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We present laboratory reflectivity results of two novel optical filters designed for the Lyman ultraviolet bandpass (LUV; 90-120 nm) and the far ultraviolet bandpass (FUV; 120-150 nm). These filters were developed in coordination with the Grupo de Óptica de Láminas Delgadas (GOLD) at the Instituto de Óptica-Consejo Superior de Investigaciones Cientìficas for the Far- and Lyman-Ultraviolet Imaging Demonstrator (FLUID) sounding rocket payload. In addition to maturing high priority band-selecting UV filter technology, FLUID will measure the LUV and far ultraviolet (FUV; 120-200 nm) morphologies of nearby galaxies in four imaging bands to provide local analogs for JWST observations of high redshift galaxies. Images in the LUV will be used to make the first ever morphological classifications of local galaxies in this bandpass. FLUID comprises four f /28.7 Cassegrain telescopes with ⪅3 arcsecond angular resolution over a 20 arcminute wide field-of-view. Each telescope receives a unique band-defining filter covering the LUV through FUV (approximately 15 nm FWHM band centered on 105 nm, and 20 nm FWHM bands centered on 140 nm, 160 nm, or 180 nm). These filters are multilayer reflectance filters, and were developed by GOLD in collaboration with CU Boulder. Evaluation of the F140M filter and the Lyman alpha (Ly-α; 121.6 nm) suppressing F110M filter witness samples, as well as the secondary and primary mirrors, were completed with optical testing facilities at both GOLD and CU. We present the measured efficiencies of the F110M optics, which all demonstrate reflectivites ⪅3% at Ly-α while maintaining ⪆40% reflectivity at 105 nm, and the F140M optics, which show show peak reflectivities for 140 nm greater than 87%. These values are used to estimate the performance of the FLUID instrument in this band. Additionally we will conduct further testing of all four filters, as well as testing age and environmental stability of the filters over the course of the project.
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