NONLINEAR SECOND HARMONIC GENERATION IN CHIRAL SMECTICS FOR FUNDAMENTAL WAVE BEING AT THE EDGE OF SELECTIVE REFLECTION BAND

Abstract

It was theoretically predicted [1–4] and confirmed experimentally [5–7] that an enhancement of the second nonlinear optical harmonic generation (SHG) in ferroelectric smectics C* (Sm-C*) liquid crystals (LC) occurs if the SH frequency is close to the edge of selective reflection band for Sm-C*. The SHG enhancement (SHGE) occurs also when the both fundamental and SHG frequencies are simultaneously close to the edges of selective reflection bands in Sm-C* for first and second diffraction orders, respectively [8]. Because the enhancement of nonlinear frequency transformation is not specific only of Sm-C* and may be of great applied importance [8–10] results of theoretical investigation of the role of diffraction of fundamental wave in the SHG enhancement are presented. For SHG in Sm-C* for collinear geometry with the waves propagation direction along the helix axis behaviour of the fundamental wave and nonlinear polarizations are investigated at fundamental frequency close to the edge of second order reflection band [11]. It is found that all terms of nonlinear polarization are sharply increased at approach of the fundamental frequency to the edge of selective reflection band. The analytical investigation of the problem is illustrated by calculations in the framework of dynamical diffraction theory [11].