Absorptance characteristics of silver and silver-on-copper mirrors.
Glancing incidence absorptance measurements are performed on bare silver and bare silver with a copper underlayer mirrors. Measurements are at a laser wavelength of 0.5145 microm, angles of incidence from 0 to 89 degrees , at both s and p polarizations. The increase in absorptance as a result of the mirrors tarnishing naturally in room air is measured over a period of 60 days. New and untarnished, the silver/copper mirror tends to have a higher absorptance at all angles of incidence compared with the silver mirror. Once exposed to room air the silver/copper mirror absorptance at normal incidence does not increase as rapidly over time as the silver mirror, which seems to indicate a greater resistance to tarnishing. However, at glancing incidence both mirrors appear to have similar tarnishing rates. After 60 days the absorptance of the silver/copper mirror has a lower absorptance at normal incidence than the silver mirror, but at glancing angles of incidence both tarnished mirrors have comparable absorptance values.
Kimura
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