Tunable high-pulse-energy mid-infrared laser source based on optical parametric amplification in ZnGeP 2

Abstract

ABSTRACT Nonlinear optical conversion of high-energy 1.064 µ m pulses from a Q-switched Nd:YAG laser to the mid-infraredis demonstrated. The experimental setup is based on a two-stage master-oscillator/power-ampli“er (MOPA)design with a KTiOPO 4 based MOPA in the “rst stage and a KTiOAsO 4 /ZnGeP 2 based MOPA in the secondstage. The setup can be tuned to provide output at wavelengths within the transparency range of ZnGeP 2 .Weobtain more than 8 mJ at 8 µ m,andupto33mJinthe3 5µ m wavelength region. Th e measured beam qualityfactors are in the range M 2 =2 4 for both wavelength regions.Keywords: Infrared and far-infrared lasers, solid state lasers, frequency conversion, nonlinear optics, parametricoscillators and ampli“ers. 1. INTRODUCTION High energy mid-infrared laser sources have several applications including spectroscopy and remote sensing. Inorder to cover a wide wavelength range, nonlinear optical conversion is commonly employed. Zinc germaniumphosphide (ZGP) is an attractive material for this purpose due to its high nonlinear coecient, good transmissionin the mid-infrared range, and high thermal conductivity. ZGP must be pumped at wavelengths above 2 µ mdue to its high absorption below 2 µ m. Such pump beams can either be g enerated directly by a laser,