Optically switchable biphotonic photorefractive effect in dye-doped liquid crystal films

This study reports the optically swichable photorefractive (PR) effect induced in a biphotonic grating in the presence of an applied dc voltage, in an azo-dye-doped liquid crystal (LC) film. When one green light is switched on (off), the PR grating can be turned on (off) by irradiating an interference field generated by two linearly polarized red lights. Experimental results demonstrate that such a PR effect follows primarily from a biphotonic process, with two mechanisms—the generation of green light-induced space charges by trans–cis isomerization, and the suppression of the formation of space charges by the red light in cis–trans back isomerization. These mechanisms apply to the dark and bright fringes of the red interference field, respectively. A spatially inhomogeneous space-charge field is then established to modulate the orientation of LCs, forming the PR grating in the presence of a dc voltage. Strong coupling of the two red lights is observable and measured dynamically during the formation of th...

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