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Optical processing with photorefractive polymers depends on achieving high optical gain, which depends exponentially on the product of the interaction length and the gain coefficient. By use of several polymer layers to increase the overall interaction length and a new high-performance photorefractive polymer composite, the overall optical one-pass gain becomes as large as a factor of 5. For a two-layer sample placed in an optical cavity made with two concave mirrors, spontaneous oscillation due to two-beam coupling gain was observed. Because only one pumping beam is required, this configuration also acts as a self-pumped phase-conjugating mirror with a reflectivity of 13 percent for an applied electric field of 75 volts per micrometer, marking a milestone for this growing class of optoelectronic materials.