Abstract:
An x-ray optical assembly for increasing the intensity of a formed x-ray beam. The optical assembly includes a capillary type optical device and an x-ray reflective mirror device configured and aligned to provide a desirable x-ray crystallography beam. An x-ray beam from an x-ray source enters the individual capillaries of the capillary optical device, where the exit beam intensity is increased. The beam exits the capillary optical device at a particular convergent or divergent angle, and is directed into the mirror device. The mirror device either focuses or collimates the beam to have a small convergent or divergent angle suitable for the sample being analyzed. The mirror device can be any suitable device known in the art, such as a grazing incidence flat mirror device, a grazing incidence bent mirror device, a grazing incidence shaped mirror device or a graded multilayer mirror device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This Application claims priority of U.S. Provisional Application No. 60/194,220, titled Optical Assembly for an X-ray Diffraction Crystallography System, filed Apr. 3, 2000. 
     
    
     GOVERNMENT RIGHTS  
       [0002] The Government may have certain rights in this invention pursuant to grant no. NAGW-813, entitled “Center for Macromolecular Crystallography, Center for the Commercial Development of Space” issued by NASA. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    This invention relates generally to an optical assembly suitable for increasing the intensity of a formed x-ray beam and, more particularly, to an optical assembly suitable for increasing the intensity of a formed beam that includes a combination of a capillary type optical device and an x-ray reflective mirror device, and has particular application for x-ray diffraction of crystals.  
           [0005]    2. Discussion of the Related Art  
           [0006]    X-ray diffraction crystallography is a well known technique for determining the structure of crystal molecules. In x-ray crystallography, an x-ray beam is directed towards a sample to be analyzed, and x-rays diffracted by and reflected from the sample are detected by a suitable detection array, such as a CCD array. The location of the reflected x-rays on the detector array are used to determine the structure of the crystal molecules.  
           [0007]    In x-ray crystallography, it is desirable that the dimensions of the x-ray beam impinging the sample be on the order of the sample size, or on the order of a location on the sample that is being examined. Additionally, the intensity of the x-ray beam should be as consistent as possible across the sample. Also, it is desirable that the intensity of the x-ray beam be high enough so that the detection time of the sample be reasonable. For single crystal diffraction of protein crystals, an x-ray beam is required which has the following critical features: (1) monochromaticity (typically at the copper K-alpha wavelength, 1.5418 Angstroms); (2) low angular divergence or convergence (less than 1.0 milliradian full cone angle); and (3) high peak flux level (x-ray photons per square millimeter per second).  
           [0008]    A known instrument which provides an x-ray beam satisfying all the above requirements is the synchroton. However, synchrotons are not available to most crystallographers. Laboratory-type diffraction systems are therefore necessary. Current laboratory systems satisfy the monochromaticity requirement, but provide beams with only marginal angular divergence or convergence and beam flux levels much less than synchrotron x-ray beams. A basic limitation to both beam collimation (i.e., angular divergency or convergency) and flux level are the x-ray beam forming optical assemblies that are available for laboratory diffraction systems.  
           [0009]    The known art of x-ray beam forming optics suitable for diffraction crystallography includes various types of optical devices. These optical devices gather x-ray photons from an x-ray source (typically a rotating anode source or an electron tube source), form the x-ray beam, and direct the beam onto the crystal target or sample. An x-ray source typically generates a very large number of x-rays, but the optical device can collect only a small percentage of those x-rays because of geometrical limits imposed by the beam forming optics. In general, the overall performance of the x-ray generating sub-system in a laboratory-type x-ray diffraction system is limited by (1) the geometrical limitation of available x-rays from the source that the optical device is capable of accepting, (2) the x-ray transmission efficiency of the optical device, (3) the capability of the optical device to suitably collimate the beam, and (4) transmission losses in a monochromator device necessary in the optical path between the x-ray source and the target crystal. The principal efforts in the prior art have been directed to improving the fraction of x-rays accepted, the transmission efficiency, and the beam collimation capability of the optical device.  
           [0010]    At present, the x-ray generating sub-systems provide x-ray beams with usable flux in the range of 10 8  to 10 9  x-ray photons per square millimeter per second at the target crystal location. A major advantage of providing an increase in beam flux is a decrease of the same magnitude in the time required to acquire a complete diffraction data set for a single crystal. This is very important from an equipment utilization standpoint because protein crystals are labile, and thus will decay with time unless cryogenically frozen.  
                                     TABLE 1                           Advanced Optics Comparison                        Beam Collimation or           Optics Type   X-Ray Collection Factor   Beam Steering Capability   Focusing   Monochromator               Pinhole collimator   1.0 - basis for comparison   None   Collimation only   No       Grazing incidence mirrors   ˜3   ≈0.5 deg   No   No       Flat       ≈1.0 deg   Yes (limited)   No       Bent       Shaped grazing incidence   &gt;150   No   Both   No       mirrors       Graded multilayer mirrors   ˜100   No   Both   Yes       Capillary (Kumakov) optics   ˜1000**   Yes (few deg)   Both, but crude   No                   (≈0.5° divergence)       Combination of Capillary and   ˜1000   Yes (few deg)   Both   No       Shaped Grazing Incidence                          
 
           [0011]    FIGS.  1 - 7  show several types of x-ray optical devices known in the art for x-ray crystallography, and Table 1 below summarizes key characteristics of each type. Other types of x-ray optics exist, but those shown here illustrate the basic principles and permit valid comparisons.  
           [0012]    [0012]FIG. 1 is a plan view of a pinhole collimator  10  that can provide the x-ray optics for a diffraction crystallography system. An x-ray source  12  emits an x-ray beam  14  that is received by an entrance pupil  16  defining the pinhole of the collimator  10 . The beam  14  propagates through the collimator  10  and exits through an exit pupil  18 . The collimator  10  is typically a metal structure having suitable dimensions for crystallography.  
           [0013]    The pinhole collimator  10  has been used widely in diffraction systems to collimate an x-ray beam, and is the standard of comparison for other types of x-ray optics. The entrance pupil  16  accepts a portion of the solid angle of x-ray emittance from the source  12 . The diameter of the exit pupil  18  together with the distance from the source  12  establishes the beam  14  to have an acceptable size and divergence at the crystal location. A basic limitation of the pinhole collimator  10  is that in order to obtain a small beam with small divergence, the solid angle of acceptance of x-ray emittance from the source  12  is very small. For example, a pinhole collimator which produces a beam of 0.5 mm in diameter with a divergence angle of 1.0 milliradian (.057 degree) has a solid angle of acceptance of 7.85×10 −7  steradians, compared to 12.57 steradians in a full sphere.  
           [0014]    A second type of x-ray optics is shown in FIG. 2, and is referred to as a flat grazing incidence mirror  22 . In this example, an x-ray beam  24  from an x-ray source  26  is incident on a reflective surface  28  of the mirror  22 . The grazing incidence mirror  22  has a critical angle of incidence θ c , such that if the angle of incidence of the x-ray beam  24  is less than the critical angle θ c , the x-ray beam  24  will be reflected from the mirror surface  28  with almost no absorption. If, however, the angle of incidence is greater than θ c , the x-ray beam  24  will be almost totally absorbed by the mirror material. The critical angle of incidence θ c  is a function of the x-ray wavelength and certain properties of the mirror material.  
           [0015]    For copper K-alpha x-rays, the critical angle is on the order of 0.2° for typical mirror materials such as glass. Because this angle is about seven times greater than the cone half-angle of a pinhole collimator, a long planar mirror can collect more x-rays from the source  26  than the pinhole collimator. However, the flat mirror  22  reflects the beam  24  so that it fans out in a direction perpendicular to the plane of FIG. 2. Consequently, an assembly of mirrors must be used to capture and shape the reflected beam. The mirror assembly produces a beam which is more intense than the pinhole collimator, but the multiplication factor is not very large, and the beam emerging from the optics has a divergence which is a large fraction of the critical angle.  
           [0016]    Often, grazing incidence mirrors are bent by mechanical devices into a desirable shape. FIG. 3 is a bent grazing incidence mirror  30  that also can be used as x-ray optics for a crystallography system. In this example, an x-ray beam  32  from a source  34  is reflected from a bent surface  36  of the mirror  30 . Bending the mirror  30  tends to make the angle of incidence θ c  of the x-ray beam  32  constant along the length of the mirror  30 , and this collimates the beam  32  in the plane of the figure. Focusing can also be provided by appropriately bending the mirror  30 . Other mirrors in a concatenated optical chain assembly can collimate or focus the beam  32  in the direction perpendicular to the figure. Sometimes referred to as “double focusing mirrors”, such an assembly captures more x-rays from the source  34  than does a pinhole collimator, but the optical gain relative to the pinhole collimator usually is less than ten.  
           [0017]    X-ray optics for crystallography systems have advanced beyond those optical devices discussed above for FIGS.  1 - 3 . FIG. 4 shows an optical assembly  40  including a mirror  42  having an elliptically shaped surface  44  and a mirror  46  having a parabolic shaped surface  46 . The assembly  40  is intended to represent part of two different x-ray optical assemblies, where the complete mirror  42  or  44  would be completely elliptical or completely parabolic, respectively. An x-ray beam  50  from a source  52  is directed towards both of the surfaces  44  and  48 . In this example, the source  52  is placed at the focal point of the elliptical surface  44  and the parabolic surface  48 . The shape of the elliptical surface  44  causes the x-ray beam  50  to be focused at a focal point  54 . The elliptical shape of the surface  44  is such that the rays of the beam  50  gently converge at the focal point  54 , and are thus suitable for crystallography. The sample being analyzed would be positioned at or near the focal point  54 . For those crystallography applications that benefit from collimated light, the parabolic surface  48  converts the x-ray beam  50  to a collimated beam. Each mirror  42  and  48  operates on the grazing incidence principle. The x-ray beam  50  is incident on the mirror  44  and  46  at any angle less than the critical angle of incidence θ c .  
           [0018]    Shaped grazing incidence mirrors are very efficient at gathering x-rays. Optical gains exceeding 100 (compared to pinhole collimation) have been measured for this technology. Of course, the beam spreads out in a direction perpendicular to the plane of the figure, so that multiple mirrors are required to capture and collimate or focus the full beam.  
           [0019]    Another type of advanced x-ray optics is a graded multilayer mirror  60  shown in FIG. 5. The graded multilayer mirror  60  operates on the principle of Bragg diffraction, rather than grazing incidence. A mirror substrate  62 , typically glass, is layered with alternating high atomic number layers  64  and low atomic number layers  66 . Many such layers are superimposed on the mirror substrate  62 . FIG. 5 is intended only to illustrate the principle of operation of the graded multilayer mirror  0 . An x-ray beam  68  incident on a top surface  70  of the mirror  60  is diffracted from the layers  64  and  66  at the angle θ. The thickness of the layers  64  and  66  is graded as a function of the distance along the mirror  60 , because the incident angle of the x-ray beam  68  from an x-ray source varies with distance along the mirror  60 . If the incident angle varies with distance, then the layer thickness must be varied in order to maintain the Bragg diffraction relationship for a constant wavelength, which is the desired wavelength for critical diffraction. The geometry of the layered mirror  60  is thus tailored to the crystal diffraction wavelength desired.  
           [0020]    There are appreciable absorption losses in the graded multilayer mirror  60 . The net reflectance for such a mirror is typically around 70 percent. Because of the trade-off between reflection and absorption in the layers  64  and  66 , there is an optimum number of layers which maximizes the net reflectance, and for copper K-alpha x-rays, this optimum number has been estimated at between 100 and 200 layers.  
           [0021]    The graded multilayer mirror  60  can be fabricated on shaped mirror substrates similar to those described above for the shaped grazing incidence mirror technology. Consequently, shaped multilayer mirrors can have the same x-ray gathering efficiency as shaped grazing incidence mirrors. However, the net reflectance of graded multilayer mirrors is lower than grazing incidence mirrors because of absorption in the layer structure. Of course, the mirrors are shaped to collimate or focus the x-ray beam.  
           [0022]    Graded multilayer mirrors possess a very significant advantage compared to the other technologies. Because their operation is based on Bragg diffraction, graded multilayer mirrors can function as monochromators as well as x-ray gatherers and beam formers. If graded multilayer mirrors are used, no other monochromator device is needed in the optical chain, and the efficiency loss associated with that monochromator device is avoided. Consequently, the comparison of overall efficiency of the optical chain must take into account and the monochromator loss experienced if grazing incidence mirrors are used. Of course, with either technology the optical chain must use multiple mirrors to form the beam both in the plane of the figure and in the plane perpendicular to the figure, as described previously.  
           [0023]    A third type of advanced x-ray optics is shown in FIGS. 6 and 7. This type of optics is referred to as capillary optics, also known as Kumakhov optics. FIG. 6 shows a single glass capillary  76  which accepts an x-ray beam  78  from a source  80 . The x-ray beam  78  travels down the capillary  76  by multiple reflections from an inside surface of the glass wall. The critical angle of incidence governs the solid angle of acceptance of x-rays from the source  80 , and for glass material, the critical angle θ c  is approximately 0.2 degree at the copper K-alpha wavelength. A simple calculation shows that, compared to a pinhole collimator which produces a beam 0.5 mm in diameter with a total divergence angle of 0.057 degree, the solid angle of acceptance of a 0.5 mm diameter single capillary is fourteen times greater than for the pinhole collimator. However, this optical gain is not completely realized. There are absorption losses as the x-ray beam  78  travels down the capillary  76  because the reflectance is not ideal and the inside surface of the capillary  76  is not perfectly smooth.  
           [0024]    [0024]FIG. 6 illustrates a disadvantage suffered by capillary optics. The divergence angle of the beam  78  exiting the capillary  76  is two times the critical angle of incidence θ c  for the capillary  76 . For glass material and copper K-alpha wavelength, this divergence angle is about 0.4 degree, which is about seven times the required limit of 0.057 degree.  
           [0025]    [0025]FIG. 7 illustrates a polycapillary optical assembly  84  developed and marketed by X-Ray Optical Systems Inc., Albany, N.Y. Such an assembly can contain hundreds, or even thousands, of single capillaries  86 . U.S. Pat. No. 5,570,408 discloses an x-ray optical system formed of a plurality of multiple-channel monolithic capillary optics of the type discussed herein. Because the capillaries  86  are flexible, the capillary assembly  84  can be formed as shown to have a focal point at the x-ray source  88  for the entrance beam  90 , and to focus the exit beam at a second focal point where a sample  92  is positioned. The flexibility of the capillaries  86  will also allow the exit beam to be collimated if desired. The capillary assembly  84  can be shaped by mechanical clamps, and, once shaped, can be fused into a monolithic structure.  
           [0026]    The polycapillary optical assembly has the largest x-ray gathering capability of all types of advanced x-ray optics. This is because the entrance aperture of the device can have many times the area, and hence the solid angle of acceptance, compared to any other device. At the entrance aperture, only a fraction (typically about half of the aperture area can gather x-rays because the glass walls of the capillaries  86  take up that fraction of the aperture area, and absorb the incident x-rays. The remaining fraction of the aperture area is composed of the tubes which accept and transmit x-rays. Within each capillary  86  there is also the transmission loss described above. However, the solid angle of acceptance of the polycapillary optic is enormous compared to all the other technologies, overwhelming the acceptance and transmission losses. In comparison with a pinhole collimator, exit beam optical gains of more than 1000 have been calculated (and substantiated by limited measurements) for the polycapillary optic.  
           [0027]    For an application in x-ray diffraction systems, there are some serious limitations of polycapillary optics which effectively reduce the available optical gain. For example, the exit beam from the capillary assembly  84  has a convergence cone angle of several degrees at the sample location which is not usable for diffraction. To get a total convergence angle on the order of a milliradian requires blocking out most of the beam and using only the central milliradian. If the beam were collimated rather than focused, the diameter of the exit beam from the assembly  84  would be on the order of several millimeters. To obtain a beam with a diameter on the order of a millimeter at the sample location would again require blocking out most of the exit beam. Also, the resulting beam could have an unacceptably large divergence.  
           [0028]    To summarize this discussion, the most important feasibility issue for x-ray crystallography has been to reduce the electrical power consumed by the x-ray source, while maintaining the x-ray beam characteristics (intensity, size, shape and crossfire) at levels at least equivalent to standard laboratory diffraction systems. Using advanced x-ray optics resolves this feasibility issue. An optical gain of about 40 can be used to reduce the electrical power dissipation in the x-ray source from a usual laboratory level of 4 kilowatts to 100 watts. Any of the three advanced x-ray optical technologies described above can achieve an optical gain exceeding 40, and probably more, making it possible to further increase beam intensity. Two of the three technologies can form the x-ray beam acceptably well. All three of the technologies are in an advanced state of development at the present time.  
           [0029]    What is needed is an x-ray optical assembly for increasing the intensity of a formed x-ray beam that can be used in connection with, for example, an x-ray diffraction crystallography system, that provides a suitable optical gain of the x-ray beam for laboratory purposes, and also provides a suitable convergence or divergence angle of the x-ray beam on the sample It is therefore an object of the present invention to provide such an optical assembly.  
         SUMMARY OF THE INVENTION  
         [0030]    In accordance with the teachings of the present invention, an x-ray optical assembly is disclosed that provides increased x-ray beam intensity and a suitable sample convergence angle. Such an x-ray optical assembly has particular use for an x-ray diffraction crystallography system. The optical assembly includes a single capillary or polycapillary optical device and a mirror device configured and aligned to provide a desirable x-ray beam. An x-ray beam from an x-ray source enters the capillary optical device, where the beam intensity is increased. The beam exits the capillary optical device at a particular convergence angle, and is directed into the mirror device. The mirror device either focuses or collimates the beam to have a divergence angle suitable for the sample being analyzed. The mirror device can be any suitable device known in the art, such as an elliptical mirror device, a parabolic mirror device, or a graded multilayer mirror device.  
           [0031]    Additional objects, advantages, and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    [0032]FIG. 1 is a plan view of a pinhole collimator for use as an x-ray optical assembly in a crystallography system;  
         [0033]    [0033]FIG. 2 is a plan view of a grazing incidence flat mirror for use as an x-ray optical assembly in a crystallography system;  
         [0034]    [0034]FIG. 3 is a plan view of a grazing incidence bent mirror for use as an x-ray optical assembly in a crystallography system;  
         [0035]    [0035]FIG. 4 is a plan view of a shaped grazing incidence mirror for use as an x-ray optical assembly in a crystallography system;  
         [0036]    [0036]FIG. 5 is a graded multi-layer mirror for use as an x-ray optical assembly in a crystallography system;  
         [0037]    [0037]FIG. 6 is a plan view of a single capillary for use as an x-ray optical assembly in a crystallography system;  
         [0038]    [0038]FIG. 7 is a plan view of a polycapillary (also referred to as a polycapillary) optical system for use as an x-ray optical assembly in a crystallography system;  
         [0039]    [0039]FIG. 8 is a plan view of an x-ray optical assembly that employs a polycapillary optical device and a shaped grazing incidence mirror device, according to an embodiment of the present invention; and  
         [0040]    [0040]FIG. 9 is a plan view of an x-ray optical assembly that employs a single capillary optical device and a shaped grazing incidence mirror device, according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0041]    The following discussion of the preferred embodiments directed to an x-ray optical assembly is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. The principal application of this invention is x-ray diffraction of single crystals composed of protein macromolecules. However, the invention also has other applications that require a high intensity x-ray beam which is finally focused or collimated such that it has a very low divergence or convergence. Examples of other applications include single crystal x-ray diffraction; powder diffraction of x-rays for material characterization; x-ray fluorescence for characterization of thin films of materials layered on other material substrates; and medical applications; such as x-ray treatment of malignancies and x-ray tomography; x-ray microscopy; and non-destructive testing of various structures, including, but not limited to, microelectronic devices during manufacturing and packaging, liquid and solid materials, and mechanical assemblies, such as welded joints, machined surfaces, and structural objects.  
         [0042]    The present invention combines two presently known optical devices into an optical assembly to provide a very substantial improvement in overall performance of the x-ray generating subsystem of, for example, a diffraction crystallography system. This is accomplished by improving both the number of x-rays from the source accepted by the optical assembly, and the ratio of usable x-rays in the diffraction beam to the number accepted. A redesign of the available optical devices will be necessary to optimize their integration into an assembly, but the current principles of operation and features of these devices from the prior art will not be changed.  
         [0043]    While it is not practicable to use a polycapillary optical device alone to achieve a large optical gain for diffraction systems, it appears possible to use a combination of a polycapillary optical assembly together with one of the other known technologies to achieve a large optical gain having an acceptable beam characteristics. For example, if the capillary optical device were to focus the exit beam at the input focal point of a shaped grazing incidence mirror, the combined optical assembly could achieve the large optical gain of the polycapillary optical device together with the beam focusing or collimating capability of the shaped mirror.  
         [0044]    [0044]FIG. 8 is a plan view of an x-ray optical assembly  100  suitable for x-ray diffraction crystallography, according to an embodiment of the present invention. The assembly  100  includes a combination of a polycapillary optical device  102  and a shaped grazing incidence mirror device  104 . The purpose of the optical assembly  100  is to accept x-ray photons from an x-ray source  106  and to form and shape a high intensity x-ray beam  108  with appropriate characteristics to be used in certain systems, such as an x-ray crystallography diffraction system. As discussed above, the polycapillary x-ray optical devices and the shaped grazing incidence mirror devices have been developed in the prior art and exist at the present time, although redesigns of both devices are anticipated to optimize the characteristics of the integrated optical assembly  100  of the invention.  
         [0045]    The optical device  102  includes a plurality of individual capillaries  110 . The individual capillaries  110  receive the x-ray beam  108  from the source  106 , and generate an exit x-ray beam  112  at an output of the device  102 , in the manner as discussed above, which is focused at a focal point  114 . The mirror device  104  has a cylindrical shaped outer surface in one embodiment, and a specially configured inner reflective surface depending on the particular application. The inner surface of the mirror  104  can be elliptical shaped to provide a slow converging beam, or parabolic shaped to provide a collimated beam, as is also discussed above. Other shapes may also be applicable. In an alternate embodiment, the mirror  104  can be any of the grazing incidence mirrors or the graded multilayer mirror discussed above. The mirror  104  is positioned relative to the focal point  114  so that the entrance aperture of the mirror  104  receives the beam  112  in a desirable manner. A beam  120  exiting the mirror  104  is directed through a monochromator  116  that filters the beam  120  to the desired wavelength. In those applications where the mirror  104  is a multilayer mirror, the monochromator  116  can be eliminated. The filtered beam  120  then impinges a sample  118  being analyzed. The detection and processing device of the crystallography system are not shown.  
         [0046]    Designing the optical assembly  100  of the invention involves optimizing the separate components for optical mating and physical assembly. Ideally, the intensity gain of the polycapillary optical device  102  is the intensity gain of the overall assembly  100  because the exit beam  112  from the polycapillary device  102  enters and is completely processed by the mirror device  104 . This is not true in practice because the exit beam  112  has an inherent divergence of 3.5 milliradians (half-angle), so the mirror device  104  must be designed to accommodate the exit beam characteristics of the polycapillary device  102  as closely as possible.  
         [0047]    As described above, the gain of the polycapillary device  102  is inherently high because the acceptance cone can be made very large by shaping and sizing this optical component. The shape and size of the polycapillary device  102  will be limited by forming the exit beam  112  to match the acceptance cone of the mirror device  104 . Also, there are significant transmission losses within the polycapillary device  102  because of absorption within the material (usually glass) of the capillary walls around and between the individual capillaries  110 , and there is absorption within the capillaries  110 , principally due to surface roughness. The polycapillary optical design problem is to maximize its acceptance cone consistent with the characteristics of the mirror component, and then to choose the optimal size versus the number of capillaries  100  that fit within the resulting size and shape envelopes to minimize transmission losses through the device  102 . Information from and coordination with a chosen polycapillary device supplier will be necessary for the design.  
         [0048]    The mirror device design problem is to optimize its acceptance cone, and the separation distance between the device  102  and the device  104 , consistent with characteristics of the exit beam  112 , so that the maximum number of x-rays from the polycapillary device  102  are processed by the mirror device  104  to form a focused or the collimated beam  120 . The design of the components must be carried out simultaneously in order to optimize the intensity gain and beam characteristics of the coupled optical assembly  100 .  
         [0049]    The optical assembly  100  will be designed, in one example, for application in a single crystal x-ray diffraction system for use in protein crystallography. The anticipated beam characteristics at the target crystal location include the following:  
         [0050]    High beam intensity (flux)—10 9  to 10 11  x-rays per square millimeter per second within the beam cross section;  
         [0051]    Very small beam divergence/convergence angle—less than 1 milliradian cone half-angle;  
         [0052]    Small beam cross sectional diameter—on the order of 1.0 millimeter;  
         [0053]    Monochromatic x-ray wavelength—copper K alpha x-rays at 1.5418 Angstroms wavelength.  
         [0054]    As discussed above, the combination of the optical device  102  and the mirror device  104  would be optimized for a particular application. In one example, the mirror device  104  has an entrance pupil of 0.45 millimeter in diameter and is located 12.5 millimeters from the focal point  114 . The mirror device  104  has an acceptance cone with a half-angle of 18.0 milliradians and solid angle of acceptance of 1.018 ×10 −3  steradians. If there were no losses within the mirror device  104 , it would have an optical gain of 1296 compared to a pinhole collimator with a total divergence angle of 1.0 milliradian (acceptance cone half-angle of 0.5 milliradian). Of course, losses do occur in the mirror  104 , but an optical gain of several hundred is likely.  
         [0055]    The design objective for the polycapillary optical device  102  is to form a beam which focuses at the focal point of the mirror device  104 , has a convergency half-angle of 18 milliradians, and contains the maximum flux within that cone. If, the exit aperture of the polycapillary optical device  102  has a diameter of 6.0 millimeters, then the polycapillary exit aperture is located about 180 millimeters (7.1 inches) from the entrance pupil of the mirror device  104 . This separation distance is entirely reasonable for the protein crystallography application.  
         [0056]    The exit beam  112  from the polycapillary optical device  102  will contain the maximum x-ray flux if the acceptance cone of the device  102  is maximized by design techniques to be consistent with its exit aperture. An optical transfer gain through this device [ratio of input solid angle of acceptance to output solid angle of convergency, times the transfer efficiency (approximately 0.4)] of about 50 should be achievable. When this is multiplied by the optical gain of the mirror device  104 , the overall gain of the optical assembly  100  should be well over 1000, compared to the pinhole collimator. This in turn should produce a beam from the optical assembly  100  which has a flux greater than 1010 x-rays per square millimeter per second, and a total convergence angle of 1.0 milliradian.  
         [0057]    [0057]FIG. 9 shows a plan view of an x-ray optical assembly  122 , according to another embodiment of the present invention. The assembly  122  is similar to the optical assembly  100  discussed above, where like reference numerals represent the same components. As discussed above, the optical assembly  100  includes a polycapillary optical device  102 . In an alternate design, the polycapillary optical device  102  can be replaced with a single capillary device  124 . In this design, the single capillary optical device  124  offers a less complex device, but does not provide as high an intensity x-ray beam as the optical device  102 . Further, in this embodiment, the optical device  124  is shown as a cylindrical capillary device, but as will be appreciated by those skilled in the art, the device  124  can be a tapered capillary device.  
         [0058]    The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.