Thermal optimization of the second harmonic generation with tapered diode lasers

Abstract

Recently, hybrid integrated compact laser sources with high optical output powers in the visible range around 488 nm were demonstrated using tapered diode lasers. This was done by single-pass second harmonic generation (SHG) using a periodically poled LiNbO3 crystal of 30 mm length. The conversion efficiency depends on the light source but is also a function of the temperature distribution along the length of the crystal. The maximum conversion efficiency of a given beam is theoretically achieved by a homogenous temperature distribution. Experiments have shown that for high power SHG different absorption mechanisms are causing a temperature gradient in the crystal. This gradient leads to an inhomogeneous poling period, which diminishes the effective crystal length and leads to a smaller conversion efficiency. In this paper we present a method for the optimization of the temperature management during the SHG. This is done by a multizone heater package that can be integrated into compact laser sources. This package can be used to create arbitrary temperature distributions and is especially able to compensate an arising temperature gradient.