Nonlinearly optical-optical isomerization cycle in azobenzene liquid crystal polymers

A nonlinearly optical method to induce the birefringence in azo liquid crystal polymers by the optical-optical isomerization cycle (O-O cycle) process is proposed in theory and implemented by experiments. In the O-O cycle, the two isomerization steps of trans-cis and cis-trans are both induced by light. In the nonlinearly O-O cycle, at least one step involves the nonlinearly optical absorption. It has been demonstrated that the permanent birefringence was induced in azo polymer P-CN films with a visible light source at 532 nm wavelength by the nonlinearly O-O cycle. The nonlinear nature of the photoisomerization process in P-CN was verified and a high nonlinear absorption coefficient of 40 cm/W was measured by use of the Z-scan technique. (C) 2001 American Institute of Physics.