Dynamics of the photoexictation of azo dye-doped liquid crystals probing by pumped attenuated total reflection

Kinetics of the photoexcitation of azo-dye doped liquid crystals (ADDLCs) is observed by the improved attenuated total reflection leading a pump light into a coupling prism, namely pumped ATR (PATR) experiment. The technique of ATR could be applied on an LC cell based on that the guide mode is overcome by the usage of an isotropic surface, which is also a usual way to observe the reaction involving the adsorption effect. The evanescent wave of the pump light induces the photoexcitation of azo dye at the limited effective depth, and the evanescent wave of the probe light detects the dynamic behavior in real time. The time response of the photoexcitation in ADDLCs in the pumped ATR experiment is less than 2ms and believed the reaction occur in the local region of 100 nm. This result is a witness of that the reaction in this local region is free of the influence of the elastic continuum of the whole LC cell. With the help of the local sensitivity and local disturbance, the detailed reactions during the photoexcitation process are clearly observed and the dynamics equation are expressed to illustrate the oscillation phenomena of LC directors as the pump light irradiates on this region.