VLBI Visible Light Broadband Imager Instrument Conceptual Design
VLBI: Visible Light Broadband Imager Instrument Conceptual Design Presentation Tom Berger Lockheed Martin Solar and Astrophysics Lab
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
VLBI Basic Concept • Simple transfer/beam conditioning optics • Thin film interference filters – 2 or 3 cavity glass subtrate – > 60% transmission – 10 Å bandpasses • Large format, fast readout CCD or CMOS detectors • Dedicated multi-TByte storage array
VLBI Preliminary Wavelengths Filter CN Violet Bandhead Wavelength Bandpass Å Å 3883 10 3933 & 3968 1 CH G-band 4305 10 Blue Continuum 4504 5 Green Continuum 5550 5 H-alpha 6563 1 Red Continuum 6684 5 Ti. O Sunspot Bands 7057 10 Ca II H & K Lines
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
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 Wavelength Focal Length Å m Plate Scale arcsec/mm F/# Field-of-View arcmin 3933 183. 1 1. 13 46 0. 69 4305 167. 2 1. 23 42 0. 76 4505 159. 8 1. 29 40 0. 79 5550 129. 7 1. 59 32 0. 98 6563 109. 7 1. 88 27 1. 16 6684 107. 7 1. 91 27 1. 18 7057 102. 02 26 1. 26
VLBI Design Limitations • Detector technology – – – 0. 015” pixels: 6 K x 6 K 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
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
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 C 1: Camera 1 C 2: Camera 2 SH 1: Shutter 1 SH 2: Shutter 2 XYZ Stage 1 XYZ Stage 2
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
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
VLBI Design Concepts • VLBI Level 2 – Dual detector subsystem – Filterwheel subsystem – Fixed focal ratio optics. L 1 removable/replaceable for F/# change.
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
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
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
- Slides: 15