Transmission Laser Welding of Preheated Glass Substrates Using Picosecond Pulses

Tear-drop morphology and welding quality using a picosecond laser beam focused at the interface between preheated glass substrates are investigated. Focal position inside preheated borosilicate substrates is predicted utilizing a thermo-optical model considering temperature-dependence of refractive index and thermal dilatation. The model is validated using focal position measurements of teardrops generated by a 10 ps laser beam scanned thorough-thickness of 10 mm thick borosilicate substrates at room temperature and 150 °C. The validation tear-drops are created using a pulse energy of 4.5, 6, 10, 14, and 18 μJ, and scanning speed of 5, 10, and 20 mm/s. Four focal positions are considered for each pulse energy, speed and temperature utilizing a distance between the lens and the glass surface in the range of 9.56 to 10.76 mm with a step of 0.4 mm. Thermal dilatation during experiments is simulated by finite element analyses using temperature profiles extracted from thermal camera images. The effects of temperature on the tear-drop morphology are assessed by defining a height (width) gain ratio. Welding experiments of 1 mm thick glass slides are performed at room temperature, and 150 °C using similar conditions to the tear-drop experiments. It is found that in the focal range of 1.6 to 3.2 mm and using a 14 μJ pulse energy, the width and height gain are more than 18% and 13%, respectively. At 150 °C, tear-drop’s aspect ratio is enhanced by around 25% at a focal position of 1 mm for the pulse energy of 4.5, 6, 10 μJ and speed of 5 mm/s. Higher pulse energy shows less aspect ratio enhancement due to excessive growth in tear-drops’ height in addition to width.