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 –1 – 10 Å bandpasses Large format, fast readout CCD or CMOS detectors Dedicated multi-TByte storage array

VLBI Preliminary Wavelengths FilterWavelength Å Bandpass Å CN Violet Bandhead Ca II H & K Lines3933 & CH G-band Blue Continuum45045 Green Continuum55505 H-alpha65631 Red Continuum66845 TiO Sunspot Bands705710

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 Wavelength Å Focal Length m Plate Scale arcsec/mm F/#Field-of-View arcmin Requirement: 2 pixels per central Airy disk of a 4-m aperture at each Hypothetical detector: 9  m pixels, 4096 x 4096 format

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

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 adjustab l e defocus of one camera C1: Camera 1XYZ Stage 1SH1: Shutter 1C2: Camera 2XYZ Stage 2SH2: Shutter 2 DCS:Detector Control System

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 Beam directly from ATST Detector subsystem Single Filter

VLBI Design Concepts VLBI Level 2 –Dual detector subsystem –Filterwheel subsystem –Fixed focal ratio optics. L1 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