Objective Quartz glass is a hard and brittle material with excellent physical and chemical properties; it is widely used in semiconductors, optics, aerospace, and automobiles. However, cutting quartz glass is challenging. For example, cutter wheel cutting causes edge collapse, microcracks, and residual stress, which affect the quality and strength of the glass. Picosecond lasers offer the advantages of high precision, zero contact, and high flexibility, thus rendering them suitable for cutting quartz glass. Therefore, based on the intensity- distribution characteristics of Bessel and Gaussian beams, this study uses a picosecond- pulse Bessel beam and a Gaussian beam to conduct a laser- ablation cutting experiment and a fragment cutting experiment on quartz glass, respectively, to investigate the process conditions of small edge chipping, small kerf loss width, and low surface roughness. Combining the above with the cutting speed, cross-sectional morphology, and processing cost, the applicable cutting thickness ranges of the two beams are determined to provide guidance regarding process selection in the picosecond laser cutting of quartz glass. Methods The materials used in this study are 1- and 2- mm- thick quartz glass. A Bessel beam with a non- diffraction distance of 815 mu m in air, which is obtained using an axicon, is used. First, a 1- mm- thick quartz glass is cut using a picosecond Bessel laser- ablation material. The effects of the defocusing distance and hole spacing on the cross-sectional morphology are investigated using an optical microscope, and the edge- chipping sizes under different defocusing distances are measured to obtain the optimal hole spacing and defocusing distance. Second, internal modification and surface ablation are performed on the glass via picosecond Gaussian laser multiple scanning, and the 2 mm- thick quartz glass is cut into fragments. The effects of the single- pulse energy and overlap rate on the width of the kerf loss and the effect of the pulse width on the width of the phase- transition region are investigated. Finally, the cross- sectional quality of the quartz glass is investigated and analyzed, and an appropriate cutting process for glass with different thicknesses is determined based on the surface roughness, cutting speed, and cross-sectional morphology. Results and Discussions When cutting quartz glass using Bessel laser ablation, full ablation cutting can be achieved when the defocusing distance is-400 mu m to-600 mu m (Fig. 6). Therefore, the Bessel beam with a maximum non- diffracting distance of 815 mu m in air can achieve the full ablation cutting of a 1.2- mm- thick quartz glass, and the full ablation cutting results in a better cross- section morphology and smaller edge chipping. The optimal defocusing distance is-500 mu m (Fig. 7). When the hole spacing is 20 mu m, the kerf edge is smooth, the cross-section morphology is favorable, the maximum cutting speed is 500 mm/s, and the surface roughness is 1.435 mu m (Fig. 8). Linear cutting and curve cutting of 2 mm quartz glass are realized by performing Gaussian laser multiple scanning (Fig. 9). The surface roughness is 7.483 mu m and the cutting speed is 30 mm/s. The kerf loss width increases with the single- pulse energy and overlap rate (Figs. 10 and 11). The width of the phase- transition region decreases with increasing pulse width (Fig. 12). The internal modification of the Gaussian laser removes more material than surface ablation (Fig. 13). As the focal depth increases, the average roughness of the three local modification regions from top to bottom decreases gradually from 8 mu m to 4 mu m (Fig. 14). From top to bottom, the cross-section of the quartz glass cut via Bessel laser ablation remains the same, the surface roughness decreases, and the cutting speed increases. To cut quartz glass, whose thickness is less than the non- diffraction distance of the beam, the Bessel beam should be the preferred light source. For quartz glass with a large thickness, the Gaussian laser multiple- scanning cutting process is superior to the high- cost Bessel laser- cutting process. Conclusions In this study, Bessel and Gaussian beam- cutting experiments of picosecond pulses are performed for quartz glass measuring 1 mm and 2 mm thick. The main conclusions are as follows: 1) Full ablation processing can yield better cross-sectional quality. For quartz glass with a thickness less than the maximum non- diffracting distance, a Bessel laser can achieve high- quality and high- efficiency ablation cutting of the material. When a Bessel beam with a non- diffraction distance of 815 mu m in air is used to cut quartz glass with a thickness of 1 mm, the edge chipping size can be controlled within 20 mu m, and the cutting speed is 500 mm/s. 2) Based on multiple scans, the thickness of the quartz glass cut by the Gaussian laser is significantly larger than the Rayleigh length of the beam. When a Gaussian beam cuts a 2- mm- thick quartz glass, the kerf loss width is within 10 mu m; however, it changes significantly depending on the single pulse energy and overlap rate. The cutting speed is set to 30 mm/s. 3) In the cross-section of quartz glass cut using a Gaussian laser, defects emerge and the surface roughness is high. Therefore, a Bessel laser should be the preferred processing light source when the glass thickness is within the non- diffraction distance of the beam. For quartz glass with a large thickness, the axicon typically used in industrial processing cannot generate a Bessel beam with a sufficiently long non- diffracting distance; in this case, a Gaussian laser can be a good alternative.
