A. A. Afanas'ev

Localization of Spherical Particles under the Action of Gradient Forces in the Field of a Zero-Order Bessel Beam. Rayleigh–Gans Approximation

The amplitude of the gradient force acting on a transparent spherical particle in the field of a zero-order Bessel beam has been calculated in the Rayleigh–Gans approximation. The expression obtained for the gradient-force amplitude takes into account the heterogeneity of the acting radiation in the volume of the particle. The optimal conditions of trapping and transportation of the particle (parameters of the particle, liquid, and of the Bessel beam) to the localization region have been determined using the solution of the kinetic equation of particle motion in a liquid. It is shown that for certain relationships between the particle radius and the Bessel beam width the localization region is shifted relative to the central maximum of the beam. This is due to the equal action of the gradient forces caused by the central maximum and the first interference ring of the Bessel beam. A qualitative comparison of the results obtained with the known experimental data has been performed.

Self-action of Counterpropagating Axially Symmetric Light Beams in a Transparent Cubic-nonlinearity Medium

Abstract The stationary effect of self-action of counterpropagating axially symmetric light beams in a medium with cubic nonlinearity is discussed. Self-similar solutions for initial radiation parameters and nonlinear medium characteristics in the case of slowly varying amplitudes of beams are found. The analysis of approximate solutions obtained on the basis of motion constants is carried out and results are compared with numerical experimental data.

Influence of the gain saturation on the output performance of quantum-well heterostructures with modified distributed-feedback cavities

Influence of the gain saturation on the output performance of quantum-well heterostructures with modified distributed-feedback cavities is considered. Taking into account symmetrical boundary conditions, distribution of the electromagnetic field in the active region of the heterostructure laser diode with a phase-amplitude grating is determined. It is shown that both the output performance of quantum-well heterostructures and distribution of the electromagnetic field in the active region depend on the pump current and optical nonlinearity characteristics.

Evolution of femtosecond solitons in a cubic medium with a two-component relaxing nonlinearity

Soliton propagation in a nonlinear cubic medium with two types of relaxing nonlinearities is investigated. Provided that the pulse duration exceeds the fast relaxation time and be shorter than the slow one, partial compensation of the concerted influence of these relaxations on the soliton dynamics is feasible. A condition for such an optimal regime of soliton pulse propagation is analytically obtained. Computer simulations are in good agreement with analytical predictions.

Modulation of Particle Concentrations in the Interference Laser Radiation Field

Spatial redistribution of microparticles in a suspension on exposure to the interference laser field depending on the parameters of the particles and the field characteristics has been analyzed theoretically. Results of experimental investigations are presented that illustrate the capture of an ensemble of polymeric small spheres and also of the lymphocytes of human blood and other microparticles in a liquid in the interference radiation bands of the He–Ne laser.

Influence of Close‐Range Dipole‐Dipole Interactions on the Real Part of the Susceptibility of a Dense Resonance Medium

Based on a solution of the stationary modified Bloch equations, an investigation is made of the influence of the effect of internal optical bistability (IOB) on the behavior of the refractive index of a dense resonance medium as a function of the constant b of close‐range dipole‐dipole interactions, frequency detuning, and the intensity of optical radiation. The conditions of existence of the IOB effect of the system dense resonance medium + optical radiation are found and the dynamics of the loop width of the hysteresis dependence of the population difference of the resonance levels of the medium on the characteristics of the system is traced. The domains of the parameters are determined in which the effects of self‐focusing and self‐defocusing of the radiation propagating in a dense resonance medium can take place.

Concentration nonlinearity of a suspension of transparent microspheres under the action of a gradient force in a periodically modulated laser field

Based on a one-dimensional Smoluchowski equation we have developed the theory of concentration nonlinearity of a suspension of transparent microspheres under the action of a gradient force in an interference laser field. The numerical solution of a system of recurrence equations resulting from the Smoluchowski equation after expansion of the microsphere concentration in the harmonic series has allowed us to determine the dependence of the concentration nonlinearity settling time on the intensity of the incident radiation. In the diffusion limit, we have derived the expression for the optical Kerr coefficient, which is found to be for an aqueous suspension of latex microspheres with a radius of and a concentration of . Diffraction of a probe wave on a light-induced concentration grating is considered as a method for studying a nonlinear concentration response of an artificial highly efficient nonlinear medium for laser radiation of long pulse duration.

High-efficient four-wave mixing in a liquid suspension of dielectric transparent microspheres

In this work a theory of the four-wave mixing (FWM) is developed in a liquid suspension of transparent microspheres (heterogeneous medium), the nonlinearity of which is caused by the change in the microspheres concentration under the action of the gradient forces in the electromagnetic field of interacting waves. The effect of suppression of four-wave mixing because of the reduction of the resulting components of the gradient forces to zero for microspheres of certain sizes and certain angles of convergence of interacting waves have been predicted. A stationary regime of four wave mixing has been analyzed in the diffusion limit and the conditions of the appearance of parametric generation of a pair of mutually conjugate waves have been determined.

Spectral and output power characteristics of DFB laser heterostructures

The computational simulation of spectralLt8hresliold characteristics of B quam tum-well heterostructure laser diode with an incorporated distributed feedback structure on the phase grating at the coupling coefficient modulation is considered. The field distribution in the active rcgion of the laser het,erost,ructure with taking int,o account gain satmation effects is calculated, The optimal parameters of such a laser diode are determined.

Transformation of Nanosecond Laser Pulses under the Conditions of Total Internal Reflection from a Layer with Thermal Nonlinearity

The nonlinear, total internal reflection of a laser pulse from an absorbing layer of finite thickness in the presence of a retrodirective mirror has been considered in the framework of the plane-wave approximation. The dynamics of reflection of a pulse from a nonlinear layer has been investigated on the basis of the solution of Maxwell equations for a refracted wave and constitutive equations for a medium with thermal nonlinearity. The numerical solution of the unsteady equations obtained allows one to determine the evolution of the reflectance of a layer. The time evolution of the energy parameters and the shape of the reflected and transmitted pulses has been numerically simulated.