Surface error correction of a Keck 10-m telescope primary mirror segment by ion figuring

Lynn N. Allen; Robert E. Keim; Timothy S. Lewis; James R. Ullom

doi:10.1117/12.134862

1 January 1992 Surface error correction of a Keck 10-m telescope primary mirror segment by ion figuring

Lynn N. Allen, Robert E. Keim, Timothy S. Lewis, James R. Ullom

Proceedings Volume 1531, Advanced Optical Manufacturing and Testing II; (1992) https://doi.org/10.1117/12.134862
Event: San Diego, '91, 1991, San Diego, CA, United States

Abstract

The ion figuring process has been successfully used to correct the residual surface figure error on a 1.8 m ZerodurTM off-axis segment of the new Keck telescope primary mirror. The segment is one of 36 hexagonal mirror segments composing the full aperture of the 10 m primary mirror. Ion figuring is an optical fabrication method that provides highly deterministic error correction of previously polished optical surfaces using a directed, inert, and neutralized Argon ion beam to physically sputter material from the surface. Figure error correction is accomplished by varying the velocity of the constant-output ion source as it scans across the optic surface. The surface figure error was reduced from 0.726 micrometers rms to 0.090 micrometers rms in two test-figure iterations. The demonstration provided information and requirements for future processing of ZerodurTM and other glass-ceramic materials, and clearly showed the applicability of ion beam figuring to the final correction of large, complex optics.

Citation Download Citation

Lynn N. Allen, Robert E. Keim, Timothy S. Lewis, and James R. Ullom "Surface error correction of a Keck 10-m telescope primary mirror segment by ion figuring", Proc. SPIE 1531, Advanced Optical Manufacturing and Testing II, (1 January 1992); https://doi.org/10.1117/12.134862

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