Resonant grating for wavelength and polarization selection in high-power lasers emitting in the 2-μm wavelength region

This paper presents the design, fabrication, and implementation of a single-layer resonant-reflection grating-waveguide structure (RR-GWS) optimized for laser operation in the 2 mu m wavelength region. The RR-GWS was designed to function effectively across a broad spectral region ranging from 1.9 mu m to 2.1 mu m. Reflectance measurements confirmed the structure's wideband performance within this spectral region, with 99% resonant reflectivity. Incorporating the RR-GWS into a Ho: YAG thin-disk laser system, as a cavity folding mirror, it demonstrated very good power-handling capability and efficacy in wavelength and polarization selection. The 2 mu m laser system achieved a linearly polarized output power of 36 W, with an optical efficiency of 34.6%. Additionally, the laser demonstrated a spectral bandwidth of < 0.5 nm full width at half maximum, i.e., 12 times narrower than that obtained with an equivalent all-mirror reference cavity.