Photorefractive rings and their polarization dependence

Abstract

In this paper we report on the observation of ring patterns that emerge from a photorefractive crystal when it is illuminated with laser light of mixed polarization. In addition, we propose a physical model and quantitatively compare theoretical predictions with experimental observations. Our observations were made in cerium-doped barium strontium potassium niobate. Although there have been many previous reports of ring patterns produced by photorefractive materials, the physical mechanism for the formation of the ring patterns considered in this paper is different from that used in earlier reports. In fact, the ring patterns described here are only observable when the photorefractive crystal is illuminated with laser light that is in a mixed-polarization state. For example, the rings are not observable by using an argon-ion laser, oscillating at only one of its laser lines, with a polarization that is either ordinary or extraordinary with respect to the crystal c-axis. They are observable, however, if the polarization of the incident laser light has both ordinary and extraordinary polarization components. The physical mechanism for the production of the ring patterns reported here is similar to that described in a recent paper. This paper reported on the observation of rings patterns emerging from a photorefractive crystal when it was simultaneously illuminated with more than one color of laser light.