Mechanism and optimization of femtosecond laser welding fused silica and aluminum

The ability to weld metals and insulators is widely required in aerospace, sensors and Micro-electro-mechanical systems (MEMS). Femtosecond laser welding is a precise and clean technique for bonding materials with benefits including high location accuracy, low heat-affected zone and little waste generation. However, the connection process is still unclear so that pump-probe microscopy and plasma image were used to reveal the welding mechanism at the contact interface. Under the irradiation of a femtosecond laser pulse, the aluminum melted after a few picoseconds, then re-solidified and connected two different materials. Additionally, plasma was limited in the interaction zone after laser irradiation for optical contact (OC), so the smaller affected region with the most absorbed energy was jointed easily with higher shear strength. Self-focusing and non-linear absorption in fused silica are key factors affecting the shear strength, since the energy absorption and modification in fused silica would induce internal stress and decrease the energy deposition at the contact interface. Our findings not only reduce the fracture of fused silica and increase shear strength up to 25.75 MPa by means of focal point pre-compensation, but also demonstrate the extraordinary potential of ultrashort laser welding in the field of precise connection of heterogenous materials.