On optical phase conjugation in polystyrene films containing the azobenzene dye Disperse Red 1

Optical phase conjugation in polystyrene films containing the commercially available azobenzene dye Disperse Red 1 was measured using CW laser radiation (lambda = 532 nm) generated by a frequency-doubled YAG laser of total power 50 mW. The degenerate four-wave mixing (DFWM) experiment allowed for measurement of the build-up time of the phase-conjugate signal and phase-conjugate reflectivity as a function of dye concentration and input beam intensities. The phase-conjugate reflectivities reached 0.1% in polystyrene films containing 2.5 wt% of the dye, with the phase-conjugate signal build-up time constants amounting to about 100 ms. The appearance of a phase-conjugate signal is linked with a build-up of absorption-induced gratings of a mixed (phase and amplitude) nature. Interesting thermally induced effects such as lensing effects and nonlinear chaotic behaviour of the phase-conjugate signal were observed.