Second-harmonic generation in achiral bent-shaped liquid crystals

Second-harmonic generation (SHG) has been observed as functions of temperature, electric field and incidence angle in the liquid crystal phases of the achiral bent-shaped molecules with octyloxy end chains (P-8-O-PIMB), In the highest temperature B-2 phase, the SHG for oblique incidence started to appear at an electric field when the texture change due to the electric-field-induced molecular and dipolar reorientations occured. The SHG interferometry clearly indicated the reversal of polarization on reversing the applied field in the B-2 phase. The other two phases, B-3 and B-4, were also SHG active even in the absence of the field, indicating the spontaneous polar ordering in these phases. It was found that similar compounds with hexyloxy end chains (P-6-O-PIMB) and octyl end chains (P-8-PIMB) are not SHG active.