Abstract:
A fiber optic plate assembly is provided for transferring optical signals to a detector or other optical element within an imaging device or imaging system. The fiber optic plate assembly comprises first and second fiber optic plates coupled via an optical coupling gel configured to permit separation of the two plates from each other to permit repair or replacement of one of the plates. Alternatively, the imaging device may comprise a single fiber optic plate coupled directly to an optical detector.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to imaging devices and, more particularly, to imaging devices and systems that employ one or more fiber-optic plates to transfer optical signals to a detector or other optical element within the imaging device or system. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention, a fiber optic plate assembly is provided for transferring optical signals to a detector or other optical element within an imaging device or imaging system. The fiber optic plate assembly comprises first and second fiber optic plates coupled via an optical coupling gel configured to permit separation of the two plates from each other to permit repair or replacement of one of the plates. The fiber optic plate assembly may alternatively comprise a fiber optic plate coupled directly to an optical detector via an optical coupling gel. 
     In accordance with one embodiment of the present invention, an electron beam imaging system is provided. The system comprises an electron beam source configured to direct a specimen analysis beam of electrons in the direction of a specimen under examination and an imaging device configured to generate an image representing the specimen. The imaging device comprises first and second fiber optic plates and an optical detector. The electron beam imaging system comprises an evacuation chamber accommodating the specimen, the beam of electrons, and the imaging device. The output face of the first fiber optic plate is optically coupled and bonded to the input face of the optical detector. The input face of the second fiber optic plate is coated with an optical scintillator while the output face of the second fiber optic plate is optically coupled to the input face of the first fiber optic plate via an optical coupling gel. The optical coupling gel is configured to flow under a given shear rate and the bond between the first fiber optic plate and the detector is configured to withstand a shear rate greater than the given shear rate at which the gel is configured to flow. In this manner, the second fiber optic plate may be disengaged from the first fiber optic plate without substantial disturbance to the integrity of the bond between the first fiber optic plate and the detector. 
     In accordance with another embodiment of the present invention, an imaging device is provided comprising first and second fiber optic plates and an optical detector. The output face of the first fiber optic plate is optically coupled to the input face of the optical detector. The output face of the second fiber optic plate is optically coupled to the input face of the first fiber optic plate via a thixotropic optical coupling gel. 
     In accordance with yet another embodiment of the present invention, the output face of the second fiber optic plate is optically coupled to the input face of the first fiber optic plate via an optical coupling gel configured to flow under a given shear rate. The bond between the first fiber optic plate and the detector is configured to withstand a shear rate greater than the given shear rate at which the gel is configured to flow, enabling disengagement of the second fiber optic plate from the first fiber optic plate without substantial disturbance to the integrity of the bond between the first fiber optic plate and the detector. 
     In accordance with yet another embodiment of the present invention, an imaging device is provided comprising a single fiber optic plate coupled directly to an optical detector. 
     In accordance with yet another embodiment of the present invention, a directed beam imaging system is provided comprising a beam source configured to direct a specimen analysis beam in the direction of a specimen under examination, and an imaging device according to the present invention. 
     Accordingly, it is an object of the present invention to provide improved imaging device and imaging systems. Other objects of the present invention will be apparent in light of the description of the invention embodied herein. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The following detailed description of specific embodiments of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIG. 1  is an illustration of an imaging device according to one embodiment of the present invention; 
         FIGS. 2 and 3  are top and front views of an enclosed imaging device according to one embodiment of the present invention; 
         FIG. 4  is a schematic illustration of an imaging device according to the present invention mounted at the bottom of a TEM column; 
         FIG. 5  is a schematic illustration of an imaging device according to the present invention mounted at the end of an imaging filter; 
         FIG. 6  is a schematic illustration of an imaging device according to the present invention mounted at the end of an electron energy loss spectrometer; and 
         FIG. 7  is an illustration of an imaging device according to an alternative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring initially to  FIG. 1 , an imaging device  10  according to one embodiment of the present invention is illustrated. Generally, the imaging device  10  comprises an optical detector  20 , a first fiber optic plate  30  and a second fiber optic plate  40 . The specific structure of these general components is beyond the scope of the present invention and may be gleaned from any of a variety of teachings in the art of optical imaging. For example, U.S. Pat. Nos. 6,570,164 and 5,065,029, the disclosures of which are incorporated herein by reference, present a more detailed discussion of fiber optic plates and optical detectors. 
     As is illustrated in  FIG. 1 , the output face  34  of the first fiber optic plate  30  is optically coupled and bonded to the input face  22  of the optical detector  20 . The output face  44  of the second fiber optic plate  40  is optically coupled to the input face  32  of the first fiber optic plate  30  via an optical coupling gel  50 . 
     The bond between the first fiber optic plate  30  and the detector  20  is configured to withstand a shear rate greater than the shear rate at which the gel  50  is configured to flow. Stated differently, the degree of securement between the first fiber optic plate  30  and the detector  20  exceeds the degree of securement between the first fiber optic plate  30  and the second fiber optic plate  40 . In this manner, the second fiber optic plate  40  may be disengaged from the first fiber optic plate  30  without substantial disturbance to the integrity of the bond between the first fiber optic plate  30  and the detector  20 . The second fiber optic plate  40  may then be repaired or replaced and re-engaged with the first fiber optic plate  30 . It is contemplated that, upon disengagement, some of the gel may remain affixed to the second fiber optic plate  40  and that subsequent re-engagement with a new fiber optic plate may require replacement of some of the optical coupling gel  50 . 
     Although it is contemplated that the optical medium  46  may comprise any medium configured to enhance optical imaging, typically, the optical medium  46  comprises a scintillator configured to emit optical photons. It is noted that replacement or repair of the second fiber optic plate  40  is often necessary because the optical medium  46  coated on the input face  42  of the second fiber optic plate  40  is often prone to environmental damage from, for example, scratching or other contact damage, excessive radiation exposure, contamination, etc. The optical medium  46  may be coated with a protective layer  48  to help protect against such damage. As will be appreciated by those practicing the present invention, the effect of the protective layer  48  on the optical imaging process should be minimized by, for example, ensuring that the protective layer  48  is transparent to the charged particles or radiation incident upon the detector  10 . 
     It is contemplated that the optical coupling gel  50  can be any of a variety of suitable optical coupling gels. Thixotropic optical coupling gels available from Nye Lubricants, Inc., of Fairhaven, Mass., and other thixotropic optical coupling gels available from similar manufacturers are examples of suitable optical coupling gels. The thixotropic gel, which defines an apparent viscosity that is inversely related to shear rate, is typically selected such that, at room temperature and under static conditions, it is capable of supporting its own weight and the weight of the second fiber optic plate  40  without substantial flow. Under substantial shear, the thixotropic optical coupling gel flows readily, permitting convenient removal of the second fiber optic plate  40  for replacement or repair. Stated differently, the thixotropic gel tends to liquefy when subject to relatively high shear rates and then solidify again when left standing. 
     Suitable thixotropic optical coupling gels will be characterized by an apparent viscosity that varies depending upon the particular design constraints of the application at issue. For example, it is contemplated that apparent viscosities as low as about 5,000 poise may be suitable in many contexts but that other applications will require apparent viscosities of at least about 7,000 poise. Further, it is noted that particular advantages reside in the use of thixotropic optical coupling gels defining an apparent viscosity of at least about 10,000 poise. 
     The detector  20  may comprise any suitable optical detector and will typically define an array of detection pixels. For example and by way of illustration, not limitation, the detector  20  may comprise a CCD array, a photodiode array, or a CMOS detector. In addition, it is contemplated that imaging devices according to the present invention may comprise the optical detector  20  and one or more of a variety of additional components selected from, for example, an energy selecting slit, a charged particle dispersing device, a charged particle lens, a charged particle deflector, a charged particle energy filter, a charged particle scintillator, a fiber optic coupler, etc. 
     As is illustrated in  FIGS. 2 and 3 , the imaging device may further comprise a compression frame  12  configured to maintain a given degree of compression on the thixotropic optical coupling gel  50  between the first and second fiber optic plates  30 ,  40 . In the illustrated embodiment, the compression frame comprises a plurality of compression bolts  14  configured to fixedly engage upper and lower portions  12 A,  12 B of the frame  12 . The compression frame  12  is configured to enclose substantially the entire imaging device  10  and define a transmission window  15  over the input face  42  of the second fiber optic plate  40 . It is contemplated that the compression frame illustrated in  FIGS. 2 and 3  is presented for illustrative purposes and that a variety of design variations will be suitable for the frame itself and the hardware used to impart compression on the gel  50 . 
     Imaging devices according to the present invention may be used in conjunction with a variety of directed beam imaging systems. For the purposes of defining and describing the present invention, it is noted that a directed beam imaging system comprises any system where a beam of electromagnetic radiation or charged particles is directed at a specimen under examination to generate an image representing the specimen. The image may be a single or multi-dimensional image, a diffraction pattern, or any other suitable representation of the specimen. By way of illustration and not limitation, as is illustrated in  FIGS. 4–6 , discussed below, electron beam imaging systems according to the present invention may comprise an evacuation chamber accommodating the specimen under examination, the beam of electrons, and the imaging device. It is contemplated that the evacuation chamber may include a set of separate sub-chambers in communication with each other, as is illustrated in  FIG. 4 . 
     By way of illustration, not limitation, as shown schematically in  FIG. 4 , an imaging device  10  according to the present invention may be mounted in the bottom of a TEM column  60 , such as, for example, the TEM described in Krivanek, U.S. Pat. No. 5,065,029, the entire disclosure of which is hereby incorporated by reference.  FIG. 4  also illustrates the use of a user interface  62  and a controller  64  programmed to enable a user to coordinate operation of the device. It is noted that the user interface  62  and the controller  64  may take a variety of suitable forms and may be utilized in a variety of embodiments of the present invention. 
     As a further example, referring to the schematic illustration of  FIG. 5 , an imaging device  10  according to the present invention may be mounted to the end of an imaging filter  70 , such as, for example, the energy-selected electron imaging filter described in Krivanek, U.S. Pat. No. 4,851,670, the entire disclosure of which is hereby incorporated by reference. 
     In yet another embodiment of the invention schematically illustrated in  FIG. 6 , an imaging device  10  of the present invention may be mounted on the end of an electron energy loss spectrometer (EELS)  80 , such as, for example, the EELS device described in Krivanek, U.S. Pat. No. 5,097,126, the entire disclosure of which is hereby incorporated by reference. 
     Referring finally to  FIG. 7 , it is noted that an imaging device according to the present invention need not include the first fiber optic plate  30 . Rather, the second fiber optic plate  30  may be bonded directly to the detector  20  via a thixotropic optical coupling gel  50 , preferably held in compression by a suitable compressive framework. The gel  50  is preferably held in compression without the interference of any intervening spacer elements or other structure present between the fiber optic plate  40  and the input face of the detector  20  that would otherwise interfere with compression of the gel  50 . 
     It is noted that terms like “preferably,” “commonly,” and “typically” are not utilized herein to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present invention. 
     For the purposes of describing and defining the present invention it is noted that the term “device” is utilized herein to represent a combination of components and individual components, regardless of whether the components are combined with other components. Further, it is noted that the term “substantially” is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term “substantially” is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.