Plasma Treatment To Remove Carbon From Indium UV Filters

The sounding rocket experiment FIRE (Far-ultraviolet Imaging Rocket Experi ment) will improve the science community’s ability to image a spectral region hitherto unexplored astronomically. The imaging band of FIRE (≈900 to 1,100 Å) will help fill the current wavelength imaging observation hole existing from ≈620 Å to the GALEX band near 1,350 Å. FIRE is a single-optic prime focus telescope with a 1.75-m focal length. The bandpass of 900 to 1100 Å is set by a combination of the mirror coating, the indium filter in front of the detector, and the salt coating on the front of the detector’s microchannel plates. Critical to this is the indium filter that must reduce the flux from Lyman-alpha at 1,216 Å by a minimum factor of 10–4. The cost of this Lyman-alpha removal is that the filter is not fully transparent at the desired wavelengths of 900 to 1,100 Å.