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The PIAACMC architecture can be designed for segmented and obscured apertures, so it is particularly well suited for ground-based observing with the next generation of large telescopes. There will be unique scientific opportunities for directly observing Earth-like planets around nearby low-mass stars. We will discuss design strategies for adapting PIAACMC for the next generation of large ground-based telescopes, and present progress on the development of the focal plane mask technology. We also present simulations of wave-front control with PIAACMC, and suggest directions to apply the coronagraph architecture to future telescopes.
Previously, we have reported experimental results on the first milestone, the demonstration of EXCEDE contrast in monochromatic light in air and more recently in vacuum. In this paper, we report on the procedure and the experimental results obtained for our second milestone demonstration of the EXCEDE starlight suppression system carried in a vacuum chamber at the Lockheed Martin Advanced Technology Center. This includes high contrast performance demonstrations at 1.2 λD, which includes a lab demonstration of 1x10-5 median contrast between 1.2 and 2.0 λD simultaneously with 3x10-7 median contrast between 2 and 11 λD in 10% bandwidth polychromatic light centered at 650 nm for a single-sided dark zone. The results are stable and repeatable as demonstrated by three measurement runs with DM settings set from scratch and maintained on the best 90% out of the 1000 collected frames per run. We compare reduced experimental data with simulation results from modeling experimental limits.
Recent advances in coronagraph technologies for exoplanet imaging have achieved contrasts close to 1e-10 at 4 λ/D and 1e-9 at 2 λ/D in monochromatic light. A remaining technological challenge is to achieve high contrast in broadband light; a challenge that is largely limited by chromaticity of the focal plane mask. The size of a star image scales linearly with wavelength. Focal plane masks are typically the same size at all wavelengths, and must be sized for the longest wavelength in the observational band to avoid starlight leakage. However, this oversized mask blocks useful discovery space from the shorter wavelengths.
We present here the design, development, and testing of an achromatic focal plane mask based on the concept of optical filtering by a diffractive optical element (DOE). The mask consists of an array of DOE cells, the combination of which functions as a wavelength filter with any desired amplitude and phase transmission. The effective size of the mask scales nearly linearly with wavelength, and allows significant improvement in the inner working angle of the coronagraph at shorter wavelengths. The design is applicable to almost any coronagraph configuration, and enables operation in a wider band of wavelengths than would otherwise be possible. We include initial results from a laboratory demonstration of the mask with the Phase Induced Amplitude Apodization (PIAA) coronagraph.
A 4-meter wide field coronagraph space telescope for general astrophysics and exoplanet observations
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