Ultrafast Laser Welding of Silicon

While ultrafast laser welding is an appealing technique for bonding transparent workpieces, it is not applicable for joining silicon samples due to nonlinear propagation effects which dramatically diminish the possible energy deposition at the interface. It is demonstrated that these limitations can be circumvented by local absorption enhancement at the interface thanks to metallic nanolayer deposition. By combining the resulting exalted absorption with filament relocation during ultrafast laser irradiation, silicon samples can be efficiently joined. Shear joining strengths >4 MPa are obtained for 21 nm gold nanolayers without laser‐induced alteration of the transmittance. Such remarkable strength values hold promise for applications in microelectronics, optics, and astronomy.