Efficient ultraviolet photorefraction in LiNbO3

A nominally undoped LiNbO₃ crystal with a slightly broadened absorption edge is used to study beam coupling effects in the UV at 351 nm. At this wavelength the crystal exhibits a diffusion-dominated charge transport mechanism, which allows steady state beam amplification of up to 700 times, comparable to BaTiO₃ in the visible. The used crystal material was characterized by an absorption coefficient =2.68 cm^–1 at 351 nm and a maximal gain coefficient =13.94 cm^–1. This high gain value in the UV can be attributed to a hole diffusion-dominated charge transport mechanism together with a low bulk photovoltaic effect. We measured photovoltaic fields of the order of 550 V/cm.