Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Silicon Optics for Wide Field X-ray Imaging
Dick WillingaleUniversity of Leicester
Macelo Ackermann and Max CollonCosine Research B.V.
SPIE Optics for EUV, X-Ray, and Gamma-Ray Astronomy
VISan Diego 2013 August 27th – 29th
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Scientific Motivation
• Soft X-ray surveys– High angular resolution– Large sky area– Faint sources – AGN, Clusters of
Galaxies…• Soft X-ray transient astronomy
– Good angular resolution– All sky– Short lived phenomena – GRBs,
Novae…
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Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Si pore optics – XEUS to Athena
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• Focal length F=12m• Rib spacing 0.83 mm• Radial width Δr=0.605
mm• Axial length 4.F.Δr/R
Si pore module – Cosine Research
Module layout – Owl design
SPO originally designed for narrow field imaging with large collecting area
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Manufacture of SPO modules
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ESA - Cosine Research
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Wide field imaging with SPO
How can we modify the baseline SPO design to achieve wide field X-ray imaging?
SPO are potentially good for wide field because the reflecting surfaces have a small axial length…
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Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Vignetting
• In-plane vignetting– Radial pore size d
(fixed)– Length of pores L– Drops to zero at
θ≈d/2L
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• Out-of-plane vignetting– Rib spacing drib
– Length of pores L– Drops to zero at
θ≈drib/2L
Ray tracing of a single module
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Field of view vs. drib for Athena+
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drib 1, 2, 3, 4, 5 mm FOV at half on-axis area 1 keV
Ray tracing full aperture
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Wide field Si pore optics – Athena+
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• Focal length F=12m• Wide rib spacing drib 3
mm• Radial width d=0.605
mm• 800 – 1000 modules
The optical design of the Athena+ mirrorWillingale, Pareschi, Christensen, den Herder arXiv:1307.1709
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
FOV, Photon Energy, Grasp – drib 3mm
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Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Angular resolution off-axis• Wolter I
– principal plane (join plane) flat
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• Wolter-Schwartzschild (W-S) Obeys Abbe sine condition– principal plane spherical radius curvature F
• Polynomial figure not useful – modules small axial Length
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Angular resolution off-axis
• Figure and alignment errors – 5 arc sec HEW on-axis
• Axial curvature – approximate Wolter I or W-S
• Conical approximation ~5 arc sec HEW for F=12m
• W-S with axial curvature – 6.5 arc sec HEW average over 50 arc mins diameter FOV
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Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Deep X-ray Transient ImagingRequire:• FOV ~20 by 20 degrees or much larger• Continuous coverage ~ 500 square degrees or much
more• Collecting area >> few cm2 • Sensitivity to transient sources - Δt 1 second - 1 day• A true imaging optic to give maximum sensitivity
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Wolter I:• FOV diameter limited to ~twice grazing angle - only ~2o
• Could use a fly’s-eye of small Wolter Is but very inefficient
• 2 in-plane reflections - lateral inversion in the image plane
Solution:• Square pore or Kirkpatrick-Baez geometry
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
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K-B Stack – Schmidt Geometry
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
K-B Si Pore module
• Module shown is a Wolter I conical approximation prototype
• Can easily be constructed in the Kirkpatrick Baez geometry
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square aperture, side length S number of plates Np=S/P P=760 μm T=150 μm D=610 μm open fraction front+rear 64%
Wolter I Si pore module – Cosine Research
• No plate curvature required• Plates wedged so point at common centre of curvature
• All stacks are identical• Rib period must match wafer thickness
No lateral inversion in image plane
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Packing of K-B stacks into an aperture
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• Focal length 5 m (needs to be > ~2.5 m for SPO manufacture)
• Collecting area ~100 cm2, angular resolution ~20 arc seconds
• Using N identical K-B SPO modules• For wide field K-B modules aligned on spherical surface R=2F – large FOV
• If co-aligned on plane surface get N narrow field foci – large area
• 4 modules can form a small narrow field instrument
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Wide field K-B stacks• Grazing angle 1 degrees
– slot width 0.605 mm– axial slot length 35 mm
• FOV 20 degrees diameter• Collecting area ~110 cm2 at 1
keV (~constant over FOV)• HEW ~22 arc seconds (constant
over FOV)• Grasp 3.46 m2 deg2 at 1 keV• Focusing gain ~13300• Area at 13 cm2 at 6.5 keV
• HEW limited by flat plates – can be improved using axially curved plates
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Vignetting at 1 keV
Area vs. energy
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Summary
• ~800 Si pore optics Wolter/W-S modules with wide rib spacing (>3 mm) can provide grasp ~same as WFXT ~0.5 m2 deg2 at 1 keV
• W-S spherical join plane and approximate axial curvature with 5 arc sec HEW on-axis will give average HEW of 6.5 arc seconds over FOV 50 arc mins in diameter
• Si pore K-B stacks in Schmidt geometry provide– 20 degree diameter FOV – ~300 deg2
– with ~100 cm2 at 1 keV and HEW of ~20 arc secs– Grasp is ~10x WFXT – focusing gain 13300– Deep wide field imaging – faint transient imaging
• Identical Si pore K-B stacks can also provide– Large area on narrow field – co-aligned over plane surface –
N foci– Multiple small narrow field telescopes e.g. X-Nav telescopes
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Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
WFXT approach• Proposal to NASA – P.I. S. Murray• Optics – INAF/Brera – G. Pareschi• Thin shell Wolter I with polynominal
figure
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Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Wide field Si pore optics
• Original pore geometry – grasp 0.19 m2 deg2 at 1 keV• Wide field pore geometry – grasp 0.34 m2 deg2 at 1 keV• HEW limited by conical approximation
– Can be improved by including axial curvature• Using Ir coating – a C overcoat would increase the low
energy area20
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Soft X-ray large sky area surveys
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Looking for 5 arc sec over 1 degree FOV with collecting area ~ 4000 cm2
Silicon Optics for Wide Field X-ray ImagingDick Willingale et al. – SPIE August 2013
Soft X-ray Transient Astronomy
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Line:Lobster module F=300 mm
Red points:Swift BAT short GRBs
Black points:Swift BAT long GRBs
Green points:Swift XRT GRB afterglowsLooking for 1 arc min over 30 degree FOV with collecting area ~ 10 cm2