Patent Publication Number: US-8526097-B2

Title: Tunable detection system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present divisional application claims priority to U.S. patent application Ser. No. 12/509,154, filed Jul. 24, 2009, entitled “TUNABLE DETECTION SYSTEM,” the disclosures of which are expressly incorporated by reference herein. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used and licensed by or for the United States Government for any governmental purpose without payment of any royalties thereon. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to devices for detecting the presence of an object or substance, and, more particularly, to devices for detecting the presence of an object or substance with a tunable detection system. 
     It is known to use Fiber Bragg gratings to selectively separate a portion of a spectrum from the remainder of the spectrum. In a Fiber Bragg grating a periodic change in index of refraction is provided in the core of the fiber. Based on the indexes of refraction of the core materials and the spacing of the periodic structure a given bandwidth is separated from an input spectrum. Fiber Bragg gratings are useful in communication and sensor applications. 
     It is desirable to have a non-fiber based tunable detection system which may be used to identify the presence of one or more elements, molecules, chemicals, biological materials, materials, substances, and objects (collectively referred to as “targets”) within an ambient environment or as part of a target of interest in a detection zone. 
     SUMMARY OF THE INVENTION 
     In an exemplary embodiment of the present disclosure, a tunable bandwidth selector is provided. In one example, the tunable bandwidth selector is non-fiber based. The tunable bandwidth selector may be used as part of a stand off chemical and/or biological agent detection device. The tunable bandwidth selector may be used as part of a hyper-spectral imaging device. The tunable bandwidth selector may be used as part of a screening system. The tunable bandwidth selector may be used in a non-imaging detection or evaluation system. The tunable bandwidth selector may be used in an imaging detection or evaluation system. 
     In another exemplary embodiment of the present disclosure, a method for separating a first bandwidth from an input spectrum including the first bandwidth is provided. The method comprising: providing a plurality of spaced apart electron sheets; introducing the input spectrum to the plurality of spaced apart electron sheets such that at least a first portion of the input spectrum transverses the plurality of spaced apart electron sheets; and adjusting the plurality of spaced apart electron sheets so that the first bandwidth is separated from the input spectrum. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings. 
         FIG. 1  is a representative view of an exemplary tunable detection system tuned to a first bandwidth; 
         FIG. 1A  is a representative view of a portion of the exemplary tunable detection system of  FIG. 1 ; 
         FIG. 2  is a representative view of the exemplary tunable detection system of  FIG. 1  being tuned to a second bandwidth; 
         FIG. 3  is a representative view of another exemplary tunable detection system; 
         FIG. 4  is a representative view of yet another exemplary tunable detection system; 
         FIG. 5  is a representative view of another is a representative view of yet another exemplary tunable detection system having a plurality of non-imaging detectors; 
         FIG. 6  is a representative view of yet another exemplary tunable detection system having a plurality of non-imaging detectors; 
         FIG. 7  is a representative view of yet another exemplary tunable detection system having a plurality of non-imaging detectors; 
         FIG. 8  is a representative view of another is a representative view of yet another exemplary tunable detection system having a plurality of imaging systems; 
         FIG. 8A  is a representative view of an exemplary imaging system; 
         FIG. 9  is a representative view of yet another exemplary tunable detection system having a plurality of imaging systems; 
         FIG. 10  is a representative view of yet another exemplary tunable detection system having a plurality of imaging systems; 
         FIG. 11  is a representative view of a portable detection system which is monitoring a piece of luggage in a detection zone; 
         FIG. 12  is a representative view of the portable detection system of  FIG. 11  wherein the luggage is radiated by an energy source located opposite of the portable detection system; 
         FIG. 13  is a representative view of the portable detection system of  FIG. 11  wherein the luggage is radiated by an energy source located generally on the same side of the luggage as the portable detection system; 
         FIG. 14  is a representative view of a luggage scanning system; 
         FIG. 15  is a representative view of the information stored on a memory accessible by a controller of any of the preceding detection systems wherein the operator specifies a characteristic of the bandwidth to be detected by the respective detection system; 
         FIG. 16  is a representative view of the information stored on a memory accessible by a controller of any of the preceding detection systems wherein the operator specifies a target to be detected by the respective detection system; 
         FIG. 17  is a representative processing sequence of the detection software executed by the controller of any of the preceding detection systems; 
         FIG. 18  is a representative processing sequence of the detection software executed by the controller of any of the preceding detection systems; 
         FIG. 19  illustrates an arrangement to provide interlaced electron sheets; and 
         FIG. 20  illustrates an arrangement to provide interlaced electron sheets. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of various features and components according to the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the present disclosure. The exemplification set out herein illustrates embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE DRAWINGS 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, which are described below. The embodiments disclosed below are not intended to be exhaustive or limit the invention to the precise form disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may utilize their teachings. It will be understood that no limitation of the scope of the invention is thereby intended. The invention includes any alterations and further modifications in the illustrated devices and described methods and further applications of the principles of the invention which would normally occur to one skilled in the art to which the invention relates. 
     Referring to  FIG. 1 , a tunable detection system  100  is shown. Detection system  100  includes a tunable bandwidth selector  102  which is supported on a support  104 . Support  104  may be any suitable type of support and may include a frame for securing the components of tunable bandwidth selector  102  and a housing for enclosing tunable bandwidth selector  102 . In one embodiment, support provides a sealed cavity including the tunable bandwidth selector  102 . The sealed cavity may define a vacuum medium  103 . The sealed cavity may include other types of medium  103 , such as a gas and other suitable mediums. 
     Tunable bandwidth selector  102  receives electromagnetic radiation  106  which includes a plurality of different wavelengths generally referred to herein as an input spectrum  108 . For illustration of the operation of tunable bandwidth selector  102 , input spectrum  108  is represented as having six bandwidths  110 A- 110 F. Each of bandwidths  110 A-F may be comprised of a single wavelength or a plurality of wavelengths. Of course input spectrum  108  may be composed of numerous bandwidths spanning various traditional spectral bands including white light, ultraviolet, infrared, and other spectral bands. 
     Tunable bandwidth selector  102  functions to separate a first bandwidth from the remainder of input spectrum  108 , if the first bandwidth is present in input spectrum  108 . In one embodiment, the first bandwidth is a spectrum centered on a specific wavelength. In one embodiment, the first bandwidth is a single wavelength. 
     Referring to  FIG. 1 , tunable bandwidth selector  102  includes a plurality of spaced apart electron sheets  112 A-G. Electromagnetic radiation  106  moves generally in direction  114  such that input spectrum  108  encounters electron sheets  112 . Each of electron sheets  112  is comprised of a plurality of electrons which are provided by an electron source  118  and are traveling towards a charged plate  120 . An exemplary electron source is a heated filament which is heated by a power supply  122 . An exemplary power supply is a high voltage DC source. In one example, the high voltage DC source may be modulated between zero volts and a first voltage. The first voltage should be of a value to create the electron sheets  112 . In one example, the first voltage is high enough to create the electron sheets and to vary the electron density of the electron sheets. In one embodiment, a variable AC source may be used to produce a modulated waveform. In one embodiment, one or more function generators may be used to produce a modulated density in the electron sheets  112 . A variation in the density of an electron sheet  112  changes the index of refraction of the electron sheet  112 . 
     The plurality of electron sheets  112  are spaced apart from adjacent electron sheets  112 . In one embodiment, the spacing of electron sheets  112  is constant. In one embodiment, the spacing of electron sheets  112  is constant between adjacent sheets, but differs across the collection of electron sheets  112 . Although seven electron sheets  112  are shown tunable bandwidth selector  102  may include less electron sheets  112  or more electron sheets  112 . In one embodiment, electron sheets  112  are generally planar sheets. In one embodiment, electron sheets  112  are generally cylindrical sheets. Additionally the cylindrical electron sheets can be of a fixed radius of curvature, a variable radius of curvature, or have an elliptical curvature where the radius varies as a function of position. 
     Each of electron sheets  112  pass through a medium  103  in the region wherein electron sheets  112  are provided. Medium  103  has a first index of refraction, n 1 . Electron sheets  112  have a second index of refraction n 2  which differs from n 1 . As electromagnetic radiation  106  moves in direction  114 , the difference in index of refraction between electron sheets  112  and medium  103  and the spacing of electron sheets  112  causes a first bandwidth of input spectrum  108  to be generally separated from the remainder of input spectrum  108 . The first bandwidth is generally reflected by tunable bandwidth selector  102  and the remainder of input spectrum  108  is generally passed by tunable bandwidth selector  102 . 
     A central wavelength of the first bandwidth is provided by the relationship in equation 1
 
λ fb =( n   1   +n   2 ) d   (1)
 
wherein λ fb  is the central wavelength, n 1  is the index of refraction of medium  103 , n 2  is the index of refraction of electron sheets  112 , and d is the spacing of electron sheets  112 . The first bandwidth is provided by the relationship in equation 2
 
Δλ=2( n   2   −n   1 )(1/π)λ fb   (2)
 
wherein Δλ is the first bandwidth, λ fb  is the central wavelength, n 1  is the index of refraction of medium  130 , n 2  is the index of refraction of electron sheets  112 , and π is a constant.
 
     As provided by equations 1 and 2, the first bandwidth separated by tunable bandwidth selector  102  may be adjusted by adjusting various parameters including the index of refraction of medium  103 , the index of refraction of electron sheets  112 , a spacing of electron sheets  112 , and combinations thereof. 
     The index of refraction of medium  103  may be adjusted by changing the medium of medium  103 . In one embodiment, the index of refraction of medium  103  may be adjusted by changing a temperature of the medium of medium  103 . 
     The index of refraction of electron sheets  112  may be adjusted by changing a density of electrons in electron sheets  112 . The density of the electron sheets is dependent upon the temperature of the electron emitting filament, the dimensions of the output aperture which establishes the geometry of the electron plane, the potential difference establishing the electron plane, the medium into which the electron planes are injected, the distance the electron plane travels, and the energy of the electron plane. In one embodiment the density of electron sheets  112  may be changed by kilo electron Volts for one particular set of index of refraction and by mega electron volts for other particular variations for a required range of indexes of refraction. In one embodiment the index of refraction of electron sheets  112  may be determined by the relationship of equation 3 
                   n   =     1   +         λ   0     +     β   ⁢          A        2           k   s                 (   3   )               
wherein n is effective index of refraction, 1 is the index of refraction resultant from being in a vacuum, λ 0  is the fundamental wavelength, β is the radiation field modifier which is a function of wave-number and variations in the energy of the electron beam, A is the amplitude of the radiation field, and k s  is the wave-number of the radiation field. In another embodiment where the electron sheets are produced by a plasma or result in the creation of a plasma the index of refraction of electron sheets  112  may be determined by the relationship of equation 4
 
                   n   =       1   -       N   elec       N   crit                   (   4   )               
wherein n is effective index of refraction, N elec  is the electron density of the plasma, and N crit  is the plasma critical density.
 
     The spacing of electron sheets  112  may be changed by adjusting the relative location of electron sheets  112 . Referring to  FIG. 1 , electron sheets  112  are generated by electrons provided by electron source  118  traveling towards charged plate  120 . These electrons are formed into electron sheets  112  as they pass through openings  138 , such as rectangular slits, in a charged filter plate  136  and extend through a detection area including medium  103  (in this case a vacuum) to charged plate  120  as represented in  FIG. 1A .  FIG. 1A  illustrates the initial spacing of the electron sheets  112  (without the influence of magnetic field  140 ). The initial spacing of electron sheets  112  is set by the spacing of the openings  138  wherein the electron sheets  112  travel straight down to charged plate  120 . 
     In addition to the electron sheets  112  shown in  FIG. 1A , additional sets of electron sheets  112  may be generated by additional sets of electron sources  118  and charged plates  120 . Referring to  FIG. 19 , electron source  118  is represented with electrons traveling in direction  142  (also shown in  FIG. 1A ) towards charged plate  120 . An additional electron source  118 A and charged plate  120 A are also provided (along with charged plate  136 A and devices  141 A which produce a magnetic field to alter the spacing of the electron sheets produced by the combination of electron source  118 A and charged plates  136 A and  120 A). Electrons travel in direction  144  (also shown in  FIG. 1A ) from electron source  118 A towards charged plate  120 A. In one embodiment, this additional set of electron source  118 A and charged plate  120 A may produce a plurality of spaced apart electron sheets which are interlaced between the electron sheets  122  of electron source  118  and charged plate  120 . For example, a first electron sheet corresponding to source  118 A may be positioned between electron sheet  112 A and  112 B and a second electron sheet corresponding to source  118 A may be positioned between electron sheet  112 B and  112 C. Assuming that the electron sheets corresponding to source  118 A are equally spaced from the surrounding electron sheets corresponding to source  118 , then the spacing between the collective electron sheets is halved. The spacing of all of the electron sheets may be varied based on the methods discussed herein. Referring to  FIG. 20 , the arrangement of  FIG. 19  is further generalized to include a third electron source  118 B and a third charged plate  120 B which produce a third set of electron sheets (along with charged plate  136 B and devices  141 B which produce a magnetic field to alter the spacing of the electron sheets produced by the combination of electron source  118 B and charged plates  136 B and  120 B). The electron sheets corresponding to sources  118 ,  118 A, and  118 B travel in directions  142 ,  146 , and  148 , respectively. The three sets of electron sheets may be interlaced to result in even further narrowing of the spacing between the collective electron sheets. Any number of electron sources and charged plates may be used to provide further narrowing of the spacing of the collective electron sheets. 
     In one embodiment, a magnetic field  140  may be introduced to alter the spacing of the electron planes  120 . By controlling the strength of the magnetic field  140  the spacing of electron sheets  112  may be altered. A plurality of devices  141  are provided to control the overall magnetic field  140  in a localized manner meaning that the field strength of magnetic field  140  may differ at different locations based on the magnetic fields produced by the devices  141  proximate to the respective locations. In one embodiment, a plurality of micro-electronic mechanical structures (“MEMS”) are provided to control the strength of the magnetic field  140  by controlling their own localized and isolated magnetic fields. Each of the MEMS devices are controlled by controller  150 . Thus, controller  150  is able to vary the magnetic field differently relative to different MEMS devices to steer the electron sheets as desired. In one embodiment, individual isolated magnetic cores are provided to control the strength of the magnetic field  140  by controlling their own localized and isolated magnetic fields. In one embodiment, the magnetic cores are selected from either C, U, and I-shaped cores with high permeability to direct magnetic fields. In one embodiment, the magnetic cores are tapered to provide a small cross-section in the area corresponding to the electron beams. In one embodiment, the magnetic cores are laminated to prevent cross-currents or eddy currents. Each of the magnetic cores are controlled by controller  150 . Thus, controller  150  is able to vary the magnetic field differently relative to different magnetic cores to steer the electron sheets as desired. 
     In one embodiment, the strength of magnetic field  140  is controlled by a controller  150  having software provided on a memory  152  accessible by controller  150 . As explained herein, controller  150  may alter one or more of the index of refraction of medium  103 , the index of refraction of electron sheets  112 , a spacing of electron sheets  112 , and combinations thereof. As such, tunable bandwidth selector  102  may be tunable to select different bandwidths at different times. In this manner, tunable bandwidth selector  102  may be used to monitor a region for a plurality of different bandwidths. As is known various targets give off characteristic electromagnetic spectrum. As such, with detection system  100  a specific type of target may be detected based on the presence and/or the magnitude of the various wavelengths that are monitored. Examples include chemical monitoring, biological monitoring, airport security systems, chemical and biological agent detection, explosives detection, spectral imaging, scanning system, and any other applications whereby an investigator is attempting to identify the presence of a target. 
     In one embodiment, the tuning of tunable bandwidth selector  102  to a specific bandwidth may be provided through an operator input  142 . Exemplary operator inputs include buttons, switches, dials, a touch screen, a graphical user interface, and a file providing the bandwidths for tuning. 
     Referring to  FIG. 1 , the index of refraction of medium  103 , the index of refraction of electron sheets  112 , and a spacing of electron sheets  112  are selected to separate spectrum  110 C from the remainder of input spectrum  108 . As shown in  FIG. 1 , spectrum  110 C travels in direction  116  while the remainder of input spectrum  108  continues to travel in direction  114 . Referring to  FIG. 2 , at least the spacing of electron sheets  112  is altered which results in spectrum  110 E being selected to be separated from the remainder of input spectrum  108 . As shown in  FIG. 2 , spectrum  110 E travels in direction  116  while the remainder of input spectrum  108  continues to travel in direction  114 . 
     The spacing of electron sheets  112  may be altered by changing the localized magnetic field  140 . In one embodiment, the spacing of electron sheets  112  may be adjusted from about 0.100 microns to about 20 microns. Each embodiment covers a specific spectral range of interest and the electron plane spacing and index of refraction are appropriately varied to cover the spectral response of the optics, the detector, as well as the spectral bandwidth of interest. In one embodiment, the range of spacing needed requires even larger spacing between electron sheets  112 . As shown in equation 1 as the spacing between electron sheets  112  increases, the central wavelength of the first bandwidth also increases. 
     Referring to  FIG. 3 , one embodiment for increasing the separation between adjacent electron sheets  112  is shown. In  FIG. 3 , a plurality of power supplies  122  are coupled to a plurality of electron sources  118 . In the illustrated embodiment, each of openings  138  has a corresponding electron source  118  positioned relative thereto. Further, a series of electron sources  118  are each tied to the same power supply  122 . As illustrated, a first power supply  122  provides power to electron sources  118 A,  118 C,  118 E, and  118 G and a second power supply  122  provides power to electron sources  118 B,  118 D, and  118 F. One way to increase the spacing between electron sheets  112  is to selectively turn off the power to one of power supply  122 A and power supply  122 B. This results in the remaining electron sheets  112  having a spacing double of when all of electron sheets  112  are present. Although two power supplies  122  are shown, any number of power supplies having multiple electron source  118  tied thereto may be used. 
     Referring to  FIG. 4 , another arrangement for increasing the spacing of electron sheets  112  is shown wherein each of electron sources  118 A-G has an independent power supply  122 A-G. The spacing between electron sheets  112  may be increased in this arrangement by selectively turning off power to various ones of power supply  122 . In one embodiment, the resultant spacing between the remaining electron sheets  112  is constant. In one embodiment, the resultant spacing between the remaining sheets  112  is variable. 
     In one embodiment, electron sheets  112  are apodized. This reduces the strength of any side lobes (unwanted bandwidth which is directed in direction  116 ). In an apodized example, the electron sheets  112  towards the ends of the collection of electron sheets  112  are closer in index of refraction to the index of refraction of medium  103 , while in the center of the collection of electron sheets  112  the index of refraction is more distinct from the index of refraction of medium  103 . In one embodiment, this is accomplished by altering the density of electrons in the respective electron sheets  112 . In one embodiment, the change in index of refraction of electron sheets  112  follows a generally Gaussian profile. In one embodiment, the change in index of refraction of electron sheets  112  follows a generally raised-cosine profile. 
     In one embodiment, the spacing of electron sheets  112  is non-constant resulting in a chirped grating. This has the effect of broadening the range of wavelengths included within the first bandwidth. 
     As pictured in  FIG. 1A , electron sheets  112  are generally normal to the direction of travel, direction  114 , of electromagnetic radiation  106 . In one embodiment, electron sheets  112  are tilted relative to the direction of travel of electromagnetic radiation  106 . This embodiment may change the center wavelength, the effective spectral range of the device, and may move the final incident location of the reflected wavelength. 
     Referring to  FIG. 5 , a detection system  210  is shown. Detection system  210  includes one of the arrangements of tunable bandwidth selector  102  shown in  FIGS. 1-4  provided in a housing  211 . Electromagnetic radiation  106  is introduced into housing  211  through input optics  212 . In one embodiment, input optics  212  are simply an optical window. In one embodiment, input optics  212  includes refractive and/or reflective optics having some power to direct electromagnetic radiation  106  towards tunable bandwidth selector  102 . In one embodiment, input optics  212  includes filters and/or polarizers to limit the range of electromagnetic radiation  106  entering tunable bandwidth selector  102 . 
     Input optics  212  presents electromagnetic radiation  106  to a notched beamsplitter  218  which passes a portion of electromagnetic radiation  106  onto tunable bandwidth selector  102 . As explained herein, tunable bandwidth selector  102  separates a first bandwidth from the remainder of electromagnetic radiation  106 . The first bandwidth travels in direction  116  back towards notched beamsplitter  218 . Notched beamsplitter  218  redirects a portion of the first bandwidth towards a detector  214 . The remainder of the input spectrum travels in direction  114  and passes out of tunable bandwidth selector  102  towards a detector  216 . In one embodiment, detector  214  and detector  216  are non-imaging detectors selected for their responsive to the various bandwidths being observed by detection system  210 . Exemplary detectors include Si for 0.4 to 0.9 microns, InGaAs for 0.9 to 1.7 microns bandwidth, InSb for 3 to 5 microns bandwidth, vanadium oxide for 8 to 14 microns, and other commercially available detectors to respond to specific commercial applications requiring observation of particular bandwidths, specifically there are detectors coupled with fixed optical filters capable of detecting any bandwidth of interest. In one embodiment, the detector is selected for microwave bandwidths. In one embodiment, detector  214  is a focal plane array which is capable of measuring the power of hyperfine lines in the electromagnetic spectrum reflected by the bandwidth selector  102 . In one embodiment, detector  214  is a single detector element which is capable of measuring the power of hyperfine lines in the electromagnetic spectrum reflected by the bandwidth selector  102 . In one embodiment, detector  214  is a focal plane array which is capable of measuring the absences of the power of the hyperfine lines in the electromagnetic spectrum not transmitted by the bandwidth selector  102 . In one embodiment, detector  214  is a single detector element which is capable of measuring the absence of the power of hyperfine lines in the electromagnetic spectrum not transmitted by the bandwidth selector  102 . 
     Each of detectors  214  and  216  are operatively coupled to controller  150  and provide an indication to controller  150  of the intensity of the first bandwidth (detector  214 ) and the overall intensity of electromagnetic radiation  106  (detector  216 ). In one embodiment, detector  216  is positioned opposite detector  214  relative to notched beamsplitter  218  to receive the portion of electromagnetic radiation  106  including the first bandwidth reflected by beamsplitter  218 . 
     Controller  150  based on the intensity level from detector  214  makes a determination of the presence or absence of a specific target corresponding to the first bandwidth tunable bandwidth selector  102  is tuned to separate from electromagnetic radiation  106 . In one embodiment, controller  150  compares the intensity level from detector  216  to the intensity level from detector  214  to reduce false positives. In one embodiment, controller  150  compares the intensity level from detector  214  to the previously recorded intensity levels of detector  214  for other wavelengths to reduce false positives. In one embodiment, controller  150  cycles tunable bandwidth selector  102  through various bandwidths to determine the presence or absence of a variety of targets or as confirmation of a single type of target. Some targets have several characteristic bandwidths associated therewith. Further, in a given situation multiple targets may be being scanned for the presence of in an ambient environment or as part of a detection zone. 
     In another embodiment, several detection systems  210  are provided as part of a detection system  220  as shown in  FIG. 6 . In the embodiment shown in  FIG. 6 , several individual detection systems  210  are used in concert to detect the presence or absence of various targets. This reduces the range of selection needed for a single tunable bandwidth selector  102 . For instance, the tunable bandwidth selector  102  of detection system  210 A may be searching for bandwidths within a first bandwidth range while tunable bandwidth selector  102  of detection system  210 B may be searching for bandwidths within a second bandwidth range. Although each of detection system  210 A and detection system  210 B are shown having a separate controller  150  and a separate memory  152 , in one embodiment, detection system  210 A and detection system  210 B share a common controller  150  and memory  152 . 
     Referring to  FIG. 7 , another detection system  210 ′ is shown. Detection system  210 ′ is the same as detection system  210 , except that a second channel with a second tunable bandwidth selector  102  is added. The second channel interacts with the electromagnetic radiation  106  initially reflected by notched beamsplitter  218 . The electromagnetic radiation  106  reflected by notched beamsplitter  218  encounters a second beamsplitter  232  which passes a portion of electromagnetic radiation  106  onto a second tunable bandwidth selector  102 . The second tunable bandwidth selector  102  is under the control of controller  150  which tunes tunable bandwidth selector  102  to a desired bandwidth. If the desired bandwidth is present in electromagnetic radiation  106 , the desired bandwidth is separated from the remainder of electromagnetic radiation  106  by the second tunable bandwidth selector  102  and is detected by a second detector  214 . The remainder of electromagnetic radiation  106  is passed onto detector  216 . 
     It should be noted that controller  150  will take into account the reduced intensity levels associated with the second channel relative to the first channel in determining the presence or absence of a given target. 
     Referring to  FIGS. 9-10 , three detection systems  250 ,  252 , and  250 ′ are shown. Each of detection systems  250 ,  252 , and  250 ′ are the same as respective detection systems  210 ,  220 , and  210 ′ described herein, except that detectors  214  and  216  are replaced with imaging systems  260  and  262 , respectively. Imaging systems  260  and  262  provide an image of the scene of detection zone  200 . 
     In one embodiment, as shown in  FIG. 8A  imaging systems  260  includes image forming optics  264  and an image detector  266 . Image forming optics  264  include any suitable optical devices for forming an image of the scene in detection zone  200 . In one embodiment, image forming optics  264  includes a zoom feature to focus on various regions of detection zone  200 . Exemplary image detectors  266  include charge-coupled devices and any other suitable devices for recording an image of detection zone  200 . As explained herein, controller  150  may use imaging systems  260  and  262  together to indicate the location of a detected target. 
     Referring to  FIG. 11 , a portable detection device  301  is shown. Portable detection device  301  includes a detection system  300 . Detection system  300  may be any of the detection systems disclosed herein. Detection system  300  is provided in a housing  302  having an optical window  304  therein. The portable detection device  301  may take any suitable shape. In one embodiment, portable detection device  301  is shaped like a hand-held device, similar to a rifle or wand, allowing an operator to easily point and aim portable detection device  301 . 
     Portable detection device  301  is shown in conjunction with a piece of luggage  310 . Portable detection device  301  examines the electromagnetic radiation  106  provided by luggage  310  to determine the contents of luggage  310  or targets otherwise carried on the surface of the luggage  310 . Referring to FIG.  12 , in one embodiment, luggage  310  is radiated by electromagnetic radiation  314  provided by an energy source  312 . In one embodiment, electromagnetic radiation  314  is selected to excite the emission of a specific first bandwidth if the corresponding target is present in or on the luggage  310 . Since energy source  312  is positioned on an opposite side of luggage  310  than portable detection device  301 , portable detection device  301  looks at electromagnetic radiation  106  based on the transmission or emission of electromagnetic radiation. Another embodiment is shown in  FIG. 13  wherein energy source  312  is positioned on the same side of luggage  310  as portable detection device  301 . As such, portable detection device  301  looks at electromagnetic radiation  106  based on the reflectance or emission of electromagnetic radiation from luggage  310 . 
     Referring to  FIG. 14 , a scanning system  328  is shown. Scanning system  328  includes a conveyor system  332  including a transport member  333  moveable in direction  336  and direction  338 . Exemplary transport members  333  include belts. As a piece of luggage  310  supported by transport member  333  moves in direction  336  it passes into a housing  334 . Inside of housing  334  an energy source  312  radiates luggage  310 . Electromagnetic radiation  106  produced by luggage  310  is detected by a detection system  330 . Detection system  330  may be any of the detection systems disclosed herein. In one embodiment, detection system  330  is an imaging system. Controller  150  of detection system  330  provides an output signal to a monitor  340 . 
     Referring to  FIG. 15 , in one embodiment, memory  152  includes detection software  350 . In one embodiment, detection software  350  receives an input characteristic  352  of a first bandwidth to detect, illustratively a central wavelength of the first bandwidth. Detection software  350  provides the instructions to controller  150  for setting the tunable bandwidth selector  102  to separate the first bandwidth, if present, from the remainder of input spectrum  108 . The instructions may include a spacing of electron sheets  112 , a density of electron sheets  112 , and an index of refraction of medium  130 . Detection software  350  receives from the detectors of the detection system an indication of the amount of first bandwidth present in input spectrum  108 . Based on these detected values, detection software  350  provides an output indication of whether the first bandwidth is detected, as represented by detection parameter  354 . In the case wherein the detectors are imaging detectors, detection software  350  may provide an image  356  representative of the location of the first bandwidth in the field of view. 
     Referring to  FIG. 16 , instead of receiving an input characteristic  352  detection software  350  receives a specific target to detect as represented by detection target input parameter  360 . Detection software  350  then through a database  362  looks up the characteristics  366  of the bandwidths that are representative of the presence of a specified detection target  364 . In one embodiment, such as for target A a single first bandwidth is to be examined. In one embodiment, such as for target B a plurality of spaced apart bandwidths are to be examined. In one embodiment, such as for target C a range of first bandwidths are to be examined. 
     Referring to  FIG. 17  an exemplary processing sequence  380  of detection software  350  is shown. Detection software  350  receives a detection type input, as represented by block  382 . In one embodiment, the detection type input is one or more characteristics of one or more bandwidths to be examined. In one embodiment, the detection type input is one or more detection targets to be examined. In either case, a plurality of inputs may be provided in a database or input file and detection software  350  adjusts the respective tunable bandwidth selector  102  sequentially for each input. In this situation, the operation of detection software  350  may automatically cycle through a plurality of inputs. This is useful in setups such as shown in  FIG. 14  wherein a plurality of items are sequentially examined in a scanning system. 
     As mentioned above, based on the input received detection software  350  adjusts the respective tunable bandwidth selector  102  to select a bandwidth corresponding to the current detection type input, as represented by block  384 . Detection software  350  then detects the radiation levels with the respective detectors of the detection system, as represented by block  386 . Based on the detected levels, detection software  350  determines if a detection of the specific bandwidth is confirmed, as represented by block  388 . In one embodiment, detection is confirmed if the detected level exceeds a threshold value. 
     If detection is not confirmed then detection software  350  provides an indication that the detection is not confirmed, as represented by block  390 . The indication may be one of audio, tactile, visual, or a combination thereof. In one embodiment, the indication is simply permitting the continued operation of a system, such as transport member  333  moving in direction  336  in  FIG. 14 . 
     If detection is confirmed then detection software  350  provides an indication that the detection is confirmed, as represented by block  392 . The indication may be one of audio, tactile, visual, or a combination thereof. In one embodiment, the indication is simply blocking the continued operation of a system, such as transport member  333  moving in direction  336  in  FIG. 14 . 
     Referring to  FIG. 18 , an exemplary processing sequence  393  for when detection is confirmed is shown for an imaging detection system. Detection software  350  provides an image of the object being interrogated, as represented by block  394 . In the case of luggage  310  in  FIG. 14 , monitor  340  displays an image  342  of luggage  310 . In one embodiment, the image  342  of luggage  310  is provided by an imaging system receiving the radiation not separated by the tunable bandwidth selector  102 , such as imaging system  262  in  FIG. 8 . Detection software  350  determines a location of the detected item in luggage  310 , as represented by block  396 . In one embodiment, an imaging system  260  provides an image of luggage  310  in the separated first bandwidth. Detection software  350  then determines which pixels are above the threshold value. These pixels are then flagged as corresponding to the location of the object being detected. Detection software  350  provides an indication of the location of the detected target on the image of luggage  310 , as represented by block  398 . In one embodiment, detection software  350  superimposes the image provided by imaging system  260  over the image provided by imaging system  262 . In situations where in the image provided by imaging system  260  is not in the visible spectrum, a visible spectrum representation of the target is provided as an image for display. The detected object or target  344  is shown by monitor  340 . In one embodiment, detection software  350  simply provides a marker or other representation of the target on the image produced by the imaging system  262 . In one example, the image produced by imaging system  262  is in the visible spectrum. 
     In one embodiment, the first bandwidth is selected to provide an image of the contents of the luggage. In one embodiment, the first bandwidth is in the millimeter wavelength range at which non-metallic items are generally transparent. In this manner, an image is formed from the first bandwidth which indicates opaque items at that wavelength, such as metallic items. The image formed by the light passing through tunable bandwidth selector  102  may form a traditional visible light image. Controller, based on the image formed from the first bandwidth may light a location of a metallic item in the visible light image for further investigation. This may be beneficial in the case of scanning human subjects to maintain the privacy of the subject during scanning. 
     While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.