Jt. Clarke et al., Laboratory studies of alkali metal filter deposition, ultraviolet transmission, and visible blocking, APPL OPTICS, 38(9), 1999, pp. 1803-1813
Far-ultraviolet alkali metal or Wood's filters have been produced and teste
d supporting the production of a flight filter for the Wide Field Planetary
Camera 2 on the Hubble Space Telescope. Sodium layers 0.5-1-mu m thick tra
nsmit up to 40% in the ultraviolet while efficiently blocking visible wavel
engths. The prevention of visible pinholes is assisted by a clean, sleek-fr
ee surface and a cooled substrate during deposition. The coatings are stabi
lized efficiently by a bismuth overcoating whose transmission spectrum is p
resented. We also report for the first time, to our knowledge, the first de
monstrated long-wavelength cutoff from a lithium filter, with a shorter cut
off wavelength than sodium and potentially higher stability for astronomica
l imaging. (C) 1999 Optical Society of America.