Femtosecond Laser Transmission Joining of Fused Silica and Polymethyl Methacrylate

In this study, polymethyl methacrylate (PMMA) is joined with fused silica using pulsed femtosecond laser transmission micro-welding. This technique enables the welding of transparent materials to each other without the need for intermediate opaque layers, through localized energy deposition. The laser parameters - peak fluence, scanning speed, and hatch distance - are systematically optimized to maximize joint shear strength. The ATR-FTIR spectroscopic analysis has proven that mechanical interlocking is the primary mechanism of joint formation between the two materials. An analytical model based on heat accumulation is developed to describe the joining process, with a good predictive quality confirmed by comparison with the experimental results. This joining approach is applied to seal a hybrid PMMA-fused silica microfluidic chip. The device has successfully passed a static leakage test by withstanding pressures up to the full-scale value of the employed microfluidic pump at 2 bar, demonstrating the effectiveness of femtosecond laser transmission welding for fabricating robust and reliable joints in hybrid microfluidic devices.