Ultrastable bonding of glass with femtosecond laser bursts

We report on the welding of fused silica with bursts of ultrashort laser pulses. By optimizing the burst frequency and repetition rate, we were able to achieve a breaking resistance of up to 96% of the bulk material, which is significantly higher than conventional high repetition rate laser bonding. The main reason for this stability increase is the reduced stress in the surroundings of the laser induced weld seams, which is proven by measurements of the stress-induced birefringence. A detailed analysis of the shape of the molten structures shows elongated structures in the burst regime. This can be attributed to stronger heating, which is supported by our thermodynamic simulations of the laser melting and bonding process.