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1. Flare Sentinel - a compact integral field spectrograph for observations of solar flares from space

   https://doi.org/10.1117/12.2691024  

   Lin, Haosheng; Sukegawa, Takeshi; Bonnet, Morgan (July 2023, SPIE Proceedings International Conference on Space Optics)

   Minoglou, Kyriaki; Karafolas, Nikos; Cugny, Bruno (Ed.)

   This paper describes Flare Sentinel, a compact integral field spectrograph (IFS) for the study of the hydrogen Balmer series spectrum from 350 to 450 nm of solar flare from space. Flare Sentinel IFS is based on a new Machined Image Slicer Compact Spectrograph Array (MICS) design. MICS consists of an image slicer that divides a continuous 2D spatial field formed by an imaging system into multiple narrow slices, and an array of miniature spectrographs, each forming the spectra of one of the slices of the 2D field. The spectra formed by all the miniature spectrographs can be projected on a common 2D focal plane to be recorded by an image sensors. The spectra can also be distributed to multiple focal planes and recorded simultaneously by multiple sensors to increase the instantaneous hyperspectral field of view of the instrument. New image slicers with slit width of 36 um and 20 um have been successfully fabricated using Canon Inc.’s ultra-precision diamond-cutting CNC mill. This capability is enabling design and fabrication of IFSs with imaging format of 102 × 102 , and spectral resolution between 100 < R < 10, 000 in a very compact package. We will present the optical design and the optical hardware of a prototype IFS that has been fabricated. 

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2. Mirror-induced reflection in the frequency domain

   https://doi.org/10.1038/s41467-022-33529-w  

   Hu, Yaowen; Yu, Mengjie; Sinclair, Neil; Zhu, Di; Cheng, Rebecca; Wang, Cheng; Lončar, Marko (October 2022, Nature Communications)

   Abstract Mirrors are ubiquitous in optics and are used to control the propagation of optical signals in space. Here we propose and demonstrate frequency domain mirrors that provide reflections of the optical energy in a frequency synthetic dimension, using electro-optic modulation. First, we theoretically explore the concept of frequency mirrors with the investigation of propagation loss, and reflectivity in the frequency domain. Next, we explore the mirror formed through polarization mode-splitting in a thin-film lithium niobate micro-resonator. By exciting the Bloch waves of the synthetic frequency crystal with different wave vectors, we show various states formed by the interference between forward propagating and reflected waves. Finally, we expand on this idea, and generate tunable frequency mirrors as well as demonstrate trapped states formed by these mirrors using coupled lithium niobate micro-resonators. The ability to control the flow of light in the frequency domain could enable a wide range of applications, including the study of random walks, boson sampling, frequency comb sources, optical computation, and topological photonics. Furthermore, demonstration of optical elements such as cavities, lasers, and photonic crystals in the frequency domain, may be possible. 

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3. KOLA: a concept for an optical multi-conjugate adaptive optics system for the W.M. Keck Observatory

   https://doi.org/10.1117/12.3020725  

   Lu, Jessica R; Dekany, Rich; Peck, Brianna; Bouchez, Antonin; Millar-Blanchaer, Max; Hinz, Philip M; Rider, Kodi; Chun, Mark; Wizinowich, Peter L; Wang, Lianqi; et al (August 2024, SPIE)

   Schmidt, Dirk; Vernet, Elise; Jackson, Kathryn J (Ed.)

   We present progress on a conceptual design for a new Keck multi-conjugate adaptive optics system capable of visible light correction with a near-diffraction-limited spatial resolution. The KOLA (Keck Optical LGS AO) system will utilize a planned adaptive secondary mirror (ASM), 2 additional high-altitude deformable mirrors (DMs), and ≳ 8 laser guide stars (LGS) to sense and correct atmospheric turbulence. The field of regard for selecting guide stars will be 2’ and the corrected science field of view will be 60”. We describe science cases, system requirements, and performance simulations for the system performed with error budget spreadsheet tools and MAOS physical optics simulations. We will also present results from trade studies for the actuator count on the ASM. KOLA will feed a new optical imager and IFU spectrograph in addition to the planned Liger optical + infrared (λ > 850 nm) imager and IFU spectrograph. Performance simulations show KOLA will deliver a Strehl of 12% at g’, 21% at r’, 53% at Y, and 87% at K bands on axis with nearly uniform image quality over a 40”×40” field of view in the optical and over 60”×60” beyond 1 μm. Ultimately, the system will deliver spatial resolutions superior to HST and JWST (∼17 mas at r’-band) and comparable to the planned first-generation infrared AO systems for the ELTs. 

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4. Alignment of the optical system of the 9.7-m prototype Schwarzchild-Coulder Telescope

   https://doi.org/10.1117/12.2564653  

   Adams, C.~B.~; Alfaro, R.~; G.~Ambrosi, Ambrosi; Ambrosio, M.~; Aramo, C.~; Benbow, W.~; Bertucci, B.~; Bissaldi, E.~; Bitossi, M.~; Boiano, A.~; et al (December 2020, Proceedings Volume 11445, Ground-based and Airborne Telescopes VIII;)

   Marshall, Heather K.; Spyromilio, Jason; Usuda, Tomonori (Ed.)

   The novel 9.7m Schwarzschild-Couder Telescope (SCT), utilizing aspheric dual-mirror optical system, has been constructed as a prototype medium size x-ray telescope for the Cherenkov Telescope Array (CTA) observatory. The prototype SCT (pSCT) is designed to achieve simultaneously the wide (≥ 8°) field of view and the superior imaging resolution (0.067 per pixel) to significantly improve scientific capabilities of the observatory in conducting the sky surveys, the follow-up observations of multi-messenger transients with poorly known initial localization and the morphology studies of x-ray sources with angular extent. In this submission, we describe the hardware and software implementations of the telescope optical system as well as the methods specifically developed to align its complex optical system, in which both primary and secondary mirrors are segmented. The pSCT has detected Crab Nebula in June 2020 during ongoing commissioning, which was delayed due to worldwide pandemic and is not yet completed. Verification of pSCT performance is continuing and further improvement of optical alignment is anticipated. 

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5. CubeSat Format 3-Mirror Spectrometer Designed with Freeform Surfaces

   Lui, Y; Bauer, A; Rolland, J (May 2019, Optical Design and Fabrication 2019 (Freeform, OFT))

   CubeSats are a type of miniaturized satellites that consist of 10×10×10 cm cubic units (1U), which is established as a standard by Jordi Puig-Suari and Robert Twiggs in 1999 to push low-cost educational and industrial space experimentation [1]. In recent years the CubeSat format has gained popularity for research and industrial purposes including Earth imaging, communication and technology demonstration. High performing optical systems such as spectrometers and imagers that can be contained in CubeSat format are also desired in many space missions. In this paper, a design study is conducted for a 3-mirror spectrometer based on the reflective triplet design form that is fully contained in 1U space. As shown in Fig. 1, the spectrometer consists of three mirrors and a plane grating serving as the aperture stop. Light from a slit enters the system and travels through the three mirrors to the grating where it is dispersed and reflected. The light then travels back through the system in reverse to the detector near the slit which results in a 2D image (or spectrum). To show the freeform advantage, we compared two designs of this spectrometer - one designed with freeform surfaces and the other with off-axis aspheres. 

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