Dual-beam ablation of fused quartz using 266 nm and VUV lasers with different delay-times

The dual-beam laser ablation of fused quartz by 266 nm laser coupled with vacuum-ultraviolet (VUV) laser beams at various delay-times of 30 ps, 2 ns, 4 ns, 8 ns and 1 s between VUV and 266 nm beams is reported. The dual-beam ablation method greatly reduced debris deposition at the circumference and increased the ablation rate in comparison with single-beam ablation. The delay-time effect on the ablation reflects the roles of excited-state and stationary absorption to 266 nm laser. The high-quality ablation can be realized at the delay-times within 4 ns due to large excited-state absorption. The surface roughness values at the circumference of patterned structure are 46.2 for 30 ps, 48.2 for 2 ns, and 55.0 nm for 4 ns, respectively. The ablation quality deteriorates with a large surface roughness of 79.3 nm when delay-time increases to 8 ns. When delay-time reaches to 1 s, the ablation quality gets even worse with a larger surface roughness of 119.0 nm, but is better than when only 266 nm laser is used due to the stationary effect. In addition, the surface roughness for 266 nm laser is increased to 176.0 nm. In the meanwhile, the ablation rate of 37 and 22 nm/pulse at 30 ps and 8 ns, respectively, indicates an influence of delay-time on the ablation rate. The ablation mechanism is discussed on the basis of the excited-state and stationary absorption to 266 nm laser.