We report the observation of intensity fluctuations in a semilinear photorefractive oscillator, consisting of a BaTiO$-3$/ crystal as the gain medium, and a multimode helium-neon laser as its pump source. Depending on the beam geometry and intensity, the periodical fluctuations range on a timescale from a few seconds to several minutes. The behavior is suspected to be caused by a competition of gratings due to the external cavity, crystal-ordinary mirror assembly, the self-pumped phase conjugate mirror due to total internal reflection.
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