An enhanced contrast evaluation testbed for next-generation microshutter arrays

Abstract

Next-Generation Microshutter Arrays (NGMSA) are customizable multi-aperture spectrograph slit masks manufactured by Goddard Spaceflight Center (GSFC) that have an advanced pure electrical actuation and latching mode, which is considerably more robust than the scanning magnetic actuation and electric latching method used by the first generation MSA devices on JWST 's NIRSpec. These first generation devices were found to have an average open-to-closed contrast ratio of ∼ 66,000 at visible and near-infrared wavelengths (Kutyrev et al. 2008). 1 NGMSA have been baselined in the multi-object UV spectroscopic designs for Habitable Worlds Observatory (HWO) and other Explorer missions. Consequently, the near-UV contrast of these devices as a function of input focal ratio is of great interest. Here we present an update to the contrast evaluation apparatus first reported in Carter et al. ( 2021), 2 but with an improved doublet projection and imaging optical train. Overall spherical aberration is considerably reduced, and the analysis of a prototype flight array yields significantly higher contrast than found in that initial work; emphasizing the need for high quality projection and imaging optics for precise contrast measurements. There is a clear monotonically increasing relationship between contrast and f/#. At ratios slower than f/15 we find single slit contrast ratios in excess of 100,000 using Hg emission line source at 1849 and 2537 Å and with a narrowband filtered continuum D 2 lamp at 3004 Å. The contrast using a 2214 Å filter with the D 2 lamp was somewhat lower (> 60,000), but may have contributions from chromatic aberration in the quartz optics and out-of-band leakage in the interference filters. Requirements for enabling the measurement of NGMSA contrast in the vacuum ultraviolet below ∼ 1800 Å are addressed.