X-ray interferometric imaging system

Abstract

We disclose an x-ray interferometric imaging system in which the x-ray source comprises a target having a plurality of structured coherent sub-sources of x-rays embedded in a thermally conducting substrate. The system additionally comprises a beam-splitting grating G 1 that establishes a Talbot interference pattern, which may be a π phase-shifting grating, and an x-ray detector to convert two-dimensional x-ray intensities into electronic signals. The system may also comprise a second analyzer grating G 2 that may be placed in front of the detector to form additional interference fringes, and a means to translate the second grating G 2 relative to the detector. In some embodiments, the structures are microstructures with lateral dimensions measured on the order of microns, and with a thickness on the order of one half of the electron penetration depth within the substrate. In some embodiments, the structures are formed within a regular array.

We claim: 
     
         1 . An x-ray interferometric imaging system comprising:
 a source of x-rays comprising:
 a vacuum chamber; 
 an emitter for an electron beam; and 
 an electron target comprising:
 a substrate comprising a first material and, embedded in the substrate, 
 at least a plurality of discrete structures comprising a second material selected for its x-ray generating properties, 
 and in which said plurality of discrete structures are arranged within a periodic pattern of sub-sources; 
 
   a beam-splitting x-ray grating positioned to diffract x-rays generated by the sub-sources of x-rays; and   an x-ray detector comprising a two-dimensional array of x-ray detecting elements, positioned to detect the x-rays diffracted by the beam-splitting grating.   
     
     
         2 . The x-ray interferometer imaging system of  claim 1 , in which the ratio (Z 2  ρ 2 )/(Z 1  ρ 1 ) for the second material and first material is greater than 12, where Z is the atomic number and ρ is the mass density. 
     
     
         3 . The x-ray interferometric imaging system of  claim 1 , in which the first selected material is selected from the group consisting of: beryllium, diamond, graphite, silicon, boron nitride, silicon carbide, sapphire and diamond-like carbon. 
     
     
         4 . The x-ray interferometric imaging system of  claim 1 , in which the second material is selected from the group consisting of: iron, cobalt, nickel, copper, gallium, zinc, yttrium, zirconium, molybdenum, niobium, ruthenium, rhodium, palladium, silver, tin, iridium, tantalum, tungsten, indium, cesium, barium, gold, platinum, lead and combinations and alloys thereof. 
     
     
         5 . The x-ray interferometric imaging system of  claim 1 , in which the plurality of discrete structures have similar shapes. 
     
     
         6 . The x-ray interferometric imaging system of  claim 5 , in which the similar shapes are selected from the group consisting of regular prisms, right rectangular prisms, cubes, triangular prisms, trapezoidal prisms, pyramids, tetrahedra, cylinders, spheres, ovoids, and barrel-shapes. 
     
     
         7 . The x-ray interferometric imaging system of  claim 1 , in which the periodic pattern for the plurality of discrete structures is a regular grid; and in which, for one or more of the discrete structures, the width in one dimension is less than  10  microns. 
     
     
         8 . The x-ray interferometric imaging system of  claim 1 , in which the periodic pattern for the plurality of discrete structures is a set of parallel lines; and in which, for one or more of the discrete structures, the width in one dimension is less than 10 microns, and the length in a perpendicular dimension is greater than 20 microns. 
     
     
         9 . The x-ray interferometric imaging system of  claim 1 , in which the target also serves as a window for the vacuum chamber. 
     
     
         10 . The x-ray interferometric imaging system of  claim 1 , in which the beam-splitting x-ray grating comprises periodic structures that form an x-ray phase-shifting grating. 
     
     
         11 . The x-ray interferometric imaging system of  claim 10 , in which the x-ray phase shifting grating comprises structures to introduce a phase-shift of approximately π radians for a predetermined x-ray wavelength. 
     
     
         12 . The x-ray interferometric imaging system of  claim 10 , in which the x-ray phase shifting grating comprises structures to introduce a phase-shift of approximately π/2 radians for a predetermined x-ray wavelength. 
     
     
         13 . The x-ray interferometric imaging system of  claim 10 , in which the beam-splitting x-ray phase-shifting grating comprises a one-dimensional x-ray phase-shifting grating, in which the period p 1  of the one-dimensional x-ray phase-shifting grating is related to a dimension a for at least one of the discrete structures of the x-ray target by: 
       
         
           
             
               
                 p 
                 1 
               
               < 
               
                 
                   λ 
                    
                   
                       
                   
                    
                   L 
                 
                 a 
               
             
           
         
       
       where λ is a predetermined x-ray wavelength, and L is the distance between the target and the beam-splitting x-ray grating. 
     
     
         14 . The x-ray interferometric imaging system of  claim 13 , in which the periodic pattern for the plurality of discrete structures is a set of parallel lines in which the dimension a corresponds to the width of one of more of the discrete structures and is less than 10 microns; and the set of parallel lines has an orientation parallel with the structures of said one-dimensional x-ray phase-shifting grating. 
     
     
         15 . The x-ray interferometric imaging system of  claim 14 , in which the period p 0  of the periodic pattern is greater than 2a. 
     
     
         16 . The x-ray interferometric imaging system of  claim 15 , in which the period p 0  of the periodic pattern is approximately 4a. 
     
     
         17 . The x-ray interferometer imaging system of  claim 10 , in which the x-ray detector is positioned at a distance from the beam-splitting x-ray grating that corresponds to an odd multiple of 1/16 th  of the Talbot Distance for that grating when used with spherical wave x-rays of a predetermined wavelength spectrum and spatial coherence; and in which the detector has a spatial resolution at least three times the Talbot fringe period for the Talbot interference pattern at said odd multiple of 1/16 th  of the Talbot Distance for that grating when used with x-rays of said predetermined wavelength spectrum and spatial coherence. 
     
     
         18 . The x-ray interferometric imaging system of  claim 1 , in which the x-ray detector comprises a scintillator, and also an array of charged-coupled devices (CCDs). 
     
     
         19 . The x-ray interferometric imaging system of  claim 1 , in which the x-ray detector comprises electronic elements comprising selenium. 
     
     
         20 . The x-ray interferometric imaging system of  claim 1 , additionally comprising: an analyzer grating placed in close proximity to the surface of the x-ray detector. 
     
     
         21 . The x-ray interferometric imaging system of  claim 20 , in which the analyzer grating comprises periodic structures that form an x-ray absorption grating. 
     
     
         22 . The x-ray interferometric imaging system of  claim 21 , in which periodic structures of the analyzer grating have a period p 2  given approximately by: 
       
         
           
             
               
                 p 
                 2 
               
               = 
               
                 
                   p 
                   0 
                 
                  
                 
                   D 
                   L 
                 
               
             
           
         
       
       where p 0  is the period of the periodic pattern for the sub-sources of the target, D is the distance between the x-ray beam-splitting grating and the analyzer grating, and L is the distance between the target and the beam-splitting x-ray grating. 
     
     
         23 . The x-ray interferometric imaging system of  claim 22 , in which the periodic pattern for the plurality of discrete structures in the target is a set of parallel lines; and
 the beam-splitting x-ray grating comprises
 a one-dimensional x-ray phase-shifting grating having an orientation parallel with the set of parallel lines; and 
   the analyzer grating comprises
 a one-dimensional absorption grating structure having an orientation parallel with the set of parallel lines. 
   
     
     
         24 . The x-ray interferometric imaging system of  claim 1 , in which the orientation of at least two of the discrete structures of the target are such that, when simultaneously bombarded by electrons from the electron emitter, the x-rays generated by one of the discrete structures overlap in part the x-rays generated by the another of the discrete structures, and the overlapping x-rays will propagate together towards the beam-splitting x-ray grating. 
     
     
         25 . The x-ray interferometric imaging system of  claim 1 , additionally comprising:
 a cooling system comprising:   a reservoir for storing a cooling fluid;   a channel within the substrate for conducting the cooling fluid;   an additional channel to conduct the fluid from the reservoir to the channel within the substrate;   an additional channel to conduct the fluid from the channel within the substrate to the reservoir; and   a pumping mechanism to pump the fluid through the system.   
     
     
         26 . The x-ray interferometric imaging system of  claim 10 , in which the x-ray phase-shifting grating comprises two-dimensional structures that introduce a phase-shift of approximately π radians for a predetermined x-ray wavelength. 
     
     
         27 . The x-ray interferometric imaging system of  claim 26 , in which the two-dimensional structures are arranged in a checkerboard pattern. 
     
     
         28 . An x-ray interferometric imaging system comprising:
 a source of x-rays comprising:
 a vacuum chamber; 
 at least two emitters for electron beams; and 
 an electron target comprising:
 a substrate comprising a first material and, embedded in the substrate, 
 at least a one set of a plurality of discrete structures comprising a second material selected for its x-ray generating properties, and 
 at least another set of a plurality of discrete structures comprising a third material selected for its x-ray generating properties, 
 and in which both of said sets of a plurality of discrete structures are arranged in a periodic pattern; 
 
   a beam-splitting x-ray grating positioned to diffract x-rays generated by the source of x-rays; and   an x-ray detector comprising a two-dimensional array of x-ray detecting elements, positioned to detect the x-rays diffracted by the beam-splitting grating.   
     
     
         29 . The x-ray interferometric imaging system of  claim 28 , in which both sets of a plurality of discrete structures, when simultaneously bombarded by electrons from the electron emitters, are aligned such that the x-rays generated by one set of discrete structures overlap in part the x-rays generated by the other set of discrete structures, and the overlapping x-rays will propagate together towards the beam-splitting x-ray grating. 
     
     
         30 . The x-ray interferometric imaging system of  claim 28 , in which the first material is selected from the group consisting of: beryllium, diamond, graphite, silicon, boron nitride, silicon carbide, sapphire and diamond-like carbon. 
     
     
         31 . The x-ray interferometric imaging system of  claim 28 , in which the second material is selected from the group consisting of: iron, cobalt, nickel, copper, gallium, zinc, yttrium, zirconium, molybdenum, niobium, ruthenium, rhodium, palladium, silver, tin, iridium, tantalum, tungsten, indium, cesium, barium, gold, platinum, lead and combinations and alloys thereof. 
     
     
         32 . The x-ray interferometric imaging system of  claim 28 , in which the third material is selected from the group consisting of: iron, cobalt, nickel, copper, gallium, zinc, yttrium, zirconium, molybdenum, niobium, ruthenium, rhodium, palladium, silver, tin, iridium, tantalum, tungsten, indium, cesium, barium, gold, platinum, lead and combinations and alloys thereof.