Investigation of the dynamic recording process of thick refractive index gratings in photorefractive crystals by the microphotometric method

Abstract

Diffraction-efficiency measurements are compared with the microphotometric determination of the intensity pattern at the exit face of a LiNbO₃-sample during the holographic recording process. The special advantage of the microphotometric method is the possibility to determine phase shifts of the refractive index grating and of the light intensity pattern simultaneously and independently. Both quantities are very important for an understanding of dynamical effects during the holographic writing process. Furthermore, direct experimental evidence for the change of the modulation degree, i.e. the change of the contrast of the light pattern writing the grating, has been found. This change is caused by a Moiré-like effect which is closely related to the energy transfer between writing beams.