Laser soldering of large lenses for applications in high-power laser systems

Within an European Space Agency (ESA) Basic Technology Research Programme (TRP) funded project a laser-based soldering technology was evaluated for a low-stress bonding of large (>100 mm diameter) lenses within mounts. Objective of the activity was to overcome limitations of traditional clamping and adhesive bonding technologies with respect to stress and long-term stability in harsh and high power environments, by applying a anorganic-metallic bonding agent, and a localized, minimal impact laser-based soldering technology, the so-called Solderjet Bumping (SJB). Fused Silica, N-LAK9 and CaF2 lens dummies were processed, respective mounts in CTE-matching materials incorporated flexures to minimize operational and non-operation environmental conditions thermo-mechanical stress. Throughout the whole process chain of assembly and testing surface P-V deviations <100 nm, birefringence changes <10 nm, and position changes <1 micron where measured. The results enable applications of the technology for high power systems e.g. in laser material processing and fusion energy creation.