Process evaluation and optimization for freeform precision glass molding

Precision glass molding is a viable process for the cost-effective volume production of freeform optics. Process development is complex, requiring iterative trials of mold manufacture and metrology, molding prototyping, optic metrology, and functional testing. This paper describes usage of chalcogenide glass molding as a lower cost, faster turnaround mold prototyping process for an Alvarez lens intended for use in visible light. The target optic has a clear aperture of 42 mm, aspect ratio of 16:1, error specifications of 20 nm – 25 nm RMS across a spatial wavelength band from 1 mm to the clear aperture (e.g. form and mid-spatial frequencies) and microroughness of 2 nm Sq. The evaluation process uses diamond turning of trial molds in metal, molding of chalcogenide glass prototypes, and comparative metrology of molds and optics to close the manufacturing and metrology loops and more rapidly converge on a viable process starting point for visible glass.