Sergei Yu. Nikitin

Red blood cells in laser beam field: calculations of light scattering

The main goal of this work is to develop a fast tool for calculation of light scattered by single large optically soft spheroidal particles. In particular, such particles mimic biological cells (e.g., red blood cells (RBC)). Methodology of calculation of light scattering by arbitrarily oriented optically soft spheroidal particles in Ray-Wave Approximation (RWA) is presented. We show that RWA permits to quickly and accurately calculate the angular distributions of the intensities of light scattered from particles mimicking RBC.

Light scattering by biological spheroidal particles in geometric optics approximation

The main goal of this work is the fast analysis of light scattered by a large optically soft spheroidal particle (size parameter ka > 20). In particular, these particles mimic single cells (e.g., red blood cells (RBC)) and their aggregates. Methodology of calculation of light scattering by arbitrarily oriented optically soft spheroidal particles in geometric optics approximation is presented. We show that the geometric optics approximation permits to quickly calculate the angular distributions of the intensities and phases of light scattered from optically soft particles, such as erythrocytes.

Laser diffraction analysis of shear deformability of human and rat erythrocytes in norm and ischemia

Ischemic diseases of people and animals are accompanied with deterioration of microrheologic properties of their blood, in particular, with impairing red blood cells (RBC) deformability. In this work, the analysis of human and rat RBC deformability in norm and ischemia was performed by means of the laser diffractometry - a modern technique allowing for measuring the flexibility of RBC, which determines the blood flow parameters in vessels. Human RBC were obtained from the blood of healthy individuals and from patients suffering from ischemic diseases. Human RBC deformability from both groups of individuals was measured. Rat RBC were obtained from a control group of animals and from a group with experimentally induced ischemia (EII). This animal model is frequently used for studying the response of an organism to ischemia. The effect of Semax, a medication that is frequently used for therapeutic treatments of human brain diseases in clinical practice, on RBC deformability was studied with its application in vitro and in vivo. It is shown that in human ischemic patients, the deformability of RBC was lower than that from healthy individuals. Both in vivo and in vitro applied semax positively influences the impaired deformability properties of RBC of ischemic rats.

Diffractomery analysis of human and rat erythrocytes deformability under ischemia

In this work, the analysis of human and rat red blood cells (RBC) deformability, internal viscosity and yield stress of RBC in norm and ischemia was performed by means of laser diffractometry - a modern technique allowing for measuring the flexibility of RBC, which determines the blood flow parameters in vessels. Ischemic diseases of people and animals are accompanied with deterioration of microrheologic properties of their blood, in particular, with impairing the RBC deformability. Human RBCs were obtained from the blood of healthy individuals and from patients suffering from ischemic diseases. The RBC deformability indices from both groups of individuals were measured. Rat RBCs were obtained from a control group of animals and from a group with experimentally induced ischemia (EII). This animal model is frequently used for studying the response of an organism to ischemia. The effect of semax, a medication that is frequently used for therapeutic treatments of human brain diseases in clinical practice, on RBC deformability was studied with its application in vitro and in vivo. It is shown that in human ischemic patients, the deformability index of RBC was lower than that from healthy individuals. Both in vivo and in vitro applied semax positively influences the impaired deformability properties of RBCs of ischemic rats.

Polarizability difference at the transition as a characteristic of Raman-active properties of a molecule

Polarizability difference at the states, forming Raman- active transition is found to be a good characteristic of a molecule properties with respect to the Raman scattering of light. Stimulated Raman gain and spontaneous Raman scattering cross-section are calculated through the polarizability difference. Estimates have been done for hydrogen molecule.

New technique for suppression of stimulated Raman scattering in the plasma of laser fusion: fast frequency modulation of the pumping radiation

A new technique based on the fast frequency modulation of the laser radiation is proposed for suppression of stimulated Raman scattering in plasma in conditions of the laser fusion. It is shown that Raman gain for the backward SRS can be reduced twice providing rate of the saw-toothed form frequency modulation as high as 2% per picosecond.

Effect of anti-Stokes scattering on the stimulated Raman gain in plasma

A correction to the stimulated Raman gain in a homogeneous plasma caused by influence of the anti-Stokes scattering is calculated. It is shown that for conditions of the laser fusion this correction does not exceed a few percent, and for limit of intense field of the pump it does not depend on intensity of the pumping radiation.

Kinetic processes in molecular and atomic gases

Theoretical description of different collisional dephasing processes in molecular and atomic gases is presented. Experimental data, obtained by time-domain CARS spectroscopy method for thulium vapors, are analyzed on the basis of the presented theory. Physical parameters of investigated atoms are obtained.

Noise pumping in nonlinear optical processes: Part II--Parametric amplification of light; Raman scattering in a selective resonator

This paper presents a theory for parametric amplification of light in the case of non- monochromatic pumping. A possibility of conversion of the optical noise into a quasiharmonic signal as a result of Raman scattering in a selective resonator is discussed for the first time.

Noise pumping in nonlinear optical processes: Part I--Stimulated Raman scattering

Characteristics of stimulated scattering and parametric amplification of light are investigated in the case of nonmonochromatic pumping on the basis of exact analytical solution of some problems. Part I provides a review of publications devoted to stimulated Raman scattering (SRS). Some new results related to backward SRS are presented as well as the theory of SRS in the pump field of random telegraph signal type. Results of theoretical calculations are compared with the existing experimental data.