Patent Number: 06041099&
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a diagrammatic view of a traditional sequentially ordered Kirkpatrick-Baez mirror system. This sequentially ordered mirror system may focus or collimate an x-ray beam in two dimensions by reflecting a divergent x-ray beam along two directions independently. The mirrors 12a and 12b are arranged in consecutive order and may be configured with a parabolic or elliptical surface. With a point source 10, this sequential order system equipped with two parabolic mirrors will provide a parallel beam. With a finite source, this parabolic mirror system will provide a beam with different divergences in two directions. When elliptical mirrors are substituted for parabolic mirrors the sequentially ordered system will provide a focused beam and give a perfect real point image with a point source at its focal point. For a field object, the image will be magnified or demagnified by the system. The magnification will vary with the distances separating the mirrors and the object. There are several limitations which greatly affect the performance of the sequential order Kirkpatrick-Baez system. There is no way to install both mirrors at the most optimized positions, which results in less flux and a larger aberration. Consider a figure deviation from the ideal curvature .DELTA..alpha. of the reflective surface, the deviation of the ray from the theoretical position at the image plan will be equal to 2.DELTA..vertline., where .vertline. is the distance between incident point and image plane. For a sequential system, the figure error on the mirror nearer to the object results in a larger deviation. When the mirrors are located at different distances from the detector, if both mirrors have the same angular deviation, the aberration from the mirror closest to the source will be larger. A sequential order Kirkpatrick-Baez system will have varied amplification because the mirrors are placed at different positions with relation to field object distance. Lastly, the alignment hardware for a sequential order Kirkpatrick-Baez mirror is bulky and complicated and the alignment procedures are difficult and time consuming since the adjustments include alignments relative to the beam and the alignments relative to both mirrors. A side-by-side Kirkpatrick-Baez system provides a solution to the problems associated with a sequential system as well as providing other advantages. In FIG. 2 a side-by-side system is shown generally as 16. The reflecting surfaces 18a and 18b are mounted adjacent at a 90 degree angle. The side-by-side system has no distance offset between reflecting surfaces as does the sequential order system, reducing potential aberration problems. FIGS. 3a-3b are diagrammatic views of a side-by-side Kirkpatrick-Baez mirror system illustrating a first working zone 20a and second working zone 20b upon the mirror surfaces. The working zones 20a and 20b are located upon and adjacent to the corner formed by the coupling of the reflective surfaces 18a and 18b. FIG. 4 is a more detailed diagrammatic view of a side-by-side Kirkpatrick-Baez system illustrating incident and reflected x-ray beam paths. Individual x-ray beams 26a and 26b are radiated from x-ray source 10 and may first be examined at the cross section 22 of the x-ray beam. The cross section 22 of the beam illustrates the many divergent directions of the x-ray beams exiting the x-ray source 10. Individual x-ray beam 26a is incident upon working zone 20a which lies generally upon the junction of reflective surfaces 18a and 18b. Individual x-ray beam 26b is also incident upon working zone 20a. The beams 26a and 26b are reflected by working zone 20a and redirected to working zone 20b which also lies generally upon the junction of reflective surfaces 18a and 18b opposite and partially overlapping working zone 20a as shown in FIG. 3a and 3b. The beams 26a and 26b then exit the system 16 and may be in divergent, collimated or focused form depending upon the shapes of the reflective surfaces 18a and 18b and the form of the x-ray source. This configuration is generally known as an single corner configuration. Any combination of parabolic or elliptical mirror surfaces for the present invention may be used. For example, one reflecting surface may have an elliptical surface and a second reflecting surface may have a parabolic reflecting surface. The reflective surfaces in the present invention are configured as multi-layer or graded-d multi-layer Bragg x-ray reflective surfaces. Bragg structures only reflect x-ray radiation when Bragg's equation is satisfied: EQU n.lambda.=2d sin (.theta.) where n=the order of reflection .lambda.=wavelength of the incident radiation d=layer-set spacing of a Bragg structure or the lattice spacing of a crystal .theta.=angle of incidence Multi-layer or graded-d multi-layered Bragg mirrors are optics with a fixed focal point which utilize their inherent Bragg structure to reflect narrow band or monochromatic x-ray radiation. The bandwidth of the reflected x-ray radiation can be customized by manipulating the optical and multi-layer parameters. The d-spacing of the multi-layer mirror can be tailored in such a way that the Bragg condition is satisfied at every point on the multi-layer mirror. The d spacing may be changed laterally or depthwise to control the bandpass of the multi-layer mirror. The multi-layer mirror has a large reflection angle resulting in higher collection efficiencies for incident x-rays. These multi-layered mirrors could increase the flux by more than an order with a fine focus x-ray tube, as compared with total reflection mirrors. Multi-layered mirrors, because of their monochromatic output, could also reduce the unwanted characteristic radiation during diffraction analysis by thousands of times. Therefor as seen in FIG. 5 when employing the single corner optic an x-ray aperture assembly 56, an aperture 58 may be placed at the entrance area, exit area or both to eliminate coaxial direct x-rays, single bounce x-rays, or scattered x-rays. The combination of side-by-side Kirkpatrick-Baez scheme and multi-layer or graded-d multi-layer Bragg x-ray reflective surfaces can provide superior optics for many applications requiring directed, focused, or collimated x-rays. FIG. 6 is a diagrammatic drawing showing the alignment method of the present invention. A Kirkpatrick-Baez mirror to work correctly must have a very specific orientation. The present invention utilizes microadjustment hardware to correctly orient a Kirkpatrick-Baez mirror. The alignment of the optic can be achieved with five freedoms of adjustments: two rotations and three translations. The rotating axes for two mirrors should go through the centers of the intersection of the two mirrors, and parallel to the mirrors respectively, as shown in the schematic picture. The two translations, which are perpendicular to the optic, should be parallel to the mirror surfaces respectively, (see the bottom of FIG. 6). These freedoms allow the adjustments of the incident angles and beam positions. It is to be understood that the invention is not limited to the exact construction illustrated and described above, but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.