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

Abstract

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.