Anti-Resonant Hollow-Core Fiber Enables Flexible Delivery and Micromachining of High-Power Picosecond Lasers

Recently, the Russell Center for Advanced Lightwave Science at the Hangzhou Institute of Optics and Fine Mechanics, together with the State Key Laboratory of Ultra-Intense Laser Science and Technology at the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences and the Laser Intelligent Manufacturing R&D Center, made significant progress in high-quality flexible delivery and precision processing of high-power picosecond lasers using anti-resonant hollow-core fiber (AR-HCF). The findings, titled "High-quality delivery of high-power picosecond lasers in single-ring anti-resonant hollow-core fiber for micromachining," were published in High Power Laser Science and Engineering.

Ultrafast lasers play an irreplaceable role in precision cutting, welding, and surface treatment, but their delivery remains challenging: free-space beam-path systems have limited processing ranges, are sensitive to environmental vibration, and are complex to maintain, while conventional solid-core fibers are constrained by nonlinear effects and damage thresholds, making it difficult to carry high-peak-power ultrafast pulses. With low nonlinearity, a high damage threshold, and weak waveguide dispersion, anti-resonant hollow-core fiber offers a new route for flexible delivery of high-power ultrafast lasers.

Figure 1 Experimental setup and anti-resonant hollow-core fibers

cross-sections of AR-HCF1 and AR-HCF2

Figure 2 Power stability and pointing stability of the laser delivery systems.

(a-b) free-space laser delivery system; (c-d) 3 m AR-HCF1 delivery system; (e-f) 3 m AR-HCF2 delivery system

The research team designed and fabricated two single-ring anti-resonant hollow-core fibers (AR-HCF1 and AR-HCF2) with different structural parameters. Experiments show that when the capillary-to-core diameter ratio (d/D) is optimized to about 0.68 (AR-HCF2), the fiber's ability to suppress higher-order modes is significantly enhanced. When 20 W, 1064 nm picosecond laser pulses with a pulse width of <15 ps were transmitted through a 3 m long AR-HCF2, the system delivered excellent performance: the output beam mode was clean, and pointing stability (θₓ=9.8 μrad, θy=8.5 μrad) was better than that of a free-space system (θₓ=26.3 μrad, θy =17.2 μrad) and AR-HCF1 with d/D≈0.5 (θₓ=14.0 μrad, θy =9.9 μrad); the power fluctuation RMS was about 0.2%, comparable to the free-space system, with lower maintenance requirements.

Figure 3 Beam profiles at the output ports of the three laser delivery systems:

(a-c) free-space laser delivery system; (d-f) 3 m long AR-HCF1 laser delivery system; (g-i) 3 m long AR-HCF2 laser delivery system

In aluminum sheet micromachining experiments, AR-HCF2 achieved processing quality close to that of the free-space system. The roundness of single-pulse processing spots reached 0.97, with good dimensional uniformity; the deviation of the in-line processed lines was only 2.38%, comparable to the 2.12% of the free-space system and clearly better than the 5.66% of AR-HCF1. This shows that improving mode purity through fiber structure optimization can effectively suppress beam instability caused by fiber microbending, thereby achieving greater system flexibility and stability while maintaining processing accuracy.

Figure 4 Results of single-pass processing on the aluminum plate surface by the three laser delivery systems: (a-c) free-space laser delivery system; (d-f) 3 m long AR-HCF1 laser delivery system; (g-i) 3 m long AR-HCF2 laser delivery system

Figure 5 Results of in-line processing on the aluminum plate surface by the three laser delivery systems at a scanning speed of 4 mm/s: (a) free-space laser delivery system; (b) 3 m long AR-HCF1 laser delivery system; (c) 3 m long AR-HCF2 laser delivery system

The study is the first to clarify the critical role of mode purity in anti-resonant hollow-core fiber on micromachining quality, providing an important basis for developing high-performance, flexible ultrafast laser processing equipment. The team will next explore the technology's potential at longer transmission distances and higher power levels, advancing its industrialization in precision manufacturing.

The related work was supported by the National Natural Science of China, the Chinese Academy of Sciences' Pilot Special Project B, and the Shanghai Science and Technology Program.