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DF: Fachverband Dielektrische Festkörper

DF 14: Electric, electromechanical and optical properties II

DF 14.9: Vortrag

Donnerstag, 28. Februar 2008, 16:40–17:00, EB 407

Optical cleaning of lithium niobate crystals for reduction of optical damage* — •Michael Kösters¹, Patrick Werheit¹, Daniel Haertle¹, Karsten Buse¹, and Boris Sturman² — ¹Institute of Physics, University of Bonn, Wegelerstr. 8, 53115 Bonn, Germany — ²Institute of Automation and Electrometry, 630090 Novosibirsk, Russia

A method for the reduction of optical damage in lithium niobate crystals is presented: The crystals are illuminated with a focused laser beam giving rise to strong bulk photovoltaic electronic currents. At the same time, application of high temperatures of about 180 °C prevents the build-up of space charge fields by enhancing the mobility of ionic compensation charges, such as hydrogen ions. Experimentally, the method is similar to "thermal fixing" used for persistent hologram recording. Optimum choice of the light pattern plus heat however dramatically decreases the concentration of photoexcitable electrons in the exposed region leading to a suppression of optical damage. Experiments with slightly iron-doped crystals have shown an increase of the threshold for optical damage of more than 100 compared to untreated crystals. Crystals treated with this method could be of great use for non-linear optics, especially for applications using periodically-poled structures to enable quasi-phase matching: in contrast to magnesium doping for optical damage reduction, the method does not affect the good poling characteristics of undoped lithium niobate.

*Financial support from the Deutsche Telekom AG is gratefully acknowledged.