Assembly Modeling and Error Analysis of Large Laser Optics

In the high power laser facility of China, 48 laser beams, passed and propagated by beampaths made up of thousands large optical units, should focus into the target centre better than 50 μm (RMS) within a few picoseconds, which poses technical challenges never seen before to technical institutions and industries. The assembly problem of large ICF optics, including to control and minimize the system's alignment error, is characterized by three crucial constraint factors, stringent positioning specifications, complex structure including thousands of components, and ambient input excitations, so, any feasible solution must be a result balancing those constraints. A significant priority in optical system assembly and mounting optimization is to develop the methodology integrated optical performance, structural response and assembly tolerances into a unified framework to find a balance among conflicting constraints. So the fundamental principles of the framework we have developed, based on a strategy of multi-loops assembly alignments and approximations to final stringent specifications, are discussed here. Error budget of large optics are allocated from the total positioning budget of beamline consisted of those large optics. And the large optics are pre-aligned and packaged very precisely into the modular opto-mechanical assemblies called line replaceable units (LRUs), with strict specifications. Once all LRUs are assembled on the support structure and formed an activated beamline, the beamline will meet its assembly performance, as the required 50 μm (RMS) positioning accuracy. The philosophy is demonstrated by an example of transport mirror LRU assembly design. A great advantage of proposed opto-mechanical modeling and analysis is to provide a promising choice for new assembly challenges in leading edge fields, some ultra-precise or fragile balance between the specifications and working conditions.