## 3 Results  
Different LIPA processing configurations were performed to understand the mechanism of LIPA. Firstly, to analyze the direct laser-quartz interaction effect, we applied 50 pulses of laser shooting at 2 J/cm\({}^{2}\) laser fluence on the bare quartz glass sample without the metal target on the bottom. There was no ablation trace on the quartz surface, proving the extremely low absorption rate of the bare quartz substrate. Subsequently, keeping the quartz sample in the same vertical position, the 304-type stainless-steel target was placed under the quartz layer, and we reapplied 50 pulses at the same laser fluence. The quartz sample after the processing is shown in Figure 3, where a well-defined ablation pattern can be observed very easily, measuring 180 \(\upmu\)m \(\times\) 180 \(\upmu\)m. Furthermore, after LIPA, some micro-cracks under the recast layer were found in the rear surface and the edge of the quartz plate [19]. Figure 1: Schematic diagram of the excimer laser processing system. Figure 2: Ultraviolet (UV) transmission spectrum of the fused quartz glass. Then, we varied the laser fluence from 0 to 4 J/cm\({}^{2}\) and performed a single-pulse ablation series with the metal target to study the dependence of depth on the laser fluence. The resulting depths measured by the surface profiler are shown in Figure 4. When the fluence was lower than 0.7 J/cm\({}^{2}\), no ablation occurred, since the laser irradiation fluence was lower than the damage threshold value. Afterward, the ablation depth increased linearly with increasing laser fluence. Next, we repeated the ablation from 1-250 laser pulses at a fixed 4 J/cm\({}^{2}\) laser irradiation energy density. Photographs of the rear surface of the glass and the top surface of the metal target are shown in Figure 5. With 10 laser pulses, the glass was modestly etched (Figure 5a); however, the ablation effect became increasingly obvious as the pulse number increased (Figure 5b). After 220 pulses, the glass broke, and edge chipping was observed (Figure 5c). On the other hand, with increasing laser pulses, the penetration depth of the stainless-steel target increased, and there was more black metal residu  
Figure 4: Profile of ablation depth after single pulse as a function of laser fluence. Figure 3: SEM photographs of the quartz samples after 50 laser pulses with the metal target: (**a**) the entire pattern; (**b**,**c**) zoomed view of the edge and the rear surface center region of the plate. The ablation depth is shown as a function of the pulse number in Figure 6. The depth value increased with the number of pulses in each position. It can be observed that, when the number of pulses was less than 70, the laser ablation effect was very modest, and the depth was less than 3 \(\upmu\)m. However, when the pulse number was greater than 70, the ablation depth significantly increased. Furthermore, when the number of pulses exceeded 130, the ablation depth increased more slowly with the number of pulses, and the ablation efficiency began to saturate. We planned to reapply the direct etching without the metal target with the etched quartz sample after LIPA processing instead of the bare one in Figure 3a, to check if the properties of the sample were changed during the etching. We firstly moved the stage to make a \(600\times 1000\)\(\upmu\)m groove; then, in each node position, 150 laser pulses of LIPA with the metal target at 4 J/cm\({}^{2}\) were performed, and the depth was measured to be around 24 \(\upmu\)m, similar to that in Figure 6. Consequently, we removed the metal target and reapplied a secondary 20-pulse direct ablation onto the grooving area at the same quartz substrate height. Figure 7 shows the morphology of the sample prior to (a) and following the secondary direct ablation (b). even without the metal target, the laser could still etch the quartz (in the red circle), which should result from an effect other than plasma etching. Figure 5: Photographs of the ablation patterns at 4 J/cm\({}^{2}\) laser fluence with different pulse number \(N\).