MECHANISM OF REFRACTIVE-INDEX CHANGE IN A CE-SBN SINGLE-CRYSTAL ILLUMINATED BY NOMINAL HOMOGENEOUS LIGHT

We report a series of experiments demonstrating that the refractive in dex n(e) of a single crystal of Ce:SBN increases when the crystal is i lluminated by a nominal homogeneous Ar laser beam. The increase is lar ger than that owing to the pure temperature rise, which is equal to th at occurring in a Ce:SBN crystal illuminated by the same laser beam. W e discovered that the difference between these Delta n(e)'s owing to t he light and to the heat caused by this light is closely related to th e crystal's history of illumination; the more it is illuminated, the l ess the difference is. Also, when the illumination exceeds the thresho ld volume for the first time, the refractive index will increase to be linear. We believe this to be the first report of these phenomena; we have introduced a theoretical explanation.