Optical cleaning of lithium niobate crystals

Abstract

Lithium niobate (LiNbO3) is an important optical material due to a unique combination of physical properties, in particular excellent electro-optic and nonlinear-optical characteristics. The main obstacle for the use of LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> crystals in optics is “optical damage” - the deterioration of light beams because of the formation of unwanted refractive index changes. The reason is the photorefractive effect: charge separation owing to the bulk photovoltaic effect leads to strong refractive index changes via the linear electro-optic effect [1]. It is accepted that remnant Fe centers are responsible for optical damage in undoped LiNbO3 crystals. Our new method for optical damage suppression, the “optical cleaning” [2], directly attacks the cause of the optical damage, namely the presence of photo-excitable electrons. It allows an effective removal of these electrons from an exposed area at sufficiently high temperatures using the bulk photovoltaic effect.