Abstract:
An x-ray focusing device and method for adjustably focusing x-rays in two orthogonal directions simultaneously. The device and method can be operated remotely using two pairs of orthogonal benders mounted on a rigid, open frame such that x-rays may pass through the opening in the frame. The added x-ray flux allows significantly higher brightness from the same x-ray source.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/381,639, filed on Sep. 10, 2010, the specification of which is incorporated by reference herein in their entirety for all purposes. 
    
    
     STATEMENT OF GOVERNMENT RIGHTS 
     This invention was made with Government support under contract number DE-AC02-98CH10886, awarded by the U.S. Department of Energy. The Government has certain rights in the invention. 
    
    
     BACKGROUND 
     The present device generally provides focusing of divergent high-energy x-rays while maintaining good energy resolution, and more particularly relates to a device and method for bending a monochromator crystal with respect to two orthogonal axes to provide both horizontal and vertical focusing of an x-ray beam. 
     An x-ray produced at a light source will spread out or diverge as it travels from the light source. X-rays produced by a beamline with a 5 milliradian divergence, for example, will spread to 5 millimeters (mm) by the time they are 1 meter away from their source, and to 50 mm when 10 meters away. This is a problem for light source scientists, who want the highest possible x-ray flux on a small spot. 
     Previous technologies for x-ray focusing relied on mirror-like surface reflections to focus x-rays. These technologies demonstrated that x-rays can be focused by bending a Bragg crystal. This approach was the first which enabled the use of a synchrotron x-ray beam having a large horizontal divergence. In the years since, the technology has improved to minimize the anticlastic bending which degrades performance of this class of focusing monochromator, but such technologies still required large active surfaces as the x-ray energy increases and/or the grazing incident angle decreases. This requirement causes technical difficulties in error control and there are theoretical limitations on the divergence of the x-rays that can be focused. Moreover, serious theoretical and practical limitations remain, limiting such technologies to low x-ray energies and small x-ray divergence. 
     For X-rays with energies above 30 keV, the Bragg angle is small and it is difficult to implement traditional bending of the crystal. Because of the decreased Bragg angle, the beam&#39;s footprint on the crystal increases. Large crystals, of length approximately 100 mm, must be used, making the control of anticlastic bending difficult, if not impossible. For example, focusing of X-rays from 40 to 60 keV has been recently achieved by combining specialized bender, high-precision cutting of hinged crystals and higher index diffraction to increase the Bragg angle. Also, at high x-ray energies, the energy bandwidth of the monochromatic beam created is dominated by the vertical opening angle of the beam, which is of the order of a few tenths of a milliradian. The resulting energy resolution may be unacceptable for some applications. Finally, the bending radius required becomes extremely small at high x-ray energies, requiring extremely thin crystals, which is impractical for such long crystals. 
     The recent availability of powerful, third-generation high-energy synchrotron radiation sources, such as the APS in the United States, the ESRF in France, and Spring-8 in Japan, and the availability of superconducting wigglers have pushed the spectrum of x-rays to much higher energies than imaginable two decades ago. Thus, practical methods were needed to focus diverging high-energy x-rays so that these facilities would not be limited to using either lower energy x-rays or a tiny part of the large horizontal fan beam. 
     Commonly owned U.S. Pat. No. 7,508,912 to Zhong et al., the specification of which is incorporated herein by reference in its entirety for all purposes, discloses an x-ray focusing device utilizing a set of Laue crystals, named for German physicist Max von Laue, to diffract an x-ray beam, as opposed to reflecting the beam. Specifically, the invention described therein uses the lattice planes inside such crystals to monochromatize and focus the x-rays, thus allowing them to be almost perpendicular to the surface of the crystal. The transmission geometry renders the beam&#39;s illumination length small, reducing the control of the crystal&#39;s figure-error from a two-dimensional problem to a one-dimensional one. This new concept takes advantage of the fact that high-energy x-rays have enough penetrating power to go through the thickness of the Laue crystal. 
     As a result, the Laue geometry of the crystals provides advantageous anticlastic bending with reduced cost and ease of operation. Moreover, simple linear translation capabilities of the device disclosed in the &#39;912 patent allowed for one-motion tuning of x-ray energy. Therefore, in addition to gains of focusing, an order-of-magnitude increase in the monochromatic intensity could be achieved while providing better energy resolution, compared to existing prior art Bragg crystals. 
     However, conventional x-ray focusing applications utilizing Laue crystals have thus far involved bending the focusing crystal in only one direction. Specifically, the crystalline structure of silicon (and other materials) selectively allows particular wavelengths of soft x-rays to be deflected at specific angles through the thickness of the crystalline material. Thus, when the crystal is bent laterally, focusing of the soft x-rays results. 
     In typical conventional x-ray focusing applications, monochromator crystals were generally purchased and/or machined flat. Where focusing in two planes (i.e., sagittal focusing) was desired, the crystals were bent laterally either using a four-bar fixture or by attaching fixed supports to two opposing ends of the crystal that would apply bending forces to the crystal through its rigid supports. Good focusing was therefore obtained in one plane, and due to the anticlastic shape that occurs naturally from lateral bending due to Poisson strain, some focusing in the meridional direction resulted. Those photons impacting the crystal from the radiation source that were not adequately focused in the meridional direction therefore made no contribution to the delivered photon brightness and were unfortunately discarded. 
     Moreover, while anticlastic curvature in the transverse direction (see “Spatially Resolved Poisson Strain and Anticlastic Curvature Measurements in Si Under Large Deflection Bending” by W. Yang, B. C. Larson, G. E. Ice, J. z. Tischler, J. D. Budai and K.-S. Chung of Oak Ridge National Laboratory, published in the Jun. 2, 2003 issue of Applied Physics Letters) results from inherent transverse shear forces and Poisson strain, this anticlastic curvature only contributes to meridional focusing of X-rays due to Poisson strain. This results in a saddle shaped crystal that inefficiently focuses photons. To date, no specific attempt has been made to control focusing in both the sagittal and meridional directions by changing the bending and therefore the three-dimensional shape of the crystal in two axes simultaneously. 
     Accordingly, it would be desirable to provide an x-ray focusing device and a method for bending at least one crystal in two orthogonal axes, sequentially or simultaneously, to control a monochromator crystal and develop an optimized shape in three dimensions. By focusing in both the sagittal and meridional directions, the bending of the crystal can provide added brightness and photon flux from the same radiation source in comparison with the resultant focusing in the meridional direction that occurs with the natural anticlastic shape from single axis lateral bending due to Poisson strain. Furthermore, since focal distances may be different for each application, the ability to fine-tune the focal length as needed for specific applications allows this invention to be used in many different applications. 
     SUMMARY 
     An x-ray focusing device generally includes a frame, at least one clamping mechanism supported on the frame, a crystal for focusing x-rays held by the clamping mechanism, at least one first bending mechanism supported on the frame and at least one second bending mechanism supported on the frame. The first bending mechanism is engaged with the crystal for bending the crystal with respect to a first axis and the second bending mechanism is engaged with the crystal for bending the crystal with respect to a second axis, wherein the second axis is preferably orthogonal to the first axis. 
     In a preferred embodiment, the device includes two first bending mechanisms disposed on opposite lateral sides of the frame and two second bending mechanisms disposed on opposite longitudinal sides of the frame, wherein the first bending mechanisms are orthogonal to the second bending mechanisms. In this case, the device preferably includes four clamping mechanisms, wherein each of the clamping mechanisms is disposed between a first bending mechanism and a second bending mechanism. Also, the frame preferably has a generally rectangular planar shape and defines an opening in a center thereof, wherein the crystal is held by the clamping mechanism in the opening of the frame. Additional attachments (not shown) to the clamping mechanisms and/or, the silicon crystal may be used in alternative embodiments to provide cooling to the Laue crystal if needed. 
     The clamping mechanism preferably includes an upper clamp member, a lower clamp member attached to the upper clamp member, a fastener attached to the frame and engaged with one of the upper and lower clamp members and a spherical bearing disposed between the fastener and one of the upper and lower clamp members. The crystal is held between the upper and lower clamp members and the spherical bearing permits angular and rotational movement of the upper and lower clamp members with respect to the frame. 
     Each of the first and second bending mechanisms preferably includes an upper jaw member, a lower jaw member attached to the upper jaw member and a drive mechanism attached to the frame and one of the upper and lower jaw members. The crystal is disposed between the upper and lower jaw members and the drive mechanism translates the upper and lower jaw members in a direction perpendicular to the frame, thereby bending the crystal. In this case, each of the upper and lower jaw members preferably includes a crystal contact surface having a convex curvature for engagement with the crystal, wherein the crystal is disposed between the convex crystal contact surface of the upper and lower jaw members. 
     In a preferred embodiment, the drive mechanism for the bending mechanism includes a reversible motor attached to the frame, a rotatable drive member driven by the motor and a bearing provided in one of the upper and lower jaw members. The bearing engages the rotatable drive member such that the upper and lower jaw members are linearly translated along the axis of the drive member upon rotation of the drive, member. In this embodiment, the motor is preferably a piezo-electric translator. 
     In an alternative embodiment, the drive mechanism for the bending mechanism includes a threaded set screw rotatably coupled to the frame and a threaded bearing provided in one of the upper and lower jaw members. The threaded bearing threadably engages the rotatable threaded set screw such that the upper and lower jaw members are linearly translated along the axis of the threaded set screw upon rotation of the threaded set screw. This alternative embodiment provides the option for manually translating the bending mechanism. 
     A method for focusing an x-ray beam generally includes the steps of directing an x-ray beam through a crystal and bending the crystal with respect to two axes to focus the x-ray beam in two directions, wherein the two axes are preferably orthogonal to each other. 
     In a preferred embodiment, the step of bending the crystal includes the steps of clamping the crystal within a frame with at least one clamping mechanism, bending the crystal about a first axis with at least one first bending mechanism supported on the frame and bending the crystal about a second axis with at least one second bending mechanism supported on the frame. Preferably, the crystal is bent by two first bending mechanisms disposed on opposite lateral sides of the frame and two second bending mechanisms disposed on opposite longitudinal sides of the frame, wherein the first bending mechanisms are orthogonal to the second bending mechanisms. Also, the crystal is preferably clamped by four clamping mechanisms, wherein each of the clamping mechanisms is disposed between a first bending mechanism and a second bending mechanism. 
     The preferred embodiments of the x-ray focusing device, as well as other objects, features and advantages, will be apparent from the following detailed description, which is to be read in conjunction with the accompanying drawings. The scope will be pointed out in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a real-space diagram showing two parallel incident x-ray beams being monochromatized and sagittally focused at a focal distance of F. 
         FIG. 2  is a reciprocal-space diagram of  FIG. 1  showing the precession of the diffraction vectors H 1  and H 2  around the axis of sagittal bending, and the resulting angle α between wave vectors k 1  and k 2  of the diffracted beams. 
         FIG. 3  is a side view of a single sagittally bent Laue crystal focusing a diverging horizontal fan-shaped beam. 
         FIG. 4  is a top view of the Laue crystal shown in  FIG. 3 . 
         FIG. 5  shows the arrangement of inverse-Cauchois geometry in the meridional plane to take advantage of the anticlastic bending of a sagittally bent asymmetric Laue crystal. 
         FIG. 6  is an enlarged cross-sectional view of the Laue crystal shown in  FIG. 5  showing the x-ray beams being diffracted by the lattice planes of the crystal. 
         FIG. 7  is a top perspective view of the two-axis focusing device. 
         FIG. 8  is a bottom perspective view of the device shown in  FIG. 7 . 
         FIG. 9  is a top plan view of the device shown in  FIG. 7 . 
         FIG. 10  is a cross-sectional view of the device shown in  FIG. 9 , taken along line A-A. 
         FIG. 11  is a cross-sectional view of the device shown in  FIG. 9 , taken along line B-B. 
         FIG. 12  is a cross-sectional view of the device shown in  FIG. 9 , taken along line C-C. 
         FIGS. 12   a ,  12   b  and  12   c  are schematic cross-sections of three variants of the clamping mechanism, with the preferred variant shown in  FIG. 12   c.    
         FIG. 13  is a top perspective view of an alternative embodiment of the two-axis focusing device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In general, the subject device uses sagittally and meridionally bent asymmetric Laue crystals to achieve both horizontal and vertical focusing of x-ray beams. The physics behind sagittal focusing with a sagittally bent asymmetric Laue crystal  12  is shown in  FIGS. 1-7  and explained in detail in Zhong et al., “Sagittal Focusing of High-Energy Synchrotron X-rays with Asymmetric Laue Crystals I: Theoretical Considerations,”  Journal of Applied Crystallography , ISSN 0021-8898, Vol. 34, pp. 504-509 (2001) and Zhong et al., “Sagittal Focusing of High-Energy Synchrotron X-rays with Asymmetric Laue Crystals II: Experimental Studies,”  Journal of Applied Crystallography , ISSN 0021-8898, Vol. 34, pp. 646-653, (2001), both of which are incorporated herein by reference. 
     As explained in these papers, it has been found that sagittally bending an asymmetric Laue crystal creates a focusing device which can be used to advantageously focus a divergent beam of x-rays. As used herein, the term “sagittally bent” means that the crystal is horizontally or vertically bent from an initial flat planar orientation to a curved orientation. The term “asymmetric” refers to a crystal whose lattice planes are not normal to the incident crystal surface. Thus,  FIGS. 1-6  show such a crystal  12  (bent horizontally) diffracting a horizontal x-ray fan beam  14 . Because of the sagittal bending, the diffraction vector H of the crystal  12  along the fan beam  14  precesses around the axis of sagittal bending, thus focusing the diffracted beam  16 . 
       FIGS. 1 and 2  depict the change (in the plane perpendicular to the scattering plane) of the direction of the diffracted x-rays in real and reciprocal space. Two incident x-ray beams are considered and assumed to be parallel, with wave vector k 0 . The first beam strikes the center of the crystal and is diffracted by the diffraction vector H 1  into a direction indicated by k 1 =k 0 +H 1 . The second beam is in the same horizontal plane as the first one, at a distance x from it. At the point where the second X-ray beam meets the crystal, the crystal&#39;s diffraction vector, H 2 , precesses by an angle φ around the axis of sagittal bending. This causes a change, α, of the direction of the diffracted X-rays of the second beam (k 2 =k 0 +H 2 ) with respect to those of the first beam. The change, α, is perpendicular to the diffraction plane for a small φ. 
     The magnitudes of φ and α are related to ΔH=|H 1 −H 2 | and x by
 
Δ H= 2 H  sin χ sin(φ/2)=2 k  sin(α/2)  (1)
 
and
 
x=R s  sin φ,  (2)
 
where H is the magnitude of the diffraction vectors H 1  and H 2 , k is the magnitude of the wave vectors k 0 , k 1  and k 2 , R s  is the radius of the sagittal bending, χ is the asymmetry angle defined as the angle between the crystal surface normal and the Bragg planes used for reflecting the x-rays, and x is the horizontal width of the incident beam.
 
     Using equations (1) and (2), and H−2k sin θ B , the sagittal focal length F s =x/α is calculated:
 
 F   s   =±R   s /2 sin θ B  sin χ,  (3)
 
     where θ B  is the Bragg angle of reflection. The upper sign is used (F s  is positive) if the diffraction vector is on the same side of the crystal as the center of the sagittal bending, i.e., the diffraction vector is on the concave side of the sagittally bent crystal, thereby focusing the x-rays. The situations shown in  FIGS. 1-4  correspond to this case. F s  is negative (lower sign) if the diffraction vector is on the convex side of the crystal, causing further divergence of the horizontal x-rays. 
     Equation (3) can be compared with that of the focal length of a sagittally focusing symmetric Bragg crystal, F Bragg =R s /(2 sin θ B ). The focal length of a sagittal Laue crystal is a factor of 1/sin χ longer (typically a factor of 1.5 to 2) than that of a Bragg crystal bent to the same radius. 
     Equation (3) shows that the sagittal focal length is infinity when the asymmetry angle is zero. Thus, a symmetrical Laue crystal does not have any sagittal focusing effect. This can be easily understood by considering the diffraction vectors H 1  and H 2  in  FIGS. 1 and 2 . The diffraction vectors would all point along the bending axis of the crystal, regardless of their positions, so that there would be no change in the direction of the diffracted x-rays in the sagittal plane. 
     Utilization of a Laue crystal  12  differs from the prior art Bragg reflection crystals in that the x-rays pass through the body of the crystal and are diffracted, rather than being reflected from a surface. At high energies, the incidence angle for the x-rays becomes very small. For the Bragg crystal, this implies a large illuminated crystal area, thereby placing serious constraints on the tolerance of optical figure efforts. In the Laue crystal  12 , the beams are almost perpendicular to the surface, and so the illuminated area is small and essentially unaffected by changes in energy. 
       FIGS. 3-6  show a Laue crystal  12  sagittally focusing a diverging horizontal fan-shaped x-ray beam  14  from a synchrotron x-ray source  18 , wherein F 1  and F 2  are the distances from the source to the crystal and the distance from the crystal to the focal point  20 , respectively. As can be seen in  FIGS. 5 and 6 , the x-ray beam  14  passing through the Laue crystal  12  is reflected by the lattice planes  22  causing the beam to be diffracted, while the curvature of the crystal simultaneously converges the beam. 
     As mentioned above, the present device and method involves bending a Laue crystal in both a sagittal, as well as a meridional direction to provide x-ray focusing in both a horizontal and a vertical direction. Thus, as shown in  FIGS. 7-13 , the two-axis focusing device  10  generally includes a frame  30 , four clamping mechanisms  32  supported on the frame and four bending mechanisms  34  also supported on the frame. In general, a crystal  36  is held within the frame  30  at four locations by the clamping mechanisms  32  and is bent in two axes by the bending mechanisms  34 . 
     Laue crystals (e.g. silicon wafers) used in such monochromator focusing applications are typically provided in a rectangular sheet form. Accordingly, in a preferred embodiment, the frame  30  has a generally rectangular planar shape and defines a generally rectangular opening  38  in the center thereof. The crystal  36  is preferably held in the opening  38  of the frame  30  by the clamping mechanisms  32  at four orthogonal locations. More particularly, the clamping mechanisms  32  are positioned on the corners  40  of the frame to clamp the crystal  36  at its corners along the periphery of the crystal. 
     Referring particularly to  FIG. 12 , each clamping mechanism  32  includes an upper clamp member  42  and a lower clamp member  44  attached to the upper clamp member  42  by at least one fastener  46 . The crystal  36  is held between the upper clamp member  42  and the lower clamp member  44  by tightening the fastener  46 . 
     Preferably, two fasteners  46  are provided for clamping the upper clamp member  42  and the lower clamp member  44  together, as shown more clearly in  FIG. 9 . The two fasteners  46  are preferably spaced apart from each other and are located so as to enable the corner  37  of the crystal  36  to be positioned between the fasteners and held securely by the clamp members  42 ,  44 . Clearance cut-outs  47  are preferably formed in the frame  30  to provide access to the fasteners with a suitable tool from beneath the frame, as shown in  FIG. 12 . 
     At least one of the clamp members  42 ,  44  is attached to the frame  30  by a fastener. In the preferred embodiment shown in the drawings, the upper clamp member  42  is attached to the frame via a threaded shoulder bolt  48  received within a threaded hole  50  provided on the frame  30 . A spacer  52  is preferably provided around the shoulder bolt  48  between the frame  30  and the upper clamp member  42  to space the clamping members  42 ,  44 , and hence the crystal  36 , a desired distance from the frame  30 . 
     The strength or force to grip the crystal  36  needs to be sufficient to counteract the pulling forces created when the crystal is bent. Therefore, the clamping mechanisms  32  grip the monochromator crystal  36  in a way that allows the crystal to deform without breaking it. To achieve this, in a preferred embodiment, a spherical bearing  54  is provided between the shoulder bolt  48  and the upper clamping member  42 . The spherical bearing  54  includes a spherical member  54   a  having a through-hole to receive the shoulder bolt in close fitting relationship. The spherical member  54   a  is pivotably retained within a bushing  54   b , which is secured in the upper jaw member  42 . Thus, the spherical bearing permits angular and rotational movement of the upper and lower clamping members  42 ,  44  so as to allow a full range of bending of the crystal  36  without breaking the corners of the crystal. 
     To further prevent damage to the crystal  36  during bending, the components of the clamping mechanisms  32  are arranged in a manner to minimize strain to the crystal. In particular,  FIG. 12   a  shows an arrangement wherein the upper and lower clamping members  42 ,  44  are reversed with respect to the frame  30 , as compared with  FIG. 12 . In this case, the upper and lower clamp members define a clamping gap  43  for receiving and retaining the crystal  36 , which is spaced in a “positive” direction with respect to the frame  30  and the center  55  of the spherical bearing  54 . Thus, a positive offset of the crystal  36  is formed. Assuming that the clamping members do not allow the crystal  36  to slip, it can be appreciated that the arrangement of  FIG. 12   a , in which a positive offset is formed, will result in the crystal being pulled in tension as the crystal deflects upon bending. Even if the clamping gap  43  is aligned with the center  55  of the bearing, thereby creating a neutral offset of the crystal  36 , there will still be a tendency to strain the crystal upon bending. 
     However, by orienting the upper and lower clamping members in a manner in which the clamping gap  43  is positioned between the frame  30  and the center  55 , thereby creating a “negative” offset, the strain on the crystal during bending is significantly reduced. Specifically, by providing a negative offset for the clamping gap  43 , the crystal  36  will allow the clamping mechanisms  32 , as a whole, to move slightly toward each other as bending occurs, thereby reducing the tendency to strain the crystal. Thus, the present device sets the distance of the negative offset to allow this compensating motion to occur. 
     As mentioned above, bending of the crystal  36  in two axes is accomplished by the bending mechanisms  34 . Returning to  FIGS. 7-11 , the bending mechanisms  34  are supported on the same side of the frame  30  as the clamping mechanisms  34  and are disposed at four orthogonal locations between the clamping mechanisms  32  to engage the peripheral sides of the crystal  36 . Preferably, the bending mechanisms  32  are positioned on the frame  30  so as to engage the crystal at the approximate mid-point of each side of the rectangular crystal. 
     Like the clamping mechanisms  32 , each bending mechanism  34  includes an upper jaw member  56  attached to a lower jaw member  58  via fasteners  60  for retaining the crystal  36  there between, as shown in  FIG. 10 . In this case, however, since the bending mechanisms  34  hold the lateral edges of the crystal  36 , the axes of the fasteners  60  must be oriented parallel to the crystal so as not to interfere with the crystal: Again, two fasteners  60  are preferably provided for securing the upper jaw member  56  and the lower jaw member  58  together, with the edge of the crystal  36  being disposed between the upper and lower jaw members. The upper and lower jaw members  56 ,  58  are preferably made from beryllium copper to better transfer heat. 
     As will be described in further detail below, the upper jaw member  56  and the lower jaw member  58  are, together, movable in a direction perpendicular to the plane of the frame  30  to bend the crystal with respect to two axes. The direction of movement of the jaw members  56 ,  58  is indicated by the arrow  62  shown in  FIGS. 10 ,  11  and  12   c.    
     To prevent the jaw members  56 ,  58  from damaging the crystal  36  during bending, the upper jaw member  56  and the lower jaw member  58  are preferably provided with respective convex contact surfaces  64 ,  66 . As more specifically shown in  FIG. 10   a , and in an exaggerated form in  FIG. 12   c , the contact surface  64  of the upper jaw member  56  preferably has a radius of curvature  68  of about 1 meter and the contact surface  66  of the lower jaw member  58  preferably has an opposite radius of curvature  69  of about 1 meter. It has been found that a radius of curvature of about 1 meter generally matches the maximum amount of bending of the crystal  36 . Such opposite convex contact surfaces  64 ,  66  eliminates sharp corners on the jaw members  56 ,  58 , which could damage the crystal upon bending. 
     The jaw members  56 ,  58  can be made from any durable material that is vacuum compatible and capable of transferring heat. The jaw members  56 ,  58  can be made from an elastic material, in which case the convex contact surfaces  64 ,  66  may no longer be needed so that the jaw members can take any desired shape. 
     As mentioned above, the jaw members  56 ,  58  are linearly translatable with respect to the frame  30  in a direction perpendicular to the plane of the frame. Thus, as shown in the drawings, when the jaw members  56 ,  58  are linearly translated in a direction away from the frame, the convex contact surface  66  of the lower jaw member  58  engages the bottom surface of the crystal  36  to bend the crystal outwardly with respect to the frame  30 . Conversely, when the jaw members  56 ,  58  are linearly translated in a direction toward the frame, the convex contact surface  64  of the upper jaw member  56  engages the top surface of the crystal  36  to bend the crystal inwardly with respect to the frame  30 . 
     Such linear translation is preferably accomplished with piezo-electric translators  70 , although other drive devices, such as stepper or servo motors, can be utilized. In particular, each bending mechanism  34  preferably includes a piezo-electric translator  70  for driving the upper and lower jaw members  56 ,  58 . The piezo-electric translator  70  is preferably attached to the bottom side  72  of the frame  30  opposite the upper and lower jaw members  56 ,  58 . The piezo-electric translator  70  is provided with a drive member, in the form of a threaded lead screw  74 , which extends through the frame for engagement with the upper jaw member  56 . In this regard, the frame  30  is preferably provided with a bearing  76  for rotatably supporting the lead screw  74  of the piezo-electric translator  70 . 
     The upper jaw member  56  is preferably provided with a threaded bearing  78 , which engages the threaded lead screw  74  such that rotation of the lead screw will translate the upper jaw member  56  in a linear direction along the axis of the lead screw. To ensure precise linear movement, two guide pins  80  are preferably press-fit into the frame  30  and are received in the upper jaw member in close sliding relationship. 
     As can be appreciated, activation of the piezo-electric translator  70  will rotate the threaded lead screw  74 . Since the lead screw  74  is threadably engaged with the threaded bearing  78  of the upper jaw member  56 , rotation of the lead screw  74  will cause the upper jaw member  56  to translate in a direction perpendicular to the plane of the frame  30 . With the crystal  36  securely held between the upper jaw member  56  and the lower jaw member  58 , while at the same time being fixed to the clamping mechanisms  32  at its corners, linear translation of the upper jaw member  56  will cause the crystal to bend. 
       FIG. 13  shows an alternative embodiment of the device  10   a  wherein the piezo-electric translators  70  have been replaced with threaded set screws  82 , which are rotated manually for linearly translating the upper jaw member. In this case, the set screws  82  are rotatably attached to the frame  30  via a bearing  84  and the set screws  82  can be rotated by hand with a suitable tool to linearly translate the upper jaw member, in either direction orthogonal to the face of the undeformed crystal  36 . 
     In both embodiments, three-dimensional deformation of the crystal  36  occurs when the linear translators  70 ,  82  move the upper and lower jaw members  56 ,  58  toward or away from the frame  30 . The crystal  36  can be thus deformed in two orthogonal axes. In a preferred embodiment, opposite pairs of upper and lower jaw members  56 ,  58  are moved simultaneously to more accurately define the desired saddle shape of the bent crystal where the radius along one dimension is smaller than the radius along the other dimension. 
     The two-axis focusing device  10 ,  10   a  will generally be used within a larger assembly that may also include a vacuum vessel and kinematic mounts or supports to allow the monochromator crystal  36  to be translated and/or rotated as needed to assure that the crystal is located at the appropriate position and orientated within the monochromator so that it can focus photons at the appropriate location. Since the device  10 ,  10   a  will typically reside inside a vacuum vessel, a means of activating and controlling the linear and/or rotary actuators  70 ,  82  will be needed to control the linear motion for each translation means so that the crystal  36  deforms in a controlled manner. 
     It would also be desirable to provide a means for transferring heat away from the focusing device  10 ,  10   a  when supported within such a vacuum vessel. A means for transferring heat through radiation may involve the positioning of one or more heat sinks within the vacuum vessel adjacent the focusing device  10 ,  10   a  to absorb head radiated from the device. 
     A means for transferring heat by conduction may involve the provision of one or more heat conducting elements in direct contact with the device  10 ,  10   a . For example, copper braids can be mechanically attached to heat dissipating members  85  provided on the frame  30  of the device. The opposite ends of such copper braids, in turn, can be mechanically attached to structural heat-sink elements of the vacuum vessel in order to transfer heat from the frame by conduction. Conventional water cooling lines can also be utilized to transfer heat by conduction. 
     It is also conceivable that a plurality of the two-axis focusing devices  10 ,  10   a  could be used in combination. For example, monochromators may utilize more than one crystal and may contain other devices in any combination such as one or more filters, beamstops, mirrors, apertures, collimators according to the needs of the specific application. All of these additional devices have specific purposes to assist and/or provide collimated, directed photons of the particular wavelengths needed for the individual scientific or industrial application. The core component (or components) that produce(s) monochromatic photons is/are the monochromator crystal(s). At least one monochromator crystal is needed in each monochromator. Therefore, a variant could include one or more additional crystals and/or mirrors, and any combination of the other devices indicated above. 
     The efficiency of the monochromator is largely determined by the amount of transmission and focusing that the monochromator can provide, that is, useful output energy/input energy. The device and method described herein provides high efficiency at low cost for hard x-rays. 
     The two-axis focusing device  10 ,  10   a  provides the ability to control bending of a crystal in two orthogonal axes. As a result, an additional benefit of at least one order of magnitude is achieved when meridional focusing and sagittal focusing is optimized for a specific monochromator application. The development of two-axis bending therefore inexpensively adds significant additional photon, flux and brightness from the same radiation source. This therefore involves both the method of controlling a monochromator crystal to develop an optimized shape in three dimensions, as well as the implementation of how to do so accurately and cost effectively. 
     Previously, two axis bending was not used for monochromator crystals. Thus, photons from an expensive radiation source that could be focused appropriately, and those that could not be adequately focused in the meridional direction were not used. The proposed device and method therefore provides added brightness from the same radiation source. 
     Although preferred embodiments of the present device and method have been described herein with reference to the accompanying drawings, it is to be understood that the herein device and method are not limited to those precise embodiments and that various other changes and modifications may be affected herein by one skilled in the art without departing from the scope or spirit of the invention, and that it is intended to claim all such changes and modifications that fall within the scope of the invention.