Abstract

Bismuth silicon oxide, BSO, is a photorefractive material of current interest.¹ Gratings with a spacing of 2 μm were written using the 442 nm line from a HeCd laser. Both write beams were switched by an electro-mechanical shutter so that the dark-decay of the grating could be monitored. The growth and dark-decays were read using a HeNe laser incident at the Bragg angle. The BSO samples were mounted on the cold- head of a dosed cycle helium refrigerator so that measurements could be made over the 20-300-K range. Figure 1 shows the growth of the grating during the write- process. At room temperature, as shown by the solid curve, the grating peaks quickly and decays to a steady value. Similar time evolutions, but over much longer times, have been reported at high temperatures by Powell and Arizmendi.² The dashed curves in Fig. 1 show that at lower temperatures a slower component appears and the fast peak goes out. The slower component comes in at the same temperature that the photochromic bands decay³ and is probably due to the same traps. The curves in Fig. 1 for 292 and 243 K were measured with a 20 ms write-time while the 210 K curve was obtained with a 50 ms writetime. At lower temperatures it was necessary to extend the write-time to allow the grating to reach saturation. Figure 2 shows the grating strength as a function of temperature for a constant 10 ms exposure and when the grating was allowed to reach saturation. The results for the constant exposure case are in good agreement with those obtained by Foldvari, et al.⁴ for BGO.

© 1994 Optical Society of America