20W of continuous-wave sodium D_2 resonance radiation from sum-frequency generation with injection-locked lasers

Abstract

A 20-W all-solid-state continuous-wave single-frequency source tuned to the sodium $D_{2}a$ line at 589.159 nm has been developed for adaptive optical systems. This source is based on sum-frequency mixing two injection-locked Nd:YAG lasers in lithium triborate in a doubly resonant external cavity. Injection locking the Nd:YAG lasers not only ensures single-frequency operation but also allows the use of a single rf local oscillator for Pound–Drever–Hall locking both the injection–slave and the sum-frequency cavities. We observe power-conversion efficiencies in excess of 55% and a linearly polarized diffraction-limited output tunable across the sodium $D_2$ line (589.156 to 589.160 nm) with no change in output power and with high amplitude and pointing stability.