Abstract
The next generation Extremely Large Telescopes (ELTs) are promising a profound transformation of humanity’s understanding of the universe by opening our eyes to a myriad of previously unseen astronomical objects across cosmic space time. Some of the key observational contributions to this transformation will, once again, be made through large-scale ultradeep spectroscopic surveys. Such surveys will call for a wide-field system to expand field of view and correct atmospheric dispersion beyond what an uncorrected ELT is canonically capable of. Although the traditional monolithic form of field correctors served our needs very well on 2- to 8-m class telescopes, we recognize challenges around scaling this traditional design to the ELT level, and hence, as detailed here, present a fundamentally different architecture, called the arrayed wide-field astronomical corrector system or AWACS, for the ELTs of two-mirror construction. The AWACS accomplishes field expansion via an array of small units populated over a telescope’s focal surface, compensating for field aberrations and atmospheric dispersion locally but simultaneously. The AWACS units share one common electro-opto-mechanical design, permitting cost-effective high-volume part manufacturing. We detail the architectural features and proof-of-concept on-sky demonstration of the AWACS. In addition, we highlight our recent development results of randomly nano-textured antireflective (AR) surface structures in terms of an immediately viable, super-broadband, high-performance AR solution for not only the AWACS optics, but also broader ranges of electro-optical devices, particularly those subjected to harsh environments such as high-power laser, cryogenic, and space systems. With continuous advances in other relevant fields, the AWACS is uniquely positioned to enable, either by itself or by complementing traditional correctors, wide-field multi-object spectroscopic surveys in the ELT era and beyond.
Highlights
The decade will see the arrival of three 30-m class Extremely Large Telescopes (ELTs).[1,2,3] These giants are promising a profound transformation in humanity’s understanding of the universe by opening our eyes to the unprecedented details of a myriad of astronomical objects
As we consider some of the pivotal roles played by astronomical surveys in the past,[4,5,6] it seems reasonable to expect that such a new transformation will, once again, be driven by much more detailed large-scale spectroscopic surveys of extremely faint astronomical objects at different physical scales across cosmic space time
Having said that we emphasize that our focus here is not so much about yet-to-be-substantiated pessimism toward the ELT-class field correctors in some traditional form, but rather about more fundamental questions such as, “Does the ELT wide-field system have to be in a traditional monolithic form?”; “What alternative field corrector architecture is plausible?”; “Do we have necessary technologies to turn this new architecture into a reality?” In our effort to address these questions, we explored an imaging architecture that is fundamentally orthogonal to the traditional design, called the Arrayed Wide-field Astronomical Corrector System or AWACS, mainly for the ELTs of two-mirror construction, such as the Giant Magellan telescope (GMT)[1] and the Thirty Meter telescope.[2]
Summary
The decade will see the arrival of three 30-m class Extremely Large Telescopes (ELTs).[1,2,3] These giants are promising a profound transformation in humanity’s understanding of the universe by opening our eyes to the unprecedented details of a myriad of astronomical objects. One would expect such surveys to produce scientific data products in unprecedented sensitivity across a broad wavelength range This would call for, on a single ELT, wide-field access by multiple back-end bench-mounted spectrographs, all operating simultaneously and possibly in different spectral regions, resolutions, and on different targets. We recognize that astronomical correctors traditionally consist of 3 to 8 large monolithic meniscus lenses[13,14] plus a set of ADC prisms (except the cases of the HET15 and the South African Large Telescope[16] where field correctors are comprised of mirrors), all following completely one-off construction process. The AWACS accomplishes desired field correction via an array of small costeffective electro-opto-mechanical (EOM) relay units populated over a telescope’s focal surface These units compensate for the telescope field aberrations and atmospheric dispersion locally and simultaneously. We compare different AR treatment options and pay a special attention to nano-structured optical surfaces as the viable pathway to a super broadband AR solution for the AWACS, thereby addressing the last question above
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