We are studying various approaches to cleaning contaminants off of optical surfaces at cryogenic temperatures. The techniques we are reviewing must be relatively efficient, portable, and not degrade the optical quality of the surface being cleaned, i.e., they must remove only the surface contamination layer, and leave the substrate untouched. Various techniques that we have considered include removal by electromagnetic waves by discharge-produced species, and by electron or ion bombardment. We have considered electromagnetic waves, generated by devices such as lasers or heat lamps, spanning a wavelength range from microwaves to soft X-rays. Proper wavelength selection offers great opportunities for efficient removal of selected contaminants. Discharge-produced species include such things as electronically excited metastables, slow ions, atoms, and free radicals. Although production efficiencies for energetic species in discharges are not high, some species contain sufficient energy to remove many contaminant molecules in one metastable-surface collision. In addition, the technique is surface specific, and should not lead to significant heating or damage of the substrate. Electron and ion bombardment techniques are widely used in a number of surface-cleaning applications. Great care, however, must be exercised in using these techniques to avoid damaging the optical quality of the surface We will present a review of the various techniques giving the strengths, weaknesses, and efficiencies of each. In addition, we have begun some experiments using selected techniques to test their efficacy. The experiment involves cleaning a thin layer of ice off a mirror surface main-tained at liquid nitrogen temperature in a vacuum chamber. An off-axis scattering technique is used to determine the degree of contamination of the surface, and, after the cleaning procedure, how well the surface quality has been restored.

Date Published: 1 January 1987
PDF: 13 pages
Proc. SPIE 0777, Optical Systems Contamination: Effects, Measurement, Control, (1 January 1987); doi: 10.1117/12.967094

Published in SPIE Proceedings Vol. 0777:
Optical Systems Contamination: Effects, Measurement, Control
A. Peter M. Glassford, Editor(s)