Abstract:
The present disclosure provides a spectrometer. In one aspect, the spectrometer includes at least one slit element located at an object plane, an optical sub-system having at least one optical element, at least one dispersive element, and at least one detecting element located substantially at an image plane. The optical sub-system is configured to substantially collimate, at said dispersive element, electromagnetic radiation emanating from said at least one slit element, configured to substantially image the substantially collimated electromagnetic radiation from said dispersive element onto the image plane, and configured to have a substantially variable focal length.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provision Application No. 61/793,844, filed Mar. 15, 2013, the entire contents of which is incorporated herein by reference and for all purposes. 
    
    
     BACKGROUND 
     These teachings generally relate to spectrometers. 
     There is a need for designs that have the capability to adjust the spatial or spectral resolution of a spectrometer. 
     SUMMARY 
     Various embodiments of the present disclosure provide a spectrometer with adjustable spatial and/or spectral resolution. 
     Certain characteristics of the present disclosure provide a spectrometer design that has adjustable spatial resolution. 
     Further characteristics of the present disclosure provide a spectrometer design that has adjustable spectral resolution. 
     Further characteristics of the present disclosure provide a spectrometer design that is compact in size. 
     Still further characteristics of the present disclosure provide a spectrometer design that has a combination of the characteristics described above with superior trade-offs than have been previously attainable. 
     For a better understanding of the present invention, together with other and further objects thereof, reference is made to the accompanying drawings and detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1B  are schematic views of a previously presented compact refractive relay spectrometer, taken along its optical axis in the plane parallel to and perpendicular to the direction of dispersion respectively: 
         FIGS. 2A-2F  are schematic views of an optical imaging system, taken along its optical axis, in accordance with an embodiment of the present disclosure; 
         FIGS. 3A-3F  are schematic views of an optical imaging system, taken along its optical axis, in accordance with another embodiment of the present disclosure; and 
         FIGS. 4A-4D  are schematic views of an optical imaging system, taken along its optical axis, in accordance with still another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Relay imagers and spectrometer designs which have adjustable spatial or spectral resolution are disclosed herein below. 
     Reference is made to  FIG. 1A , which is a schematic view of a conventional refractive relay spectrometer  100 , taken along its optical axis  60  in the plane parallel to the direction of dispersion. See, for example, U.S. Pat. No. 7,061,611, which is incorporated here by reference in its entirety for all purposes. Reference is made to  FIG. 1B , which is a schematic view of the refractive relay spectrometer  100  illustrated in  FIG. 1A , taken along its optical axis  60  in the plane perpendicular to the direction of dispersion. 
     In operation, 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 (in this embodiment, but not limited to, a slit or other method of extracting a line image, hereinafter referred to generally as a slit element  110 ) is incident on an optical system  120 , which is capable of substantially receiving a portion of the light emanating from the slit  110  and substantially collimating the light at a plane  140 . The light is then incident on a dispersing element  135 , which is located substantially at the center plane  140  and capable of substantially receiving the light from the optical system  120  and capable of substantially reflecting the light and dispersing it according to its wavelength. The reflected dispersed light is then incident on the optical system  120 , which is capable of substantially receiving the reflected dispersed light from the dispersing element  135  and substantially focusing the light to a detecting element  150 . 
     In certain applications, it is often desirable for reasons such as, but not limited to, illumination conditions, spectral or spatial feature sizes of the desired target, or data collection rates, to have the capability to adjust the spatial or spectral resolution of a spectrometer. Spectrometer designs having the dynamic system resolution of the present teachings can provide this capability. 
     One embodiment of an optical imaging system is illustrated in  FIGS. 2A-2F , where the spectral imaging characteristics for two different zoom configurations, a first configuration having a maximum spectral resolution and a second configuration having a minimum spectral resolution, are shown in  FIG. 2A  and  FIG. 2D  respectively. In  FIG. 2A , the spectrometer is zoomed to its maximum spectral resolution configuration by translating at least one portion of the optical elements of an optical system  220 , in this embodiment made up of, but not limited to, the two portions  230  and  240 , such that the effective single pass focal length of the optical system  220  is at a maximum value. In this maximum spectral resolution configuration, light that is passed by the slit  210  is first collimated by the optical system  220  onto the dispersing element  250 , where it is then reflected and dispersed according to its wavelength, and is finally focused by the optical system  220  in its second pass onto a detecting element  260 . 
     In  FIG. 2D , the optical system  220  is zoomed to its minimum spectral resolution configuration by translating at least one portion of the optical elements of the optical system  220 , in this embodiment made up of, but not limited to, the two portions  230  and  240 , such that the effective single pass focal length of the optical system  220  is at a minimum value. Since the dispersion of the dispersing element  250  is unchanged, the shorter focal length of the optical system  220  results in a smaller spatial extent of the dispersed imagery on the detecting element  260 , which for a fixed spatial detector resolution results in a lower spectral resolution. 
     Reference is made to  FIG. 2A , which is a schematic view of an embodiment of an optical imaging system  200 , taken along its optical axis  205  in the plane parallel to the direction of dispersion. In operation, light emitted or reflected by the source, located at the slit element  210 , is incident on the optical system  220 , in this embodiment made up of, but not limited to, refractive elements  222 ,  223 ,  224 ,  225 ,  226 , and  227 , which is capable of substantially receiving a portion of the light emanating from the slit  210  and substantially collimating the light substantially at the dispersing element  250 , which is capable of substantially receiving the light from the optical system  220  and capable of substantially reflecting the light and dispersing it according to its wavelength. The reflected dispersed light is then incident on the optical system  220 , which is capable of substantially receiving the reflected dispersed light from the dispersing element  250  and substantially focusing the light to the detecting element  260 . 
     Reference is now made to  FIG. 2D , which is a schematic view of an embodiment of an optical imaging system  300 , taken along its optical axis  205  in the plane parallel to the direction of dispersion, where a portion of the optical elements in the optical system  220  of the embodiment of the optical system  200  illustrated in  FIG. 2A  are translated along the optical axis  205 . In operation, light emitted or reflected by the source, located at the slit element  210 , is incident on the optical system  320 , in this embodiment made up of, but not limited to, refractive elements  222 ,  223 ,  224 ,  225 ,  226 , and  227 , which is capable of substantially receiving a portion of the light emanating from the slit  210  and substantially collimating the light substantially at the dispersing element  250 , which is capable of substantially receiving the light from the optical system  320  and capable of substantially reflecting the light and dispersing it according to its wavelength. The reflected dispersed light is then incident on the optical system  320 , which is capable of substantially receiving the reflected dispersed light from the dispersing element  250  and substantially focusing the light to the detecting element  260 . 
       FIG. 2B  and  FIG. 2C  illustrate the spatial imaging characteristics of the embodiment of the optical imaging system  200  illustrated in  FIG. 2A  in its maximum spectral resolution configuration while  FIG. 2E  and  FIG. 2F  illustrate the spatial imaging characteristics of the embodiment of the optical imaging system  300  illustrated in  FIG. 2B  in its minimum spectral resolution configuration. In both embodiments of the optical system  200  and  300 , light emanating from the slit  120  is first collimated by the optical systems  220  and  320  respectively onto the dispersing element  250 , as illustrated in  FIG. 2B  and  FIG. 2E  for the maximum and minimum spectral resolution configurations of the embodiments of the optical imaging system  200  and  300  respectively. The light is then reflected and dispersed according to its wavelength by the dispersing element  250 , and is focused by the same optical system  220  and  320  onto the detecting element  260 , as illustrated in  FIG. 2C  and  FIG. 2F  respectively, for the maximum and minimum spectral resolution configurations of the embodiments of the optical imaging system  200  and  300  respectively. In both embodiments of the optical system  200  and  300 , the spatial magnification of the light emanating from the slit  210  is maintained substantially at unity regardless of the change in spectral resolution due to the symmetry of the double pass design form. 
     Another embodiment of an optical imaging system  400  is illustrated in  FIGS. 3A-3B , where a zoom imager, the working principles of which may be known in the art, is inserted in front of the slit, such that the image plane of the zoom imager is located substantially at the slit element of optical imaging system  200  illustrated in  FIG. 2A , in order to provide an image of a the scene with a variable spatial resolution. 
     In  FIG. 3A , the spectral imaging characteristics of the optical imaging system  400  are illustrated where the zoom imager  420  is shown providing imagery to the slit  210  of optical imaging system  200  illustrated in  FIG. 2A , and the optical system  220  of optical imaging system  200  illustrated in  FIG. 2A  is in its maximum spectral dispersion configuration. 
     Reference is made to  FIG. 3B , where the zoom imager  420  is zoomed to its maximum focal length configuration by translating at least one portion of the optical elements of the zoom imager  420  comprising two portions  430  and  440 . The spatial imaging characteristics of optical imaging system  400  are illustrated where the zoom imager  430  is shown in its maximum focal length configuration, providing narrow field of view imagery to the slit. 
     Reference is now made to  FIG. 3C , which is another embodiment of an optical imaging system  500 , where the zoom imager  420  of optical imaging system  400  illustrated in  FIG. 3B  is zoomed to its minimum focal length configuration by translating at least one portion of the optical elements in the zoom imager  420  comprising two portions  430  and  440 . The spatial imaging characteristics of optical imaging system  500  are illustrated where the zoom imager  430  is shown in its minimum focal length configuration, providing wide field of view imagery to the slit. This variation in field of view of the imager  420  results in a corresponding variation in the spatial resolution of the embodiments of the optical imaging system  400  and  500  at both the slit  210  and detector  260 . 
     These embodiments of the optical imaging systems  400  and  500  illustrated in  FIGS. 3A-3B  and  FIG. 3C  respectively are further illustrated in  FIGS. 3D-3F , where the optical imaging system  200  has been adjusted to its minimum spectral resolution configuration, as illustrated in optical imaging system  300  of  FIG. 2D . 
     In  FIG. 3D , the spectral imaging characteristics of optical imaging system  600  are illustrated where the zoom imager  420  is shown providing imagery to the slit  210  of optical imaging system  300  illustrated in  FIG. 2D , and the optical system  320  of optical imaging system  300  illustrated in  FIG. 2D  is in its maximum spectral dispersion configuration. 
     Reference is made to  FIG. 3E , where the zoom imager  420  is zoomed to its maximum focal length configuration by translating at least one portion of the optical elements of the zoom imager  420  comprising two portions  430  and  440 . The spatial imaging characteristics of optical imaging system  600  are illustrated where the zoom imager  430  is shown in its maximum focal length configuration, providing narrow field of view imagery to the slit. 
     Reference is now made to  FIG. 3F , which is another embodiment of an optical imaging system  700 , where the zoom imager  420  of optical imaging system  400  illustrated in  FIG. 3B  is zoomed to its minimum focal length configuration by translating at least one portion of the optical elements in the zoom imager  420  comprising two portions  430  and  440 . The spatial imaging characteristics of optical imaging system  500  are illustrated where the zoom imager  430  is shown in its minimum focal length configuration, providing wide field of view imagery to the slit. This variation in field of view of the zoom imager  420  results in a corresponding variation in the spatial resolution of optical imaging system  600  and  700  at both the slit  210  and detector  260 . The combination of the zoom imager  420  with optical imaging system  200  and  300  results in a hyperspectral imaging system that provides the capability to vary the spatial and spectral resolutions independent of one another. 
     A further embodiment of an optical system is illustrated in  FIGS. 4A-4B , where the spectral imaging characteristics for two different zoom configurations, a first configuration having a maximum spectral resolution and a second configuration having a minimum spectral resolution, are shown in  FIG. 4A  and  FIG. 4B  respectively. 
     In  FIG. 4A , the spectrometer is zoomed to its maximum spectral resolution configuration by translating at least one portion of the optical elements of a first optical system  820  comprising two portions  830  and  840 , and a second optical system  870  comprising two portions  880  and  890 , such that effective single pass focal lengths of the first optical system  820  and the second optical system  870  are at a maximum value. In this maximum spectral resolution configuration, light that is passed by the slit  810  is collimated by the first optical system  820  onto the dispersing element  850 , where it is then transmitted and dispersed according to its wavelength, and is focused by the second optical system  870  onto the detecting element  860 . 
     In  FIG. 4B , the first optical system  820  and the second optical system  870  are zoomed to their minimum spectral resolution configuration by translating at least one portion of the optical elements of the first optical system  820  comprising two portions  830  and  840 , and the second optical system  870  comprising two portions  880  and  890 , such that the effective single pass focal lengths of the first optical system  820  and the second optical system  870  are at a minimum value. Since the dispersion of the dispersing element  850  is unchanged, the shorter focal length of the second optical system  870  results in a smaller spatial extent of the dispersed imagery on the detecting element  860 , which for a fixed spatial detector resolution results in a lower spectral resolution. The first optical system  820  and second optical system  870  are typically substantially symmetric about the dispersing element  850 , where the two portions  830  and  840  of the first optical system  820  and the two portions  880  and  890  of the second optical system  870  are symmetrically slaved to one another respectively. This design form is essentially an unfolded version of the zoomed double pass design described previously and illustrated in  FIGS. 2A-2F . 
     Reference is made to  FIG. 4A , which is a schematic view of an embodiment of an optical imaging system  800 , taken along its optical axis  805  in the plane parallel to the direction of dispersion. In operation, light emitted or reflected by the source, located at the slit element  810 , is incident on the first optical system  820  comprising refractive elements  822 ,  823 ,  824 ,  825 ,  826 , and  827 , which is capable of substantially receiving a portion of the light emanating from the slit  810  and substantially collimating the light substantially at the dispersing element  850 , which is capable of substantially receiving the light from the optical system  820  and capable of substantially transmitting the light and dispersing it according to its wavelength. The transmitted dispersed light is then incident on the second optical system  870  comprising refractive elements  872 ,  873 ,  874 ,  875 ,  876 , and  877 , which is capable of substantially receiving the transmitted dispersed light from the dispersing element  850  and substantially focusing the light to the detecting element  860 . 
     Reference is now made to  FIG. 4B , which is a schematic view of an embodiment of an optical imaging system  900 , taken along its optical axis  805  in the plane parallel to the direction of dispersion, where a portion of the optical elements in the optical system  820  of optical system  800  illustrated in  FIG. 4A  are translated along the optical axis  805 . In operation, light emitted or reflected by the source, located at the slit element  810 , is incident on the first optical system  920  comprising refractive elements  822 ,  823 ,  824 ,  825 ,  826 , and  827 , which is capable of substantially receiving a portion of the light emanating from the slit  810  and substantially collimating the light substantially at the dispersing element  850 , which is capable of substantially receiving the light from the first optical system  920  and capable of substantially transmitting the light and dispersing it according to its wavelength. The transmitted dispersed light is then incident on the second optical system  970  comprising refractive elements  822 ,  823 ,  824 ,  825 ,  826 , and  827 , which is capable of substantially receiving the transmitted dispersed light from the dispersing element  850  and substantially focusing the light to the detecting element  860 . 
       FIG. 4C  illustrates the spatial imaging characteristics of the embodiment of the optical imaging system  800  illustrated in  FIG. 4A  in its maximum spectral resolution configuration while  FIG. 4D  illustrates the spatial imaging characteristics of optical imaging system  900  illustrated in  FIG. 4B  in its minimum spectral resolution configuration. In both embodiments of the optical system  800  and  900 , light emanating from the slit  220  is first collimated by the first optical systems  820  and  830  respectively onto the dispersing element  850 , as illustrated in  FIG. 4C  and  FIG. 40  for the maximum and minimum spectral resolution configurations of the embodiments of the optical imaging system  800  and  900  respectively. The light is then transmitted and dispersed according to its wavelength by the dispersing element  250 , and is focused by the second optical systems  870  and  970  respectively onto the detecting element  860 . In both embodiments of the optical system  800  and  900 , the spatial magnification of the light emanating from the slit  820  is maintained substantially at unity regardless of the change in spectral resolution due to the symmetry of the refractive relay design form. 
     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 disclosure, 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.