Dynamic photoinduced changes of optical characteristics and effect of optical memory in amorphous As–S film-based waveguides

Metastable and transient photoinduced phenomena in as-deposited amorphous As _xS _{100- x} films (15 ≤ x < 30) are studied using a waveguide technique. A detailed investigation of the optical stopping effect is performed. Dynamics of the photostimulated variation of the sub-bandgap mode absorption in the film waveguide is determined by competition of two independent processes: (i) external optical recording with a relatively durable non-volatile memory and (ii) sub-bandgap waveguide mode-initiated erasure by removal of the preceding optical record. Irreversible changes and transient variation of the amorphous As _xS _{100- x} film refractive index under above-bandgap laser illumination, accompanying the stopping effect, are investigated. The transient variation of the film refractive index is due to a photoinduced increase of the interatomic bond strength and a decrease of polarizability, primarily in the vicinity of sulphur atoms.