeneities. This report is devoted to the usual scheme generalization able to overcome mentioned restrictions. It is shown that utilizing arbitrary paraxial probing beams, characterized by space-angle intensity moments, enables us to solve this task effectively. The equations for evolution of moments in lens-like media with small- scale stochastic inhomogeneity are derived and analyzed, on which basis some recommendations are made for fast and suitable measurement of medium parameters.

Diagnostics of lens-like biological media

The application of probing beam space-angle intensity moments for investigation of optically inhomogeneous biological objects is considered. Special attention is paid to measurements of lens-like inhomogeneities in the presence of scattering caused by small-scale fluctuations of refraction. The results can be used in ophthalmology for non-invasive early detection of cataractous changes in human eye lens and in laboratory experiments with blood fluxes.

Optical beam distortion in biotissues with large-scale inhomogeneities

The new model of biotissue as a medium with two kinds of inhomogeneities -- small-scale, representing randomly placed scatterers and absorbers, and large-scale, corresponding to the macroscopic structures -- is proposed. The first and second moments of space-angle intensity distribution of the optical beam propagating in such medium are considered. It is shown that the possibility exists to define parameters of each scale inhomogeneity separately through the moments measurements for conditions often realized in medicine. The results are suitable for development of optical non-invasive diagnostic methods.

Characterization of laser beams with different scale inhomogeneities by means of space-angle moments

The use of space-angle intensity moments in description and characterization of a paraxial laser beam with small-scale inhomogeneities of its transverse shape is presented. The connection between the moments and customary beam characteristics is discussed. The equations of moments evolution in lens-like optical media with small-scale scattering inhomogeneity are derived and analyzed, on the basis of which some recommendations for fast and suitable medium parameters determination are made.

Express-control method of frequency nonreproducibility sources in frequency-stabilized He-Ne lasers

The discharge current influence on the homogeneous broadening of the spectral lines in the gas-discharge media by direct collisions of the excited atoms with free electrons and also through collision broadening changing because of the gas heating by discharge current is considered. It was established that homogeneous broadening and hence the frequency shift of the spectral line depend essentially on the thermal condition of the laser work. The theoretical calculations are confirmed by the experimental measurements of the dependence of the homogeneous broadening of spectral line 3s2 - 2p4 neona in the He-Ne laser on the discharge current magnitude. For the homogeneous broadening determination by the experimentally measured Lamb dip characteristics a new computation method was developed, which can be used both in single-mode and two axial modes conditions of laser generation. It has been shown that on its basis and using known dependencies of the collision broadening of the spectral lines on the pressure, there can be realized an express-control of the main sources of the generation frequency unreproducibility in the sealed off discharge tubes, such as gas pressure and relative excitation of the laser system.

Intracavity diagnostics of optical inhomogeneity

Direct measurements of radial optical inhomogeneity in long narrow elements (gas-discharge tubes, optical fibers, filamental crystals, etc.) entail some difficulties conditioned both by geometry and by littleness of optical properties absolute variations, especially critical in absorptive photothermospectroscopy. At the same time, in many such cases transverse optical inhomogeneity is close to lens-like type. It allows us to realize convenient and accurate procedure for measuring such inhomogeneity, disposing the inhomogeneous sample into the laser resonator and observing the inhomogeneity effect on the characteristics of generated radiation. This report presents general theoretic foundations for the proposed approach. Some variants of this procedure are analyzed and their advantages over common ones are shown. Experimental examination of the proposed method with an example of the He-Ne discharge element has shown its validity and usefulness.