Photoinduced Absorption and Pulsed Recording of Dynamic Holograms in Bismuth Silicate Crystals

Abstract

The dynamics of photoinduced absorption and holographic-grating recording in photorefractive crystals of bismuth silicate is studied. It is shown that, with the use of nanosecond laser pulses and of the intensity on the order of 1 MW/cm2 or higher, the induced absorption due to population of the short-lived trapping levels, with characteristic relaxation times about several milliseconds or tens of milliseconds, is the case. Recording of dynamic holograms has been realized in these conditions in bismuth silicate crystals. Two mechanisms of holographic-grating recording, with the lifetimes differing by three orders of magnitude, are established. At relatively low intensities, about 1 MW/cm2 or lower, the medium response is determined by a photorefractive mechanism of nonlinearity, with relaxation times of several seconds. At the intensities exceeding 5 MW/cm2 , one can observe a fast (ms relaxation times) component that may be associated with population of the short-lived traps. It is shown that the contribution of each mechanism is greatly dependent on the intensity of laser radiation and, for the intensities above 10–15 MW/cm2, the short-lived traps having millisecond lifetimes play the decisive role.