Efficient high-power continuous-wave multi-slab Fe:ZnSe laser at 4.1 μm

We report high-efficiency continuous-wave operation of a cryogenically cooled Fe²⁺:ZnSe laser at 4.167 µm using a four-slab configuration (2.75 mm each, 4.3-7.9 × 10¹⁸cm^-3) optimized for pump absorption and gain distribution. Cooled to 90 K and double-end pumped at 2.832 µm by two fiber-bulk hybrid Cr:ZnSe lasers (17 W and 13 W), the system achieved complete pump absorption (η_a ≈ 99.68%), delivering 13.9 W output with 41% slope efficiency. Beam quality was near diffraction-limited (MX2=1.13±0.11,MY2=1.24±0.12). The lasing wavelength red-shifted from 4.036 to 4.167 µm with power, attributed to thermal and gain-spectrum dynamics. This architecture mitigates thermal lensing and supports efficient mid-infrared power scaling.