Abstract

We investigate the effects of fanning and beam coupling on volume hologram superposition in high-gain photorefractive materials. The recording capability of cerium-doped SBN:60 can be enhanced by applying an external voltage, which increases the recording sensitivity and maximum index modulation. At the optimum voltage (≈15 kV/cm), however, the gain coefficient can be as high as 100 cm⁻¹, so coupling between the recording beams and photorefractive fanning effects dominate the recording process, thereby reducing the beam contrast ratio and increasing the background noise. These effects are important for multiple-hologram superposition, because subsequent exposures reduce the index modulation of earlier recordings, making it necessary to "overexpose" the early holograms (record more than a full cycle of index modulation).

© 1990 Optical Society of America