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Filters for the International Solar Terrestrial Physics Mission far-ultraviolet imager

The far-ultraviolet (FUV) imager for the International Solar Terrestrial Physics (ISTP) Mission is designed to image four features of the aurora: O I lines at 130.4 and 135.6 nm and the N2 Lyman-Birge-Hopfield (LBH) bands between 140 and 160 nm (LBH long) and 160 and 180 nm (LBH long). We report the design and fabrication of narrowband and broadband filters for the ISTP FUV imager. Narrowband filters designed and fabricated for the O I lines have a bandwidth of less than 5 nm and a peak transmittance of 23.9 and 38.3% at 130.4 and 135.6 nm, respectively. Broadband filters designed and fabricated for LBH bands have the transmittance close to 60%. Blocking of out-of-band wavelengths for all filters is better than 5 x 10-3% with the transmittance at 121.6 nm of less than 10-6%.