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Innovative Strategies for NGAO: Beamsplitters and Adaptive Optics in Astronomy

The NGAO Meeting #6, led by Anna Moore on April 26, 2007, explored key drivers for utilizing light from tip-tilt (TT) stars, emphasizing the challenges and considerations of beamsplitters in adaptive optics. The discussion focused on the manageable beam size of Keck observatories compared to TMT, highlighting the need for careful management of simultaneous band coverage in science instruments. Techniques from existing instruments like AAT and VLT were examined for TT light pick-off strategies. Ideas about robotic positioners and the integration of optical switchyards to enhance performance were also presented.

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Innovative Strategies for NGAO: Beamsplitters and Adaptive Optics in Astronomy

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  1. Object selection ideas for NGAO NGAO Meeting #6 Anna Moore April 26, 2007

  2. Key drivers • Light from TT stars is close to or at same wavelength as science field • limited use of beamsplitters to pick-off light • Shame… as unlike TMT the Keck beam size is manageable wrt dichroics • (6-8” diameter ok, ~$20k)

  3. 1 of n beamsplitters Science H/K band Have to be VERY careful about max. simultaneous band coverage for science arm Plus likely larger non-common path errors than picking off TT at science focal plane? (not for super high contrast) TT sensors J Beamsplitter-fed TT mode? • IF one can do TT sensing close to but out of the science band • Have a slide with a user selectable range of beamsplitters ahead of the science instrument (aka optical switchyard of Indian Wells?) • Only feeding 3 TT sensors in any case (!), positionable over max 240” FoR (180mm)

  4. Key drivers • Keck Plate scale is 0.75mm/arcsec • TMT has larger real estate for fitting in mechanical pick-offs (2.25 mm per arcsec) • Should keep in mind AAT/VLT etc like pick-off devices and maybe get inspiration from those for 30m…

  5. Steering mirrors lines DMs Parabolas Field mirrors arrays TMT IRMOS Caltech/LAM • Richard Ellis (PI) et al • Prieto/Taylor/Moore based on KMOS2 concept

  6. TMT IRMOS Florida/HIA • Steve Eikenberry PI et al

  7. IRMOS includes TT pick-off • Both TMT IRMOS instruments had to provide means of picking off TT light at instrument focal plane. This has the benefit of sampling TT light delivered to the instrument. • NGAO could go this way however: • Requires full TT field relayed to science instrument • Possibly will have restricted access to central FoR due to vignetting of science field • Requires at least 2 TT pick-off systems, with 3 MEMS per system, one for d-IFU and one for the on-axis instruments

  8. 24 IFUs, 3 spectrographs 24 Arms field Near-future 8m d-IFU concept: KMOS VLT 2010 Durham/ATC et al Courtesy of Allington-Smith NB: KMOS is NOT combined with AO Still, quite possible to have (d-ifu) NGAO requirement of ~13 pick-offs though at what cost… should be a simpler solution To IFU and spectrograph

  9. More radical solutions? • Kickbot/Starbug concepts for focal plane pick-off (Moore/McGrath) • In principle low cross sectional area robotic positioners • Cheap, reliable at -40C (piezo driven, like Echidna) • Need vertical path length compensation Drawing by Andrew McGrath, AAO

  10. Kickbots for NGAO? From telescope • Maybe… Transparent horizontal glass window (must be clean!) To science instrument/s

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