Laser welding of highly reflective metal with absorbance-enhanced surface structure fabricated using picosecond laser.

We present a method to stably weld a copper at lower laser power by blackening the surface. Since the reflectivity of copper is approximately 97% in the infrared range, a precise and stable processing of copper is difficult even at high power using infrared laser. To decrease the reflectivity, we fabricated light-absorbing nano-structure on copper surface using picosecond laser pulses. The structure consists of aggregations of nano-particles, and is capable of absorbing as much as 80% of incident light. We demonstrated that a copper with this structure can be welded using 70% lower irradiation power than a copper without it. Additionally, we theoretically investigated the light-absorbing nano-structure using 3D finite-difference time-domain (FDTD) method. [ABSTRACT FROM AUTHOR]