Reversible photo-darkening effect in chalcogenide glassy films, where under a light irradiation, a very essential (up to 20-50 times) decrease of the film transparency, continues to attract attention of many researchers and engineers. Both very short (ns) pulse excitation photo-darkening processes and CW excited photo-darkening are now clarified; however, the peculiarities of photo-darkening phenomena occurring in the intermediate µs time intervals continues to be vague. Together with the pure scientific interest, photo-darkening under action of µs light pulses is of interest to different fields of modern electro-optics, in particular for short pulse light photo-recording and photolithography.

In this paper the photo-darkening phenomena in the amorphous As₅₀Se_50, Se, and Se₉₅Te₅ films at the µs light pulses irradiation are investigated. The process of photo-darkening during each of the individual 1 µs, 10 µs or 100 µs pulses as well as the processes proceeding between successive pulses are recorded and analyzed. Photo-darkening is very strongly dependent on the light pulse fluency. In the case of amorphous Se and Se₉₅Te₅ films, the darkened film was shown to restore initial optical properties, after a period in darkness, without any additional irradiation or heating.