Effects of Preheating on Glass Welding Strength using Ultra-fast Laser Pulses

Transmission laser glass welding involves focusing a laser beam at the interface between optically contacted transparent substrates utilizing nonlinear absorption phenomenon. The localized nonlinear absorption triggers the initiation of a plasma modified region, which grows by linear absorption leading to local glass melting and welding of the workpieces. Preheating is expected to enhance the internal modification size and weld seam width that contributes to welding strength. In the current work, a laser beam of 184 fs and 10 ps pulse duration, and 1028 nm wavelength are utilized in welding of preheated borosilicate using pulse energies of 10, 14, and 18 µJ and a repetition rate of 200 kHz. The laser beam is focused on the interface between 1 mm thick glass slides using an objective lens of NA= 0.3. Welding experiments are conducted using pre-clamped slides at room temperature and 200˚C with a scanning speed of 10 and 20 mm/s. Samples are welded using multiple scans and inspected by optical microscopy to characterize welding quality and defects. Five replicates for each process parameter combination are tested using a lap shear compression test to determine the welding strength. The optimum laser parameters and scan to scan hatching spacing are identified by investigating the welding strength.