Effects of space exposure on optical filters

Optical transmittance characteristics of nine optical filters were remeasured after nearly 6 years in space aboard the NASA Long-Duration Exposure Facility. Three different filter types were included. In general, transmittance decreased for most filters. The center frequency and bandpass of a narrow-band filter under an aluminum cover were unchanged, while narrow-band filters exposed directly to the space environment tended to show a shift in center frequency and increased bandwidth. A pair of infraredreflecting mirrors exhibited reduced transmittance in the visible, with a mirror under an aluminum cover less degraded than a mirror exposed to space. The bandpass was unchanged for both of these mirrors. Neutral density filters showed a slight increase in transmittance for an uncovered filter; essentially no change for the filter under the aluminum cover.