Abstract:
The present disclosure provides an optical imaging system with adjustable magnification. In one aspect, the optical imager, which defines an optical axis, includes an object plane and an image plane, an optical sub-system located along the optical axis and optically disposed between the object plane and the image plane, the optical sub-system being configured to substantially image electromagnetic radiation emanating from the object plane onto the image plane, and at least one detecting element located substantially at the image plane. In one example, the object plane and the image plane are separated by a fixed distance. In one example, the optical sub-system is configured to mechanically translate along the optical axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 61/792,375, filed on Mar. 15, 2013, which is incorporated by reference herein in its entirety and for all purposes. 
    
    
     BACKGROUND 
     These teachings relate generally to relay imagers and spectrometers. More particularly, these teachings relate to relay imagers and spectrometer designs which have adjustable spatial or spectral magnification. 
     Relay imagers have been used in optical spectrometers and other applications. In the conventional designs, the relay imagers have constant spatial and spectral magnification. Accordingly, there is a need for relay and spectrometer designs that have adjustable spatial and spectral magnification. 
     SUMMARY 
     Various embodiments of the present disclosure provide relay imagers and spectrometers with adjustable spatial and spectral magnification. 
     Characteristics of these teachings provide a relay imager design that has adjustable spatial magnification. 
     Characteristics of these teachings provide a spectrometer design that has adjustable spatial magnification. 
     Characteristics of these teachings provide a spectrometer design that has adjustable spectral magnification. 
     Further characteristics of these teachings to provide a spectrometer design that is compact in size. 
     Still further characteristics of these teachings provide a spectrometer design that has a combination of the characteristics described above with superior trade-offs than have been previously attainable. 
     For better understanding of these teachings, reference is made to the accompanying drawings and detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a relay imaging system, taken along an optical axis of the relay imaging system; 
         FIGS. 2A and 2B  are schematic views of an optical imaging system, taken along an optical axis of the optical imaging system, in accordance with an embodiment of the present disclosure; 
         FIGS. 3A and 3B  are schematic views of a compact refractive relay spectrometer, taken along an optical axis of the spectrometer in the plane parallel to and perpendicular to the direction of dispersion respectively; and 
         FIGS. 4A and 4B  are schematic views of an optical imaging system, taken along an optical axis of the optical imaging system in the plane parallel to the direction of dispersion, in accordance with an embodiment of the present disclosure and its scope will be pointed out in the appended claims. 
     
    
    
     DETAILED DESCRIPTION 
     Relay and spectrometer designs that have adjustable spatial and spectral magnification are disclosed hereinbelow. 
     Reference is made to  FIG. 1 , which is a schematic sectional view of a relay imaging system  100 , taken along its optical axis  10 . Electromagnetic radiation, typically in the ultraviolet, visible, and/or infrared bands, hereinafter referred to generally as light, emitted or reflected by a given object, either real or virtual, hereinafter referred to generally as the source, located at the object plane  20  is re-imaged to a focus position, hereinafter also referred to as an image plane  30 , such as but not limited to a CCD array, phosphorescent screen, photographic film, microbolometer array, or other means of detecting light energy, hereinafter referred to generally as the detector, through an optical system  40  comprising either refractive or reflective elements or combination thereof. In this embodiment, optical system  40  comprises refractive elements  52 ,  53 ,  54 ,  55 ,  56 ,  62 ,  63 ,  64 ,  65 ,  66 , and  70 . A view of a representative image  32  at the image plane  30  for this embodiment  100 , taken along a plane perpendicular to the optical axis  10 , is shown next to the image plane  30 . 
     The first order imaging relationship between the object and image plane positions of an optical relay imaging system is given as 
                 1     s   o       +     1     s   i         =     1   f           
where s o , s i , and f are the first order object distance, image distance, and focal length of the system respectively. From this relationship, the image distance for a corresponding object distance can therefore be calculated as
 
     
       
         
           
             
               s 
               i 
             
             = 
             
               
                 
                   f 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     s 
                     o 
                   
                 
                 
                   
                     s 
                     o 
                   
                   - 
                   f 
                 
               
               . 
             
           
         
       
     
     The first order object to image distance D is given to be
 
 D=s   o   +s   i  
 
and substitution of the above expression for the image distance in terms of the object distance yields the first order relationship
 
     
       
         
           
             D 
             = 
             
               
                 
                   s 
                   o 
                 
                 + 
                 
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                   i 
                 
               
               = 
               
                 
                   
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                       f 
                       ⁢ 
                       
                           
                       
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                         s 
                         o 
                       
                     
                     
                       
                         s 
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                 = 
                 
                   
                     
                       s 
                       o 
                       2 
                     
                     
                       
                         s 
                         o 
                       
                       - 
                       f 
                     
                   
                   . 
                 
               
             
           
         
       
     
     Differentiating this expression with respect to small changes in the object distance results in 
     
       
         
           
             
               
                 ∂ 
                 D 
               
               
                 ∂ 
                 
                   s 
                   o 
                 
               
             
             = 
             
               
                 
                   ∂ 
                   
                     ∂ 
                     
                       s 
                       o 
                     
                   
                 
                 ⁢ 
                 
                   ( 
                   
                     
                       s 
                       o 
                       2 
                     
                     
                       
                         s 
                         o 
                       
                       - 
                       f 
                     
                   
                   ) 
                 
               
               = 
               
                 
                   
                     
                       2 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           s 
                           o 
                         
                         ⁡ 
                         
                           ( 
                           
                             
                               s 
                               o 
                             
                             - 
                             f 
                           
                           ) 
                         
                       
                     
                     - 
                     
                       s 
                       o 
                       2 
                     
                   
                   
                     
                       ( 
                       
                         
                           s 
                           o 
                         
                         - 
                         f 
                       
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                     2 
                   
                 
                 = 
                 
                   
                     
                       
                         
                           ( 
                           
                             
                               s 
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                         2 
                       
                       - 
                       
                         f 
                         2 
                       
                     
                     
                       
                         ( 
                         
                           
                             s 
                             o 
                           
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                         ) 
                       
                       2 
                     
                   
                   = 
                   
                     1 
                     - 
                     
                       
                         
                           f 
                           2 
                         
                         
                           
                             ( 
                             
                               
                                 s 
                                 o 
                               
                               - 
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                             ) 
                           
                           2 
                         
                       
                       . 
                     
                   
                 
               
             
           
         
       
     
     The nominal first order magnification, m, of an optical relay system is given by 
     
       
         
           
             m 
             = 
             
               
                 
                   s 
                   i 
                 
                 
                   s 
                   o 
                 
               
               . 
             
           
         
       
     
     For a relay system with a nominal magnification of unity, the object and image distances s o  and s i  are therefore equal to one another and can be expressed in terms of the focal length as
 
 s   o   =s   i =2 f  
 
which when substituted into the differential equation above results in
 
     
       
         
           
             
               
                 ∂ 
                 D 
               
               
                 ∂ 
                 
                   s 
                   o 
                 
               
             
             = 
             
               
                 
                   ∂ 
                   
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                       s 
                       o 
                     
                   
                 
                 ⁢ 
                 
                   ( 
                   
                     
                       s 
                       o 
                       2 
                     
                     
                       
                         s 
                         o 
                       
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                       f 
                     
                   
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               = 
               
                 
                   1 
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                       f 
                       2 
                     
                     
                       
                         ( 
                         
                           
                             2 
                             ⁢ 
                             f 
                           
                           - 
                           f 
                         
                         ) 
                       
                       2 
                     
                   
                 
                 = 
                 0. 
               
             
           
         
       
     
     The significance of this relationship is that for a unity magnification optical relay, small changes in the object distance can be compensated for by the image distance such that the object to image distance is maintained. 
     Substitution of the expression for the image distance in terms of the object distance into the expression for the system magnification results in 
             m   =         s   i       s   o       =     f       s   o     -   f               
and differentiation of that expression with respect to small changes in the object distance results in
 
     
       
         
           
             
               
                 ∂ 
                 m 
               
               
                 ∂ 
                 
                   s 
                   o 
                 
               
             
             = 
             
               
                 
                   ∂ 
                   
                     ∂ 
                     
                       s 
                       o 
                     
                   
                 
                 ⁢ 
                 
                   ( 
                   
                     f 
                     
                       
                         s 
                         o 
                       
                       - 
                       f 
                     
                   
                   ) 
                 
               
               = 
               
                 
                   
                     - 
                     f 
                   
                   
                     
                       ( 
                       
                         
                           s 
                           o 
                         
                         - 
                         f 
                       
                       ) 
                     
                     2 
                   
                 
                 = 
                 
                   - 
                   
                     
                       1 
                       f 
                     
                     . 
                   
                 
               
             
           
         
       
     
     The significance of this relationship is that for a unity magnification optical relay, small changes in the object distance produce a substantially linear change in magnification that is inversely proportional to the focal length of the relay, while the object plane to image plane distance remains substantially unchanged. 
     Reference is made to  FIGS. 2A and 2B , there are illustrated schematic views of an optical imaging system  200 , taken along its optical axis, in accordance with an embodiment of the present disclosure. 
     Reference is made to  FIG. 2A , an optical imaging system  200  including relay imager  40  illustrated in  FIG. 1 . In one embodiment, relay imager  40 , which comprises, but not limited to, refractive elements  52 ,  53 ,  54 ,  55 ,  56 ,  62 ,  63 ,  64 ,  65 ,  66 , and  70 , is translated along the optical axis  10  towards the object plane  30  according to the first order optical relationships described herein such that the magnification of the optical imaging system  200  is increased relative to that of the optical imaging system  100  illustrated in  FIG. 1 , while the distance between the object plane  20  and the image plane  30  is maintained. A view of a representative image  232  at the image plane  30  for this embodiment  200 , taken along a plane perpendicular to the optical axis  10 , is shown next to the image plane  30 . 
     Reference is also made to  FIG. 2B , an optical imaging system  300  including relay imager  40  illustrated in  FIG. 1 . In one embodiment, relay imager  40 , which comprises, but not limited to, refractive elements  52 ,  53 ,  54 ,  55 ,  56 ,  62 ,  63 ,  64 ,  65 ,  66 , and  70 , is translated along the optical axis  10  towards the image plane  30  according to the first order optical relationships described herein such that the magnification of the optical imaging system  300  is decreased relative to that of the optical imaging system  100  illustrated in  FIG. 1 , while the distance between the object plane  20  and the image plane  30  is maintained. A view of a representative image  332  at the image plane  30  for this embodiment  300 , taken along a plane perpendicular to the optical axis  10 , is shown next to the image plane  30 . 
     Reference is made to  FIG. 3A , which is a schematic view of a refractive relay spectrometer  400 , taken along an optical axis  410  in the plane parallel to the direction of dispersion. See, for example, U.S. Pat. No. 7,061,611, which is incorporated herein by reference in its entirety for all purposes. In operation, light emitted or reflected by a source located at the object plane (for example, a slit or other method of extracting a line image, hereinafter referred to generally as a slit element  420 ) is incident on an optical relay imager  440 . In one embodiment, a refractive relay spectrometer  400  comprises, but not limited to, refractive elements  452 ,  453 ,  454 ,  455 ,  456 ,  462 ,  463 ,  464 ,  465 , and  466  and a dispersing element  470 . 
     In one embodiment, dispersing element  470  is a transmission diffraction grating, which can separate light energy angularly according to its wavelength (hereinafter referred to generally as a dispersing element). The optical relay imager  440  is capable of substantially receiving a portion of the light emanating from the slit  420  and substantially reimaging the light from the slit  420  and dispersing it according to its wavelength and substantially focusing the light to an image plane  430 . A view of a representative image  432  at the image plane  430  for refractive relay spectrometer  400 , taken along a plane parallel to image plane  430 , is shown next to the image plane  430 . 
     Reference is made to  FIG. 3B , which is a schematic view of refractive relay spectrometer  400 , taken along its optical axis  410  in the plane perpendicular to the direction of dispersion. In operation, light emanating from the slit element  420  is imaged by the optical relay imager  440  onto the image plane  430  in this embodiment with, but not limited to, unity magnification. 
     Reference is made to  FIG. 4A , which illustrates a schematic view of an optical imaging system  500 , taken along its optical axis  410  in the plane parallel to the direction of dispersion, in accordance with an embodiment of the present disclosure. In this embodiment, the relay imager  440  of the spectrometer  400  illustrated in  FIG. 3A  is translated along the optical axis  410  towards the slit  420  according to the first order optical relationships described herein such that the magnification of the optical imaging system  500  is increased relative to that of the optical imaging system  400  illustrated in  FIG. 3A , while the distance between the slit  420  and the image plane  430  is maintained. A view of a representative image  532  at the image plane  430  for optical imaging system  500 , taken along a plane parallel to the image plane  430 , is shown next to the image plane  430 . 
     Reference is also made to  FIG. 4B , which illustrates a schematic view of an optical imaging system  600 , taken along the optical axis  410  in the plane parallel to the direction of dispersion, in accordance with an embodiment of the present disclosure. In this embodiment, the relay imager  440  of the spectrometer  400  illustrated in  FIG. 3A  is translated along the optical axis  410  towards the image plane  430  according to the first order optical relationships described herein such that the magnification of the optical imaging system  600  is decreased relative to that of the optical imaging system  400  illustrated in  FIG. 3A , while the distance between the slit  420  and the image plane  430  is maintained. A view of a representative image  632  at the image plane  430  for optical imaging system  600 , taken along a plane parallel to the image plane  430 , is shown next to the image plane  430 . 
     The translation of the relay imager  40  in the embodiments of the optical imaging systems  200  and  300  and the translation of the relay imager  440  in the embodiments of the optical imaging systems  500  and  600  can be accomplished through any number of means, including but not limited to, a moveable platform, having the platform attached to rails and having a component such as but not limited to a drive motor or screw, that causes the motion of the platform, or by mounting the relay imager within a mechanical housing that is translated by means of displacing components such as but not limited to shims or spacers. 
     In addition to changing the magnification of the hyperspectral imager, the optical system  400  illustrated in  FIG. 3A  is also capable of changing the spectral resolution of the optical system, as the relay imager  440  is translated along the optical axis  410 , where translation towards the slit  420  increases the spectral resolution and translation towards the detector  430  decreases the spectral resolution. It should be noted that the relay imager components of the various embodiments can be made up of any combination of refractive or reflective optical elements. 
     As used herein, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. Except where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” 
     For the purpose of better describing and defining the present invention, it is noted that terms of degree (e.g., “substantially,” “about,” and the like) may be used in the specification and/or in the claims. Such terms of degree are utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, and/or other representation. The terms of degree may also be utilized herein to represent the degree by which a quantitative representation may vary (e.g., ±10%) from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     Although embodiments of the present teachings have been described in detail, it is to be understood that such embodiments are described for exemplary and illustrative purposes only. Various changes and/or modifications may be made by those skilled in the relevant art without departing from the spirit and scope of the present disclosure as defined in the appended claims.