Watt level pulsed Tm:YLF / KGW Raman laser operating at near-IR wavelengths

We demonstrate an external-cavity KGd(WO₄)₂ (KGW) Raman laser, pumped by an actively Q-switch Tm:YLF MOPA. The fundamental spectral line emitting at 1881 nm allowed the KGW bi-axial crystal to lase at two separate output spectral lines, 2198 and 2265 nm, depending on the seed polarization axis relative to the KGW's axis. The Tm:YLF seed was amplified using a double-pass Tm:YLF crystal based MOPA setup. After amplification, the seed achieved an output power of 9.15 W, and an energy pulse of 4.57 mJ, a pulse duration of 43 ns at a repetition rate of 2 kHz. The max output average power achieved for the 2265 nm was 1.85 W, with a pulse energy of 0.923 mJ at a repetition rate of 2 kHz implying a conversion efficiency of ∼20.5%. We noticed a very low conversion efficiency of the shorter KGW spectral shift (at 2198 nm). The reason for this efficiency drop was validated to be the 2^nd stokes forming and thus consuming the 1^st stokes energy. In favor of the KGW inherent properties and according to the aforementioned results, this crystal appears to be suitable for power scaling as well as for improvement of the Raman conversion efficiency in this spectral range. The KGW crystal is well known for its use in shorter spectral wavelengths. To the best of our knowledge, it is the highest average power achieved by lasing in the 2 μm region using SRS with KGW.