Transient Reorientation of a Doped Liquid Crystal System under a Short Laser Pulse

The transient optical nonlinearity of a nematic liquid crystal doped with azo-dye DR19 is examined. The optical reorientation threshold of a 25-mu m-thick planar-aligned sample of 5CB using a 50 ns pulse duration 532 nm YAG laser pulse is observed to decrease from 800 mJ/mm(2) to 0.6 mJ/mm(2) after the addition of 1 vol% azo dopant, a reduction of three orders of magnitude. When using a laser pulse duration of 10 ns, no such effect is observed. Experimental results indicate that the azo dopant molecules undergo photoisomerization from trans-isomer to cis-isomer under exposure to light, and this conformation change reorients the 5CB molecules via intermolecular coupling between guest and host. This guest-host coupling also affects the azo photoisomerization process.

National Natural Science Foundation of China 10674033 Natural Science Foundation of Guangdong Province 8151009001000055 Science and Technology Program of Guangdong Province 2007B010600060 Supported by the National Natural Science Foundation of China under Grant No 10674033 the Natural Science Foundation of Guangdong Province (8151009001000055) and the Science and Technology Program of Guangdong Province (2007B010600060).