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BlueMUSE Optical DesignAlexandre Jeanneau (CRAL), Optical Designer
BlueMUSE Science workshop – November 9, 2020
Outline
• Salient features
• Design drivers
• Sub-system walkthrough
• Fallback 1 arcmin² design
• End-to-end performance
• Conclusion and next steps
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Salient Features
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Salient Features
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BlueMUSE Top Level Requirements (TLR)
Design Drivers
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Make it wide, make it blue, make it work
• Option 1: scaling-up MUSE• Also means scaling the detector (⟶ 6k x 6k): too costly
• … and scaling/stiffening the platform: too big/heavy
• Option 2: doubling the IFUs• Too costly/heavy
• Option 3: zooming-out• Same detector format
• Coarser sky-sampling (0.3 instead of 0.2’’/pixel)
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Make it wide, make it blue, make it work
Conserving the étendue
𝐷𝑡𝑒𝑙𝜃𝑡𝑒𝑙 =𝑑𝑝𝑖𝑥
𝐹𝑐𝑎𝑚
• Coarse 𝜃𝑡𝑒𝑙 (sky sampling) yields a fast/complex camera
• 𝐹𝑐𝑎𝑚 ≈ 1.3 (MUSE was F/1.9)
• Image quality criterion gets more stringent
Shifting towards the blue
• Need to fight against both glass and atmospheric cut-off at 350 nm
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Major impact on spectrograph design
Sub-system walkthrough
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BlueMUSE subsystem breakdown
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Expected appearance
BlueMUSE footprint with respect to MUSE on the VLTNasmyth platform
MUSE instrument on the Nasmyth platform
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Expected appearance
BlueMUSE footprint with respect to MUSE on the VLTNasmyth platform
System breakdown
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Fore-Optics
even asphere
cylinder
• Derotates the FoV
• Anamorphoses the FoV with an anamorphic ratio of 2 in the spectral direction, in order to comply with Nyquist criterion for spectral sampling
• Relays the FoV to the Field Splitter, with the appropriate magnification
• Makes a pupil plane accessibleBlueMUSE Science workshop – November 9, 2020 12
(most complex lenses)
Splitting and Relay Optics
• Splits the FoV in 24 subFoVs
• Relays each subFoV to its matching IFU, with the appropriate magnification
• Ensures output telecentricityBlueMUSE Science workshop – November 9, 2020 13
Image Slicer
• Transforms a rectangular FoV in a series of mini-slits, re-arranged along a pseudo-slit located at the entrance of the spectrograph
• Images the input pupil at the entrance pupil of the spectrograph
Image Dissector Array
Focusing Mirror Array slit
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to spectrograph
fromsplitting and relay
Spectrograph
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MUSE
BlueMUSE
R = 500 mmdetector
(most complex lenses)even asphere
cylinder
Curved detector
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Pros• Help to correct off-axis aberrations as field
curvature or astigmatism• Optical as well as size benefit
Cons• Associated risks (breakage during curving,
repetability of curvature, sphericity error)• Fast design = sensitive design
• Sensitivity increases• Image quality requirement is more stringent
• Associated costs
≈ 1/𝐹𝑐𝑎𝑚
𝛿𝑧
spot diameter ≈ 𝛿𝑧/𝐹𝑐𝑎𝑚
perfect spotfocused
perfect spotdefocused
Curved detector
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Pros• Help to correct off-axis aberrations as field
curvature or astigmatism• Optical as well as size benefit
Cons• Associated risks (breakage during curving,
repetability of curvature, sphericity error)• Fast design = sensitive design
• Sensitivity increases• Image quality requirement is more stringent
• Associated costs
≈ 1/𝐹𝑐𝑎𝑚
spot diameter ≈ 𝛿𝑧/𝐹𝑐𝑎𝑚
perfect spotdefocused
perfect spotfocused
𝛿𝑧
Fallback 1 arcmin² design
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1 arcmin² spectrograph
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MUSE
BlueMUSE(2 arcmin² FoV)
BlueMUSE(1 arcmin² FoV)
(most complex lenses)even asphere
cylinder
End-to-end performance
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Throughput (2 arcmin² FoV)
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spectrograph related
Spectrograph(excl. grating)
Image slicer
Splitting andRelay Optics
Fore-opticsCCD QE
Grating
what we can optimise
Image quality (2 arcmin² FoV)
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Conclusion and next steps
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Conclusion and next steps
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baseline(curved-detectors)
fallback solution (cheaper and less risk)
Today’s discussion will guide us in
exploring solutions
Any feedback is welcome, thank you !email: [email protected]
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