Optical control of the pitch in cholesteric liquid crystals

It has been shown that optical control of a spiral pitch in cholesteric liquid crystals (CLCs) by laser light irradiation is possible. Because of the spiral periodic structure, the CLCs shows unique optical characteristics with various polarization dependence. Then, the CLCs have a potential for application to polarization selective device whose properties can be changed by light irradiation. The CLC used was a mixture of cholesteryl chloride and cholesteryl pelagonate, and a mixing ratio selected for the wavelength of a probe laser was CC : CP= 33.3 : 66.4. To control the pitch, CLCs was doped with azobenzene at a concentration of 5 mol%. Optical isomerization of the dye molecules induced a change of the pitch, and hence the selective reflection band is shifted. Irradiation by a He-Cd and an Ar+ laser shifted the selective reflection band of sample to shorter and longer wavelength, respectively. Hereby the spiral pitch in CLC was reversibly changed by10 nm.