Power and energy scaling of an acousto-optically Q switched Raman deep-red laser

An efficient high-power nanosecond pulsed deep-red laser at 745 nm is produced by intracavity frequency-doubling an acousto-optically Q switched Nd:YLF/KGW Raman laser using a lithium triborate (LBO) crystal. The critically phase-matched type-I LBO crystal with an optimized length of 25 mm is adopted to enable efficient second-harmonic generation and to suppress unwanted cascaded Stokes fields. Under a repetition rate of 4 kHz, the maximum average output power of 4.1 W is obtained with the launched pump power of 50 W, resulting in an overall optical power conversion efficiency of 8.2%. The average beam quality factor is determined to be M² = 1.46. The pulse energy is scaled up to 3.3 mJ at the repetition rate of 1 kHz, corresponding to a pulse width of 4.2 ns and a peak power of up to 0.8 MW. Moreover, we theoretically investigate the dependence of the conversion efficiency on the walk-off angle as well as the fundamental and first-Stokes losses, which will guide further optimization of experimental devices.