Teams led by Shao Jianda and Jin Yunxia from the High-Power Laser Component Technology and Engineering Department, Shanghai Institute of Optics and Fine Mechanics, CAS, have achieved new advances in high-power continuous-wave mid-infrared laser spectral beam combining. The paper titled *High power continuous-wave mid-infrared laser spectral beam combining via Jigsaw-grating architecture* was published in *Optics Letters*.

Mid-infrared lasers are vital for spectroscopic analysis, free-space communications, gas sensing, biomedicine and national security. Spectral beam combining scales laser power and spectral coverage while preserving beam quality, serving as a key route to break the power limit of single mid-infrared laser beams. Nevertheless, as combining channels increase, conventional dual-grating systems demand large-aperture gratings with high efficiency and excellent wavefront quality. Fabricating gratings with large aspect ratios becomes especially challenging for broad mid-infrared bands, forming a major bottleneck for multi-channel high-power combining systems.

Figure 1. Principle of spectral beam combining with jigsaw gratings

To tackle this limitation, the team proposed a jigsaw-grating spectral beam combining architecture. Multiple small-aperture sub-gratings are distributed and assembled within an equivalent large-aperture space to efficiently combine multiple mid-infrared laser beams. This design removes the need for monolithic ultra-large gratings, greatly easing fabrication difficulties and improving system scalability.

For experimental validation, the researchers built a four-channel continuous-wave OPO spectral beam combining system using self-developed high-efficiency gold-coated mid-infrared gratings. Four OPO laser beams with central wavelengths from 3.1–3.7 μm hit the jigsaw grating at a 50° incidence angle. A combined continuous-wave mid-infrared output of 50.8 W was achieved with a grating combining efficiency of 92.1%. The merged beam maintained good quality, with Mx²=1.76 and My²=1.46. This power level ranks among the highest reported values for spectral beam combining in the 3–5 μm mid-infrared band.

Figure 2. (a) Beam quality of spectrally combined output; (b) Spectrum of output beam; (c) Comparison of output power for spectral beam combining in the 3–5 μm band

This work offers a new technical pathway to scale mid-infrared multi-channel spectral combining systems from tens of watts to the hundred-watt regime. It also provides references for building high-power laser platforms covering visible to terahertz bands.

The research was supported by the National Natural Science Foundation of China, the Young Talent Support Project of the China Association for Science and Technology, and the China Postdoctoral Science Foundation.