Thermal lens spectrometry in pyroelectric lithium niobate crystals

Abstract

In this work, the light-induced lens effect due to thermal and/or photorefractive processes was studied in pyroelectric (undoped and Fe2+-doped) lithium niobate crystals (LiNbO3) using thermal lens spectrometry with a two-beam (pump–probe) mode-mismatched configuration. The measurements were carried out at two pump beam wavelengths (514.5 and 750 nm) to establish a full understanding of the present effects in this material (thermal and/or photorefractive). We present an easy-to-implement method to determine quantitative values of the pyroelectric coefficient (dP s/dT), its contribution to the thermal effect and other thermo-optical parameters like thermal diffusivity (D), thermal conductivity (K) and temperature coefficient of the optical path length change (ds/dT). These measurements were performed in LiNbO3 and LiNbO3:Fe (0.1 ppm Fe2+) crystals with c axis along the direction of laser propagation.