Optically switchable biphotonic gratings based on dye-doped cholesteric liquid crystal films

This study elucidates optically switchable gratings (BGs) based on biphotonic effect in dye-doped cholesteric liquid crystal films. When one circularly polarized green beam is switched on (off), the gratings can be turned on (off) by illumination with an interference field generated by two linearly polarized red beams. The biphotonic gratings are formed by two mechanisms-green-beam-induced dye reorientation through trans-cis isomerization and red-beam-induced suppression of dye reorientation by cis-trans back isomerization. These mechanisms result in a spatially periodic distribution with homeotropiclike and planarlike structures, respectively, in dark and bright regions of the interference field, generating the BGs. (c) 2007 American Institute of Physics.