Abstract:
An integrating sphere for a spectrometer, including: an integrating spherical body with a light entrance window for allowing an entry of light emitted from a sample, a first light detection window, and a second light detection window; a first detector attachment section located on the outside of the first light detection window; and a second detector attachment section located on the outside of the second light detection window in such a manner that the detection field of a detector to be attached to the second detector attachment section coincides with the detection field of a detector to be attached to the first detector attachment section.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an integrating sphere used in a spectrometer or similar device, as well as a spectrometer using such an integrating sphere. More specifically, it relates to an integrating sphere that can be suitably used in the case of performing a spectrometric measurement using a plurality of detectors, as well as a spectrometer provided with such an integrating sphere. 
       BACKGROUND ART 
       [0002]    In the case where a measurement of light reflected by or transmitted through a sample is performed with a spectrometer, if the light is diffuse light, an integrating sphere is used to maximally introduce the light from the sample into a detector. An integrating sphere has a light entrance window and light detection window. The light from the sample is introduced through the light entrance window into the integrating sphere. This sphere internally has a reflection surface with a high level of reflectance. The light which has entered the integrating sphere is reflected by the inner surface of the integrating sphere, to eventually pass through the light detection window and fall onto the detector (a portion of the light directly reaches the detector). In the case where the irradiation of a sample with light is performed via the integrating sphere, a light introduction window is additionally formed in the integrating sphere, allowing light from an external source to be introduced through this light introduction window into the sphere and cast onto the sample. 
         [0003]    In the case of performing a spectrometric measurement over a wide range of wavelengths, two or more types of detectors having different wavelength-sensitivity characteristics are normally used. Conventionally, two types of detectors have been used for such purposes, i.e. a PMT detector, which has a high level of sensitivity to ultraviolet-visible light, and a PbS detector, which has a high level of sensitivity to near infrared radiation. 
         [0004]      FIGS. 1 and 2  show an integrating sphere  1  with a light introduction window, which allows for the use of two types of detectors and has the following elements arranged: a light introduction window  2 , light entrance window  3 , two light detection windows  10  and  11 , as well as two detectors  10   a  and  11   a . As shown in  FIG. 1 , a light entrance window  3  is formed in the integrating sphere  1 . With the straight line connecting the center of the integrating sphere  1  and the light entrance window  3  defined as the X axis, and one arbitrary straight line which passes through the center of the integrating sphere  1  perpendicularly to the X axis defined as the Z axis, the light detection windows  10  and  11  are placed at the points of intersection of the Z axis and the integrating sphere  1  (these points are hereinafter called the “polar points”), with the detectors  10   a  and  11   a  placed on the outside of the light detection windows. With the axis passing through the center of the integrating sphere  1  perpendicularly to both of the X and Z axes defined as the Y axis, the light introduction window  2  is placed at a position on the X-Y plane opposite from the light entrance window  3  with respect to the center of the integrating sphere  1 , being slightly displaced from the point of intersection of the X axis and the integrating sphere  1 . This displacement is made in order that the directly reflected (mirror-reflected) ray of the light which is reflected by the surface of the sample  4  and enters the light introduction window  2  to the outside. 
         [0005]    The light which has been generated from the light source and has entered the integrating sphere  1  through the light introduction window  2  is cast onto the sample surface through the light entrance window  3 . After undergoing absorption at specific wavelengths to the sample, the light is reflected through the light entrance window  3  into the integrating sphere  1 . After being reflected on the inner surface of the integrating sphere  1 , the light falls onto the detectors through the light detection windows (a portion of the light directly reaches those detectors). The intensity of the reflected light changes with the reflection angle, with its intensity distribution expressed as a cosine distribution which is symmetrical with respect to the X-Y plane. Since the two types of detectors  10   a  and  11   a  located at the two polar points have symmetrical detection fields with respect to the X-Y plane, the detection surfaces of the detectors  10   a  and  11   a  receive light from the detection fields which have equal intensity distributions of the diffuse reflected light. Therefore, when the measurement of the diffuse reflected light is performed with the wavelength of the incident light gradually changed, no discrepancy in the detection result (“measurement discrepancy”) occurs when the detectors  10   a  and  11   a  are switched taking into account their wavelength-sensitivity characteristics. 
       CITATION LIST 
     Patent Literature 
       [0006]    Patent Literature 1: JP 2006-23284 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]      FIG. 3A  shows the wavelength-sensitivity characteristics of a PMT detector and PbS detector. As can be seen in the figure, both PMT and PbS detectors have low levels of sensitivity to the light within a wavelength range around 900 nm in which the two detectors are switched. To overcome this problem, the idea of using three types of detectors including an InGaAs detector which has a high level of sensitivity to the light in the aforementioned wavelength range has been proposed (Patent Literature 1). With this system, a wide range of wavelengths of light from 150 nm to 3000 nm can be detected with high levels of sensitivity, as shown in  FIG. 3B . 
         [0008]    In the case of using three types of detectors  10   a ,  11   a  and  12   a , two detectors  10   a  and  11   a  can be placed at the aforementioned polar points, whereas the remaining detector  12   a  must be arranged at a position different from the polar points.  FIG. 4  shows one example, in which the third detector  12   a  is placed at a light detection window  13  formed at a position displaced from the polar points toward the side where the sample  4  is located. In this case, the intensity distribution of the diffuse reflected light within the detection field of the detector  12   a  is not equal to the intensity distribution within the detection fields of the two other detectors  10   a  and  11   a . In other words, the light incident on the detection surface of the third detector  12   a  originates from a detection field where the light has a different intensity distribution from the light incident on the two other detectors  10   a  and  11   a . Therefore, a measurement discrepancy occurs when the detector used for the measurement is switched from the first detector  10   a , or second detector  11   a , to the third one  12   a.    
         [0009]    The problem to be solved by the present invention is to provide an integrating sphere and spectrometer which is configured to reduce the measurement discrepancy which occurs when light emitted from a sample is detected with a plurality of detectors via the integrating sphere. 
       Solution to Problem 
       [0010]    The integrating sphere for a spectrometer according to the present invention developed for solving the previously described problem includes: 
         [0011]    a) an integrating spherical body with a light entrance window for allowing an entry of light emitted from a sample, a first light detection window, and a second light detection window; 
         [0012]    b) a first detector attachment section located on the outside of the first light detection window; and 
         [0013]    c) a second detector attachment section located on the outside of the second light detection window in such a manner that the detection field of a detector to be attached to the second detector attachment section coincides with the detection field of a detector to be attached to the first detector attachment section. 
         [0014]    Each of the windows may be either a simple through hole or an opening covered with a plate made of a material that allows the passage of light within a range of wavelengths that need to be detected. 
         [0015]    In the integrating sphere according to the present invention, the detector attached to the first detector attachment section and the one attached to the second detector attachment section have the same detection fields. Accordingly, the two detectors attached to the integrating sphere according to the present invention receive light from the detection fields which have equal intensity distributions, so that the measurement discrepancy which occurs when the two detectors are switched is reduced. 
         [0016]    In the integrating sphere according to the present invention, the first detector attachment section and/or the second detector attachment section may preferably be provided with a position adjuster for adjusting the position of the detectors so as to make the detection fields of the detectors attached to the first detector attachment section and the second detector attachment section coincide with each other. 
         [0017]    The position adjuster may be a mechanism for providing a larger attachment distance from the outer surface of the integrating sphere for the detector having a larger detection angle among the detectors attached to the first and second attachment sections, or a mechanism for providing a smaller attachment distance from the outer surface of the integrating sphere for the detector having a smaller detection angle. With this configuration, even in the case of using two types of detectors having different viewing angles, their detection fields can be made to coincide with each other to reduce the measurement discrepancy. 
         [0018]    The present invention also provides a spectrometer including any of the previously described modes of the integrating sphere with a detector attached to each detector attachment section. For example, a PMT detector, InGaAs detector and PbS detector can be used as the detectors. 
       Advantageous Effects of the Invention 
       [0019]    In the integrating sphere according to the present invention, the detector attached to the first detector attachment section and the one attached to the second detector attachment section have the same detection fields. Accordingly, the two detectors attached to the integrating sphere according to the present invention receive light from the detection fields which have equal intensity distributions, so that the measurement discrepancy which occurs when the two detectors are switched is reduced. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  is a configuration diagram showing the main components of a spectrometer including a conventional integrating sphere. 
           [0021]      FIG. 2  is a diagram illustrating the arrangement of the detectors in a spectrometer including a conventional integrating sphere. 
           [0022]      FIGS. 3A and 3B  are diagrams showing the wavelength-sensitivity characteristics of a PMT detector, PbS detector and InGaAs detector. 
           [0023]      FIG. 4  is a diagram illustrating the detection fields of the detectors in a spectrometer including a conventional integrating sphere. 
           [0024]      FIG. 5  a configuration diagram showing the main components of a spectrometer including an integrating sphere according to the present invention. 
           [0025]      FIG. 6  is a diagram showing a comparison of the measurement discrepancy between the case where the spectrometer of the present embodiment is used and the case where a conventional spectrometer is used. 
           [0026]      FIGS. 7A and 7B  are diagrams illustrating one embodiment of the detector attachment section having a position adjuster. 
           [0027]      FIG. 8  is a diagram illustrating a variation of the integrating sphere according to the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0028]    An embodiment of the spectrometer including an integrating sphere according to the present invention is hereinafter described with reference to  FIGS. 5-8 . 
         [0029]      FIG. 5  shows the configuration of the main components of one embodiment of the spectrometer including an integrating sphere according to the present invention. The present embodiment is a spectrometer in which light generated from a light source outside the integrating sphere is introduced through a light introduction window  2  into the sphere to irradiate a sample  4  with the light and detect diffuse light reflected by the sample  4 . In the present embodiment, the X, Y and Z axes are defined in a similar to the previously described example, with the points of intersection of the Z axis and the integrating sphere referred to as the “polar points”. 
         [0030]    In the spectrometer of the present embodiment, the integrating sphere is provided with a light introduction window  2 , light entrance window  3 , as well as three light detection windows  10 ,  11  and  13 . First, second and third detector attachment sections  10   b ,  13   b  and  11   b  are provided at the three light detection windows. The light detection windows  10  and  11  are located at the polar points, while the light detection window  13  is formed at a position displaced from the polar points toward the side closer to the sample  4 . The first, second and third detectors  10   a ,  13   a  and  11   a  are attached to the first, second and third detector attachment sections  10   b ,  13   b  and  11   b , respectively. 
         [0031]    The spectrometer of the present embodiment is characterized in that the detector attachment sections allow the direction of the detector attached to each attachment section to be freely changed. In the spectrometer of the present embodiment, this feature is utilized so as to make the detection field of the detector  10   a  attached to the first detector attachment section coincide with that of the detector  13   a  attached to the second detector attachment section  13   b . In the present embodiment, only the detector  13   a  at the second detector attachment section  13   b  is attached in a different direction from the conventional case ( FIG. 4 ). It is also possible to change the attachment direction of the detectors at both the first and second detector attachment sections  10   b  and  13   b  so as to make the detection fields of the two detectors  10   a  and  13   a  attached to the two attachment sections coincide with each other. As already explained with reference to  FIG. 2 , the detection field of the detector  11   a  attached to the third detector attachment section  11   b  is equal to the detection field of the first detector  10   a.    
         [0032]    As just described, the detection fields of the detector  10   a  and  13   a  in the present embodiment are made to coincide with each other, so that these detectors receive light from detection fields having equal intensity distributions. Therefore, the measurement discrepancy becomes smaller than in the case of a conventional spectrometer in which the intensity of the light from a sample is measured with a detector located at a position different from the polar points. Although three detectors are used in the present embodiment, the number of detectors may be arbitrarily changed, because the position of the detector attachment sections in the integrating sphere according to the present invention is not limited to the polar points. 
         [0033]    The measurement discrepancy which occurs when the detectors are switched in the spectrometer of the present embodiment has been investigated and compared with the measurement discrepancy which occurs in a conventional spectrometer. In any of these spectrometers, three types of detectors (PMT detector, InGaAs detector and PbS detector) were used and the detector-switching operation was performed at wavelengths of 830 nm and 1650 nm. The result shown in  FIG. 6  demonstrates that the measurement discrepancy can be dramatically reduced by using the spectrometer present embodiment. 
         [0034]    In the previous embodiment, detectors with the same viewing angles are used. It is also possible to use a plurality of detectors having different detection angles. In this case, a detector attachment section having a position adjuster for adjusting the position of the detector is used in order to make the detection fields of the detectors coincide with each other.  FIGS. 7A and 7B  show one example of the detector attachment section  14   b  having the position adjuster. Specifically,  FIG. 7A  shows the detection angle of the detector  14   a  attached in the same manner as in the previous embodiment, while  FIG. 7B  shows the detection angle of the detector  14   a  attached at a farther position from the outer surface of the integrating sphere. As can be seen in  FIGS. 7A and 7B , the effective detection angle can be changed by moving the detector  10   a  closer to or farther from the outer surface of the integrating sphere using the position adjuster. With this mechanism, the detection fields of a plurality of types of detectors can be made to coincide with each other even those detectors have different detection angles. 
         [0035]    The previous embodiments are mere examples and can be appropriately changed within the spirit of the present invention. 
         [0036]    The previously described embodiment is concerned with the case where the attachment sections are configured so that the direction of the detector attached to each attachment section is freely changeable (moveable). If the types of detectors to be used are previously specified, the detector attachment sections may be configured so that the detectors attached to those sections will be fixed in such directions where their detection fields coincide with each other. 
         [0037]    In the previously described embodiment, at least one detector attachment section is provided at one of the polar points. However, it is not always necessary to provide the detector attachment sections at the polar points. For example, it is possible to provide detector attachment sections as indicated by numerals  13   b  and  15   b  in  FIG. 8 , with the detectors  13   a  and  15   a  attached as shown. 
         [0038]    The previously described embodiment is a spectrometer in which light generated from a light source outside the integrating sphere is introduced through a light introduction window to irradiate a sample with the light and detect diffuse light reflected by the sample. However, the integrating sphere according to the present invention can be used in various forms of spectrometers, such as a spectrometer in which light generated from a light source outside the integrating sphere is cast onto a sample and the light transmitted through the sample is introduced into the integrating sphere and thereby detected, as well as a spectrometer in which the light source is located within the integrating sphere. Depending on the configuration of the spectrometer, an integrating sphere with no light introduction window  2  is appropriately used. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1 . Integrating Sphere 
           2 . Light Introduction Window 
           3 . Light Entrance Window 
           4 . Sample 
           10 ,  11 ,  12 ,  13 ,  14 ,  15 . Light Detection Window 
           10   a ,  11   a ,  12   a ,  13   a ,  14   a ,  15   a . Detector 
           10   b ,  11   b ,  12   b ,  13   b ,  14   b ,  15   b . Detector Attachment Section