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

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

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

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  1. AXRO December 2012 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

  2. AXRO December 2012 Motivation • Study of new technologies for large X-ray telescopes • Extraordinary requirementson 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

  3. AXRO December 2012 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

  4. AXRO December 2012 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 opticsis expensive http://www.x-ray-optics.de http://imagine.gsfc.nasa.gov/

  5. AXRO December 2012 Apertures for ray-tracing simulation • 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) Wolter I Kirkpatrick-Baez

  6. AXRO December 2012 KB W Type of optics Parabolic-parabolic planar Parabolic-hyperbolic rotational Number of reflections 2 2 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 substrate 300 mm 300 mm Material substrate silicon glass Surface gold gold Ray-tracing simulations

  7. AXRO December 2012 Large X-ray telescope composed of modules Cartesian design Sunflower design Radial design 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) The simple cartesian packing used as an alternative to the sunflower tessellation for the KB design Radial packing of modules used for the Wolter I design The design, manufacture and predicted performance ofKirkpatrick-Baez Silicon stacks for the International X-rayObservatory or similar applications, Optics for EUV, X-ray and Gamma-ray Astronomy IV (Proc. of SPIE Vol.7437) Willingal and Spaan, 2009.

  8. AXRO December 2012 Studied KB X-ray modules • Modules are assembled from • thin reflection foils (Schmidt arrangement) or • rectangular channels (Angel arrangement) with precise shape and with low microroughness

  9. AXRO December 2012 Novel design of X-ray optical KB Flower system (KBF) • X-ray KBFoptical 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)

  10. AXRO December 2012 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

  11. AXRO December 2012 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)

  12. AXRO December 2012 X-ray optical systems - apertures • 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 Kirkpatrick-Baez system Wolter system Flower system

  13. AXRO December 2012 X-ray optical systems - comparison W – Wolter system, KB – Kirkpatrick-Baez system, KBF – KB Flower system, P – Parabolic system (“Wolter without hyperbolic part”) • Focal length of KB, KBF and Parabolicsystem is two times larger than that of Wolter system

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

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

  16. AXRO December 2012 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)

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

  18. AXRO December 2012 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

  19. AXRO December 2012 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: • Testing of optics assembling technology and focusing properties in elliptic geometry (point-to-point imaging) • 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)

  20. AXRO December 2012 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’’

  21. AXRO December 2012 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

  22. AXRO December 2012 Comparison of glass and Si mirrors Simulation and test results • Symmetric geometry, flat mirrors, focal length 9 m • Glass module – vertical, Si module – horizontal Ray-tracing simulation (ideally flat mirrors considered) X-ray tests at CASA CU

  23. AXRO December 2012 Comparison of glass and Si mirrors • 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. AXRO December 2012 Comparison of glass and Si mirrors glass Si Figure error Angular error

  25. AXRO December 2012 Development of improved Si wafers for X-ray optics applications • 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 Standard wafer Improved surface improvement by factor of 5!

  26. AXRO December 2012 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

  27. AXRO December 2012 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)

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

  29. AXRO December 2012 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

  30. AXRO December 2012 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

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

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

  33. AXRO December 2012 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)

  34. AXRO December 2012 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

  35. AXRO December 2012 THANK YOU FOR ATTENTION Prague

  36. AXRO December 2012

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