UPF Optical Design

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UPF Optical Design

• David Henry
• 30th January 2009

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UPF Design Baseline Concept

• Cross dispersed echelle spectrograph
• R 70,000, 2.5 pixel sampling
• White pupil collimator design
• Refractive camera
• Optical design similar to HARPS, UVES, MRS
  spectrographs
• Fixed echelle, cross disperser, camera
• No mechanisms (in main optical path)
• Floor mounted, fibre fed

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UPF Baseline Optical Layout

• Input slit
• 0.46 arcsec wide, 0.36 x 0.047mm effective size,
  f/5
• Focal reducer
• Convert from f/5 to f/13
• Single collimator
• Parabolic mirror, f1100mm, 85mm collimated beam
  diameter
• Spectrum mirror
• Spectrally dispersed image at intermediate focal
  plane

• Echelle
• 31.6 lines/mm, R4 (75 blaze angle)
• Cross disperser
• Reflective grating or prism
• Camera
• f450mm, f/5.3
• Detector
• 2 x 2K2 HAWAII-2RG arrays

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Optical Layout - Grating Cross Disperser
Cross disperser - Reflective grating - 100
lines/mm - m1
Camera - f450mm - 5 lenses - All spherical
surfaces
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Spectral Format Grating Cross Disperser
Detector array footprint 2 x 2K2 HAWAII-2RG
arrays 73.728 x 36.864mm
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Image Quality Grating Cross Disperser

• Example spot diagram
• Order 48
• Each box represents 1 detector pixel
• Airy disk also shown
• Imaging performance in other orders is similar

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Optical Layout - Prism Cross Disperser
Cross disperser - Prism (SF59) - 55 apex
angle - 190 x 170 x 90
Camera - f450mm - 6 lenses - All spherical
surfaces - Optimised for 1.0 1.8mm
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Spectral Format Prism Cross Disperser
Detector array footprint 2 x 2K2 HAWAII-2RG
arrays 73.728 x 36.864mm
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Image Quality Prism Cross Disperser

• Example spot diagram
• Order 48
• Each box represents 2 detector pixels
• Imaging performance in other orders is similar
• NB 6 Lens camera only optimised for 1.0 1.8mm

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Throughput Estimate
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WFCAM Mounted Fibre Pickoff Option 1

• Fibre pickoff and acquisition system mounted
  behind WFCAM field lens and guider optics
• Guide camera rigidly mounted to fibre pickoff to
  minimise guider error
• Second fibre from calibration source, coupled
  into object fibre via mirror mechanism, for
  daytime calibration
• Manually installed for UPF operation, removed for
  WFCAM operation

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WFCAM Mounted Fibre Pickoff Option 2

• Remove field lens tower (normal operation for
  WFCAM installation/removal)
• Cryostat remains in place
• Fit second tower containing fibre pickoff
  guiding assembly at f/9 focus
• Enhanced throughput over option 1

Field Lens Tower
Cryostat
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Fibre Slicer Concept