Laser soldering of large lenses for applications in space-born lidars and imaging systems

Within an European Space Agency (ESA) Basic Technology Research Programme (TRP) funded project the laser-based soldering technology of Solderjet Bumping (SJB) was evaluated for a low-stress bonding of large (>100mm diameter) lenses, e.g. made of N-LAK9, 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 space environments, by applying an anorganic-metallic bonding agent, and a localized, minimal impact laser-based soldering technology. Fused Silica and N-LAK9 lens dummies were processed, respective mounts in CTE-matching materials incorporated flexures to minimize operational and non-operation environmental conditions thermo-mechanical stress. Throughout a whole process chain of assembly and testing a surface P-V deviation <100nm, birefringence changes <10nm, and position changes <1 micron where measured. The results enable applications of the technology for space-born lidar and imaging applications, in particular also for high powers and non-conventional wavelengths.