| Abstract Scope |
As in-space manufacturing capabilities progress, laser beam welding (LBW) in vacuum presents unique physical phenomena that must be understood to ensure process stability and optical system longevity. One critical issue is the generation and behavior of metal vapor during welding, which interacts with optical components used to deliver the laser beam. Metal vapor is inherently produced due to localized surface temperatures exceeding the boiling point of the material regardless of ambient pressure. However, in high vacuum (~10⁻5 torr), the absence of atmospheric gas allows vapor to expand freely and deposit on surrounding surfaces without convective cooling or dispersion. In this study, LBW experiments were conducted under vacuum using aerospace-relevant alloys in both conduction and keyhole mode. Although comparative data between modes is ongoing, vapor production was evident in both regimes. Over repeated welds, visible condensation of metallic vapor was observed on the optical window, leading to lens fogging and reduced laser transmission. This deposition occurs primarily via line-of-sight transport from the weld plume, forming a thin, reflective coating that progressively degrades beam quality. Interestingly, portions of the optical window directly in the laser beam path remained relatively clean, suggesting a thermally driven re-evaporation or “self-cleaning” effect. This points to the potential benefit of intentionally heating the lens to suppress vapor condensation. These findings emphasize the need for integrated contamination mitigation strategies such as sacrificial optics, thermal lens control, or shielding. Understanding vapor plume dynamics and condensation behavior in vacuum is essential to developing reliable, long-term LBW systems for in-space fabrication and repair. This work supports the broader effort to make welding-based in-space assembly feasible for future missions. |