交变电场下向列相液晶的非线性光学增强效应

Nonlinear Optical Enhanced Effect in Nematic Liquid Crystals by AC Field

本文研究了向列相液晶在交变电场作用下引起的Fredericks转变,测量了交变电场和直流电场作用下5CB和MBBA的阈值电场。文中还论述了MBBA在交变电场(450Hz)作用下产生的非线性衍射束的增强效应。

Because there exist charged particles and conductance anisotropy in liquid crystals, charge transfer and redistribution are bound to occur under the action of a dc field or low frequency ac field. In this case, the effects from both dielectric and conductance must be taken into consideration. However, under the action of high frequency ac field, as the movement of charge particles will lag behind the field charge, the conductance effect can be neglected. For the threshold of electric field intensity theoretically derived for Fredeicks transition in direction n only the dielectric effect has been considered. Therefore, it is expected that the experimental threshold intensity obtained under high frequency ac field will be closer to the theoretical one than that obtained under dc field. Measured results for 5CB and MBBA liquid crystals confirm the prediction. The enhanced effect of nonlinear diffracted beam in MBBA under the action of 450Hz ac field has been observed and the gain is found to be 35%-50%.