Aspheric lens processing of chalcogenide glass via combined PGM-SPDT process

Chalcogenide glass (ChG) is widely studied due to its wide infrared transmission window, low refractive index temperature coefficient, and low dispersion coefficient. Precision glass molding (PGM) and single-point diamond turning (SPDT) are representative high-efficiency and high-precision methods for ChG processing. However, the high softening degree of ChG under high-temperature conditions leads to abnormal gas release and severe mold adhesion which deteriorate surface quality. Although SPDT typically facilitates high-precision machining, it has limited efficacy in long-term, large-area, large-depth processing; this limitation causes severe tool wear due to the high hardness and brittleness of ChG material. A new process combining the advantages of PGM and SPDT technology is proposed to fabricate aspheric lenses on ChG (IRG202) by ultra-precision and high-efficiency machining. The pre-molding of ChG by PGM reduces cutting loss during aspheric lens machining by SPDT. The machined aspheric lenses have the high quality with a form error of PV 103.5 nm and surface roughness Ra of 8.3 nm. The processing efficiency of each single lens is increased by almost 8 times over the traditional method. The proposed ChG aspheric lens fabrication process maintains high precision even under mass production conditions.