vlbi: visible light broadband imager
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VLBI: Visible Light Broadband Imager. Instrument Conceptual Design Presentation Tom Berger Lockheed Martin Solar and Astrophysics Lab. VLBI Science Requirements. - PowerPoint PPT PresentationTRANSCRIPT
VLBI: Visible Light Broadband ImagerInstrument Conceptual Design Presentation
Tom BergerLockheed 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
Filter WavelengthÅ
BandpassÅ
CN Violet Bandhead 3883 10Ca II H & K Lines 3933 & 3968 1CH G-band 4305 10Blue Continuum 4504 5Green Continuum 5550 5H-alpha 6563 1Red Continuum 6684 5TiO Sunspot Bands 7057 10
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
WavelengthÅ
Focal Length
m
Plate Scalearcsec/mm
F/# Field-of-Viewarcmin
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 102.0 2.02 26 1.26
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
adjustable defocus of one camera
C1: Camera 1
XYZ Stage 1
SH1: Shutter 1
C2: Camera 2
XYZ Stage 2
SH2: Shutter 2
DCS:Detector Control System
C2
C1
CBS
F2
F1
SH2
SH
1
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 directlyfrom ATST Detector subsystem
Single Filter C2
C1
CBS
F2
F1
SH2
SH
1
VLBI Design Concepts
• VLBI Level 2– Dual detector subsystem– Filterwheel subsystem– Fixed focal ratio optics. L1 removable/replaceable for F/#
change.
C2
C1
CBS
F2
F1
FW1
CLFL
AS
F0
SH2
SH
1
L1
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
C2
C1
CBS
F2
F1
FW1
CLFL
AS
F0
FW3
FM1 L1
L2
FM2 FM3
FM4 SH2
SH
1
FW2ATST 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
Zoom LensSystem
C2
C1
CBS
F2
F1
FW1
CLFL
AS
F0FW2
FW3 SH2
SH
1
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