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VLBI Visible Light Broadband Imager Concept Design Summary

Design presentation for VLBI instrument concept with spatial resolution of 0.03” at 330 nm, temporal resolution of 5-10 seconds, and field-of-view of 3’x3’ to 5’x5’. Utilizes thin film interference filters with large format CCD or CMOS detectors. Modular construction for easy assembly and scalability.

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VLBI Visible Light Broadband Imager Concept Design Summary

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  1. VLBI: Visible Light Broadband Imager Instrument Conceptual Design Presentation Tom Berger Lockheed Martin Solar and Astrophysics Lab

  2. VLBI Science Requirements • WBFI Mission statement: record the highest spatial and temporal resolution movies from the ATST across the visible spectrum from 330 nm to 1.1 m. • Spatial resolution: 0.03” at 330 nm • Temporal resolution: 5 – 10 seconds • Field-of-view: 3’ x 3’ minimum, 5’ x 5’ goal • Spectral resolution: 1 – 10 Å • Polarimetric requirements: none

  3. VLBI Basic Concept • Simple transfer/beam conditioning optics • Thin film interference filters • 2 or 3 cavity glass subtrate • > 60% transmission • 1 – 10 Å bandpasses • Large format, fast readout CCD or CMOS detectors • Dedicated multi-TByte storage array

  4. VLBI Preliminary Wavelengths

  5. VLBI Instrument Requirements • Spatial resolution • Plate scale: 2 pixels per Airy disk at a given  • Optical quality: < /4 per 2 cm on all elements incl. filters • Phase diversity: wavefront measurement and image restoration capability • Temporal resolution • Filter change and settle: 2 seconds • Camera readout: 3 seconds • Filter Characteristics • TFI filter diameter: 10 cm (3’ x 3’ F/20 telescope beam) • Optical • Flat focal plane over full 3’ x 3’ FOV • Telecentric beam: probably not required

  6. VLBI Plate Scales & F/#s Requirement: 2 pixels per central Airy disk of a 4-m aperture at each  Hypothetical detector: 9 m pixels, 4096 x 4096 format

  7. VLBI Design Limitations • Detector technology • 0.015” pixels: 6K x 6K format to cover 1.5’ x 1.5’ • QE > 90% • Exposure ~10 msec, Readout < 3 seconds • Such cameras do not exist • Unknown pixel size means plate scale cannot be specified • Utility and science must be balanced • Must be first-light instrument - cannot be delivered late • Must have immediate science potential - publicity quality images must be produced • Cost

  8. VLBI Design Philosophy • Modular construction • Provide subsystems that can be used individually, in sets, or in a turn-key “black box” • Major subsystems • Filterwheels • Detectors • Feed optics/focal plane conditioners • Mountable at Gregorian or Coudé focal planes • Conform to ATST controls interface • Easily accommodate detector upgrades • Room temperature operation

  9. C1: Camera 1 XYZ Stage 1 SH1: Shutter 1 C2: Camera 2 XYZ Stage 2 SH2: Shutter 2 VLBI Modular Subsystems • Detector subsystem • Two detectors mounted on x-y-z translation stages • Cube beamsplitter feeds cameras simultaneously. CBS is easily removable. • Allows small format detectors to “roam” over the ATST focal plane • Allows dual-camera phase diversity at any wavelength via adjustable defocus of one camera DCS:Detector Control System

  10. VLBI Modular Subsystems • Filterwheel subsystem • Four aperture wheel - three 10 cm filters, one blank • Brushless DC motor drive - TRACE/EPIC heritage • Optical encoder positional readout • Edge gear/worm drive mechanism • 3 wheels in series for up to 9 wavelengths • Beam height above table ~15 cm for wheel clearance

  11. VLBI Design Concepts • VLBI Level 1 • Dual detector package • Integrated single filter holder • No transfer/conditioning optics Single Filter Beam directly from ATST Detector subsystem

  12. VLBI Design Concepts • VLBI Level 2 • Dual detector subsystem • Filterwheel subsystem • Fixed focal ratio optics. L1 removable/replaceable for F/# change.

  13. VLBI Design Concepts • VLBI Level 3, Option A • Dual detector subsystem • Multiple filterwheel subsystem • Two channel (Red/Blue) transfer/conditioning optics: F/25 & F/45 ATST Focal Plane

  14. VLBI Design Concepts • VLBI Level 3, Option B • Detector subsystem • Multiple filterwheel subsystem • Varifocal zoom lens transfer/conditioning optics: F/20  F/60 ATST Focal Plane

  15. VLBI Concept Summary • Modular instrument • Will be designed to Level 3 configuration • Level 3 option TBD • Built as subsystems that can be assembled/disassembled easily to create Level 2 and Level 1 instruments

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