Ultrabroadband Infrared Polarization Beam Combiner Based on Calomel Crystals with High Efficiency Exceeding 92% and Low Wavefront Distortion

Midwave and long-wave infrared (MW & LWIR) lasers are essential for applications such as infrared detection and counteraction. However, generating high-power MW & LWIR lasers directly is challenging. Polarization beam combining technology provides an effective method to achieve high-power lasers with excellent beam quality. This study introduces Glan–Foucault type polarization beam combiner (PBC) based on the calomel (Hg2Cl2) single crystal (SC), which exhibits an exceptionally wide transmission range (0.38–25 μm), ultrahigh birefringence of [email protected] μm, and a favorable laser-induced damage threshold (LIDT(001) = 8.06 J/[email protected] μm). The designed PBCs demonstrate an outstanding extinction ratio (ER) of up to 40 dB and a theoretical maximal transmittance of 81% across the full spectrum. When two fundamental mode Gaussian beams from the quantum cascade lasers (QCLs) were combined, the PBCs with infrared antireflection (AR) coatings achieved combining efficiencies of 93.5% at 4.6 μm and 92.4% at 9.2 μm, along with beam quality factors M2 of 1.23 and 1.17, respectively, without noticeable degradation. This work presents a novel polarization component for efficiently scaling the laser output power and maintaining good beam quality across mid- and far-infrared range.