Vladimir A. Egorenkov

Influence of external electric field on laser-induced wave process occurring in semiconductor under the femtosecond pulse acting

We analyze laser-induced periodic structures developing in a semiconductor under both femtosecond pulse acting and external electric field action. These structures are appeared due to optical bistability appearance, which is caused by nonlinear dependence of semiconductor absorption coefficient from charged particles concentration. Dependence of the semiconductor absorption is induced as by the Fermi energy level renormalization so by the Burstein-Moss effect. The electron mobility, electron diffusion, and laser-induced electric field are taken into account for laser pulse propagation analyzing in semiconductor. We found out that an external electric field causes complicated motion of high absorption domain in a semiconductor. In certain cases, it causes drops developing of charged particles. External electric field acting can result in helical structures appearing of high concentration of generated charged particles. Moreover, under the action of the external electric field one can expect developing of chaotic spatio-temporal structure of charged particles which will induce chaotic changing of time-dependent optical radiation distribution. In turn, such spatio-temporal structures generate electro-magnetic waves with complicated pulse shape and spatial profile. It may be important at generation of the THz radiation because it changes the radiation generation direction.

Helical auto-waves of electron-hole plasma in semiconductor induced by femtosecond pulse at presence of external electric field

We analyze laser-induced periodic structure developing in a semiconductor under the condition of both optical bistability existence and external electric field presence. Optical bistability occurs because of nonlinear dependence of semiconductor absorption coefficient on charged particles concentration. This dependence of the semiconductor absorption takes place due to the Burstein-Moss effect. The electron mobility, diffusion of electrons, and laser-induced electric field are taken into account for laser pulse propagation analyzing. We found out that an external electric field could induce helical auto-waves of high absorption domain in semiconductor if electron mobility influences on electron motion. The electron mobility causes electron motion from high absorption domain to domains with lower concentration of free charged particles. As a consequence, the laser energy absorption increases in these domains and new domains with high absorption appear. External electric field together with electric field of free electrons and ionized donors governs the electron motion. As a result, at certain conditions the additional positive inverse loop between electron motion and electric field caused by redistribution of free charged particles appears. Together with an explosive absorption existence, which arises from optical bistability, as a result of these two mechanisms presence the helical wave for free charged particles concentration of electron-hole plasma in semiconductor develops. Such type of wave may be seen also for a propagation of laser pulse with micro-, and nano-, and picoseconds duration because an optical bistability based on increasing absorption takes place for effecting of these pulses as well. For computer simulation of a problem under consideration a new finite-difference scheme is proposed. The main feature of proposed methods consists in constructed iterative process.

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.

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.

Developing of 2D helical waves in semiconductor under the action of femtosecond laser pulse and external electric field

We analyze laser-induced periodic structure developing in a semiconductor under the condition of both optical bistability existence and action of 2D external electric field. Optical bistability occurs because of nonlinear dependence of semiconductor absorption coefficient on charged particles concentration. The electron mobility, diffusion of electrons and laser-induced electric field are taken into account for laser pulse propagation analyzing. 2D external electric field together with electric field, induced by free electrons and ionized donors, governs the charged particle motion. Under certain conditions, the additional positive inverse loop between electron motion and electric field, caused by redistribution of free charged particles, appears. As a result, the helical wave for free charged particle concentration of electron-hole plasma in semiconductor develops under the electric field action. For computer simulation of a problem under consideration, a new finite-difference scheme is proposed. The main feature of proposed method consists in constructed two-step iteration process. We pay a special attention for calculation of initial functions distributions. For their calculation we solve the set of 2D stationary partial differential equations by using additional iteration process that is similar to the iteration process, applied for the main problem solution.

Fast and slow light observation at laser pulse interaction with contrast structures induced in semiconductor due to its nonlinear absorption and optical beam diffraction

We analyze laser pulse propagation in a semiconductor with nonlinear absorption depending on free electron concentration and a concentration of ionized donors. Under certain conditions this interaction is accompanied by a resonator-less optical bistability appearance. It is an attractive modern problem because of developing the all-optical methods for data treatment. In contrast to many investigations made early we take into account a longitudinal diffraction of the optical beam. It means that we consider optical beam diffraction along coordinate of its propagation. This results in the presence of the optical radiation reflection from spatio-temporal contrast structure induced by the laser pulse. As a result, we observe a propagation of the fast light corresponding to wave reflected from a semiconductor as well as unmoving part of the pulse placed near the semiconductor face. The reflection of laser pulse from the boundary of high absorption domain is demonstrated. This phenomenon takes place due to presence of high gradient of optical properties of a medium.

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.

Switching waves dynamics in optical bistable cavity-free system at femtosecond laser pulse propagation in semiconductor under light diffraction

We consider a propagation of laser pulse in a semiconductor under the conditions of an occurrence of optical bistability, which appears due to a nonlinear absorption of the semiconductor. As a result, the domains of high concentration of free charged particles (electrons and ionized donors) occur if an intensity of the incident optical pulse is greater than certain intensity. As it is well-known, that an optical beam must undergo a diffraction on (or reflection from) the domains boundaries. Usually, the beam diffraction along a coordinate of the optical pulse propagation does not take into account by using the slowly varying envelope approximation for the laser pulse interaction with optical bistable element. Therefore, a reflection of the beam from the domains with abrupt boundary does not take into account under computer simulation of the laser pulse propagation. However, the optical beams, reflected from nonhomogeneities caused by the domains of high concentration of free-charged particles, can essentially influence on a formation of switching waves in a semiconductor. We illustrate this statement by computer simulation results provided on the base of nonlinear Schrödinger equation and a set of PDEs, which describe an evolution of the semiconductor characteristics (concentrations of free-charged particles and potential of an electric field strength), and taking into account the longitudinal and transverse diffraction effects.

Ultrafast switching based on field optical bistability in nano-film of semiconductor

Using computer simulation, we show a possibility of ultrafast switching between stable states of an optical bistable device based on nano-film of semiconductor. Optical bistability occurs because of nonlinear dependence of semiconductor absorption coefficient on electric field potential. Electric field is induced by a laser pulse due to charged particles generation. The main feature of this bistable element is low absorption energy, which is necessary for switching, in comparison with bistable element based on other physical mechanism of laser energy absorption. For computer simulation of a problem under consideration a new finite-difference scheme is proposed using the original iterative process.

Laser-induced 2D periodic structures of charged particles concentration in semiconductor under the condition of optical bistability existence

We analyze evolution of laser-induced 2D periodic structures in semiconductor under the condition of optical bistability occuring. Optical bistability appears due to nonlinear dependence of semiconductor absorption coefficient on charged particles concentration because of both the Fermi energy level renormalization and the Burstein-Moss effect. The electron mobility, diffusion of electrons and laser-induced electric field are taken into account for analyzing the laser pulse propagation in the semiconductor. We found out various modes of laser-induced spatial structures developing of charged particles concentrations in dependence of optical intensity and the absorption coefficient. One of them consists in periodic appearance and moving of stable spatial electrons distribution. We discuss also the finite-difference schemes, which can be used for computer simulation of considered problem.