Far-ultraviolet alkali metal or Wood’s filters have been produced and tested supporting the production of a flight filter for the Wide Field Planetary Camera 2 on the Hubble Space Telescope. Sodium layers 0.5–1-μm thick transmit up to 40% in the ultraviolet while efficiently blocking visible wavelengths. The prevention of visible pinholes is assisted by a clean, sleek-free surface and a cooled substrate during deposition. The coatings are stabilized efficiently by a bismuth overcoating whose transmission spectrum is presented. We also report for the first time, to our knowledge, the first demonstrated long-wavelength cutoff from a lithium filter, with a shorter cutoff wavelength than sodium and potentially higher stability for astronomical imaging.
© 1999 Optical Society of America
John T. Clarke, Wilbert R. Skinner, Mark B. Vincent, Todd Irgang, Vasanth Suratkal, Heinz Grassl, and John T. Trauger, "Laboratory Studies of Alkali Metal Filter Deposition, Ultraviolet Transmission, and Visible Blocking," Appl. Opt. 38, 1803-1813 (1999)