Abstract
The design and features of a 2-m evaporator suitable for coating large mirrors uniformly with Al + MgF2 and Al + LiF films of high reflectance in the vacuum uv are described. The techniques used for monitoring film thicknesses during the film deposition and for producing films of uniform thicknesses over large areas are discussed. It is shown that the Al films for MgF2- and LiF-protected mirrors of highest reflectance in the vacuum uv down to 1000 Å should be 700–800 Å thick. Data on the vacuum uv reflectance of Al coated with MgF2 films of various thicknesses are presented. It was found that mirror coatings prepared in a large evaporator have a higher reflectance in the vacuum uv than those deposited under the same vacuum and deposition conditions in a small vacuum unit. At λ = 1216 Å, the reflectance of Al overcoated with 250 Å of MgF2 was measured to be about 85%.
© 1969 Optical Society of America
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