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Advanced Design for High-Resolution Imaging and Spectroscopy in Astronomical Observations

This document outlines the intricate specifications and components of a cutting-edge astronomical instrument designed for high-resolution imaging and spectroscopy. Featuring a 2k detector array with 18µm pixels, 0.9mm slice sampling, and a multi-slit spectrograph, the instrument aims for an impressive field of view (FoV) of around 1.52 arcseconds. The setup includes innovative optical components, such as adaptive mirrors for direct imaging and IFU spectroscopy, addressing challenges in field size and resolution requirements. Additionally, considerations for optical performance within an effective cryogenic system are discussed.

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Advanced Design for High-Resolution Imaging and Spectroscopy in Astronomical Observations

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  1. DL – IFU(Prieto/Taylor) • Slicer: • 25mas sampling … 0.9mm slices • ~f/250 (assuming no anamorphism) • Detector = 2k array of 18um pixels • Slit subtends 1-pixel (spectral dithering as for TiPi) • Camera f-ratio = f/5 (double TMA a la JWST system) • Full window requires ~800 pixels • 4 slits per spectrograph/detector • Slit height = ~1000 pixels or 30-by-30 slicer with FoV ~0.752 arcsec. • 4 slits gives FoV ~1.52 arcsec. • Is this a sufficient field ? Or do we need 2 or 4 units ? • NB: SRD asks for ~42 arcsec • If only we could use a 42k, 9m pixel, array at f/2.5 ! • Assume fore-optics can switch in factor of 5 magnification to give: • 25mas ; 20mas; 15mas; 10mas; 5mas • 5mas option would feed spectrograph at f/12.5 • What beam-size would be required ? 50mm OK ?

  2. Optical Components • Cool box: • 45 deg. fold to vertical • Pupil imager onto ~25mm DM • Field lens or Field mirror ? (not exactly at focus) • DM as steering mirror • feeding mirror at field stop (as in TiPi) • but also an imaging system (as in TiPi) to give ~10 arcsec D-L field • DM can switch from IFU to direct imaging field by small tip/tilt • Object can be viewed directly and then selected into IFU field • Surrounding objects can be imaged directly while doing IFU spectroscopy

  3. Optical Components • Cryo box: • Magnification optics and scale changer optics • Non-anamorphic (25mas ; 12.5mas ; 5mas) • Cold stop (rotating ?) • 2 contiguous 60-slice slicer units • square FoV • 2 slits into 1 spectrograph • Double TMA spectrograph (a la JWST/NIRSPEC) • Collimator somewhere between f/10 and f/20 (tbd) • Camera f/5 • Beam size ~50mm (plus pupil diffraction)

  4. Scope of Work • Optical concept at same level as TiPi • Field lens/mirror • DM – steering & image/IFU selector • Imaging system (FoV ~10” D-L) • Fore-optics / scale changer • Slicer unit • Spectrograph • Approx. wave-front error budget ? • Challenges: • Larger FoV ~3 arcsec2 ? • Faster cameras ~f/2.5 ?

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