Optical cleaning of lithium niobate crystals

Abstract

An all-optical method for the removal of photoexcitable electrons from photorefractive centers to get rid of optical damage in lithium niobate crystals is presented, the so-called "optical cleaning". The method combines the photovoltaic drift of electrons with ionic charge compensation at sufficiently high temperatures of about 180 °C. Optimum choice of the light pattern plus heat dramatically decreases the concentration of photoexcitable electrons in the exposed region leading to a suppression of optical damage. Experiments with slightly iron-doped lithium niobate crystals have shown an increase of the threshold for optical damage of more than 1000 compared to those of untreated crystals.