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

The End

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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