Measurement of thermal expansion and thermo-optic coefficients in LiNbO 3 and KTiOPO 4 crystals using dual-interferometric techniques

Abstract

We describe a dual-interferometric setup for simultaneous and independent measurement of the thermal expansion coefficient and thermo-optic coefficients in ferroelectric crystals (LiNbO 3 and KTiOPO 4 ). The crystal temperature varies from room temperature up to 200°C by an actively stabilized oven. The thermal expansion coefficient is determined using a moire interferometer and monitoring, as a function of the temperature, the period of a grating written on one side of the crystal sample. The thermo-optic coefficients of the ordinary and extraordinary axes of LiNbO 3 crystal are estimated by measuring the optical path variation measured using a Mach-Zehnder interferometer.