The Prime Focus Imaging Spectrograph
Design and Capabilities
Eric B. BurghSALT/PFIS Instrument Scientist
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging Spectrograph
• First generation, all-purpose spectrograph for SALT
• Optical Imaging Spectroscopy and Spectropolarimetry 320 – 900 nm.
• All-refractive collimator and camera using crystals for UV throughput
• Upgrade capability for infrared camera
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging SpectrographOptics Layout
• F/4.2 collimator, 150 mm diameter (fold mirror not shown)
• Volume Phase Holographic gratings– Lead to need for articulating camera
• F/2.2 camera, first element asphere– Articulates up to 100 degrees
• (VPH grating =50 deg in Littrow)
• Polarimetric Optics– ¼ and ½ waveplates, Wollaston beamsplitter
• Double-etalon Fabry-Perot system
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging SpectrographDesign Highlights
• Prime Focus:– Weight/space constraints– Accessibility
• Wavelength coverage:– Crystals (CaF2 and NaCl)– Anti-reflection coatings (0.5% reflections)– High UV Quantum Efficiency CCDs (Marconi)
• Multiple configurations:– Complex mechanisms/interfaces
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging Spectrograph
Open Truss Structure
Grating Server
Articulation Rail
Camera
Detector Dewar
Filter Server
Collimator Optics
Slit Mask Server
Fabry-Perot Etalons
Waveplate Mechanism
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging Spectrograph
Filter Mechanism
Detector
Collimator Optics Fold Mirror
Grating Mechanism
Shutter Slit Mask Server
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging Spectrograph
Wave Plate Mechanism
Articulation
Etalon Inserters
Slit Mask Server
Camera Focus
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging SpectrographExpected Performance
• Expected system throughput of “fixed” optics.
• Includes anti-reflection coatings and fold mirror reflectivity.
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging SpectrographExpected Performance
• Measured CCD efficiency for PFIS mosaic chips.
• Chips will be arranged to take advantage of the high QE of Chip SALT-03 at “blue” end of mosaic.
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging SpectrographGrating Complement
• Grating Complement (5 VPH gratings and one standard surface relief transmission grating)
Grating Wavelength Coverage
Usable Angles (degrees)
Bandpass per tilt (nm)
Resolving Power (1.25 arcsec slit)
SR300 390—900 nm 390/440 250—600
G0900 320—900 nm 12—20 ~300 600—2000
G1300 390—900 nm 19—32 ~200 1000—3200
G1800 450—900 nm 28—50 150—100 2000—5500
G2300 380—700 nm 30—50 100—80 2200—5500
G3000 320—540 nm 32—50 80—60 2200—5500
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging SpectrographVPH Grating Performance
• VPH gratings have tunable blaze.
• Best efficiency when used near Littrow (=)
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging SpectrographVPH Grating Performance
• VPH grating complement superblaze curves.
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging SpectrographVPH Grating Performance
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging SpectrographDouble-Etalon Fabry-Perot System
• Double-etalon system isolates high-resolution, narrow bandpass.
• High- and low-resolution modes: – R=500—12500
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging SpectrographCurrent Status:
• Optics: virtually all elements fabricated (some coated)
• Mechanisms: Slit mask completed and wired, waveplate almost completed
Science with SALT – Cape Town29 October 2003
The Prime Focus Imaging SpectrographUpcoming Schedule Milestones
• Structure fabrication (Rutgers) Jan 2004• Optomechanical assembly Feb 2004• Integration and testing thru Aug 2004• Commissioning begin Sep 2004
Relevant web pages:
• Observer’s guide v1.0 – http://www.sal.wisc.edu/~ebb/pfis/observer/
• VPH Spectroscopy simulator – http://www.sal.wisc.edu/~ebb/pfis/observer/specsim.html
• PFIS photos – http://www.sal.wisc.edu/~ebb/pfis/pics/