Novel design of large X-ray optical system for astrophysical application

Novel design of large X-ray optical system for astrophysical application

L. Pina1, R. Hudec1, V. Tichy1,

A. Inneman2, D. Cerna2 , J. Marsik2, V. Marsikova2,

W. Cash3, A. F. Shipley3 and B. R. Zeiger3, T. D. Rogers3,

R. Melich4

1Czech Technical Univ. in Prague, Czech Republic

2Rigaku Innovative Technologies Europe, Czech Republic

3Univ. of Colorado at Boulder, United States

4CAS IPP, TOPTEC, Turnov, Czech Republic

AXRO December 2012 1

Motivation

• Study of new technologies for large X-ray telescopes

• Extraordinary requirements on accuracy – resolution of optical system around few arcsec

• This type of optical system has to be assembled from many small segments and thousands of mirrors (unlike only a few nested mirrors in other projects)

• Manufacturing of Wolter I system needs very expensive mandrels (3D aspheric)

• Manufacturing of KB system can be easier and cheaper (2D aspheric)

• Substrates can be glass and/or silicon with excellent flatness and micro-roughness which is necessary for long-focal optics


Wolter system

• Double reflection X-ray optics • Rotationally symmetric mirrors of parabolic

and hyperbolic shape• Set of nested mirrors is arranged

concentrically to the optical axis• Each ray is reflected at the parabolic

surface first, then at the hyperbolic surface• Quality of the focal spot depends on

quality of substrates (shape, microroughness)

• Optical error is rectified (astigmatic and coma error)

• Replicated technology requires expensive mandrels

XMM

http://imagine.gsfc.nasa.gov


horizontal focusing mirror

vertical focusing mirror

Kirkpatrick-Baez system

• Double reflection X-ray Optics • Two mirror sets vertical and horizontal• Mirrors in both sets have to be curved

parabolically • Single focal point is formed in the

intersection of the horizontal and vertical focal planes

• Quality of the focal spot depends on quality of substrates (shape, microroughness)

• Technology is not necessarily based on precise and expensive mandrel

• Classical manufacturing technology of laboratory KB optics is expensive

http://imagine.gsfc.nasa.gov/

http://www.x-ray-optics.de


Apertures for ray-tracing simulation


Wolter I Kirkpatrick-Baez

• Comparison of aperture sizes of W and KB systems

• Diameter of Wolter 2 m, KB aperture 2 × 2 m

• Similar reflection angle considered

• Reflectivity of edge mirror 70% (for energy 1 keV)


KB W

Type of optics Parabolic-parabolic planarParabolic-hyperbolic

rotational

Number of reflections

2 2

Focal length - Aperture

20 m – 913 x 913 mm40 m – 1826 x 1826 mm

10 m – radius 913 mm20 m – radius 1826 mm

First mirror134 mm from axis268 mm from axis

134 mm from axis268 mm from axis

Number of mirrors420 840

394 788

Length of substrate 300 mm 300 mm

Material substrate silicon glass

Surface gold gold

Ray-tracing simulations

Large X-ray telescope composed of modules

Sunflower configuration uses Fibonacci numbers (the lines from the centre to the corner of each module indicate the direction in

which 2-reflection rays are deflected)

Radial packing of modules used for the

Wolter I design

The simple cartesian packing used as an alternative to the

sunflower tessellation for the KB design

Radial design Cartesian design Sunflower design

The design, manufacture and predicted performance of Kirkpatrick-Baez Silicon stacks for the International X-ray Observatory or similar applications, Optics for EUV, X-ray and Gamma-ray Astronomy IV (Proc. of SPIE Vol.7437) Willingal and Spaan, 2009.


Studied KB X-ray modules• Modules are assembled from

o thin reflection foils (Schmidt arrangement) or

o rectangular channels (Angel arrangement)

with precise shape and with low microroughness


Novel design of X-ray optical KB Flower system (KBF)

• X-ray KBF optical system is assembled from minimally 5 segments (petals)

• Each segment (petal) is assembled from modules (one or more)

• Each module is assembled from

thin reflection foils or rectangular channels

• Energy range 50 eV – 10 keV (EUV, SXR, XR)


X-ray segment of KBF system

• Segment is a sector of a circle with central angle 18°- 72° (usually 45°)

• Segment is assembled from modules

• Diagonals of all modules are parallel with symmetry axis of segment

• Black narrow area is nonfunctional area


Design of KBF system

• X-ray optical system is assembled from segments (minimally 5)

• Symmetry axis of each segment intersects symmetry axis of the optical system

• Arrangement of segments approaches a circular aperture

• Patent pending (PV 2011-297)


X-ray optical systems - apertures

Kirkpatrick-Baezsystem

Wolter systemFlower system


• Size limited by the critical angle – the same maximum incident angle for all systems for 1 keV

(reflectivity 70% after 1st reflection, 50% after 2nd reflection)

• Wolter I and KB systems have the same aperture size

• KBF system has more than two times larger aperture than the others

X-ray optical systems - comparison

System Focal length(m)

Active aperture(m2)

Number of reflections

KB 20 2.6 2 (R = 50%)

W 10 2.6 2 (R = 50%)

KBF 20 5.6 2 (R = 50%)

P 20 2.6 1 (R = 70%)


W – Wolter system, KB – Kirkpatrick-Baez system, KBF – KB Flower system, P – Parabolic system (“Wolter without hyperbolic part”)

• Focal length of KB, KBF and Parabolic system is two times larger than that of Wolter system


KB – Kirkpatrick-Baez system

W – Wolter system

KBF - KB Flower system

P – Parabolic system

• 1 keV : KBFKBF(F=20m) > PP(F=20m) > WW(F=10m) > KBKB(F=20m)

• 10 keV : PP(F=20m) > WW(F=10m) ≥ KBFKBF(F=20m) > KBKB(F=20m)→ COMBINATION



=> COMBINATIONKBFKBF and PP

(in SXR - XR region)

logarithmic scale


linear scale

Novel X-ray optical system KBF+P combination

• Non-functional (blind) central area of KBF system can be filled with thin rotationally symmetric foils (classical nested mirrors with parabolic shape P)

=> improvement of KBF optical system aperture effective area for higher

energies

• Patent pending (PV 2011-297)


Advantages of KBF+P combination:

•KBF design has the largest effective aperture in SXR region

•KBF design allows higher efficiency in XR region using combination with parabolic mirrors filling the KBF non-functional area

•more homogeneous beam can be achieved by rotation of the whole optical system

•precise expensive mandrels are not needed for KBF part

•silicon or glass thin planar mirrors can be used in KBF part


X-ray optical system KBF+P combination

Applications of KBF+P system

• Astrophysical application (X-ray telescopes)

• Laboratory application (EUV, XUV, SXR and XR optics)

• EUV /XUV microscopy and tomography

• EUV/XUV lithography

• X-ray Compton imaging

• Focusing of electrons and/or neutrons

• XRF analysis


Experiments X-ray tests of KBF elements

• X-ray testing of astronomical long-focal optics requires parallel beam and long vacuum chambers, which makes testing rather difficult

• New testing method was proposed

• Testing is divided into two parts:

1. Testing of optics assembling technology and focusing properties in elliptic geometry (point-to-point imaging)

2. Application of verified optical technologies to final optics design with parabolic geometry

• KB modules were tested in vacuum chamber in Center for Astrophysics and Space Astronomy (CASA, University of Colorado at Boulder, USA)


Testing vacuum chamber at CASA UC

• X-Ray source with Ti anode (Lα, 453 eV, 2.73 nm)

• X-Ray beam diameter(diameter of vacuum tube) 8 cm

• Total vacuum chamber length 20 m

• MCP detector, diameter 1’’


Comparison of glass and Si mirrors

• 2 modules were assembled from glass mirrors and Si standard wafers

• Housing - Al profile

• Mirror size: 100 × 100 mm (glass), 100 × 75 mm (Si)

• Mirror thickness: 0.4 mm (glass), 0.7 mm (Si)

• Au surface coating



Comparison of glass and Si mirrorsSimulation and test results

Ray-tracing simulation(ideally flat mirrors considered)

X-ray tests at CASA CU

• Symmetric geometry, flat mirrors, focal length 9 m

• Glass module – vertical, Si module – horizontal



Taylor-Hobson profilometermodule RMS (μm) RMS (arcsec)

glass 1.6 ÷ 21.3 34.7 ÷ 279.4

Si 0.4 ÷ 0.6 12.1 ÷ 17.1

simulation measurementmodule FWHM (mm) FWHM (arcsec) FWHM (mm) FWHM (arcsec)

glass 0.46 2.6 6.14 35.2Si 0.36 2.1 1.54 8.8

• Mirrors were measured on Taylor-Hobson profilometer

• Si mirrors have better flatness

• High variance of glass mirrors

• Difference between simulation and experiment (broadening of focus) is caused by poor quality of glass mirrors



Figure error

Angular error

glass Si

Development of improved Si wafers for X-ray optics applications


Standard wafer

Improved surface

•Standard silicon wafer (150 mm diameter):

- thickness in the wafer center: 628.81 µm,

minimal measured thickness: 630.40 µm,

maximal measured thickness: 632.50 µm, - total thickness variation: 2.10 µm, flatness: 1.76

µm

•Highly flat silicon wafer developed for sub-micron technologies in ON Semiconductor Czech Republic

(150 mm diameter):

- thickness in the wafer center: 610.92 µm,

minimal measured thickness: 610.58 µm,

maximal measured thickness: 611.03 µm,- total thickness variation: 0.45 µm, flatness: 0.29

µm improvement by factor of 5!

KB modules - specification

• 144 commercially available 525 μm thick Si wafers with Au surface coating

• 1st mirror is at a distance of approx. 16 mm from optical axis

• Mirrors arranged into planar-ellipsoidal shape with axial symmetry

• Mirror size 100 × 100 mm

• 3 sets of 24 (18+6) mirrors in each module

• Spacing 1.5 ÷ 2.5 mm


Experimental arrangement

• Modules were designed for vacuum chamber at CASA (Univ. of Colorado)

• Point-to-point imaging - elliptical geometry

• Source to optics distance: 10 m

• Optics to detector distance: 8 m

• Distance between modules: 10 cm

• Module position adjustment donewith visible light (Xe lamp)


Test results

• FWHM = 1.63 mm

• Anglular resolution: 10.2 arcsec (after ellips. correction)


Ray-tracing simulations

Input parameters (mirror material properties, arrangement of mirrors in modules, experiment geometry, …) are the same as in the experiment


Theoretical focus:FWHM = 0.58 mm

≈ 3.7 arcsec

Theoretical focus with 0.2 mm source diameter and 2 μm manufacturing errors:

FWHM = 0.59 mm

Optics with piezoelements

• Piezoelements were studied in order to improve resolution

• Glued striped piezoelements enable mirrors bending which approximates aspherical shape of KB mirror

• Two stacked mirrors (optical surfaces) were tested in vacuum chamber

• Mirror size 100 × 55 mm

• Distance of mirrors from optical axis - 40 cm

• Mirrors bent to radius 250 m


• Focus behavior depending on piezoelement voltages was studied

• Voltage for optimum focus was found


Optics with piezoelements

• Joint focus of two mirrors with piezoelements obtained

• FWHM = 1.35 mm

• Anglular resolution: 7 arcsec (after correction)


Optics with piezoelementsTest results

Conclusion

• X-ray optical system based on Kirkpatrick-Baez modules in novel arrangement (KBF) and its combination with nested parabolic mirrors in the KBF center area were studied

• Proposed system has better light efficiency in comparison with relevant KB and Wolter X-ray optical systems

• Commercial Si wafers can be effectively used in KBF part, which was experimentally verified within X-ray testing at CASA (University of Colorado)

• Potential of active optics for resolution improvement was demonstrated• Novel KBF system can be used for astrophysical applications as well as for

laboratory applications (focusing and imaging in EUV, SXR and XR) • Patent pending of KBF design and combination KBF+P (PV 2011-297)


Aknowledgements

• Ministry of Education, Youth and Sports of the Czech Republic, project ME09028 and ME09004

• Team of Prof. Webster Cash, University of Colorado at Boulder• ESA PECS Project No. 98039• MEYS ESF Project CZ.1.07/2.3.00/20.0092• Drs. J. Sik and M. Lorenc from ON Semiconductor Czech Republic


THANK YOU FOR ATTENTION


Prague


Novel design of large X-ray optical system for astrophysical application

Documents

xray modulesmodules

type of optical system

focal spot

optical axiseach ray

reflection rays

systemsdiameter of wolter

focal opticsaxro

vertical focal planes