The article is devoted to nonlinear effects in lithium niobate crystals. The possibility of using digital holographic interferograms obtained with the help of laser radiation of different duration at different moments of time for the reconstruction of dynamic phase changes is shown. Holograms were recorded on lithium niobate crystals doped with iron ions in various concentrations using He-Ne and He-Cd lasers, and the diffraction efficiency was calculated. Also, the effect of gamma radiation on the optical properties of LiNbO3 and LiNbO3:Fe crystals was studied. At the same time, it was determined that the band gap of the samples decreases, as a result of which the refractive index, absorption coefficient and photorefractive sensitivity increase several times.