axro, december 2009

AXRO, DECEMBER 2009 1

X-ray Optics:

Wolter versus KB system

Veronika Marsikovaa, Libor Sveda b, Adolf Inneman a,

Jiri Marsik a, Rene Hudecc, Ladislav Pinab

a) Rigaku Innovative Technologies Europe, s.r.o.

b) Czech Technical University in Prague, FNSPE

c) Astronomical Institute of Academy of Sciences of Czech Republic


Motivation

• Manufacturing Wolter system needs very

expensive mandrels (3D aspheric).

• Manufacturing 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 focus optics.


Wolter system

• Double reflection X-ray Optics - Wolter type I optics consists of rotationally symmetric mirrors which are parabolic mirror followed by a hyperbolic mirror.

• Set of nested mirrors is arranged concentrically to the optical axis. Each ray coming is reflected at the parabolic surface first, then at the hyperbolic surface.

• The quality of the focal spot image of the X-ray source depends on quality of substrates (shape, microroughness).

• Optical error is rectified (astigmatic and coma error).

• Replicated technology requires very expensive mandrel.

XMM

http://imagine.gsfc.nasa.gov

horizontal focusing mirror

vertical focusing mirror


KirckPatrick Baez system

• Double reflection X-ray Optics consists of two mirror sets – one is aligned vertically and the second is aligned horizontally.

• Both mirrors have to be curved parabolically – the first mirror focuses in vertical plane and the second mirror focuses in horizontal plane. Single focal point is formed in the crossection of the two focal planes.

• The quality of the focal spot image depend on quality of substrates (shape, microroughness).

• Technology is not necessarily based on precise and expensive mandrel.

• Classic technologies for laboratory KB-mirrors are expensive, complicated and based on heavy optics.

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

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

Design and simulation



ComparisonKB W

Type of optics Parabolic-parabolic planar Parabolic-hyperbolic rotational

Number of reflections 2 2

Focal length - Aperture20 m – 913 x 913 mm

40 m – 1826 x 1826 mm10 m – dia 913 mm

20 m – dia 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


Focal length

W system

KB system

If W and KB have the same aperture, focal length of KB system is

twice as large as Wolter system.

L

2L


Input conditions• Minimum distance between mirrors: 1 mm• Energy range: 1.0 – 10.0 keV• Last mirror reflection:

70% reflection (after 1st reflection @ 1keV)

50% reflection (after 2nd reflection @ 1keV)


Aperture optics system

KB system

W system


Reflectivity at first mirror set

(Focal length 10m KB and 20m W)

KB systemW system


Source spectrum

• Crab Nebula

Images of Crab Nebula from Chandra X-ray Observatory. Physics News Graphics, AIP.

http://chandra.harvard.edu/photo/0052/index.html

]///1[)( 2)1( HzscmAS

2

Toor & Seward (1974)


Off-axis source images


KB system W system

Focal peak intensity – not normalized


Focal peak intensity - normalized


Focal FWHM [mm] – not normalized


Focal FWHM [arcsec] – normalized


Focal length optimization


• “ideal” focal length for both sets results in asymmetric peak

• focal length of mirror set one was optimized

• Difference ideal-optimal ~ 4 mm

Next year enhancements

• Reflectivity efficiency maps.

• Segment based KB design as a result of efficiency maps (flower-like KB).

• Comparison to standard designs.


Flower – like KB


Manufacturing



RITE technologies

• Based on industrial substrates (glass and or Si wafer) with very

good surface quality (shape, microroughness) => low cost.

• Technology process retains surface quality and polishing

process is not needed.

• Technology allows composite materials and/or relatively light-

weight materials.

• Cubic geometry means easer assembling of the system.

Gorenstein, Paul,Proc. SPIE Vol. 3444, p. 382-392

ISRO Meeting Prague, October 2009 23

MFO technology

X-ray optics–Substrates

•Glass•Silicon•Nickel

–Type of optics•KB system•Lobster Eye

Si substrates

AFTERBEFORE


Si substrates

Analysis of formed Si wafer by TH profilometer.

Analysis of formed Si wafer by AFM.

Comparison of convex side of bent Si wafers (left) and flat Si wafer (right)


RITE modules

•Model based on ray-tracing (11 profiles)

•Two sets of mirrors from Si chips 100x100x0.525 mm

•Total optics length 600 mm, aperture 40x40 mm

Tests



Conclusion

• KB vs. W

• Comparable effective area at f=2*f

• KB has more homogeneous intensity

• KB has comparable angular resolution

• KB samples manufactured from multiple small Si chips

(substrates)

• Tests are expected at the beginning of 2010

• Future enhancements of KB (simulation + manufacturing

– silicon and glass substrates)


Acknowledgment• We acknowledge support of:

• Grant Ministry of Education, Youth and Sports, grant

“Applications of Kirkpatrick Baez Imaging Systems in

Space”, No. ME09004.

• Grant ESA - PECS, grant “Novel X-ray Optics Technologies

for ESA X-ray Astrophysics Missions”, No. 98039.

• Grant Agency of Academy of Sciences of the Czech

Republic, grant “Material and X-Ray Optical Properties of

Formed Silicon Monocrystals”, No. IAAX01220701.

• Project MSMT INGO “Vyzkum v ramci Mezinarodniho centra

husteho magnetizovaneho plasmatu”.


THANK YOU FOR YOUR ATTENTION.

axro, december 2009

Documents

focal planes

ideal focal length

focal length optimizationaxro

focal spot image

kevlast mirror reflection

single focal point

parabolic mirror

hyperbolic mirror