1. Novel design of large X-ray optical system for astrophysical application L. Pina 1, R. Hudec 1, V. Tichy 1, A. Inneman 2, D. Cerna 2, J. Marsik 2, V. Marsikova 2, W. Cash 3, A. F. Shipley 3 and B. R. Zeiger 3, T. D. Rogers 3, R. Melich 4 1 Czech Technical Univ. in Prague, Czech Republic 2 Rigaku Innovative Technologies Europe, Czech Republic 3 Univ. of Colorado at Boulder, United States 4 CAS IPP, TOPTEC, Turnov, Czech Republic AXRO December 2012 1

2. 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 AXRO December 2012 2

3. 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 AXRO December 2012 3

4. 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 AXRO December 2012 4

5. Apertures for ray-tracing simulation AXRO December 2012 5 Wolter IKirkpatrick-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)

6. AXRO December 2012 6 KBW Type of opticsParabolic-parabolic planar Parabolic-hyperbolic rotational Number of reflections 22 Focal length - Aperture 20 m – 913 x 913 mm 40 m – 1826 x 1826 mm 10 m – radius 913 mm 20 m – radius 1826 mm First mirror 134 mm from axis 268 mm from axis 134 mm from axis 268 mm from axis Number of mirrors 420 840 394 788 Length of substrate300 mm Material substratesiliconglass Surfacegold Ray-tracing simulations

7. 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 designSunflower 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. AXRO December 2012 7

8. 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 AXRO December 2012 8

9. 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) AXRO December 2012 9

10. 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 AXRO December 2012 10

11. 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) AXRO December 2012 11

12. X-ray optical systems - apertures Kirkpatrick-Baez system Wolter system Flower system AXRO December 2012 12 Size limited by the critical angle – the same maximum incident angle for all systems for 1 keV (reflectivity 70% after 1 st reflection, 50% after 2 nd reflection) Wolter I and KB systems have the same aperture size KBF system has more than two times larger aperture than the others

13. X-ray optical systems - comparison System Focal length (m) Active aperture (m 2 ) Number of reflections KB202.62 (R = 50%) W102.62 (R = 50%) KBF205.62 (R = 50%) P20202.61 (R = 70%) AXRO December 2012 13 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

14. X-ray optical systems - comparison KB – Kirkpatrick-Baez system W – Wolter system KBF - KB Flower system P – Parabolic system KBFPWKB 1 keV : KBF (F=20m) > P (F=20m) > W (F=10m) > KB (F=20m) PWKBFKB 10 keV : P (F=20m) > W (F=10m) ≥ KBF (F=20m) > KB (F=20m) → COMBINATION AXRO December 2012 14

15. X-ray optical systems - comparison => COMBINATION KBFP KBF and P (in SXR - XR region) logarithmic scale AXRO December 2012 15 linear scale

16. 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) AXRO December 2012 16

17. 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 AXRO December 2012 17 X-ray optical system KBF+P combination

18. 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 AXRO December 2012 18

19. 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) AXRO December 2012 19

20. 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’’ AXRO December 2012 20

21. 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 AXRO December 2012 21

22. AXRO December 2012 22 Comparison of glass and Si mirrors Simulation 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

23. Comparison of glass and Si mirrors AXRO December 2012 23 Taylor-Hobson profilometer module RMS (μm)RMS (arcsec) glass 1.6 ÷ 21.334.7 ÷ 279.4 Si 0.4 ÷ 0.612.1 ÷ 17.1 simulationmeasurement moduleFWHM (mm)FWHM (arcsec)FWHM (mm)FWHM (arcsec) glass 0.462.6 6.1435.2 Si 0.362.1 1.548.8 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

24. Comparison of glass and Si mirrors AXRO December 2012 24 Figure error Angular error glassSi

25. Development of improved Si wafers for X-ray optics applications AXRO December 2012 25 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!

26. KB modules - specification 144 commercially available 525 μm thick Si wafers with Au surface coating 1 st 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 AXRO December 2012 26

27. 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 done with visible light (Xe lamp) AXRO December 2012 27

28. Test results FWHM = 1.63 mm Anglular resolution: 10.2 arcsec (after ellips. correction) AXRO December 2012 28

29. Ray-tracing simulations Input parameters (mirror material properties, arrangement of mirrors in modules, experiment geometry, …) are the same as in the experiment AXRO December 2012 29 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

30. 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 AXRO December 2012 30

31. Focus behavior depending on piezoelement voltages was studied Voltage for optimum focus was found AXRO December 2012 31 Optics with piezoelements

32. Joint focus of two mirrors with piezoelements obtained FWHM = 1.35 mm Anglular resolution: 7 arcsec (after correction) AXRO December 2012 32 Optics with piezoelements Test results

33. 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) AXRO December 2012 33

34. 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 AXRO December 2012 34

35. THANK YOU FOR ATTENTION AXRO December 2012 35 Prague

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