X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
1999-11-29
2001-11-13
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
C378S145000
Reexamination Certificate
active
06317483
ABSTRACT:
TECHNICAL FIELD
The present invention relates to doubly curved optical elements, and in particular, to a doubly curved optical device having multiple reflection planes separated by a spacing d which varies in at least one direction.
BACKGROUND OF THE INVENTION
Crystalline materials, which have periodic structure, can be used to reflect x-rays based on diffraction. The reflection of x-rays from crystal planes can only occur when the Bragg condition is met:
2
d
sin &thgr;=
n&lgr;
Where &lgr; is the x-ray wavelength, d is the spacing of reflection planes, &thgr; is the incident angle with respect to the reflection planes, and n is the reflection order. The d spacings for natural crystals and most synthetic crystals are constant. In order to reflect x-rays of the same wavelength efficiently, a crystal optical element must have a near constant incident angle with respect to the reflection planes of the crystal on every point of the surface. Crystal optics based on Bragg reflection have been widely used for x-ray monochromators and high-resolution spectroscopy. However, the applications of crystal optics for focusing and collimating x-rays from a laboratory source have been limited because of the strict requirement of the Bragg condition and the narrow rocking curve widths for most useful crystalline materials.
For many applications of microanalysis, an intense monochromatic x-ray beam based on a laboratory type source is needed. Three-dimensional focusing of x-rays from a laboratory source involves doubly bent crystal optics. The practical use of a toroidal crystal to focus 8 ke V x-rays has been demonstrated recently with the use of a mica crystal based on the Johann type point to point focusing geometry. For example, reference an article by Z. W. Chen and D. B. Wittry entitled “Microanalysis by Monochromatic Microprobe X-ray Fluorescence-Physical Basis, Properties and Future Prospects”, J. Appl. Phys., 84(2), page 1064 (1998). However, the Bragg condition cannot be satisfied on every point of the crystal using this approach due to the geometrical aberration of the Johann geometry in the Roland circle plane, which will limit the collection solid angle of the optic. The spot size of the focused beam is also limited by the geometrical aberration of the toroidal surface.
On the other hand, a parallel monochromatic x-ray beam is useful for many x-ray diffraction applications. Conventional crystal optics with constant d spacing cannot provide efficient collimation of hard x-rays from a divergent source since the incident angle must vary from point to point for any type of collimating mirror. For high-resolution x-ray diffraction applications, the monochromaticity provided by conventional multilayer optics is relatively poor and the divergence is not small enough.
SUMMARY OF THE INVENTION
Briefly summarized, the present invention comprises in one aspect an optically curved device which includes a plurality of curved atomic planes, at least some of which are separated by a spacing d which varies in at least one direction. The device further includes an optical surface which is doubly curved and disposed over the plurality of curved atomic planes. The spacing d varies in the at least one direction and is determined from a Bragg equation, where a Bragg angle is an incident angle of an x-ray from a source impinging on the optical surface on at least some points of the optical surface.
To restate, it is an object of this invention to provide significantly improved curved crystal optical elements for focusing, collimating and imaging of x-rays. These curved crystal optics are characterized in that the lattice parameters change laterally in at least one direction. The variation of the crystal lattice parameter can be produced by growing a crystal made of two or more elements and changing the relative percentage of the two elements as the crystal is grown. By varying the d spacing laterally across the surface of a crystal optic, the Bragg angle &thgr; on every point of the crystal can be matched to the incident angle exactly, which improves significantly the efficiency of curved crystal elements and eliminates any geometric aberration.
The optical shapes of two-dimensionally curved graded crystal elements can be circular, ellipsoidal, parabolic, spherical, and other aspherical shapes. An example of a doubly curved element is given in
FIGS. 3A & 3B
.
FIG. 3A
shows that the element can be elliptically curved in one-dimension, while
FIG. 3B
shows that the element can be circularly curved in the other dimension. This provides point-to-point focusing. The ellipsoidal geometry provides point to point focusing of monochromatic x-rays. Graded crystal elements with an ellipsoidal shape can capture a large solid angle from a small x-ray source and form a micro monochromatic x-ray beam, useful for micro beam analysis, e.g., monochromatic micro XRF (X-ray Fluorescence), small spot XPS (X-ray Photoelectron Spectroscopy). The paraboloid geometry provides a collimating x-ray beam from a point source. Crystal elements with graded d spacing planes curved to a paraboloid shape can capture significant solid angle and produce a collimating beam from a pont-type laboratory source. Due to the narrow energy bandwidth of the crystal optic, the collimating beam can be highly monochromatic with small divergence, which is required for high-resolution x-ray diffraction. Finally, graded crystal optics with a spherical geometry can be applied to image hard x-rays. The combination of spherical optics, such as Schwarzschild optics, can provide strong demagnification and form a sub-micron x-ray beam based on a laboratory source.
REFERENCES:
patent: 4599741 (1986-07-01), Wittry
patent: 4780899 (1988-10-01), Adema et al.
patent: 4949367 (1990-08-01), Huizing et al.
patent: 5027377 (1991-06-01), Thoe
patent: 5646976 (1997-07-01), Gutman
patent: 5737137 (1998-04-01), Cohen et al.
patent: 5799056 (1998-08-01), Gutman
patent: 5843235 (1998-12-01), Bergman et al.
patent: 6226349 (2001-05-01), Schuster et al.
patent: 0200261 (1989-04-01), None
patent: 0339713 (1989-11-01), None
patent: 02160517 (1990-06-01), None
Sasanuma Y et al., “A point-focusing small-angle x-ray scattering camera using a doubly curved monochromator of W/Si multilayer”, Review of Scientific Instruments, vol. 67, No. 3, Mar. 1, 1996, 1996 American Institute of Physics, pp. 688-692.
Nakajima K et al., “Growth of Ge-rich SixGe1-x single crystal with uniform composition (x=0.02) on a compositionally graded crystal for use as GaAs solar cells”, Journal of Crystal Growth, vol. 205, No. 3, Sep. 1999, 1999 North-Holland Publishing Co., pp. 270-276.
Z.W. Chen and D.B. Wittry, “Micronanalysis by Monochromatic Microprobe X-ray Fluorescence—Physical Basis, Properties and Future Prospects”, J. Appl. Phys., 84(2), p.1064 (1998).
J.E. Bijorkholm, J. Bokor, L. Eichner, R.R. Freeman, J. Gregus, T.E. Jewell, W.M. Mansfield, A.A. Mas Dowell, E.L. Raab, W.T. Silfvast, L.H. Szeto, D.M. Tennant, W.K. Waskiewicz, D.L. Windt, and O.R. Wood, and J.H. Bruning, “Reduction imaging at 14 nm using mutlilayer coated optics: Printing of features smaller than 0.1 nm”, p. 1509, (Nov./Dec. 1990).
Robert K. Smither and Patricia B. Fernandes, “Variable-metric diffraction crystals for x-ray optics”, Rev. Sci. instrum. 68(2), pp. 1755-1762, (1991).
Z.W. Chen and D.B. Wittry, “Microprobe x-ray fluorescence with the use of point-focusing difffractors”, Appl. Phys. Lett. 71 (13), Sep. 29, 1997, 1997 American Institute of Physics, pp. 1884-1886.
Z.W. Chen and D.B. Wittry, “Microanalysis by monochromatic microprobe x-ray fluorescence-physical basis, properties, and future prospects”, Journal of Applied Physics, vol. 84, No. 2, Jul. 15, 1998, 1998 American Institute of Physics, pp. 1064-1073.
Porta David P.
X-Ray Optical Systems, Inc.
LandOfFree
Doubly curved optical device with graded atomic planes does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Doubly curved optical device with graded atomic planes, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Doubly curved optical device with graded atomic planes will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2574055