Distinct temporal evolution of PILS distribution in congruent and near-stoichiometric LiNbO3:Fe crystals detected by in-situ dynamic angular spectra

Abstract

In this paper, congruent and near-stoichiometric LiNbO3:Fe (CLN:Fe and SLN:Fe) crystals are prepared through Czochralski and Vapour-transport-equilibration techniques, and the temporal evolution of the photoinduced light scattering (PILS) in both crystals are studied at different temperatures by using an in-situ dynamic angular spectrum technique. It is found from a series of in-situ dynamic angular spectra that, the PILS angular distribution becomes narrow with the time elapsed in both crystals but the narrowing extent and its temperature dependence are quite different in the congruent and near-stoichiometric LiNbO3:Fe crystals. The narrowing of the PILS angular distribution is suggested to be connected with the competition between the noise gratings with the different wave vectors, and the distinct PILS characteristics in the two crystals are explained by the crystal conductivity varying with both the temperate and Li composition of the crystal. In particular, at the high temperatures above 170 °C two columns of PILS distributing in the angular regions of −\u20097°\u2009~\u2009−\u200917° and −\u200917°\u2009~\u2009−\u200925° are found in the congruent LiNbO3:Fe crystal but none in the near-stoichiometric LiNbO3:Fe crystal. The prolonged temporal evolution of these two columns of PILS are attributed to the competition between the two groups of noise gratings formed by the high-concentration protons with low mobility in the congruent LiNbO3:Fe crystal.