Molecular motion analysis in nematic liquid-crystal cells using linear and nonlinear optical techniques

The molecular motion of nematic liquid-crystal (NLC) molecules in a NLC cell was analyzed upon the switching on, the switching off, and the sign reversal of an external electric field. Both time-resolved nonlinear optical second-harmonic generation, which is sensitive to induced molecular dipole moments, and time-resolved linear optical transmission measurement, which is sensitive to the birefringence of the NLC molecules, were used. The combination of these techniques allowed a detailed analysis of both the molecular reorientation in the external field (through transmission experiments) and the dynamics of the electrically induced molecular dipole moments (through second-harmonic generation), which are again responsible for the molecular reorientation. Different time constants for the linear and the nonlinear optical experiments that correspond to different time-resolved phase measurement is introduced to analyze the sign reversal of the susceptibility of the NLC molecules induced by the polarity reversal of an external electric field. (C) 1997 Optical Society of America.