Flexible manufacturing of large aspheres for VLT's Optical Tube Assemblies

For the ESO Very Large Telescope, TNO is making four Optical Tube Assemblies for the Four Laser Guide Star Facility. Each OTA is a large 20x Galilean beam expander, which expands a empty setO15 mm, 25W CW 589 nm input laser beam to a steerable empty set300 mm output. The L2 lens is a empty set380 conical convex lens with a radius of curvature of 637 mm and conic constant k = -0.4776. This paper describes the flexible manufacturing technique that TNO applies to make these kind of optics. With the combination of deterministic polishing and the NANOMEFOS measurement machine, these optics can be manufactured quickly and efficiently, without the need for a dedicated test setup. Final performance testing of the OTA validates all the intermediate steps in the flexible process value chain.