Abstract

Grating translation technique (GTT), which employs a momentary shift of the light fringes during recording, has proven to be a powerful tool for characterization of various photorefractive materials including polymers. It has been used in the transmission geometry. Recently, the reflection geometry with ultra-low grating spacing (Λ ≈100 nm) has become a topical issue for two-wave mixing experiments with LiNbO₃:Fe crystals [1]. Stabilization of the light fringes by means of a feedback loop and application of extremely large external electric fields (up to 650 kV/cm) has allowed to improve greatly the apparent photorefractive characteristics and to enter a new challenging range of material parameters. Distinguishing features of our case are as follows: (a) We deal with strong space-charge saturation effects, (b) the feedback stabilization is able to modify strongly the photorefractive response by introduction of a frequency detuning between the light beams, and (c) a low-frequency resonance has been predicted just in the actual range of experimental parameters [2].

© 2003 Optical Society of America