Microphotometric investigation of fixed holograms

Holographic gratings are written in copper-doped LiNbO 3 crystals at temperatures of about 180 degrees C. At room temperature the gratings are fixed. The subsequent development process under homogeneous illumination is investigated by the microphotometric method. Measurements of the light intensity pattern at the exit face of the crystal reveal not only the change of the amplitude but also a phase shift of nearly pi . The dynamics of the development process can be fully understood by the assumption of a quasi-permanent modulated charge distribution and a second modulated charge distribution of optically excitable ions.