Millisecond laser ablation of metal assisted by high-energy nanosecond laser-induced air filament.

Combined Pulse Laser (CPL) irradiation provides substantial benefits for high-energy laser damage studies. However, in most reported CPL schemes, the millisecond laser is restricted to small spots (hundreds of microns) and peak power densities around 10⁶ W/cm², which are far from practical damage conditions. Here, we propose a filament-assisted CPL strategy in which high-energy nanosecond pulses (0.4-1.0 J) are focused by a 1 m lens to generate a 3-5 cm-long air filament, intersecting a millisecond laser beam (1.2 mm spot, 4.42 × 10⁴ W/cm²) at ~15°. This configuration enables efficient energy coupling between the filament plasma and the heated target. Experimental results reveal that the filament-assisted CPL increases ablation depth from 0.09 mm to 1.01 mm and boosts material removal efficiency from 0.11 mm³/J to 1.55 mm³/J. An integrated diagnostic system combining high-speed thermography, high-speed imaging, and morphological characterization was used to analyze the ablation dynamics. The proposed CPL approach significantly improves ablation effectiveness and offers a promising pathway for advanced high-energy laser damage applications.