Maria M. Loginova

Anomalous influence of electrons diffusion on absorption optical bistability realization

An influence of electrons diffusion on the intensities of switching for absorption optical bistability based on high-intensity femtosecond laser pulse interaction with semiconductor is studied. The dependence of absorption coefficient on free electrons concentration and on induced electric field strength or its potential is considered. With the help of computer simulation an anomalous influence of electrons diffusion on intensities of switching under taking into account of free electrons mobility.

2D wave structure induced by femtosecond laser pulse in semiconductor

We simulate interaction of a femtosecond laser pulse with semiconductor. As it is well known, under certain conditions the optical bistability (OB) takes place due to a nonlinear absorption of the optical energy, for example. We investigate the 2D wave process, occurring in such conditions and appearing because of instability of one from the bistable element states. Due to laser pulse propagating and electrons diffusion, the instability of the states of the optical radiation-semiconductor system causes the 2D wave propagation of free-electrons and ionized donors in semiconductor. This process can essentially change properties of the bistable element.

Comparison of some difference schemes for problem of femtosecond pulse interaction with semiconductor in the case of nonlinear mobility coefficient

A difference scheme for problem of femtosecond pulse interaction with semiconductor is proposed in the case of nonlinear dependencies of light energy absorption coefficient and mobility of free electrons from electric field strength. Comparison of some difference schemes efficiency for computation of various regimes of laser pulse interaction with semiconductor is carried out. It is shown that approach developed by us allows to analyze regimes for which difference schemes known earlier are unsuitable.

Conservative Finite-Difference Scheme for Computer Simulation of Field Optical Bistability

We investigate 2D switching wave of nonlinear absorption in a semiconduntor under the high intensive laser pulse action. A laser pulse interaction with semiconductor is described by the set of 2D nonlinear differential equations. To solve these equations numerically we have developed the conservative finite-difference scheme. It’s realization is based on the original two-stage iteration process. It is very important, that the finite-difference scheme is conservative one on each of iterations because we have to provide a simulation on big time interval.

Conservative finite-difference scheme for a two-dimensional problem of plasma generation in a semiconductor under a laser pulse action

In the given paper we proposed an effective finite-difference scheme for a two-dimensional problem of femtosecond pulse influence on a semiconductor in the case of nonlinear dependence of light energy absorption coefficient on electric field potential.

Formation of sub-femtosecond sub-pulses at THG of femtosecond laser pulse

THG is used nowadays in many practical applications such as a substance diagnostics, and biological objects imaging, and etс. Therefore, THG features understanding are urgent problem and this problem attracts an attention of many researchers. In this paper we demonstrate a formation of sub-pulse comb with subfemtosecond duration at THG of femtosecond laser pulse propagating in a medium with cubic nonlinear response. This pulse comb has a regular structure in many cases of interacting waves. The sub-pulse duration is governed by the incident femtosecond pulse duration. We consider both incident chirped and un-chirped pulse. Consideration is based on computer simulation of the laser pulse propagation with taking into account a self- and cross- modulation of interacting waves, and their SOD, and phase mismatching. Observed sub-pulse formation can be used for generation of sequence of attosecond pulses with soliton or soliton-like shape.

Incident femtosecond pulse chirp influence on nonlinear localization of laser energy in 2D photonic crystal

We investigate laser energy localization in 2D photonic crystal with Kerr nonlinear response in dependence of the incident femtosecond pulse chirp. Such kind of energy localization appears due to soliton formation in certain elements of photonic crystal. Their positions, in which the soliton appear, depend on the incident pulse chirp and the pulse intensity. It is important to emphasize that a soliton occur in separate elements of the photonic crystal. Therefore, their sizes must be less than sizes of the photonic crystal elements. Consequently, an intensity of the incident pulse must be greater than certain crucial value. A process of energy localization strongly depends on relation between the wave packet carrier frequency and a frequency characterizing a photonic crystal. These solitons move with slow velocity inside the PC elements. Under certain conditions, the soliton can stop. The problem under consideration is described by a nonlinear Schrödinger equation with respect to amplitude slowly varying in time only. We investigate a femtosecond pulse interaction with photonic crystal numerically and analytically.

Comb generation of second and third harmonics at high-intensive femtosecond pulse in medium with quadratic and cubic nonlinearities

SHG is used in many practical applications such as a substance diagnostics, and imaging of various processes as well as for a frequency conversion of an optical pulse. As a rule, the frequency doubling is used also for a generation of the optical wave with tripled frequency by using the mixing of optical radiation with the basic and doubled frequencies. Nevertheless, THG can occur in a medium with cubic nonlinear response and in a medium with quadratic nonlinear response if the incident laser pulse intensity of the basic wave is enough high or if the intensities of the interacting waves increase until such values which are sufficient for occurring the cubic nonlinearity of a crystal. As a consequence, THG may occur. We investigate an efficiency of comb frequency generation if an intensity of the incident femtosecond pulse is sufficiently high . Obviously, one of these generation processes occurs with a big phase mismatching. We investigate comb generation efficiency in a dependence of the phase mismatching between interacting waves and other parameters. As a result, we observe various regimes of comb generation. It should be emphasized that we find out the generation regime with synchronic changing of the maximal intensities of all waves. At the same time, shape of the appearing sub-pulses at these frequencies are similar to Gaussian one. Our consideration is based on computer simulation with taking into account the SOD, phase mismatching, selfand cross-modulation for interacting waves.

Laser pulse self-similar propagation in a medium with noble nanoparticles under conditions of non-stationary processes

We investigate the possibility of femto- or picoseconds pulse self-similar propagation in a medium containing noble metal nanorods. The main attention is devoted to the nonlinear chirped solitons propagation. Our investigation is bases on the semi-classical approach. Using this approach, we derive the set of equation, which describe the atomic states and electric field dynamics. We take into account non-stationarity of the density matrix elements, two-photon absorption of laser radiation and the non-stationary process of nanorods aspect ratio changing due to the nanorods reshaping under the action of laser radiation. On the basis of numerical calculations, we reveal the influence of the non-stationarity of the density matrix elements on the possibility of the laser pulse self-similar propagation in the medium with nanorods.

Conservative finite-difference scheme for the 2D problem of femtosecond laser pulse interaction with kink structure of high absorption in semiconductor

ABSTRACT The problem of high-intense laser pulse interaction with a semiconductor under the condition of a light energy nonlinear absorption, which results in high absorption domains formation, is considered. Such interaction allows reaching a construction of an element for all-optical data treatment. For its adequate description we propose new mathematical model taking into account the longitudinal and transverse diffraction effects. The longitudinal diffraction induced a reflection of laser radiation from boundaries of the high absorption domains that results in changing of their spatial structure. The conservative finite-difference scheme (FDS) is developed for numerical computation of the complicated nonlinear processes. The property of the FDS conservatism is proved. For the proposed FDS realization the two-stage iteration method is proposed. Computer simulation results are presented. We show the uniform boundedness of the mesh functions at the iterations and the convergence of the iteration process. We show also positiveness and boundedness of the mesh function corresponding to free-charged particles. We discuss some properties of differential problem including the problem invariants, positiveness of the free-charged concentrations.