Laser Welding of Preheated Glass Substrates using Picosecond Pulses

Laser welding of transparent materials utilizes nonlinear absorption phenomenon taking place at the interface between closely contacted surfaces. The focused laser beam modifies the glass surfaces by plasma generation through ionization and localized melting, which bridge the gap between the glass surfaces leading to a weld seam. Despite the extensive research that has been reported so far, the effect of substrate glass temperature as a preconditioning parameter on laser welding has not been considered in the literature. In the current work, 10 ps pulse duration and 1028 nm wave length are utilized in welding of preheated borosilicate glass slides using pulse energies in the range of 6 to 30 µJ and a repetition rate of 200 kHz. The laser beam passes through the first sample and is focused at the interface using an objective lens of NA= 0.3 or 0.4. The depth of focus is determined using an analytical model that predicts the point of focus utilizing the ray tracing method. The glass samples are secured in a fixture by four bolts and heated using a heat gun, which is attached to the stage to ensure a constant temperature while laser is scanned over the interface of the samples in contact. The substrate glass temperature is monitored and measured using a thermal camera. Two temperature levels are used: room temperature and high temperature of around 150 ˚C. The assembly is attached to a stage where the welding speed is controlled in the range of 1 to 20 mm/s. The processed glass slides are inspected using optical microscopy to characterize welding quality and defects. The processing window of pulse energy, scanning speed and temperature that produce a successful welding are identified for the respective parameters.