Abstract

Unlike for the conventional photorefractive effects, in interband photorefraction the photocarriers are excited by with photons whose energy exceeds the material energy bandgap. Because of the higher absorption (α ≈ 10³ cm^-1), the charge photoexcitation process is much more efficient and gives the possibility to generate a space-charge electric field by modulating the density of the free charges which are not trapped into midgap energy levels. The advantages are faster response times combined with a higher sensitivity. Time resolved four wave-mixing experiments in pure KNbO₃ crystals have shown that even at low intensities of few mW/cm², response times in the μs range can be achieved with a consequent holographic sensitivity of the order of few cm²/J [1].

© 1998 IEEE