Fixed photorefractive holograms with maximum index-of-refraction modulation in LiNbO3:Fe

Abstract

We report the recording of a fixed good quality transmission hologram in LiNbO3:Fe with maximum index-of-refraction modulation using the simultaneous recording/compensation process at 120 °C in a specially designed setup with λ=514.5 nm. This process was shown to be reproducible and in good agreement with an already reported theoretical model. The analysis of this recording process showed that material saturation was reached so that the maximum possible fixed index-of-refraction modulation was achieved. From the comparison of theoretical and experimental recording/compensation process data some material parameters (dielectric relaxation time τMe≈15 min, saturation space-charge field Eq=18.8 kV/cm, and photovoltaic-to-saturation field ratio Eph/Eq=0.80) were determined. The diffraction efficiency of this grating was measured using a λ=633 nm probe laser beam in an independent setup and its actual value computed, taking into account the angular divergence of the probe beam. The good grating performance as an optical Bragg filter was experimentally characterized by independently measuring its angular (approximately 1.2 mrad) and spectral (approximately 0.1 nm) selectivities, both at the probe beam wavelength of 633 nm.