Toward laser welding of glasses without optical contacting

The welding of transparent materials with ultrashort laser pulse at high repetition rates has attracted much attention due to its potential applications in fields such as optics, microfluidics, optofluidics and precision machinery. One demanding issue is the stable and reliable welding of different materials without the utilization of an intermediate layer or an optical contact. In this work, we maximized the size of the molten volume in order to generate a large pool of molten material which is able to fill an existing gap between the samples. To this end, we used bursts of ultrashort laser pulses with an individual pulse energy of up to $$10\,\upmu \hbox {J}$$10μJ. The laser-induced welding seams exhibit a base area with a size of up to $$450\,\upmu \hbox {m}\,\times 160\,\upmu \hbox {m}$$450μm×160μm. Using these large modifications, we are able to overcome the requirement of an optical contact and weld even gaps with a height of about $$3\,\upmu \hbox {m}$$3μm. Bulging of the sample surface and ejection of molten material in the gap between the two samples allow to bridge the gap and enable successful welding. We also determined the breaking strength of laser-welded fused silica samples without an optical contact by a three-point bending test. The determined value of up to 73 MPa is equivalent to 85 % of stability of the pristine bulk material.