The reflection behavious of nonlinear optical interface between glass and liquid crystal were studied systematically. The reflection behaviours of such interface with isotropic liquid phase was studied by using a Q-switched ruby laser. The threshold intensity of transition from TIR (tolal internal reflection) to partial transmission for different incident angle were measured at T-Tc = 2.5℃. It agrees with the plane wave theory of Kaplan. The time resolved reflection of nonlinear interface was also measured and hysteresis loop of reflectivity was observed. The hysteresis loop of reflectivity can be attributed to the deorientation relaxation processes of liquid crystal molecules. The nonlinear optical interface between glass and ne-matic liquid crystal was also studied using an Ar+ laser. The transition from TIR to partial transmission was observed at the intensity 700 W/cm2. This transition can be attributed to thermal induced phase transition from nematic mesophase to isotropic liquid phase.
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