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Vacuum deposition of iridium on large astronomical mirrors for use in the far UVAn iridium coating has been deposited by electron-beam evaporation on a 0.91-m mirror which serves as the telescope primary of a sounding rocket instrument for far-UV spectrometry. The evaporation was carried out by applying 8 kV at 400 mA to the electron gun. Zone refined Ir of 99.99% purity was used, and the electron beam was electromagnetically swept over the surface of the evaporant. Under these conditions, deposition rates of 0.55 A/sec were achieved. The reflectance distribution achieved at a wavelength of 584 A was extremely uniform; the mean reflectance was 21.2% with a standard deviation of only 0.3%. This represents a substantial improvement over Al + MgF2 and Al + LiF coatings for applications involving multiple reflections and weak signals, as might be expected in a high-resolution spectrograph studying distant celestial objects.
Document ID
19820035252
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Herzig, H.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Spencer, R. S.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 10, 2013
Publication Date
January 1, 1982
Publication Information
Publication: Applied Optics
Volume: 21
Subject Category
Astronomy
Accession Number
82A18787
Distribution Limits
Public
Copyright
Other

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