Glass-welding with USP-lasers and long working distances

The joining of optical glasses is a challenge even with the latest technology. Welding with ultrashort pulsed lasers is a way to join similar or dissimilar glasses without additives or macroscopic thermal tensions. The laser beam is focused through the work piece on the interface to be welded. Due to the high intensity in the laser focus, the beam is absorbed via nonlinear effects in a volume with about 20 µm in diameter. Several laser pulses heat up the material to the working point, while the thermal conductivity limits the heat affected zone well below 1 mm. This process is usually conducted with microscope objectives. Their short working distance limits the thickness of the work piece, the usable laser power and the feed rate of the process. To increase the possible dimensions of the welding partners and the process speed to industrial levels, we present USP-welding with a galvoscanner and a common F-theta-lens. Despite self-focusing effects, our experiments show that the process is stable and controllable. Furthermore, filamentation of the laser beam occurs and long cylindrical weld zones of some micrometers diameter and several hundreds of micrometers height are generated. The enormous length of this molten zone significantly lowers the demands on the work piece adjustment. Tensile tests were conducted on the welded samples. The tests show that the weld can reach a breaking strength in the order of magnitude of the base material.