Вynamics of light-absorption variations induced in a bismuth silicate crystal by visible laser illumination

We present the results of experimental studies of the dynamics of the photoinduced optical absorption in a bismuth silicate crystal subject to continuous laser irradiation with wavelengths of 532 and 655 nm. The semiconductor-laser light beam with the wavelength λ = 655 nm causes the crystal bleaching at this wavelength, whereas its exposure to a shorter-wavelength irradiation from the optical-spectrum green region with a wavelength of 532 nm increases the optical absorption at both wavelengths, of 532 and 655 nm. The experimental results are interpreted using the theoretical model which assumes that the crystal has deep defect centers of two types so that an electron at each of these centers can be in one of the states characterized by different photoionization cross sections