High Contrast Spectroscopy Testbed for Segmented Telescopes

The Caltech High Contrast High-Resolution Spectroscopy for Segmented Telescopes Testbed (HCST), in the ET Lab is aimed at filling a gap in technology development for future exoplanet missions, and pro- viding the US community with an academic facility to test coronagraph, spectroscopy, and wave- front control technologies for future large ground-based and space-based telescopes (Figure 5). The goal of HCST is multi-fold and addresses high-contrast direct imaging and spectroscopy of exoplanets from space in support of LUVOIR, HabEx (and, accessorily in this context, the Thirty Meter Telescope, TMT).

HCST includes two supercontinuum white-light lasers with an NKT VARIA tunable single line filter, which allows us to precisely scan in wavelengths and define arbitrary bandwidths in the visible. Our baseline design contains the telescope simulator, a downstream wavefront corrector which includes one Boston Micromachine (BMC) kilo-DM (32 × 32 actuators), followed by a classical 3-plane single-stage coronagraph (entrance apodizer, focal-plane mask, Lyot stop), and an imaging camera (Neo sCMOS). We have a series of achromatic vector vortex focal plane masks with various topological charges from 2 to 8. Our facility is also equipped with a fiber-fed optical spectrum analyzer (OSA) which will be used to analyze the chromaticity of our wavefront control solutions and compare them to theory. The HCST is now operational. We recently achieved a single monochromatic (2% bandwidth) dark hole with raw contrast of 1E−8.

The HCST facility in the Caltech ETL is currently funded by various internal sources at Caltech and JPL and supporting exoplanet imaging technology demonstrations currently funded by the NASA ROSES APRA AND SAT programs.