Light-induced modulated structures, intrinsic optical multistability and instabilities for the competitive wave interactions in liquid crystals

Abstract

2014 On étudie à la fois théoriquement et expérimentalement la multistabilité et les instabilités temporelles de processus ondulatoires non linéaires dans les conditions de transfert d'énergie et de compétition entre les différentes composantes de polarisation, pour un milieu anisotrope inhomogène présentant une non-linéarité à seuil. Dans de telles interactions, il se produit un couplage rétroactif lorsque le rayonnement laser induit un réseau d'indice de réfraction dans le milieu, à cause de la réponse non locale du milieu élastique anisotrope au champ extérieur. Abstract. 2014 The multistability and temporal instabilities of nonlinear wave process with an energy transfer and competition between different light polarization components have been studied both theoretically and experimentally for a nonhomogeneous anisotropic medium with threshold nonlinearity. A feedback for such wave interactions, when the laser radiation induces the bulk-gratings of refractive index, arises because of the non-local response of the anisotropic elastic medium on the external field.

<title>Limiting states of the short laser pulses in a DFB system</title>

“…In the simplest case of one-dimensional sinusoidal grating in the medium the linear susceptibility can be represented in the form15: =+2fiocosGoz (1) where the parameter j3 characterizes the depth of spatial modulation ( fl I < x o fi o < 0 ) G determines the periodicity (over coordinate z) , G = 2c I P , P is the grating period The initial system of two coupled equations for slowly varying complex amplitudes (which are the multipliers at phase terms exp (-iw t ik o,h z) of passing o) and scattered (Ah) waves is following13: dA0/ dz=iyAhexp(-iz) (2) -dAhi dz-iyAoexp(iz) where y = 2rw fl I / c (1 + 4Yrx 1/2 is the coupling parameter for waves (w is the optical frequency, c is the light velocity), is a constant of phase detuning from the Bragg resonance condition determined by relation 2 k= + we suppose that the wave vectors kand kare equivalent ( I ki = I ki k) . Furtherwe consider the most effective case of dynamic scattering for the exact Bragg resonance ( = 0).…”

“…(S.3) and as well in integrals of the system (S.5) we have analytical dependence for IAOh V5 t for the point with coordinates z,x: I Ao,h 2 çl exp(_2r2/rf-) + 1 exp(_2T2/rJ-Li = iagi -2 (1 +4o)2vcos/6Jrk2(3)hw2 2 the intensity of radiation. (S.6) in eq.…”