Abstract

We record polarization holograms in 1 % methyl red doped PCB liquid crystals by using the trans isomer absorption of the azo dye at 514 nm. The hologram is probed at 633 nm. Holographic dynamics are determined by the surface treatment of the glass substrate. In the unexposed sample, the liquid crystal molecular director is aligned by surface forces. Surface memory plays a crucial role in the holographic effects we observe. Using the Ericksen–Leslie theory, we derive the characteristic time constant for dynamic hologram formation and decay. The erasing time depends on the grating spatial frequency. It varies from 4 ms to 60 ms as we change the writing angles from 9° to 1.5°. Photochemical isomerization in a nematic liquid crystal host drives reorientation dynamics of the liquid crystal molecules either by a simple splay and twist in competition with the surface stabilized planar alignment or by triggering an isothermal phase transition from the nematic to isotropic. The Freedericksz threshold intensity is found to be about 3.0 mW/cm².

© 1992 Optical Society of America