In recent years, the high-precision sealing welding of glass materials has attracted wide attention because of its potential applications in high-end optoelectronic devices and microfluidic chips. Traditional glass-joining methods typically utilize adhesives, which lead to limitations in high-temperature resistance, bonding strength, and durability. When nonlinear absorption at the interface is used between two materials, ultrafast laser welding offers several advantages, including high accuracy, high strength, and good thermal stability. However, achieving high strength and good sealing with high throughput remains challenging. In this study, we propose a picosecond laser sealing welding method based on two-step galvanometer scanning.

Fused silica glass pieces with a thickness of 1 mm were used as welding materials. An infrared picosecond laser emitting a laser beam with a wavelength of 1064 nm was guided into a galvanometer scanner and focused using an F-theta lens with a focal distance of 100 mm. The welding process included the following four steps: 1) a small amount of ethanol or ethanol dispersion containing SiO₂ microspheres with different diameters was added into the glass gap to change the gap between the two glass pieces; 2) the laser pulses were set at a high pulse energy and a repetition rate of 100?300 kHz, and the laser beam focused at the joining interface was used to scan the glass pieces at a high speed of 200?500 mm/s; 3) the laser pulses were set at a low pulse energy and a repetition rate of 1000?1500 kHz, and multiple repeated scans were performed along the original path at a low speed of 20?50 mm/s; 4) the effects of various processing parameters on the two-step scanning welding, such as picosecond laser parameters, weld spacing, scanning speed, and scanning times, were investigated.

For picosecond laser glass welding with a long focal length scan lens, one challenge is to reduce the thermal cracks caused by laser irradiation. However, the laser pulse energy must be sufficiently high to induce multiphoton absorption at the glass interface. To address this issue, fast scans relative to glass pieces with a high pulse energy were first performed to produce the initial welding microstructures at the joining interface, and then slow scans with a low pulse energy were conducted to enlarge the weld pool. To demonstrate the advantages of two-step scanning welding, several comparative experiments were performed between single-step scanning welding with a fixed pulse energy and two-step scanning welding with different pulse energies. Measurement results with optical microscopy show that the average weld joint widths by single- and two-step scanning are approximately 39 μm and 56 μm, respectively, revealing that two-step scanning welding can effectively enlarge the weld pool (Fig.3). However, the average shear strength of two-step scanning welding reaches 45 MPa, which is significantly higher than that of single-step scanning welding under a high pulse energy. The higher shear strength of two-step scanning welding could be attributed not only to the enlargement of the weld pool by secondary welding but also to the reduction or fusion of thermal cracking by lower pulse energy scanning (Fig.4). To explore the effects of the gap width between the two glass pieces on the welding strength, a small amount of ethanol dispersion containing SiO₂ microspheres of different diameters was added to the glass gap. The results show that the glass pieces with a gap of 27 μm can be joined with a shear strength of ~2.4 MPa using two-step scanning welding, and the welding strength decreases with an increase in the gap width (Fig.5). To check the sealing performance, the welded samples were immersed in water for one week. For the sample obtained by single-step scanning welding, the original interference fringes inside the ring-shaped weld joint disappear, indicating that water penetrates the middle region through the weld joint. However, for the sample prepared by two-step scanning welding, no significant change was observed in the middle region of the ring-shaped weld joint after immersion. It can be deduced that two-step scanning welding not only achieves uniform and continuous welding but also has good sealing stability (Fig.6). To demonstrate the potential application of two-step scanning welding in microchannel packaging, an open microgroove fabricated by picosecond laser ablation in a single glass piece was sealed with another glass piece through fast scanning welding. It can be clearly seen that the dye solution is confined within the weld joint (Figs.7 and 8).

To achieve rapid glass seal welding, a two-step picosecond laser scanning strategy was proposed by combining fast and slow scanning approaches with high and low pulse energies, respectively. For two naturally stacked fused silica pieces, the welding strength and sealing performance of the sample prepared by the two-step scanning strategy with two different pulse energies were demonstrated to be better than those of the sample prepared by the conventional single-step scanning process with a fixed pulse energy. Based on this technique, rapid preparation of a packaged microchannel was successfully realized using picosecond laser scanning. This technique combines nonlinear multiphoton absorption induced by high-energy laser pulses and molten pool enlargement derived from low-energy and high-repetition-rate laser pulses. The technique can effectively alleviate the generation of thermal cracks in the glass welding process and has broad applications in the connection and packaging fields of optoelectronic devices, optical components, and microfluidic chips.