Abstract:
Spectrofluorometer employing a pair of linear variable spectral filters to produce a three dimensional data output is disclosed. A collimated white light source is used that first passes through a first linear variable spectral filter, then through a sample where fluorescence occurs, then the resultant light passes through a second linear variable spectral light filter that is oriented at ninety degrees from the first filter. The light is then detected by a CCD sensor for conversion into data. This arrangement provides a very simple, rugged and compact instrument that can be used almost anywhere, such as at the scene of a contamination accident.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION  
       [0001]    This application is a continuation of commonly owned application Ser. No. 09/678,709, the disclosure of which is hereby incorporated herein by reference thereto; which is a continuation-in-part of application Ser. No. 09/443,392, filed Nov. 19, 1999. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Fluorescence instrumentation has been used for many years to identify unknown materials. Generally, the principle involved is that a material excited with light of a particular wavelength will emit light energy in the form of an emission spectrum whose amplitude profile, over the range of wavelengths emitted, constitutes a “fingerprint” which can give the identity and nature of the unknown material.  
           [0003]    In the most demanding applications, a sample is excited with light of a single wavelength and the fluorescence emission spectrum is recorded. The wavelength of the excitation source is then advanced incrementally along the range of excitation wavelengths of interest, and the process repeated to record the fluorescence emission spectrum at the incremented wavelength. The process is continued until the entire range of excitation wavelengths of interest has been covered by the instrument. The result is a highly accurate, so-called three-dimensional fluorescence emission spectrum, showing excitation wavelengths, corresponding emission wavelengths and their amplitudes. Such instruments are of particular interest in scientific research where subtle variations in the characteristics of the spectrum may contain useful information to understand the effects of relatively subtle changes in the system. Typically, instruments of this sort have resolutions on the order of between 0.1 to 0.5 nm.  
           [0004]    However, many applications have far less demanding requirements. For example, if one is merely interested in identifying the identity of a particular sample of material, far less resolution will suffice. Accordingly, a class of instruments having resolutions on the order of five to ten nanometers have seen widespread application in industry. Typical applications include the identification of samples of such material as blood, oil, pollutants and the like. Such instruments differ from other fluorescence instruments in that they are designed to perform measurements much more quickly, by measuring the fluorescence of a material over a range of wavelengths simultaneously.  
           [0005]    Such a prior art system is illustrated in FIG. 1. Measurement of the fluorescence spectrum is achieved by having a system which comprises an excitation spectrograph  1  which is used to excite a sample  2 , typically contained in an elongated cuvette  3 . The elongated cuvette  3  is excited by an elongated image of a spectrum extending from a low wavelength to a high wavelength.  
           [0006]    This results in fluorescence emission by sample  2  in cuvette  3 . The emission is received and collimated by a collimating concave mirror  4 , which reflects the fluorescence emission to focusing concave mirror  5 , which, in turn, focuses the emitted fluorescence light at a slit  6 , through which the light which comprises the fluorescence emission passes to fall on the planar mirror  7 . Planar mirror  7  reflects the light toward a spectrograph  8  formed by a concave aberration-corrected diffraction grating. Spectrograph  8  disperses a spectrum on a CCD detector  9  which in a single row of pixels can produce the complete emission spectrum of the excited material.  
           [0007]    In a typical instrument of this type, a xenon source is imaged as a bright line placed over a cuvette in a vertical line. Thus, the full spectrum will excite any homogeneous sample placed in the sample compartment of the cuvette. The resulting fluorescence emission is dispersed orthogonally over the active area of a rectangular CCD, or charge-coupled device, which is, essentially, a two-dimensional array of light detectors. The horizontal axis of the CCD records the emission spectra at different excitation wavelengths along the vertical axis, and gives the intensity for each wavelength. Thus, this instrument will produce, for each wavelength in the range of excitation wavelengths, the spectrum of emitted wavelengths. For example, if the system has a resolution of 5 nm, and covers a range of 100 nm, one could view the output as twenty different spectra.  
           [0008]    The ability to complete a reading of the emission spectrum simultaneously opens up many possibilities for enhanced performance functions. For example, a cuvette may be fed by a high pressure liquid chromatography column, allowing the facile real-time generation of fluorescence emission spectra of the various materials in a sample being analyzed by the chromatography column.  
           [0009]    While this system has many advantages over the prior art systems which measured a fluorescence spectrum one wavelength at a time, it still had a number of deficiencies. First, the volume required for the system is relatively large and precludes use of the system in a compact system. Moreover, the system comprises numerous expensive parts, and costs may be prohibitive for many applications. In addition, assembly of the system is unduly expensive requiring careful alignment of parts to ensure proper operation of the system. Similarly, the system is not as rugged as other systems, and is liable to become misaligned during use on account of shock and vibration. Finally, the system is limited to producing a fluorescence spectrum.  
         SUMMARY OF THE INVENTION  
         [0010]    The invention, as claimed, is intended to provide a remedy. It solves the problems of large size, lack of ruggedness and cost by providing a simple instrument that can be implemented in a compact design. In accordance with the present invention, an excitation light source provides optical radiation over a range of wavelengths or spectra for illuminating a sample. The inventive instrument performs fluoresence analysis of samples, and comprises a light source emitting light into an illumination light path, and a first spectral filter in the illumination light path for transmitting light within a selected wavelength range. This defines a sample illumination light path. A second spectral filter is spaced from the first spectral filter forming a sample receiving space therebetween.  
           [0011]    The illumination light path passes through the first spectral filter. The sample receiver and the second spectral filter lie in the light path, and the second spectral filter is displaced angularly relative to the first spectral filter. A sensing element in the resultant light path measures absorption spectra and fluorescence light. The first spectral filter and the second spectral filter have a characteristic which varies along an axis thereof. In accordance with the preferred embodiment of the invention, the variable characteristic is a variable bandpass wavelength in various filter regions of the spectral filter. Also in accordance with the preferred embodiment, the second spectral filter is angularly displaced at a substantially othogonal angle.  
           [0012]    The above described embodiment of the invention has the advantage of providing along a diagonal region of the CCD the absorption spectrum of the material sample under analysis.  
           [0013]    In accordance with an alternative embodiment of the invention, a third spectral filter in the resultant light path is oriented in a direction, and position in a position which are substantially the same as the direction and position of the first spectral filter. This third filter serves the function of a blocking filter thereby preventing excitation light energy that has passed through a sample receiver from passing to the sensing element or CCD array. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    One way of carrying out the invention is described in detail below with reference to the drawings which illustrate one or more specific embodiments of the invention and in which like reference characters represent like elements:  
         [0015]    [0015]FIG. 1 is a schematic view of a typical prior art apparatus;  
         [0016]    [0016]FIG. 2 is a schematic view of the present invention showing the compactness of the components;  
         [0017]    [0017]FIG. 3 is an exploded schematic view of the apparatus of the present invention showing a pair of linear variable spectral filter and a CCD type of sensing element;  
         [0018]    [0018]FIG. 4 is an exploded view similar to FIG. 3 including a cartridge containing a sample to be tested;  
         [0019]    [0019]FIG. 5 is a schematic view of a CCD sensing element, as is employed in the embodiments illustrated in FIGS. 4 and 5;  
         [0020]    [0020]FIG. 6 is a schematic view of a CCD sensing element, as is employed in the embodiments illustrated in FIGS. 4 and 5, illustrating the absorption spectrum position when filter elements are not matched in the system of the present invention;  
         [0021]    [0021]FIG. 7 is a perspective view of an alternative embodiment of the present invention;  
         [0022]    [0022]FIG. 8 is a perspective view of an alternative embodiment of the inventive spectrofluorometer incorporating a further improvement;  
         [0023]    [0023]FIG. 9 is a view similar to FIG. 4 of an alternative embodiment of the invention including an excitation light blocking filter; and  
         [0024]    [0024]FIG. 10 is a perspective view of an embodiment of the invention similar to that illustrated in FIG. 9 and incorporating minimized light paths. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    Referring now to FIG. 2 and  3 , major components of a spectrofluorometer  10  are shown. Optical radiation traveling along an excitation light path  12  passes into a linear variable spectral filter  14 .  
         [0026]    Spectral filter  14  is a device which has bandpass wavelength characteristics which vary along its length. More particularly, at the bottom of filter  14 , one wavelength would be passed in the region defined by the dashed lines. In the next filter region above that filter region like having a different wavelength will be passed, perhaps a wavelength which is 5 nm longer. This sort of device is made by advancing a mask having the width of one of the regions illustrated in dashed lines in the figure, from one discrete position to another and applying a different multilayer structure at each position to give the corresponding stripe of bandpass material the desired optical bandpass characteristic.  
         [0027]    The manufacture of such a filter is known in the art and forms no part of the present invention. Such filters may be purchased on the open market and are available from, for example, Reynard Corporation under their catalog No. 4610. Such a filter has a spectral range of 400 to 700 nm. It is relatively small and compact, being 60 mm long, 25 mm wide and 5 mm thick. A typical spectrum length would be 44 mm, with dispersion varying between 0.12 and 0.17 mm/nm.  
         [0028]    The linear variable spectral filters sold by this corporation tend to vary in their characteristics, with a spectrum length varying form 37 to 51 mm. matching of the filters used in the embodiment of FIG. 2 is desirable. Alternatively, a computer reading the output of the system may calibrate the software against a known source.  
         [0029]    A sample receiver  16  is located between the first spectral filter  14  and a second linear variable spectral filter  18 . Sample receiver  16  is a vessel which defines a volume for receiving a sample which is to be analyzed. It may be a rectangular solid made of glass, plastic or any suitable material. It may also be as simple as a glass slide with a smear of the sample, or even a solid film of the sample material, such as tissue, paper from a paper mill whose operation is being monitored, and so forth.  
         [0030]    Such a sample may be a solution derived from a material being tested, blood, the output of an HPLC liquid chromatography column, or the like. If the output of an HPLC column is being monitored, the receiver  16  may have a liquid input port and a drain, and the dimensions of the receiver would be such that capillary action insures the presence of sample material throughout the excited regions of receiver  16 . A close-coupled discharge (CCD) sensing element  20  measures the relative position and intensity of light rays traveling along a resultant light path  12 . See FIG. 3.  
         [0031]    Sensing element  20  is preferably a CCD type of sensor although other types can be used depending upon the type of excitation light used and the sample to be tested. In FIGS. 3 and 5, detector  20  is shown as a  36  element matrix detector. The small number of elements or pixels is merely for the convenience of illustration and the illustration of the principles of the invention. In a real device, the number of detectors easily ranges into the hundreds of thousands of elements, and, depending upon the performances desired and the nature of the software reading out the signal from the detector, the number of elements in detector  20  may range into the millions of pixels.  
         [0032]    In principle, even film can be used in place of detector  20 . An absorption spectrum and lamp profile (without sample) is shown as diagonal line  56  in FIG. 5. In connection with the preferred embodiment of the invention, a suitable sensing element is the CCD sold by Instruments SA on the Spectrum One. Each of these elements are described in detail below.  
         [0033]    Referring back to FIG. 3, the borders defining the filter regions with different spectral characteristics in the first and second optical filters  14  and  18  are shown as dashed lines. First filter  14  is a linear variable spectral filter that changes its bandpass wavelength along the length or planar axis  15  of the filter. Wavelengths outside the desired transmission ranges are blocked by the respective filter regions.  
         [0034]    In a preferred embodiment, the spectral range from 400 to 700 nm is oriented vertically, e.g., with shortest wavelength filter region  24  at the bottom, then longer wavelength filter region  26 , still longer wavelength filter region  28 , a filter region  30  which passes a range of wavelengths longer than those of filter region  28 , a filter region  32  which passes a range of wavelengths longer than those of filter region  30 , and the longest wavelength bandpass filter region than  34  at the top. While the invention has been implemented with a spectral filter having the aforementioned wavelength characteristics, other visible and non-visible bandpass characteristics can be used depending on the nature and characteristics of the sample to be tested.  
         [0035]    The second optical filter  18  is substantially the same as the first optical filter  14  except that it is oriented in such a manner that its gradations are not in line with those of first filter  14 . The strips defining the bandpass filter regions on filter  18  are preferably at ninety degrees to those of filter  14 . The advantages of this relationship will now be described in connection with the operation of the inventive system.  
         [0036]    A light source  36  which may comprise a xenon lamp whose output is collimated by a lens or reflector, or any other suitable optical components produces an excitation white light ray bundle  38 , sometimes referred to as illumination light, that travels along excitation light path  12  with a wide range of wavelengths striking the surface of filter  14 . As white light ray bundle  38  passes through filter  14 , selected wavelengths are passed by each filter region, such that a wavelength “gradient” from short to long wavelengths is produced. This is referred to herein as a sample excitation light  42 .  
         [0037]    As sample excitation light  42  passes through second filter  18 , only those wavelengths of light that are not blocked pass completely through the filter  18 . Since filter  18  is oriented at a right angle to filter  14 , most of sample excitation light  42  is blocked. By way of example, λ 1  passes through filter  14  and filter  18 , while λ 2  passes through filter  14 , but is blocked by filter  18 . In this manner a diagonal spectral line  56  is transmitted onto sensing element  20 . The theoretical center of this line it illustrated in FIG. 5 by phantom line  56 . This intrinsic relationship between the two linear variable spectral filters provides for simplicity of design, ruggedness and compact size of the inventive spectrofluorometer  10 .  
         [0038]    Referring now to FIG. 4, a sample receiver  16  is located between filter  14  and filter  18 . Sample receiver  16  may be any of a number of conventional sample holding types or techniques. As sample excitation light passes through sample  44  some of the light energy is converted into fluorescence emissions. The physics of this conversion are well understood and generally involve the photon of excitation radiation raising the energy level of electrons in the excited atom to a higher energy level or shell. When the electron snaps back into its unexcited state, it emits a photon with an energy level lower that the exciting photon, thus resulting in the fluorescence having a wavelength longer than the excitation wavelength.  
         [0039]    Some of the sample excitation light is “absorbed” by sample  44  and does not contribute to the emission. The net result is to increase the kinetic energy of the atoms of the sample, and thus raise the temperature of the sample.  
         [0040]    A resultant light ray bundle  50 , exiting sample receiver  16 , comprises light rays which have exited filter  14  and fluoresence emissions from molecules that have been excited by light rays which have exited filter  14 . Resultant light ray bundle  50  then passes into filter  18  where a selected wavelengths of both spectral light and fluorescent light are selectively blocked along the spectral gradient. The portions of light ray bundle  50  passing through to sensing element  20  constitutes the absorption spectrum  52  of the material being analyzed and appears along imaginary line  56  in FIG. 5. This can be used to identify sample  44 .  
         [0041]    As may be understood with reference to FIG. 4, filters  14  and  18  are substantially identical, but are positioned with their bandpass filter strip filter regions  24 - 34  and  35 - 44  oriented at right angles to each other. In accordance with the preferred embodiment of the invention, filter region  24  has the same bandpass characteristic as filter region  34 . In accordance with the preferred embodiment of the invention, filter region  26  has the same bandpass characteristic as filter region  42 . Filter region  28  has the same bandpass characteristic as filter region  40 . Filter region  30  has the same bandpass characteristic as filter region  37 . Filter region  32  has the same bandpass characteristic as filter region  36 . Filter region  34  has the same bandpass characteristic as filter region  35 .  
         [0042]    Thus, the CCD elements  70 , lying along line  56  in FIG. 5, are the only elements that will be illuminated by the white light ray bundle  38  coming from the excitation source. Moreover, because the fluorescence spectrum constitutes only wavelengths longer than the excitation wavelength, they will be blocked from reaching elements  70  by filter  18 . Thus, only the absorption spectrum can be seen along imaginary line  56  to provide a first identification of the sample.  
         [0043]    Likewise, because the fluorescence spectrum constitutes only wavelengths longer than the excitation wavelength, these longer wavelengths will be passed by filter  18  to those elements  58  of the CCD which lie below line  56  in FIG. 5. Thus, the elements  58  of the CCD which lie below line  56  in FIG. 5 produce the fluorescence emission spectra of the sample under analysis. The resultant fluorescence emission is used to identify sample  44 .  
         [0044]    Referring back to FIG. 4, the operation of the inventive system may be better understood. In particular, the output of the xenon lamp  36  constituting a broadband emission which is collimated into white light ray bundle  38  is caused to fall on filter  14 , which outputs a plurality of stripes of light energy at different wavelengths. Because filters  14  and  18  are very thin, as is sample container  16 , the output of filter  14  is effectively “imaged” on the sample in sample receiver  16 . The output of sample container  16  is likewise effectively “imaged” on filter  18 . Finally, in turn, the output of filter  18  is effectively “imaged” on the surface of CCD elements  58 . The system works because all of the above thin elements are in contact with each other and CCD  20  to form the sandwich illustrated in FIG. 2.  
         [0045]    As noted above, light ray  72 , which is one of the light rays in white light bundle  38 , because it is in the bandpass range of filter region  34  on filter  14 , and, naturally, in the bandpass of optically identical filter region  35 , will pass through both filters and fall on CCD  20 , if it is not absorbed by the sample. The same is true for light ray  74 , which is in the bandpass of filter regions  24  and  44 .  
         [0046]    Light rays  76  and  78  will, on the other hand, be blocked by filter  18 , after being limited to the different bandpass of facing filter regions of filter  14 . Moreover, any fluorescence emissions  77  and  79 , corresponding respectively to light rays  76  and  78  will also be blocked by filter  18 , as they must be longer in wavelength than the bandpass of the filter region of filter  14  that they pass through, and they fall on filter regions of filter  18  that are formed by filter regions that have shorter wavelength bandpass characteristics.  
         [0047]    In contrast, light ray  80  has a wavelength corresponding to filter region  28 , and thus more energy than light passed by filter region  36 . Thus, it is physically possible that the sample will fluoresce with a lower energy and correspondingly longer wavelength light ray  81  that will pass through filter region  36  of filter  18 . Likewise, highest energy light ray  82  which passes through filter region  26  and the sample may emit a low energy photon  83 , which passes through filter region  35  and falls on the CCD detector.  
         [0048]    Conversely, it is physically impossible that a sample will fluoresce with a higher energy and correspondingly shorter wavelength. Thus, a photon of light energy  84  passing through filter region  34  of filter  18  has the lowest energy in the system and the sample cannot emit a higher energy photon, and thus any light  85 , whether transmitted or emitted by the sample will be blocked by filter region  38  which has a shorter bandpass wavelength than filter region  34 . Thus, any such light will not reach the CCD detector.  
         [0049]    Referring to FIG. 6, it can be seen that line  56 , in the case where filter  14  is identical to filter  18 , is a simple diagonal line. However, due to the nature of the manufacturing process use to produce filters  14  and  18 , the layout of the various bandpass filter regions varies rather considerably. Accordingly, it is necessary to accommodate such variations if one cannot go to the trouble of trying to match identical filters very carefully.  
         [0050]    Such variations may cause line  56  to shift to the position illustrated by reference number  56   a  in FIG. 6. Such variation occurs because the distance of oval which the series of spectral filters is dispersed is greater in filter  18  as compared to filter  14 .  
         [0051]    In the case of such variations, it is merely necessary to calibrate the software to the pattern on CCD  20 . This can be done by determining the presence of the absorption spectrum and then mathematically adjusting the position of the fluorescence spectrum accordingly. This is done on the basis that the opposite ends of the absorption spectrum represent the horizontal and vertical limits of the fluorescence spectrum. Such determination can most easily be made without having a sample in the inventive fluorescence instrument  10 .  
         [0052]    As is alluded to above, filters  14  and  18  are made by depositing stripes of material which form bandpass filters on a substrate. As is also alluded to above, maximizing the thinness of instrument  10  will also maximize performance. More precisely, improved performance can be obtained by minimizing the distance between the active filter layer of filters  14  and  18  as well as minimizing the distance between the active layer of filter  18  and the sensitive face of detector  20 . Thus, exceedingly thin substrates may be used to optimize the performance of the instrument.  
         [0053]    Yet another approach is illustrated in FIG. 7. In FIG. 7 the convention of labeling parts with identical or analogous functions with numbers which vary by multiples of  100  has been followed.  
         [0054]    In FIG. 7, the inventive spectrofluorometer  110  is excited by excitation light  138  along path  112 . Excitation light  138  first falls on filter  114 , causing it to pass through the active layer  115  of filter  114  on the far side of filter  114 . Light  138  then passes through the sample in receiver or carrier  116 . Light  138  then passes through the active layer  117  of filter  116 . Active layers  115  and  117  are formed on the substrates of their respective filters. Such substrates may be glass, plastic or any other suitable material. After passing through active layer  117 , light  138  passes through the substrate of filter  116  and on to the sensitive face of detector  120 , from which it is sent to a computer or other suitable device for interpreting and displaying the output of the detector.  
         [0055]    Yet another approach is shown in FIG. 8. Here spectrofluorometer  220  is excited by excitation light  238  along path  212 . Excitation light  238  first falls on filter  214 , causing it to pass through the active layer  215  of filter  214  on the far side of filter  214 . Light  238  then passes through the sample in receiver or carrier  216 . Light  238  then passes through the active filter layer  217 , which is disposed and manufactured onto the output face of carrier or receiver  216 . Alternatively, active filter layer  217  may be disposed on and manufactured onto the input face of detector  220 . After passing through active layer  217 , light  238  passes onto the sensitive face of detector  220 , from which it is sent to a computer or other suitable device for interpreting and displaying the output of the detector.  
         [0056]    As will the apparent from FIG. 8, the distance between filtered light exiting the first active bandpass layer in the inventive system  220 , and the sensitive face of detector  220  is minimized in FIG. 8. Accordingly, light which is not traveling perpendicular to the faces of the filters, then, accordingly, is dispersed in itself, travels over a minimized path length and, accordingly, the dispersion is minimized, thus eliminating the need for the focusing optics, which are so important in prior art systems.  
         [0057]    Referring to FIG. 9, a spectrofluorometer  310  having the feature of being able to block the excitation wavelength of the system is illustrated. This is desirable because the amplitude of the excitation wavelength will often spread and overload the detector receiving light from adjacent filter regions. The instrument illustrated in FIG. 9, operates in the same manner as the instrument illustrated in FIG. 4, except for this additional feature.  
         [0058]    In particular, it has a filter  314 , a sample carrier  316 , a filter  318 , and a detector  320 . The characteristics of all of these systems is the same as the instrument illustrated in FIG. 4. However, it also has a spectral band reject filter  354 , which is aligned, filter region by filter region, to substantially identically opposite filter  314 .  
         [0059]    More particularly, in accordance with the preferred embodiment of the invention, filter region  323  has a band reject characteristic with the same wavelength range as the wavelength range of the bandpass characteristic of filter region  324 . In accordance with the preferred embodiment of the invention, filter region  325  has a band reject characteristic with the same wavelength range as the wavelength range of the bandpass characteristic of filter region  326 . Filter region  327  has a band reject characteristic with the same wavelength range as the wavelength range of the bandpass characteristic of filter region  328 . Filter region  329  has a band reject characteristic with the same wavelength range as the wavelength range of the bandpass characteristic of filter region  330 . Filter region  331  has a band reject characteristic with the same wavelength range as the wavelength range of the bandpass characteristic of filter region  332 . Filter region  333  has a band reject characteristic with the same wavelength range as the wavelength range of the bandpass characteristic of filter region  334 . The blocking of excitation wavelengths is thus assured and the detection of low amplitude fluorescence signals is enhanced.  
         [0060]    Another embodiment, shown in FIG. 10, is substantially identical to the instrument of FIG. 9, except that active filter layer  415  of spectrofluorometer  410  is deposited on the substrate of filter  414  on the side of filter  414  closer to the sample to be analyzed, and active filter layers  417  and  455  are deposited on the sensitive face of CCD  420  (on the side of filter  414  closer to the sample to be analyzed). This is done in order to minimize the lengths of paths of dispersion, and thus minimize dispersion and optimize the operation of the instrument. Active filter layer  455  is identical to filter  354  in FIG. 9.  
         [0061]    Active filter layer  415  is made by advancing a mask along the substrate of filter  414  having the width of one of the regions illustrated in the figure, from one region to the next and applying the appropriate multilayer structure at each position to give the desired stripe of bandpass material the desired optical bandpass characteristic. Active filter layer  417  is made by performing the same process, first applying to the sensitive face of CCD  420  the same series of different multilayer structures at their respective positions to give the corresponding stripes of filter layer  417  the desired optical bandpass characteristic. CCD  420  is then rotated in the plane of its sensitive face by  90  degrees.  
         [0062]    Active filter layer  455  is made by advancing, along the rotated substrate of CCD  420 , a mask having the width of one of the regions illustrated in FIG. 10, from one region to the next and applying the appropriate multilayer structure at each position to give the desired stripe of band reject material the desired optical band reject characteristic. When the process is completed, the result is a filter layer  455  is the band reject analog of bandpass filter layer  415 .  
         [0063]    In accordance with the present invention, it is may be desirable, in order to accommodate the insertion of different sample receivers or carriers  416 , to vary the distance between filter layers  415  and  417 . This may be achieved by mounting filter  414  on a horizontally moveable table  491  or other mechanism. This enables movement in the directions indicated by arrow  492 .  
         [0064]    The positions of layers  417  and  455  may be reversed by reversing their order of deposit. Likewise, the active filter layers may be deposited on the sample receiver or carrier to provide sample carriers that have filter patterns which may embody the operation of any of the systems described above. Such sample carriers may be specialized to optimize the analysis of certain classes of analysis tasks, such as blood work, where it may be desirable to perform special filtering, to block, transmit or study certain portions of the spectrum. One or more filter layers may be placed on either or both sides of the sample carrier.  
         [0065]    While an illustrative embodiment of the invention has been described, it is, of course, understood that various modifications of the invention may be made by those of ordinary skill in the art without departing from the spirit and scope of the invention which is limited and defined only by the appended claims.