Process regimes during welding of glass by femtosecond laser pulse bursts

Ultra-Short-Pulse Laser Welding of Glass to Metal with a Shear Strength Above 50 MPa

We report an ultra-short-pulse laser welding process that allows one to consistently weld Borofloat® 33 glass to aluminum with a shear strength above 50 MPa. We explored the morphology of the welding seam and quantified the quality of the bonding by statistically determining the shear strength with more than 30 samples. The results of the shear strength tests indicate that the intrinsic shear strength of the aluminum serves as the upper limit of the glass-to-metal bond.

In-Volume Glass Modification Using a Femtosecond Laser: Comparison Between Repetitive Single-Pulse, MHz Burst, and GHz Burst Regimes

In this study, we report, for the first time, to the best of our knowledge, on in-volume glass modifications produced by GHz bursts of femtosecond pulses. We compare three distinct methods of energy deposition in glass, i.e., the single-pulse, MHz burst, and GHz burst regimes, and evaluate the resulting modifications. Specifically, we investigate in-volume modifications produced by each regime under varying parameters such as the pulse/burst energy, the scanning velocity, and the number of pulses in the burst, with the aim of establishing welding process windows for both sodalime and fused silica.

Ultrafast laser bursts welding glass and metal with solder paste to create an ultra-large molten pool

A novel, to our knowledge, method is proposed for the welding of glass and metal with a large gap filled with solder paste using ultrafast laser bursts. The addition of solder paste enables a reliable glass-metal connection even at gaps of hundreds of microns, while the position of the glass can be flexibly adjusted. By ultrafast laser bursts, the volume of the molten pool increases significantly, and the height of the molten pool reaches approximately 350 µm, which is more than an order of magnitude higher than that of conventional ultrafast lasers (10-20 µm). Cross-sectional analysis of the welded region shows that extensive material mixing and element diffusion occur, and stable connections are achieved at multiple interfaces. An analysis of the interaction between the ultrafast laser bursts and the material, as well as the mixing of multiple materials during the welding process, leads to a clear welding mechanism.

Process monitoring based on plasma emission for power-modulated glass welding with bursts of subpicosecond laser pulses

Defects and process irregularities influence the bonding strength and thus the stability and lifetime of welded glass components. The present paper proposes to monitor the laser-based glass welding process by means of a single photodetector that records the radiation emitted from the laser-induced plasma. It is shown that the plasma emission provides information about irregularities of the welded seam height, gap bridging, process interruptions, and the position of the seam. The method is suitable for different welded glass types.

Reproducible process regimes during glass welding by bursts of subpicosecond laser pulses

During welding of glass with ultrafast lasers, an irregular formation of weld seams was prevented by modulation of the average laser power and spatial beam shaping. The formation of individual molten volumes in regular intervals was achieved by means of power modulation, resulting in a predictable and reproducible weld seam with a regular structure. At constant average power, a homogeneous weld seam without a periodic signature was alternatively achieved by means of a shaped beam generating an elongated interaction volume and resulting in a continuous melting of the material. The influence of the two approaches, and their combination on the process dynamics, was analyzed by means of high-speed videos of the plasma emission and of the formation of the seams.

Spatial zigzag evolution of cracks in moving sapphire initiated by bursts of picosecond laser pulses for ultrafast wafer dicing

Spatial zigzag evolution of cracks in moving sapphire wafer was observed after irradiation with sequences of picosecond laser pulses (bursts). The Gaussian beam was tightly focused inside the sapphire. The spatial position of laser initiated cracks moved in vertical and horizontal directions when a wafer was translated at a controllable speed perpendicular to the beam propagation direction. The cracking plane consisting of the periodically repeating inclined modifications and cracks was observed. The period of modifications and the inclination angle had a linear dependence on the wafer translation speed. The model of spatial zigzag crack evolution was created and the physical origin of modification growth at a measured speed of 1.3 ± 0.1 m s-1 is discussed. The zigzag cracking was applied for ultrafast stealth dicing and cleavage of the sapphire: dicing speed 300 mm s-1, wafer thickness 430 μm, laser power 5.5 W, repetition rate 100 kHz, sub-pulse duration 9 ps, the temporal distance between sub-pulses in burst 26.7 ns, and the number of sub-pulses 13.