Photorefractive grating formation in the region of large intensity modulation

Abstract

A new method of measuring Bragg diffraction more accurately is introduced. When three formulas of photorefractive grating formation are given as functions of intensity modulation as m, 2m (1+ 1−|m| 2) , and 2m (1+ 1−|M| 2) , where M = m [1 + ( K K o ) 2] , and K is the grating wavenumber and K o is the Debye inverse screening length, their predictions for the Bragg diffraction are derived analytically and numerically by using the interrelation between two-beam energy coupling and Bragg diffraction in the photorefractive crystal. By fitting the predictions to the experimental data the behavior of the formulas is checked in the region of large m. It is shown that the general formula, 2m (1+ 1−|m| 2) , predicts the Bragg diffraction well within the experimental error even for m equal to unity, while the other two hold only for m smaller than 0.2 in the energy-gain orientation and smaller than 0.5 in the energy-loss orientation. In the limit of small K where the formula reduces to 2m (1+ 1−|m| 2) , it is shown to predict Bragg diffraction always larger than the experimental data. In the limit of small m where the formula reduces to m, it is shown to predict Bragg diffraction always smaller than the experimental data.