Optical holographic grating formation in dye-and fullerene-doped liquid crystalline system

Summary form only given. There have been intense research interests in nonlinear optical materials capable of recording permanent holographic planar or volume gratings. Among the goals to be achieved are low writing intensity, high storage density and fast recording/erasure times. We present recent results of an extended study on nematic liquid crystal films doped either with dyes or fullerene C/sub 60/. Nematic liquid crystals doped with azo-dyes have been demonstrated to be a very sensitive medium for optical storage application. In these samples, we were able to write permanent optical gratings using energy density as low as 3 J/cm/sup 2/, with a resolution higher than 100 lines/mm. The memory effect is due to a light induced anchoring on the illuminated surface and is caused by surface adsorption of excited dye molecules. A similar electro-optical holographic storage grating effect is observed in C/sub 60/-doped nematic liquid crystal films. The effect is attributed to molecular axis reorientation caused by the combination of an applied DC field and an optically induced DC space charge field. The observed nonlinear sensitivity S [defined by S=/spl delta/n/F, where /spl delta/n is the induced index modulation, and F is the incident laser energy fluence in units of energy/area] obtained in our preliminary studies already ranks among the largest compared to other materials. We have shown that a value of S/spl sim/5/spl times/10/sup -5/ cm/sup 2//J can be easily achieved with these films. This is mainly due to the unusually large optical birefringence and dielectric anisotropy of nematic liquid crystals.