Photorefractive beam-fanning effect and self-pulsations in coated LiNbO3 slabs

We investigate the dynamical behavior of optical Fabry-Perot resonators consisting of LiNbO3 slabs (x and c cut) that are coated with different (absorbing or lossless) dielectric multilayers deposited on both sides of the slabs. Bistable switching is observed experimentally. The buildup of beam fanning with time leads to destructive interference for a portion of the incident beam, inducing a change in absorption and heating, hence to switching off. As a result, self-pulsations appear whose frequency depends strongly on the input light intensity, the spot size, and the focusing. Switching and self-pulsations are not observed in the case of lossless coatings or for bare LiNbO3 slabs, although strong photorefractive beam fanning is still present. We also study the influence of the incident-beam characteristics (width and focusing) on the beam-fanning process and the pulsating behavior.