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A phase-conjugate wave is generated by degenerate four-wave mixing in an amorphous chalcogenide As(2)S(3) thin film. The time-dependent behaviors of the phase-conjugate wave, the nonlinear absorption coefficient, and the refractive index are treated analytically, and the results are compared with those of experiment. The analyses are based on the rate equations obtained from a simplified energy-band model of amorphous As(2)S(3).

Photoinduced changes in the optical properties of amorphous chalcogenide As(2)S(3) thin films are explained by using the density matrix formalism. The treatment based on the double well potential model for a four-level system gives an improved analytic expression for nonlinear optical absorption coefficients and explicitly shows the break of reciprocity law between illumination intensity and exposure. Photodarkening and photobleaching kinetics obtained theoretically are compared with experimental results obtained in the present work.

Theoretical explanations of the kinetics of scalar and vector holographic gratings are developed, and experimental results are obtained in amorphous AS(2)S(3) thin films. The large nonlinear-optical susceptibilities are evaluated from experimental data in the vicinity of the fundamental absorption edge, and it is found that chi((3))(1111) congruent with 3.2 x 10(-2) esu and chi((3))(1122)/chi((3))(1111) congruent with 0.98.

We report on nonlinear optical image processing, such as image addition and subtraction, using photoinduced anisotropy in amorphous As(2)S(3) thin film and propose a method for contrast reversal and edge enhancement of an image.