The Prime Focus Imaging Spectrograph

Design and Capabilities

Eric B. Burgh

SALT/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/