Quartz glass is widely used in the semiconductor, optics, and biomedicine fields, among others. However, because of its high hardness and brittleness, the processing accuracy and edge quality of traditional methods are limited. As an advanced processing technology, which has developed rapidly recently, femtosecond laser machining has the advantages of high precision and a small heat-affected zone, demonstrating its potential for high-end quartz glass processing. Unfortunately, currently, the removal rate of femtosecond laser ablation is low, which limits its industrial application. To achieve high-efficiency scribing on fused silica using a femtosecond laser, a composite scanning strategy that combines high-speed galvanometer scanning and slow direct writing with an X-Y translation stage is proposed in this study. We believe that this technique will significantly improve the efficiency of quartz glass laser processing and enable the flexible control of the cross-sectional geometry of laser-ablated microgrooves.

First, a quartz glass sample is placed on a 2D motorized translation stage. A circularly polarized femtosecond laser with a wavelength of 1064 nm and pulse duration of 800 fs is guided into a galvanometer scanner. After passing through the galvanometer and 4f system, the laser is focused on the quartz glass surface using an objective lens. To implement high-efficiency femtosecond laser scribing, a 2D translation stage is used to realize laser scribing along a predetermined trajectory, while the galvanometer scanning system enables dynamic oscillatory scanning of the laser focus spot around the trajectory. By maintaining the same laser irradiation fluence (laser power and irradiation time) for each oscillating scan, the effects of the oscillating scanning path, scanning amplitude, and stage translation speed on the laser-ablated microgrooves are investigated in detail. Additionally, an oscillatory scanning path is used to change the laser energy deposition distribution and thus control the cross-sectional geometry of the laser-ablated microgrooves.

Compared with its counterpart without oscillatory scanning, the depth and width of the microgrooves produced via dynamic oscillatory scanning with four different paths are substantially increased (Fig. 2). The reasons for this can be summarized as follows: 1) the dynamic oscillatory scanning increases the microgroove width and relieves the sidewall shielding effect; 2) by virtue of the high-speed scanning of the galvanometer, the laser spot dwell time is very short, which not only suppresses the plasma shielding effect but also makes the ablated debris smaller and easier to eject; 3) the optical pressure generated by the high-speed laser scanning can aid debris ejection and reduce debris buildup in the microgroove. Additionally, the surface morphologies of the microgrooves with and without oscillatory scanning are discussed (Fig. 3). It can be seen that the oscillatory scanning process has a smaller heat-affected zone and recast layer, which can be attributed to the spatial dispersion of laser pulses over a large area. As the stage translation speed increases from 0.1 mm/s to 2.0 mm/s, the microgroove depth using four different oscillatory scanning paths decreases from ~300 μm to ~100 μm, while those without oscillatory scanning remain constant at ~20 μm. The microgroove depths produced by the concentric-circle and cross oscillatory scanning have a slower decline, which can be attributed to the laser spot overlapping being more homogeneous when the scanning is implemented in both the parallel and perpendicular directions (Fig. 4). As the concentric-circular oscillatory scanning amplitude increases, both the microgroove depth and depth-to-width ratio initially increase and then decrease (Fig. 5). When the dynamic oscillatory scanning paths are modified, the cross-sectional geometries of the microgrooves change from V-shape to U-shape, which can be attributed to the change in the spatial distribution of the laser pulse (Fig. 6).

In this study, a dynamic oscillatory scanning strategy that combines high-speed scanning with a galvanometer scanner and slow direct writing using a translation stage is proposed. Compared with its counterpart without oscillatory scanning, the inscription depth is improved and the generation of recast layers is effectively suppressed with the dynamic oscillatory scanning strategy. Experimental results show that the microgroove depth decreases as the translation speed increases, while the microgroove depths by concentric-circle and cross oscillatory scanning have a slower decline. As the scanning amplitude increases, both the microgroove depth and depth-to-width ratio initially increase and then decrease. Additionally, the dynamic oscillatory scanning strategy enables the flexible control of the cross-sectional geometry of laser-ablated microstructures by changing the oscillatory scanning path. Femtosecond laser surface scribing assisted by dynamic oscillatory scanning opens up new opportunities for the high-efficiency and high-quality processing of various surface microstructures.