Nonlinear optical properties of epitaxial lithium tantalate thin films

Abstract

Epitaxial lithium tantalate thin films were grown on prismatic sapphire substrates by a specially designed ultrasonic nozzle assisted liquid injection metalorganic chemical vapor deposition system. The films were characterized by x-ray diffraction and transmission electron microscopy. They contained two crystallographic iso-variants. The relative volume of two variants in the as-grown films was nearly equal. The optical loss in the films, measured by photographic method, was 2 dB/cm. Second harmonic properties of the films were measured in transmission. Compared to bulk single crystals, the as-grown thin film had a weak second harmonic response in the range of 1 pm/V, which was ascribed to the antiparallel domains in the films. Mathematical equations are derived to correlate this microstructure to second harmonic generation. The films were successfully poled by the application of in-plane electric field. After poling the second harmonic generation coefficient increased to 12 pm/V.