Patent Number: 063303019
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a diagrammatic view of the optical system 10 of the present invention. An x-ray beam 12 is generated by an x-ray source 14 that is directed towards an optic 16, such as an elliptical mirror, that focuses the x-ray beam 12. The optic 16 has a reflective surface which may be comprised of bent graphite, bent perfect crystal, a total reflection mirror, a mulitlayer Bragg reflector which may be depth or laterally graded, or any other x-ray reflective surface known in the art. The optic 16 directs the x-ray beam through a first slit (or pinhole) 18 and a second slit (or pinhole) 20 to form and define a coherent x-ray beam 21. Scattering and interference patterns or noise created by the first slit 18 are blocked by the second slit 20. The focal point 22 of the x-ray beam 21 is located between the second slit 20 and an x-ray detector 30. A sample chamber 24, containing a sample structure 26 to be analyzed, includes a third slit 28 to eliminate scattering and interference patterns created by the second slit 20. The x-ray beam 21 flux at the sample chamber 24 and the x-ray beam 21 size or incident area on the x-ray detector 30 depend on where the focal point 22 of the optic 16 is located. Flux passing through the second slit 20 and reaching the sample chamber 24 is the greatest when the focal point 22 of the optic 16 is positioned on the second slit 20, and the x-ray beam 21 size on the x-ray detector 30 is also the greatest in this situation. The x-ray beam 21 size on the x-ray detector 30 is the smallest if the focal point 22 of the optic 16 is positioned on or at the x-ray detector 30, therefore the resolution of a system using this focal point 22 position would be the greatest. However, the flux in this case would also be the smallest. Therefore, the position of the focal point 22 in the system is determined by the trade-off between intensity and resolution of x-rays incident on the x-ray detector 30. In certain cases, due to the intrinsic divergence of the x-ray beam 21, the resolution would reach its limit at certain positions of the focal point 22. Accordingly, moving the focal point 22 closer to x-ray detector 30 would not improve the resolution and would only reduce the flux. Thus, in this case, there would be no benefit to focus the x-ray beam 21 on the x-ray detector 30. Since the minimum accessible angle of the system is determined by the slit (pinhole) configuration, it is independent of the position of the focus. The first and second slits 18 and 20 of the optical system 10 determine the size and shape of the x-ray beam 21 and the third slit 28 blocks parasitic scattering. The x-ray beam 21, because of its focused nature, enables maximum flux to be concentrated on the sample structure 26. The x-ray detector 30 is able to detect the diffusion pattern created by the small angle scattering from the sample structure 26 because of the increased flux on the sample structure 26 and the elimination of divergence and scattering. The x-ray detector 30 is further equipped with a beam stopper 32 to prevent direct x-ray beam damage to the x-ray detector 30 and noise. The exact location of the focal point 22 between the second slit 20 and the x-ray detector 30 depends on the desired flux and resolution characteristics of the optical system 10. The optical system 10 of the present invention is preferably enclosed in a vacuum path or pre-flight beam pipe 27 to eliminate scattering and absorption caused by atmospheric gases and particles. The pre-flight beam pipe 27 is comprised of a number of individual pipes which may be mixed and matched to optimize and change the length of the system. The slits 18, 20, and 28 in the preferred embodiment, are formed as pinholes that are precision machined as round holes. Rounded pinholes create significant difficulty in alignment, especially when the sizes of the pinholes are small and multiple pinholes are used. The present invention includes a pinhole plate 34 having an alignment window 36 equipped with a triangle shaped nose 38 offset and aligned with a pinhole 40. During alignment of an x-ray beam, the x-ray beam is adjusted to enter and exit the alignment window 36. An x-ray detector is used as feedback to ensure that the x-ray beam is passing through the alignment window 36. The pinhole plate 34 is then moved manually or automatically in a vertical and horizontal fashion in the direction of the pinhole 40. If the x-ray detector does not detect the x-ray beam during an indexing of the alignment window 36 relative to the x-ray beam, the pinhole plate 34 will be moved to its last position and indexed in the opposite vertical or possibly horizontal direction. In this manner, the x-ray beam position is always known and the x-ray beam may be traversed to the vertex 37 of the triangle 38. The x-ray beam follows, in relative fashion, the cutout of the alignment window 36 until it reaches the vertex 37 of the triangle 38. At the vertex 37 of the triangle 38, movement will block or reduce the flux of the beam in both vertical directions and horizontal movement in the direction of the pinhole 40 will also block or reduce the beam. Accordingly, when such a condition is reached it is known that the beam is at the vertex 37 of the triangle 38. The pinhole 40 is a known fixed distance from the vertex 37 of the triangle 38. Thus, when the x-ray beam is found to be at the vertex 37 of the triangle 38, the pinhole plate 34 or x-ray beam may be precisely indexed this known distance to the pinhole 40, ensuring precise alignment of the pinhole 40 and the x-ray beam. Accordingly, the position of the x-ray beam will be known. In a first embodiment, the pinhole plate 34 is manually moved relative to the x-ray beam 21 using a precision x-ray table. The operator will read the x-ray detector 30 output and move the pinhole plate 34 accordingly. In alternate embodiments the operator will move the x-ray beam relative to the pinhole plate 34. In a second embodiment of the present invention, the pinhole plate 34 is moved using an automated servomotor or linear actuator system. The detector 30 feedback is transmitted to a computer which controls the x-y indexing of the x-ray beam or pinhole plate 34. In response to feedback from the detector 30, the computer will give the actuator system position commands to properly align the x-ray beam 21 and the pinhole plate 34. Referring to FIG. 3, an alternate embodiment of the pinhole plate 34' of the present invention is shown. The pinhole plate 34', as in the first embodiment 34, includes an alignment window 36' equipped with a triangle shaped nose 38' having a vertex 37'. A rotating aperture plate 42, having multiple apertures 44, rotates about a point 46 in the directions of arrow 48. The rotating aperture plate 42 allows multiple apertures 44 having various aperture diameters to be used in the present invention. Each aperture 44 may be indexed or rotated about point 46 to a position with a known offset from the vertex 37' of the triangle shaped nose 38'. The center of each aperture 44 in the rotating aperture plate 42 is the same radial distance from the point 46, allowing each aperture 44 to be correctly offset from the vertex 37' of the triangle shaped nose 38'. A rotary position feedback device such as an encoder or a manual latch may be used to precisely position the apertures 44 with respect to the vertex 37' of the triangle shaped nose 38'. 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.