Patent Publication Number: US-2023145637-A1

Title: Attenuated total reflection measuring apparatus capable of raman spectral measurement

Description:
RELATED APPLICATION 
     This application claims the priority of Japanese Patent Application No. 2021-181521 filed on Nov. 5, 2021, the disclosure of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to an Attenuated total reflection (ATR) measuring apparatus capable of performing Raman spectral measurement simultaneously. 
     BACKGROUND ART 
     The ATR accessory for Fourier-transform infrared spectrometer (FTIR) described in Patent Literature 1 is an apparatus capable of performing Attenuated total reflection measurement and Raman spectral measurement simultaneously. In the ATR accessory, an optical fiber for Raman measurement is embedded into a pressure bar on a sample stage. An excitation light from the end of the fiber irradiates the sample, and the ATR accessory collects Raman scattering light from the sample through the end of the fiber to detect the same with a Raman detection mechanism. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: International Publication No. WO2019/092772 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the Attenuated total reflection measuring apparatus of Patent Literature 1, an irradiation range of the excitation light emitted from the optical fiber is widened. Accordingly, it was problematic in the point that, upon measuring a small amount of a sample or a thin sample by Raman spectral measurement, a Raman peak derived from the ATR prism embedded into the stage overlaps the measurement result. 
     The object of the present invention is to provide an Attenuated total reflection measuring apparatus capable of performing Raman spectral measurement simultaneously, the Attenuated total reflection measuring apparatus capable of performing Raman spectral measurement while suppressing influence of a Raman peak derived from an ATR prism. 
     Solution to Problem 
     That is, the Attenuated total reflection measuring apparatus according to the present invention performs Attenuated total reflection measurement by bringing an Attenuated total reflection crystal (ATR crystal) having a refractive index higher than that of a sample into contact with the sample, the apparatus comprises an infrared optical instrument and a Raman spectroscopy instrument, wherein: 
     the infrared optical instrument is disposed on the ATR crystal side of the sample, and is provided to irradiate the ATR crystal with an infrared light and collect the infrared light from the ATR crystal; 
     the Raman spectroscopy instrument is disposed on a side opposite to the ATR crystal side relative to the sample, and comprises an excitation light source that emits an excitation light, a guide tube having a cylindrical shape that outputs the excitation light from an end of the guide tube to the sample, and a lens portion that is disposed inside the guide tube and collects the excitation light toward the end of the guide tube; 
     the end of the guide tube is provided at a position to push the sample to the ATR crystal; and 
     the Raman spectroscopy instrument further comprises a lens position adjustment mechanism for moving the lens portion along an excitation optical axis of the excitation light, and a spectroscope provided to spectrally disperse a Raman scattering light collected by the lens portion from the sample to detect the spectrally dispersed Raman scattering light. 
     This configuration is characterized in that the infrared optical instrument including the ATR crystal and the Raman spectroscopy instrument for Raman spectral measurement are disposed at positions interposing the sample. That is, since the end of the guide tube of the Raman spectroscopy instrument is disposed at the position to push the sample toward the ATR crystal, ATR measurement can be performing while the sample is in contact with the ATR crystal. Moreover, the excitation light from the guide tube irradiates the sample, and the Raman scattering light from the sample is collected by the guide tube, so that Raman spectral measurement can also be performed. Therefore, ATR measurement and Raman spectral measurement can be performed simultaneously. 
     In addition, since Raman spectral measurement is performed while the end of the guide tube is in contact with the sample, an external light coming into the guide tube can be blocked and Raman spectral measurement can be performed while influence of the external light is suppressed in a space where light is blocked. 
     Furthermore, the lens portion can be moved by the lens position adjustment mechanism, and, for example, the position of the lens portion can be adjusted to match the focusing position of the excitation light with the surface or inside of the sample; therefore, it becomes easier to avoid a Raman peak derived from the ATR crystal to overlap with the result of Raman spectral measurement. 
     Moreover, it is preferred that 
     the lens portion is fixed to a lens tube configuring a double cylindrical structure with the guide tube, 
     the lens position adjustment mechanism comprises a movable material that moves along the excitation optical axis, and a fixing material that supports the movable material, 
     the lens tube is retained to the movable material, and 
     the guide tube is retained to the fixing material. 
     In this configuration, since the lens tube is retained to the movable material of the lens position adjustment mechanism and the guide tube is retained to the fixing material of the lens position adjustment mechanism, the double-cylindrical structure of the lens tube and the guide tube is disposed on the sample side of the lens position adjustment mechanism. Therefore, the position of the lens position adjustment mechanism is away from the sample for the length of the tubes. Since the double-cylindrical structure of the lens tube and the guide tube does not comprise the lens position adjustment mechanism and can be made as thin as possible, a measurer can easily see and confirm the contact state of the guide tube and the sample, and the position of the Raman spectroscopy instrument can be easily adjusted. 
     Moreover, it is preferred that the lens tube is provided such that the position of the lens tube can be adjusted by the lens position adjustment mechanism so that the lens portion fixed to the end of the lens tube or the end of the lens tube comes into a position to push the sample to the ATR crystal. 
     In this configuration, both of the tubes configuring the double-cylindrical structure can be brought into contact with the sample. As for the lens tube, the position of the lens tube may be adjusted by the lens position adjustment mechanism such that either of the end of the lens tube or the lens portion fixed to the end of the lens tube comes into contact with the sample. Accordingly, the contact state of the sample and the ATR crystal can be made more certain, and a better result can be achieved in the ATR measurement. 
     Moreover, it is preferred that the lens tube is detachably retained to the movable material, and the guide tube is detachably retained to the fixing material. 
     In this configuration, if both of the two tubes configuring the double-cylindrical structure are detachable, the tubes can be exchanged easily, and also the tubes can be changed to tubes of different lengths easily. Moreover, as for the lens tube, it can be selected from lens portions of a plurality of types easily, and as for the guide tube, materials or shapes of the pressing part of the end of the guide tube can be changed in accordance with the sample easily. 
     Moreover, it is preferred that the lens position adjustment mechanism is configured such that the position of the sample and the position of the ATR crystal are within an adjustment range of the position of a focusing point of the lens portion. 
     In this configuration, since the position of the focusing point of the excitation light upon Raman spectral measurement can be adjusted to the positions of the sample and the ATR crystal, a differential spectrum between these spectra can be calculated. Accordingly, in a case of a sample of which a fluorescence from the ATR crystal may affect Raman measurement, a Raman peak derived from the ATR crystal can be eliminated effectively. 
     Moreover, since the position of the focusing point can be set to a position closer to the sample than the position of the end of the guide tube, Raman spectral measurement can be performed to the inner part of the sample. Furthermore, in a case of which a cap is put onto the end of the guide tube to improve the contact state of the ATR crystal and the sample and is pressed to the sample, the focusing point can be set to the sample by moving the position of the focusing point to the sample for the thickness of the cap; therefore, Raman spectral measurement can be performed while the cap is put on. 
     Moreover, it is preferred that the shape of the lens portion is a hemisphere or a sphere, and the lens portion is provided to be position adjustable by the lens position adjustment mechanism such that the lens portion comes into a position to push the sample to the ATR crystal. 
     Moreover, it is preferred that the Raman spectroscopy instrument comprises: 
     a collimating lens position adjustment mechanism that adjusts the position of a collimating lens disposed at an exit of the excitation light source in a direction of the optical axis of the excitation light; and 
     an imaging lens position adjustment mechanism that adjusts the position of an imaging lens disposed in front of the spectroscope in a direction of the optical axis of the Raman scattering light. 
     In this configuration, a half-ball lens or a ball lens is used, so that a lens having a large numerical aperture and a short back focus (BFL) can be selected easily. Accordingly, even when the lens portion is pressed to a sample of a small amount or a thin sample, the focusing point of the excitation light can be set to the sample by operating the collimating lens position adjustment mechanism and the imaging lens position adjustment mechanism, and the Raman scattering light of such sample can be measured. In addition, measurement with excellent confocality can be performed when the numerical aperture of the lens portion is large; therefore, a Raman peak derived from the ATR crystal can be more easily avoided from overlapping with the result of Raman spectral measurement. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    illustrates a whole configuration of an ATR accessory according to a first embodiment. 
         FIG.  2    illustrates a configuration of a Raman module in the ATR accessory. 
         FIG.  3    illustrates a configuration of a focus adjustment mechanism of the Raman module. 
         FIG.  4 A  illustrates a method of eliminating a peak derived from an ATR prism by a differential spectrum, and illustrates a focusing point upon acquiring a spectrum of a sample. 
         FIG.  4 B  illustrates a method of eliminating a peak derived from an ATR prism by a differential spectrum, and illustrates a focusing point upon acquiring a spectrum of the ATR prism. 
         FIG.  5 A  illustrates a state when a pressing cap is put onto the end of the guide tube. 
         FIG.  5 B  illustrates a state when a window plate is fit to the end itself of the guide tube. 
         FIG.  6    illustrates an example of applying a ball lens to the Raman module. 
         FIG.  7    illustrates an example of applying a half-ball lens to the Raman module. 
         FIG.  8 A  illustrates a mechanism for moving the focusing point in the direction of the optical axis while the sample is pressed. 
         FIG.  8 B  illustrates a mechanism for moving the focusing point in the direction of the optical axis while the sample is pressed. 
         FIG.  9    illustrates a state when the guide tube and the lens tube are removed from the Raman module. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of an ATR accessory (corresponds to the Attenuated total reflection measuring apparatus) according to the present invention are described in detail with reference to the drawings. 
       FIG.  1    is a schematic drawing that illustrates a configuration of an ATR accessory  100  according to a first embodiment. The ATR accessory  100  is an accessory for a Fourier-transform infrared spectrometer (FTIR)  300  used to perform Attenuated total reflection measurement by bringing an ATR prism (corresponds to an ATR crystal)  200  having a refractive index higher than a sample into contact with the sample, and is installed to a sample chamber  310  of the FTIR  300 . 
     As shown in  FIG.  1   , the ATR accessory  100  has: the ATR prism  200  that is fit to a hole at the center of a stage  210 ; an infrared optical instrument  220  that is disposed underneath the stage  210 ; an elevating equipment  240  on the stage  210 ; and a Raman module (corresponds to Raman spectroscopy instrument)  10  detachably mounted to a moving part (lifter) of this elevating equipment  240 . 
     &lt;Infrared Optical Instrument&gt; 
     The infrared optical instrument  220  has a light receiving window  222  of an infrared light, a plurality of reflecting mirrors  224   a  to  224   f , and a light emitting window  226  of the infrared light, and they are disposed inside a housing  228  having the stage  210  as a top plate. The infrared light from an infrared light source  320  of the FTIR  300  is condensed by a condenser lens  330  in front of the light receiving window  222  of the ATR accessory  100 , and enters the housing  228  from the light receiving window  222 . In the housing  228 , the infrared light is reflected at the plurality of reflecting mirrors  224   a  to  224   c  on the entrance side, enters the ATR prism  200 , and is totally reflected at a surface in contact with the sample inside the ATR prism  200 . A totally-reflected light thereof exits the ATR prism  200 , is reflected at the plurality of reflecting mirrors  224   d  to  224   f  on the exit side, and exits from the light emitting window  226 . Then, it becomes a parallel light by a collimating lens  340  disposed outside the light emitting window  226 , and is sent to an infrared detector  350 . 
     &lt;Elevating Equipment&gt; 
     Next, the elevating equipment  240  has: a column  242  that stands on the stage  210 ; an arm  244  supported at an upper end of the column  242 ; and a lifter  246  supported to be movable upward and downward having this arm  244  as a base. A commercially available product can be used as this elevating equipment  240 , and one which has a mechanism of which the lifter  246  moves up and down when a measurer rotates a knob  248  may be adopted, for example. The arm  244  may be supported to be rotatable around the central axis of the column  242 . The central axis of the column  242  is in a vertical direction, and is shown as Z axis in  FIG.  1   . 
     &lt;Raman Module&gt; 
     The Raman module  10  is detachably supported to the lifter  246  of the elevating equipment  240 . A screw or a magnet may be used to mount the Raman module  10  to the lifter  246 . The Raman module  10 , which will be described in detail with reference to  FIG.  2   , has a module main body (housing  28 ), a focus adjustment mechanism (corresponds to the lens position adjustment mechanism)  40  connected to a lower end of the module main body, and a cylindrical guide tube  60  that outputs an excitation light from the lower end, and is supported to the lifter  246  in a posture of which an opening of a lower end of the guide tube  60  faces the ATR prism  200 . The Raman module  10  is a size that can be held with one hand when it is taken off from the lifter  246 , and is configured to be capable of performing Raman spectral measurement alone. 
     The measurer elevates the Raman module  10  mounted to the elevating equipment  240 , and places a sample on the ATR prism  200  of the stage  210 . For example, a small amount of a powder sample or a sample in form of a thin sheet is placed thereon. Then, the Raman module  10  is descended by the elevating equipment  240 , and the lower end of the guide tube  60  is slowly brought into contact with the sample on the stage  210 . The knob  248  of the elevating equipment  240  may be provided with a torque limiter (a mechanism of which the knob  248  idles when a torque more than the set value acts on the knob  248 ) such that the end of the guide tube  60  does not press the sample too hard. 
     The sample is not limited to a solid or a powder, and may be a liquid sample or a mixture thereof. Moreover, as for the amount of the sample, the sample ranging from a small amount of the sample placed on a placement surface to a large amount put in a container or a bag can be measured. 
     As shown in  FIG.  2   , an excitation light source  12 , a collimating lens 15   c , a dichroic mirror (DM)  14 , a spectroscope  16 , a photodetector  18 , a control circuit  20  having a microprocessor and a memory, a power source  22 , an analog/digital (A/D) converter  24 , and a communication interface (I/F)  26  are disposed inside the housing  28  of the Raman module  10 . A battery may be provided to the power source  22 ; however, a power supply unit (e.g., A/C adapter) may be directly provided without using a battery. 
     The excitation light source  12  is a laser diode or the like, and outputs a laser light as an excitation light. By providing an opening cover to the housing  28  and configuring the excitation light source  12  to be detachable, the excitation light source  12  can be easily changed to one having a wavelength in accordance with the type or form of the sample. 
     In the configuration of  FIG.  2   , the excitation light from the excitation light source  12  becomes into a parallel light by the collimating lens  15   c , transmits the dichroic mirror (DM)  14 , passes through the focus adjustment mechanism  40  and the guide tube  60 , and irradiates the sample. A shutter  30  is provided between the DM  14  and the focus adjustment mechanism  40 . The shutter  30  is closed when the Raman module  10  is not used to avoid unnecessary emission of the excitation light. 
     Moreover, the returned light (here, Raman scattering light (from the sample)) from the guide tube  60  passes through the focus adjustment mechanism  40 , and is reflected at the DM  14 . Then, it is dispersed by the spectroscope  16  via an imaging lens  15   a  and a slit  15   b  into different wavelengths, and detected as a spectral distribution of a light intensity by a CMOS image sensor or the like that configures the photodetector  18 . The DM  14  is an optical element capable of separating a necessary light (Raman scattering light) from an incident light by reflecting the incident light of a specific wavelength region and transmitting other lights, and may be replaced by other optical elements having the same function. 
     In the present embodiment, a detector or a sensor without a cooling function is used as the photodetector  18  for miniaturization, weight-saving and power-saving; however, one having a cooling function may be used. When S/N ratio is small, measurement time may be extended to increase integration of detected signals. The detected signal from the photodetector  18  is converted into a digital signal by the A/D converter  24 , and sent to the control circuit  20 . The control circuit  20  calculates a spectral information of the sample based on the detected signal, and stores the same. Moreover, the control circuit  20  outputs the spectral information to an external computer (PC)  400  via the communication I/F  26  such as a USB, and can display the spectral information on its monitor. The external PC  400  may be a portable computer such as a smart phone. The portable computer may encrypt the measured spectrum of the Raman module  10  into an encrypted mail, and further send it to a server computer having an external database. The measured spectrum received by the server computer may be analyzed in detail, and the portable computer may receive the analysis result thereof and display the same on a monitor. 
       FIG.  3    illustrates an example of the configuration of the focus adjustment mechanism  40  and the guide tube  60  that are connected to the housing  28  of the Raman module  10 . 
     &lt;Focus Adjustment Mechanism&gt; 
     The focus adjustment mechanism  40  has a fixing material  42  fixed to the housing  28 , and a movable material  44  supported to be movable in the Z direction relative to the fixing material  42 . The fixing material  42  has a through hole  46  along the optical axis of the excitation light from the housing  28 . An inner screw  48  is processed to the inner surface closer to the housing  28  of the through hole  46 . Moreover, at the central part of the through hole  46 , a relatively large opening for operating a knob  52  of the movable material  44  is formed in a direction perpendicular to the Z direction. 
     The movable material  44  is a cylindrical material that forms the optical path of the excitation light, and an outer screw  50  that fits the inner screw  48  of the fixing material  42  is processed to the outer surface closer to the housing  28 . Moreover, the knob  52  having a diameter larger than the part of the outer screw  50  is formed at the end closer to the sample of the movable material  44 . At the through hole  54  of the movable material  44 , a cylindrical lens tube  56  is detachably mounted from the sample side. Moreover, a lens portion (a convex lens or an achromatic lens)  58  is supported in the vicinity of the end on the sample side of the lens tube  56 . 
     &lt;Guide Tube&gt; 
     At the through hole  46  of the fixing material  42 , the guide tube  60  is detachably mounted from the sample side. The inner diameter of the end on the sample side of the through hole  62  of the guide tube  60  is small, and is formed such that the lens tube  56  can move in the Z direction when the end of the lens tube  56  is inserted. 
     The guide tube  60  and the lens tube  56  form a double cylindrical structure. Since the outer guide tube  60  is supported to the fixing material  42 , and the inner lens tube  56  is supported to the movable material  44 , the end of the lens tube  56  moves in a direction getting closer/farer to/from the sample when the measurer rotates the knob  52  to descend/elevate the movable material  44  in the Z direction. By forming the double cylindrical structure of the guide tube  60  and the lens tube  56 , the focus adjustment mechanism  40  can be provided at a position away from the sample, and the double cylindrical structure can be made extremely thin. Therefore, the measurer can easily confirm the contact state of the end of the guide tube  60  and the sample, and the position of the Raman module  10  can be easily adjusted. 
     The excitation light (parallel light) that travels inside the lens tube  56  is collected by the lens portion  58 , and forms a focusing point P at a position that is out from the end of the lens tube  56  to the sample side. The position of the focusing point of the excitation light by the lens portion  58  and the slit  15   b  in front of the spectroscope  16  are in a conjugated positional relationship. When the movable material  44  is in a reference position (at a position where the knob  52  is the closest to the housing  28 ) as shown in  FIG.  3   , the position of this focusing point P becomes the position of the end of the guide tube  60  exactly. 
     In the present embodiment, as shown in  FIG.  3   , the measurer operates the elevating equipment  240  to descend the Raman module  10  and press the sample to the ATR prism  200  by the lower end of the guide tube  60 , so that the sample can be brought into contact with the ATR prism  200 , and ATR measurement can be performed in a good condition. 
     Simultaneously, since the lower end of the guide tube  60  is in a position in contact with the sample, the inside of the guide tube  60  becomes blocked from light, and Raman spectral measurement can be performed without being affected by an external light. 
     Furthermore, the measurer can operate the focus adjustment mechanism  40  to adjust the position of the focusing point P of the lens portion  58  in the Z direction, and, in particular, the focusing point P can be adjusted to the surface or the inside of the sample, so that a peak derived from the ATR prism  200  can be avoided from overlapping with the result of Raman spectral measurement. 
     Therefore, ATR measurement and Raman spectral measurement can be performed simultaneously under good conditions, respectively. 
     The Raman module  10  has the collimating lens  15   c  at the exit of the excitation light source  12 , the lens portion  58  near the sample, and the imaging lens  15   a  at the entrance of the spectroscope  16 , and they configure a confocal optical system, so that Raman measurement with a high confocality is performed. For example, when the sample has a multiple layer structure, the focusing point P can be positioned on a measurement surface of the ATR prism  200  by operating the focus adjustment mechanism  40 , and it can be consistent with ATR measurement. As shown in  FIG.  4   , the confocal optical system of the Raman module  10  and the focus adjustment mechanism  40  of the lens portion  58  are used to move the focusing point P of the excitation light in the optical axis direction. When a Raman peak derived from the ATR prism  200  and a Raman peak of the sample are overlapped, the position of the focusing point P is changed to measure a Raman spectrum of the sample of  FIG.  4 A  and a Raman spectrum of the diamond ATR prism of  FIG.  4 B . Then, with respect to the Raman spectrum of the sample, a coefficient is multiplied to the Raman spectrum of the ATR prism to calculate the differential spectrum between the two Raman spectra, so that the Raman peak derived from the ATR prism  200  can be removed by calculation. At least two measurement points, the measurement point of the ATR prism and the measurement point of the sample, may be used. 
     &lt;Pressing Cap&gt; 
       FIG.  5 A  shows a state which a pressing cap  64  is mounted to the lower end of the guide tube  60 . The pressing cap  64  covers the opening of the guide tube  60 , and has a hole  65  of a small diameter at the central part where the collected excitation light is output therefrom. By mounting the pressing cap  64 , an area where the guide tube  60  presses the sample becomes larger, and thus the contact state of the ATR prism  200  and the sample improves. Moreover, by operating the focus adjustment mechanism  40  to adjust the position of the focusing point P of the lens portion  58  in the Z direction for the thickness of the pressing cap  64 , the position of the focusing point P in the sample can be set to the same state as before the pressing cap  64  is mounted. 
     One that is suitably selected from pressing caps  64  having lower ends of different shapes may be used. For example, it is preferred that the measurer can choose one pressing cap  64  of which the contact surface with the sample is made of metal or resin. Moreover, it is preferred that the measurer can choose one pressing cap  64  of which the contact surface with the sample is flat or concave shape. Moreover, it is preferred that the measurer can choose one pressing cap  64  of which the contact part with the sample is flexible type so as to move freely. 
     &lt;Guide Tube with a Window Plate&gt; 
       FIG.  5 B  shows a state which the opening at the lower end of the guide tube  60  is closed with a window plate  72 , not with a cap. The window plate  72  is preferably made of a material such as quarts that does not emit light that may disrupt Raman spectral measurement. By mounting the window plate  72 , the excitation light transmits the window plate  72 , but the sample may not enter the guide tube  60  even if the sample is liquid or gel. Accordingly, the lens portion  58  inside may not be contaminated, and ATR measurement and Raman spectral measurement can be performed easily. 
     &lt;Other Lens Portions&gt; 
     If the numerical aperture of the lens portion (convex lens)  58  of  FIG.  3    is large, the sample can be pressed with the end of the lens tube  56  by operating the focus adjustment mechanism  40  to further descend the lens tube  56 . However, when the sample is in a small amount, or the thickness of the sample is thin, the focusing point P of the lens portion  58  may deviate from the sample; therefore, attention needs to be paid for the result of Raman measurement overlapping with the Raman peak derived from the ATR prism  200 . 
     Whereas, an embodiment using a lens portion having a different shape is illustrated in  FIG.  6    and  FIG.  7   . In  FIG.  6   , a ball lens  66  is fixed to the end of the lens tube  56 , and a part of the ball lens  66  is protruded from the lens tube  56  to the lower side. The ball lens  66  has a large numerical aperture and a short back focus (BFL), so that sensitivity and spatial resolution are increased. That is, since the distance from the lower end of the ball lens  66  to the focusing point P is short, the position of the focusing point P can be set not to deviate from the sample even if the position of the ball lens  66  is lowered by the focus adjustment mechanism  40  to bring the ball lens  66  in contact with the sample. 
     Similarly, since a half-ball lens (e.g., a solid immersion lens (SIL))  68  has a large numerical aperture and a short back focus (BFL) too, Raman spectral measurement in a contact state with the sample can be performed like the ball lens  66 . Moreover, the half-ball lens  68  can be in surface contact with the sample, not point contact like the ball lens  66 .  FIG.  7    illustrates a half-ball lens having a combined shape of a hemispherical shape and a cylindrical shape as an example. 
     Both of the guide tube  60  and the lens portion can be brought into contact with the sample by using the ball lens  66  and the half-ball lens  68 , so that the contact state of the sample and the ATR prism  200  can be made more precise, and a better result of ATR measurement can be achieved. 
       FIG.  8    illustrates an example of the Raman module  10  provided with a collimating lens position adjustment mechanism  80  of the collimating lens  15   c , and an imaging lens position adjustment mechanism  82  of the imaging lens  15   a . When the lens tube  56  having the ball lens  66  or the half-ball lens  68  is used, as shown in  FIG.  8 A , the position of the focusing point P of the ball lens  66  can be changed without operating the focus adjustment mechanism  40  by operating the collimating lens position adjustment mechanism  80  to move the position of the collimating lens  15   c  at the exit of the excitation light source  12  in a direction of the optical axis of the excitation light. In this case, since the image formation position at the slit  15   b  of the spectroscope  16  moves too, the position of the collimating lens  15   c  and the position of the imaging lens  15   a  disposed in front of the slit of the spectroscope  16  need to be synchronized. Accordingly, by providing the imaging lens position adjustment mechanism  82  that adjusts the position of an imaging lens  15   a  in a direction of the optical axis of the Raman scattering light like in  FIG.  8 B , the image formation position can be adjusted to the position of the slit  15   b  even if the position of the focusing point P of the ball lens  66  is moved. When using not only the convex lens  58  but also the lens tube  56  with the ball lens  66  or the half-ball lens  68 , the position of the focusing point P in the depth (optical axis) direction can be changed while the sample is pressed. 
     &lt;Exchangeability&gt; 
     As shown in  FIG.  3   , one or more of a ball plunger  70  is embedded to the inner surface of the through hole  54  of the movable material  44 . The ball plunger  70  is configured of a spring and a ball, and is retained such that a part of the ball is protruded from the inner surface of the through hole by a spring force. Moreover, a groove corresponding to the ball of the ball plunger  70  is formed at a circumference in the vicinity of the upper end of the lens tube  56 . When the lens tube  56  is pressed into the through hole  54 , the ball fits into the groove and the lens tube  56  becomes retained to the movable material  44 . Moreover, when the lens tube  56  is pulled with a specific force, the fitted state of the ball and the groove becomes released, and the lens tube  56  is removed from the through hole  54 . As described, the lens tube  56  can be easily mounted and released to/from the movable material  44 . 
     Similarly, a detachable structure using the ball plunger  70  is adopted between the through hole  46  of the fixing material  42  and the guide tube  60 , and the guide tube  60  can be easily mounted and released. 
       FIG.  9    illustrates a state which the lens tube  56  and the guide tube  60  are removed from the focus adjustment mechanism  40 . Moreover, the pressing cap  64  removed from the guide tube  60  is also illustrated. By suitably selecting and using such detachable lens tube  56 , guide tube  60 , and pressing cap  64 , they can be easily exchanged, and also can be easily changed to a tube of different length. Moreover, as shown in  FIG.  9   , the lens tube  56  can be easily selected and exchanged from a plurality of types of lens portions (convex lens  58 , ball lens  66 , half-ball lens  68 ). Moreover, as for the guide tube  60 , the material or shape of the pressing part at the end can be easily changed in accordance with the sample like the pressing cap  64 . Examples of the guide tube  60  provided with a small opening  74  at the end and the guide tube  60  provided with the window plate  72  are also illustrated in  FIG.  9   . 
     The elevating equipment  240  can be elevated/descended electrically, not manually, and the focus adjustment mechanism  40  can be driven electrically, not manually. 
     Moreover, as shown in  FIG.  1   , a camera  230  that images the ATR prism  200  from lower side may be provided. The camera  230  images a visible light image of the sample through the ATR prism  200 . The visible light image of the sample is useful in adjusting position of the measurement part of the sample. Furthermore, it is also useful in positioning the focusing point P of the excitation light for Raman spectral measurement in the optical axis direction, and adjusting the measurement part of the sample to the focusing point P of the excitation light. 
     REFERENCE SIGNS LIST 
     
         
           10  Raman module (Raman spectroscopy instrument) 
           12  Excitation light source 
           15   a  Imaging lens 
           15   c  Collimating lens 
           16  Spectroscope 
           40  Focus adjustment mechanism (lens position adjustment mechanism) 
           42  Fixing material 
           44  Movable material 
           56  Lens tube 
           58  Convex lens (lens portion) 
           60  Guide tube 
           66  Ball lens (lens portion) 
           68  Half-ball lens (lens portion) 
           80  Collimating lens position adjustment mechanism 
           82  Imaging lens position adjustment mechanism 
           100  ATR accessory (Attenuated total reflection measuring apparatus) 
           200  ATR prism (ATR crystal) 
           220  Infrared optical instrument 
           300  Fourier-transform infrared spectrometer (FTIR)