Femtosecond laser welding of non-optical-contact ceramic and fused silica

Reliable bonding of non-optical-contact ceramic and glass is crucial for the fabrication of microdevices but remains challenging due to their distinct thermophysical properties and non-uniform interface. In this study, femtosecond laser welding of alumina ceramics with a surface roughness of 4.82 μm and fused silica under non-optical-contact conditions were achieved with a weld strength of 13.75 MPa. The laser parameters (200 fs, 1030 nm, 1000 kHz, 23.8 μJ, 40 mm/s scanning speed) were used for welding. Under the rapid thermal accumulation induced by the high-repetition rate femtosecond laser, the high-speed imaging system captured the coexistence of internal and interfacial plasma, occurring during the welding process. The internal plasma generated by nonlinear absorption remained localized at an almost constant height above the interface during the steady melting stage, while interfacial plasma showed continuous upward growth in sequence and finally produced a discrete modified region both within fused silica and at the interface, indicating it as a highly stable welding process. Detailed analysis revealed that the dual-plasma interaction promotes localized melting, interfacial diffusion, and mechanical interlocking between fused silica and ceramics. This work elucidates the feasibility and dynamic mechanism of femtosecond laser welding of alumina ceramics and fused silica under non-optical-contact conditions, providing experimental and theoretical guidance for precision joining of dissimilar materials.