Abstract:
A multi-beam x-ray system includes an x-ray source which emits x-rays and a housing with a first part and a second part. The second part is moveable relative to the first part and includes a plurality of optics of different performance characteristics. Each optic, through the movement of the second part relative to the first part, is positioned to a working position so that the optic receives the x-rays from the x-ray source and directs the x-rays with the desired performance attributes to a desired location.

Description:
BACKGROUND OF THE INVENTION 
     Typical x-ray analytical instruments include an x-ray source and an x-ray optical system that provide an x-ray probe beam. Characteristics of the probe beam determine the characteristics and capabilities of the instrument. Performance parameters of the probe beam include divergence for spatial definition, bandwidth for energy definition, and intensity for a given cross section. These parameters, however, cannot be independently optimized, since improving one parameter often reduces the performance of the other parameters. Most x-ray probe beams use characteristic emission lines that result from the interaction between target atoms and accelerated electrons. The spectrum that an optical system can deliver is limited by the available spectrum from a specific target. 
     Current technologies in x-ray sources and x-ray optics cannot deliver an ideal probe beam, which has the attributes of absolute parallelism, very narrow energy bandwidth, variable wavelength, and very high intensity. Instead, different optical systems are constructed and arranged to deliver beams with different characteristics. Combined with different x-ray source designs, the optical systems deliver beams required for different instrument capabilities, functions, and applications. This approach usually involves multiple optical systems and even multiple x-ray tubes or multiple targets and, thus, is inconvenient to manage and is costly. 
     Some systems employ multilayer optics that include a bending mechanism to change the curvature of the multilayer optic for different wavelengths. Although such systems enable the use of different sources, mechanical systems which can reliably and accurately form a curvature matching a specific wavelength are difficult to fabricate. In addition, the multilayer optic which is designed to work with multiple wavelengths cannot be optimized for each specific wavelength. 
     These multilayer optic systems may also include multiple sections of optics in which each section is designed for a specific wavelength. The section of the optic is mechanically moved to the working position when a specific working wavelength is needed. However, these systems do not address issues associated with 2-dimensional cases. 
     Such multilayer optical systems further include multiple multilayer coating arrangements as a stack of structures, in which each structure is designed for a specific wavelength. Although these systems offer convenience and low cost, their performance is compromised because of the lower reflectivity for every specific wavelength and high background noise due to the Bragg reflections at different energies off different multilayer coating structures. 
     Other systems have been employed as 2-dimensional systems which include two 2-dimensional optics in a face-to-face arrangement. Each optic is designed for a different energy or wavelength. However, such an arrangement has one or both optics at a source take-off angle that is far from the ideal take-offs that are optimal for performance. 
     Even when the optics designed for the same energy, there might be a need for quickly changing the configuration among various beam configurations, such as parallel beam and focusing beam configurations. 
     Accordingly, a probe beam system which can deliver beams of different characteristics is needed. 
     BRIEF SUMMARY OF THE INVENTION 
     In one form, a multi-beam x-ray optical system includes an x-ray source which emits x-rays and a housing with a first part and a second part. The second part is moveable relative to the first part and includes a plurality of optics of different performance characteristics. Each optic, through the movement of the second part relative to the first part, is positioned to a working position so that the optic receives the x-rays from the x-ray source and directs the x-rays to a desired location. 
     The benefits of the x-ray optical system include improved functionalities, improved performance, enabled instrument capabilities, convenience and low cost. 
     Further features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, incorporated in and forming a part of the specification, illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the views. In the drawings: 
         FIG. 1A  is an expanded perspective view of a multi-beam x-ray system in accordance with the invention; 
         FIG. 1B  is a cutaway view of the multi-beam x-ray system of  FIG. 1A ; 
         FIGS. 2A and 2B  are schematic views illustrating the principles of the multi-beam x-ray system of  FIG. 1A ; and 
         FIGS. 3A and 3B  are schematic views of illustrating the principles of another embodiment of the multi-beam x-ray system. 
     
    
    
     DESCRIPTION 
     An x-ray optical system capable of delivering beams with different characteristics is described herein. The optical system includes multiple optics, and each optic has unique performance characteristics for meeting different application needs. The beam characteristics may include variations in spatial definition, such as parallel beam optic and focusing optic, spectral differences, such as Cu Kα, Mo Kα, Ag Kα and other wavelengths, different trade-offs between divergence, and flux on the sample or all of above. The optical system delivers a specific beam when a corresponding optic is mechanically positioned to the desired optical path. 
     Referring now to  FIGS. 1A and 1B , a multi-beam x-ray system embodying the principles of the present invention is illustrated therein and designated at  10 . As its primary components, the x-ray system  10  includes an optical system  12  enclosed within a housing  14  and a cover  16 . 
     The multi-beam x-ray system  10  employs a mechanism to position a specific optic to a desired working position, which is defined as the working position in which each optic, within certain constraints, has its optimized take-off angle, designed source-optic distance, matched source focal spot and optic focus, and correct Bragg angle. The constraints may include designed interception points of all beams, intended beam orientation and position, as well as any other desired constraints. In the arrangement shown in  FIGS. 2A and 2B , the optical system  12  includes a rotating mechanism to position an optical element  18  with a pair of optics  20  and  22  to a desired working position, in which the optics  20  and  22  are arranged in a circular geometry and the optical system  12  is rotated around its axis so that each optic  20  and  22  is positioned in and out of the working position. 
     The optical element  18  may have a coarse alignment mechanism for each optic  20  and  22  so that the optics are aligned in such a way that when the system  10  is positioned for an optic in its working position, the optic  20  or  22  is coarsely aligned to the intended source focal spot  26  or  28  of a source  24  and the system  10 . Alternatively or additionally, the optical system  12  and the optics  20  and  22  are fabricated so that when the optical system  12  is positioned for a desired optic in its working position, the optic is pre-aligned with an accuracy and precision of the coarse alignment to the intended source focal spot. 
     When in use, the source  24  emits x-rays from either source focal spot  26  or  28  at respective optics  22 ,  20  which in turn focuses the beam at a focus point  30 , a detector, a sample, or any other suitable position. In particular, in the arrangement shown in  FIGS. 2A and 2B , the housing  14 , referred to as a rotary housing, has a structure with two shells  15  and  17  ( FIG. 1B ). The inner shell  15  provides multiple locations for the optics  20 ,  22  with different characteristics. The inner shell  15  can be rotated in either direction around the axis of the optical instrument  12  as indicated by the arrow  19  relative to the outer shell  17  so that either optic  20 ,  22  can be positioned to a pre-defined working position. As indicated above, each optic  20 ,  22  is pre-aligned or coarsely aligned relative to the respective source focal spot  28 ,  26  and intended direction or position when it is moved in the working position. Each optic  20 ,  22  may have its own coarse alignment mechanism or it can be factory installed in the optical system  12  with the precision of the coarse alignment mechanism. The stationary outer shell may be equipped with an alignment mechanism that provides all the needed alignment motions for fine alignment, which may include transverse translations across the primary beam direction, Bragg angle alignment, and optional translation along the primary beam. 
     Alternatively, the optical system  12  can be equipped with an alignment mechanism that provides all the needed alignment motions for fine alignment, which may include transverse translations across the primary beam direction, Bragg angle alignment, and optional translation along the primary beam. 
     Another arrangement shown in  FIGS. 3A and 3B  illustrates an optical system  112  with a translation mechanism to position an optical element  118  with a pair of optics  120  and  122  back and forth as indicated by arrow  132  to the desired working position relative to an outer shell  117  all enclosed in housing similar to the housing  14  ( FIG. 1A ). The optics  120  and  122  are arranged in a linear array or a 2-dimensional matrix if more optics are included in the system, and a particular optic is translated to the working position. Similarly, the source  24  emits x-rays from either focal source point  26  or  28  at the respective optic  122 ,  128  which in turn focuses the beam at the focal point  30 , a detector, a sample, or any other suitable position. 
     The optics  120 ,  122  have different properties such as different spatial definitions or different energies. For the case of different energies, the optics  120 ,  122  can be employed for different spectrums and can be aligned to different source focal spots. Each optic  120 ,  122  may be pre-aligned or coarsely aligned relative to the respective source spot  28 ,  26  and intended direction or position when the optic is positioned to its desired working position. Each optic  120 ,  122  may have its own coarse alignment mechanism or it may be factory installed with the precision of a defined coarse alignment. The housing  117  can be equipped with an alignment mechanism that provides all the desired alignment degrees of freedom for fine alignment, which may include transverse translations across the primary beam direction, Bragg angle alignments, and optional translation along the primary beam. 
     Alternatively, the optical system  112  can be equipped with its own alignment structure which provides all the desired alignment degrees of freedom for fine alignment, which may include transverse translations across the primary beam direction, Bragg angle alignments, and optional translation along the primary beam. 
     The optical arrangements discussed above can be employed with different target materials for forming two or more source focal spots with different emission characteristics. Each optic is aligned to a specific focal spot on a specific target material. A beam with a different wavelength is delivered by actuating a different target focal spot and using a slit to select the beam. 
     The optical system may be designed to provide beams with the same energy but difficult spatial characteristics, such as parallel beam and a focus beam. The arrangements in this case use the same target material and the same source spot. 
     The optical system can deliver multiple beams with mixed characteristics such that some beams have different energies and some beams have only different spatial definitions. In this case, multiple target materials and source emission spots can be employed and multiple optics can be aligned to a single source spot. 
     In any of the aforementioned arrangements, the x-ray source  24  is a point source having a single target material or multiple target materials. The x-ray sources (both sealed tubes and rotating anodes) with multiple target materials can include a target with multiple strips, each strip being a different target material. The source focal spots associated with different target materials can have different locations. Therefore, the x-rays optics can be designed for different target materials with different focal spots on the target. Alternatively, the target can be an alloy of different elements, which emits a spectrum including all the characteristic lines from all the elements. The optics can have the same focal spot regardless of the working wavelength. 
     When the x-ray source  24  is used with different target materials having a strip structure, the source  24  may include a cathode and the target may be mechanically movable so that the different target materials can be positioned to a desired focal spot where the electron beam interacts with the target. The electron beam can be electronically steered to different target materials so that different spectrums can be generated at different focal spots. 
     In a particular arrangement, the x-ray source  24  provides point projection and the system  10  includes a rotary housing with multiple 2-dimentional optics as shown in  FIGS. 2A and 2B . The x-ray source has a single target and delivers different characteristic emission lines such as Kα and Kβ. The optics can deliver beams with different spatial definitions such as parallel beams, focusing beams with different focal length, and beams with different spectral definitions such as different working wavelengths (Kα, Kβ, Lα . . . ) and different bandwidths. Each optic can be rotated to the working position to deliver the designed beam characteristics. 
     In another arrangement, the x-ray source  24  delivers emission spectrums from one or multiple target materials, such as Cr Kα/Kβ, Cu Kα/Kβ, Mo Kα/Kβ, as well as others, and the system  10  includes a rotary housing with multiple 2-dimensional optics. Each optic is employed for a specific wavelength and/or has a set of specific characteristics. X-rays of a single target or different targets can be emitted from the same source spot, if it is a single target material or the target is made of mixed alloys, or different source points, if the source target consists of straps of different materials. Each optic is configured and coarsely aligned to have its focus aligned to the intended source focal spot and delivers a beam according to the direction and position designed. A rotation mechanism is able to position any optic in the circular structure to the working position. A fine alignment structure engages the optic in the working position to finely align the optic for optimal performance. 
     Yet in another arrangement, the x-ray source  24  delivers emission spectrums from one or multiple target materials, such as Cr Kα, Cu Kα/Kβ, Mo Kα/Kβ as well as others, and the optical system  10  includes a linear array or a matrix housing with multiple 2-dimensional optics (see, e.g.,  FIGS. 3A and 3B ). Each optic is configured for a specific wavelength and/or has a set of specific characteristics. X-rays from a single target or different targets can be emitted from the same source spot, if it is a single target or the target is made of mixed alloys, or multiple source spots. Each optic is configured and coarsely aligned to have its focus aligned to the intended source focal spot and delivers a beam according to the desired direction and position. A translation mechanism positions any of the optics in the array or matrix to the working position. A fine alignment structure engages the optic in the working position to finely align the optic for optimal performance. 
     The x-ray source  24  may include an anode with different materials and a cathode that delivers an electron beam to different materials to form different source focal spots emitting different spectrums. The cathode can be an electron gun with an electro-magnetic deflection mechanism to steer the electron beam to different target materials. Alternatively, the anode can be repositionable so that different materials can be positioned under an electron beam to generate x-rays with different spectrums. 
     The optics can be multilayer optics. The multilayer optics can be graded multilayer optics and any combination of collimating optics and focusing optics with different focal lengths. 
     In certain implementations, each 2-dimensional optic is made of two 1-dimensional optics either in a sequential geometry such as in the Kirkpatrick-Baez scheme or in the “side-by-side” arrangement as described in U.S. Pat. Nos. 6,042,099 and 6,014,423, both of which are incorporated herein by reference in their entirety. The 2-dimensional optics can be single reflection optics having a parabloidal geometry for collimating optics or an ellipsoidal geometry for focusing optics. 
     The aforementioned as well as other embodiments are within the following claims.