As the next generation of Earth science programs demand more spectral bands, larger fields of view, faster speeds and reduced size, the optical designer will need to adapt to these new requirements. With the advent of manufacturable freeform optical surfaces, compact high-performance optical systems utilizing these surfaces are becoming practical. Freeform optics provide additional degrees of freedom for the optical designer which allow for more compact optical systems of equal performance, potentially operating at faster speeds or over wider fields of view. While numerous design studies on freeform systems have been published, little has been presented in the open literature on as built freeform systems. In this paper we describe the successful outcome of a hardware development program where we designed, built, aligned, and tested a compact WFOV three-mirror telescope with freeform surfaces. It is important that in addition to good optical performance, excellent stray light control is required in Earth remote sensing systems to minimum calibration errors across spectral bands. While compact size is often emphasized in the design of freeform systems, this needs to be balanced against the requirement for good stray light control. As such, the telescope presented in this paper balances the desire for small size with good stray light control. We present the results of the computer-aided alignment of the telescope along with measured stray light performance.
The 2020 decadal survey presents a clear message of the grand astronomy goals of the next decade and beyond, and of the urgent need for technology maturation that will enable the next flagship observatory to observe potentially habitable exoplanets. For a segmented implementation of a large ultra-stable telescope, low TRL areas such as segment sensing and control at the picometer scale have been identified as critical areas for significant technological improvements to accomplish the survey’s grand goals. We present exciting results on picometer scale sensing and actuation in certain temporal and spatial bandwidths as key advances towards addressing this technology gap. We have designed and demonstrated a capacitive testbed for informing different edge sensing architectures, and qualified our novel ultra-fine stage actuator using an optical distance measuring interferometer. We have also integrated the capacitive sensor and our ultra-fine stage actuator for an integrated demo with few picometer noise floor, sensing and actuator resolution. These key results will roll into the design of subscale demonstrations of these components in a future flight-like layout.
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