Water Vapour Differential Absorption Lidar measurements at 935 nm using a Nd:YGG laser

Abstract

A novel diode-pumped, single-frequency laser system emitting at 935 nm was developed to serve as the transmitter for water differential absorption lidar measurements. This laser uses Nd:YGG (Y3Ga5O12) as the active medium. The system was directly diode-pumped at 806 nm and was built up in a master-oscillator power-amplifier configuration. It consists of a stable resonator in rod geometry and employs as the amplifier a stable-unstable hybrid resonator in an end-pumped slab design. Single frequency operation is achieved by injection seeding. The range of continuously tunable single-frequency radiation extends to ~0.4 nm centered around 935.31 nm. More than 30 mJ of pulse energy at 100 Hz repetition rate with a beam quality (M2) of better than 1.4 and Q-switched pulse duration of 52 ns in single frequency mode were generated. Since water vapor DIAL demands for stringent requirements for the spectral properties those were carefully investigated. Values of the spectral purity of >99.995% were determined using long-pass absorption measurements in the atmosphere exceeding the requirements by a large margin. Finally, first time water vapor DIAL measurements were performed using a Nd:YGG laser. The reported results show much promise of these directly pumped lasers at 935 nm for future space-borne and airborne water vapor lidar systems.