Optically switchable, rapidly relaxing cholesteric liquid crystal reflectors.

Reversible, fast, all-optical switching of the reflection of a cholesteric liquid crystal (CLC) is demonstrated in a formulation doped with push-pull azobenzene dyes. The reflection of the photosensitive CLC compositions is optically switched by exposure to 488 and 532 nm CW lasers as well as ns pulsed 532 nm irradiation. Laser-directed optical switching of the reflection of the CLC compositions occurs rapidly, within a few hundred milliseconds for the CW laser lines examined here. Also observed is optical switching on the order of tens of nanoseconds when the CLC is exposed to a single nanosecond pulse with 0.2 J/cm(2) energy density. The rapid cis-trans isomerization typical of push-pull azobenzene dye is used for the first time to rapidly restore the reflection of the CLC from a photoinduced isotropic state within seconds after cessation of light exposure.