Thermosetting enhancement of the light-induced polar orientation stability of molecules in polymers

Two kinds of polymers with disperse red 19 pendant groups, a thermal-imidization polyimide and a thermal-crosslinking polyurethane, were used in thermal-assisted optical poling to improve the photostability of the optically induced polar orientation of molecules. During the seeding process, samples heated in an oven were irradiated simultaneously by the coherent superposition of the 1064 nm fundamental and the 532 nm second-harmonic light of a nanosecond-pulsed Nd: YAG laser. The second-order optical nonlinearity of the polymer films seeded at elevated temperatures kept stable at room temperature even under illumination of the intense 1064 nm fundamental light. The nonlinear optical coefficient d(33) was estimated to be 6.9 pm/V for the azopolyimide film and 12.7 pm/V for the azopolyurethane film, respectively. Experimental results indicated that the optically aligned azodye molecules were fixed by the thermosetting polymer matrix during the thermal-assisted optical poling process. (C) 1999 American Institute of Physics. [S0021-8979(99)05812-0].