Infrared microscope equipped with detector having multiple elements of different sizes

Abstract

Provided is an infrared microscope in which an infrared element having an optimal size can be selected according to the size of a sample, the opening size of an aperture, or the amount of light received by a detector. This infrared microscope 10 comprises: a sample stage 22; an upper Cassegrain mirror 24 that condenses infrared light from a sample; an aperture 40 that is located at a position where a sample image is formed; a condensing mirror 50 that collects light passing through the aperture; a mirror mount 60 that moves the condensing mirror 50; and a detector 70 that detects the light condensed by the condensing mirror 50. The aperture 40 is selected from a plurality of apertures having different opening sizes. The detector 70 has a plurality of infrared elements 76, 78 arranged on the surface of a dewar 72. The plurality of infrared elements 76, 78 have different sizes from each other and are arranged with an interval therebetween of 10 mm or less. The mirror mount 60 is provided so as to be capable of moving the condensing mirror 50 so that the position of an opening image formed by the condensing mirror 50 coincides with the positions of the plurality of infrared elements 76, 78.

Description

Infrared microscope with a multi-element detector of different sizes

[0001] The present invention relates to an infrared microscope that uses infrared light to obtain optical information of a minute area on a sample.

[0002] An infrared microscope is a device that irradiates a sample placed on a movable stage with infrared light, collects and detects the transmitted light, reflected light, or total reflected light from a small area on the sample, and obtains its infrared spectrum.

[0003] This section explains the typical optical system (Cassegrain mirror, aperture, and focusing mirror in front of the detector) from the sample on the movable stage of an infrared microscope to the detector. First, a magnified image of a small area on the sample is obtained using the Cassegrain mirror. An aperture is placed at the position of the magnified image, allowing only light from the desired measurement area to pass. The focusing mirror in front of the detector forms an image of the aperture opening on the infrared element of the detector, and the infrared element detects the intensity of the infrared light. The signal processing unit performs a Fourier transform on the intensity signal of the infrared light detected in this way to calculate the infrared spectrum.

[0004] As described in paragraph 0010 of Patent Document 1, the aperture is configured so that the size and shape of the opening can be changed to adjust the measurement area according to the size of a minute part of the sample. For example, if the target substance is minute in size, changing to an aperture with a smaller opening will narrow the measurement area, allowing for the acquisition of only the optical information of that substance.

[0005] Japanese Patent Application Laid-Open No. 2006-208016

[0006] However, when only one detector can be installed in an infrared microscope, the size of the infrared element remains the same even if the aperture opening size is reduced, and as shown in Figures 9(A) and 9(B), the area on the light receiving surface of the infrared element where light is not detected increases.

[0007] In Figure 9(A), the size of the aperture image is appropriate for the infrared element, enabling high-sensitivity measurement with a good S / N ratio. However, if the aperture image is made too small, as in Figure 9(B), the proportion of the area that does not receive light, i.e., the proportion of thermal noise relative to the received light signal, becomes excessive, resulting in insufficient detection sensitivity. This problem is not limited to when the aperture opening size is made small; it can also occur when the amount of light received by the detector is low due to the small size of the sample itself.

[0008] So, is it enough to replace the detector with one that has a small-sized infrared element? However, every time a detector with a large-sized element is replaced with a detector with a small-sized element, adjustment work is required to accurately position the small aperture image on the small-sized infrared element, and such adjustment work is very difficult for an ordinary user to perform.

[0009] So, what if we could install two detectors, one with a large element and one with a small element? However, because the detectors are integrated with a cooling mechanism (Dewar) such as liquid nitrogen to avoid errors caused by thermal fluctuations in the infrared elements, a certain amount of space must be reserved for each detector. Therefore, installing two detectors would make the infrared microscope significantly larger. Furthermore, even if two detectors could be installed, the distance between the large and small infrared elements would be several centimeters or more, which would typically increase the time required to switch the optical path, making it difficult to switch the optical path quickly.

[0010] An object of the present invention is to provide an infrared microscope that allows selection of an infrared element of an optimum size depending on the size of the sample, the opening size of the aperture, or the amount of light received by the detector.

[0011] That is, the infrared microscope of the present invention comprises a sample stage on which a sample is placed, an objective mirror that collects infrared light from the sample, an aperture provided at the position of a sample image formed by the objective mirror, a collecting mirror that collects infrared light that has passed through the opening of the aperture, a collecting mirror drive unit that moves the collecting mirror, and a detector that detects the infrared light collected by the collecting mirror, wherein the aperture is selected from a plurality of apertures having different opening sizes or shapes, or is configured so that the size or shape of the opening is variable, the detector has a detection element holder and a plurality of infrared elements that are arranged on the surface of the detection element holder, the plurality of infrared elements having different sizes and being arranged at intervals of 10 mm or less, and the collecting mirror drive unit is configured to move the collecting mirror so that the position of the aperture image formed by the collecting mirror coincides with the respective positions of the plurality of infrared elements.

[0012] With this configuration, the infrared microscope of the present invention can select an infrared element of an optimal size according to the size of the sample, the aperture opening size, or the amount of light received by the detector. For example, selecting a large-sized infrared element enables bright measurements using a large aperture opening, while selecting a small-sized infrared element enables highly sensitive measurements of a minute area by narrowing the aperture opening. In other words, it is now possible to perform different types of measurements simultaneously.

[0013] Furthermore, since multiple infrared elements of different sizes are arranged at intervals of 10 mm or less in one detection element holder, the installation space for the detector is not increased, and the movement of the focusing mirror by the focusing mirror drive unit is small, so that the infrared elements can be switched quickly and accurately.

[0014] Here, the infrared light from the sample can be infrared light that has been transmitted through the sample, infrared light that has been reflected by the sample, or infrared light that has been totally reflected by the sample. The multiple infrared elements may be arranged parallel to the axis of incidence of the infrared light on the focusing mirror, or may be arranged two-dimensionally with a direction parallel to the axis of incidence of the infrared light on the focusing mirror and a direction perpendicular to the axis of incidence.

[0015] The focusing mirror driver may be configured to move the position or the attitude of the focusing mirror, or both the position and the attitude of the focusing mirror. For example, the focusing mirror driver may be configured to vary the angle of incidence of infrared light onto the focusing mirror. For example, the focusing mirror driver may be configured to translate the focusing mirror along the axis of incidence of infrared light.

[0016] Furthermore, for example, the collecting mirror drive unit may be configured to translate the collecting mirror along the incident axis of infrared light and to rotate the collecting mirror around the incident axis of infrared light. Furthermore, for example, the collecting mirror drive unit may be configured to vary the incident angle of infrared light onto the collecting mirror and to rotate the collecting mirror around the incident axis of infrared light.

[0017] Since the movements of the focusing mirrors exemplified above all require small movements, by using a focusing mirror drive unit, it is possible to quickly and accurately align the aperture image of the infrared light with the respective positions of multiple infrared elements of different sizes arranged one-dimensionally or two-dimensionally on the detector.

[0018] Furthermore, it is preferable that the infrared microscope of the present invention further comprises a computer connected to the focusing mirror drive unit, and the computer is configured to select an infrared element of an optimal size based on information on the opening size of the aperture provided at the position of the sample image, information on the energy value of the infrared light received by the detector, or both, and to control the focusing mirror drive unit so that the focusing mirror focuses the infrared light onto the selected infrared element.

[0019] Alternatively, the infrared microscope of the present invention preferably further comprises a computer connected to the focusing mirror drive unit, and the computer acquires and stores, for each infrared element, information on the aperture size range within which the infrared light energy values ​​measured in advance for each aperture opening size by the detector in the absence of a sample exhibit linearity, and is configured to select an infrared element of an optimal size based on the information on the aperture opening size provided at the position of the sample image and the information on the aperture size range within which linearity is exhibited, and to control the focusing mirror drive unit so that the focusing mirror focuses the infrared light onto the selected infrared element.

[0020] Using this automatic infrared element selection function, it is possible to automatically switch to an infrared element of the optimal size depending on the size of the sample, the opening size of the aperture, or the amount of light received by the detector. Because the focusing mirror is moved by a very small distance using the focusing mirror drive unit, the switching of the infrared element can be completed in a short time, resulting in a seamless series of measurements involving the use of multiple infrared elements. Furthermore, because the appropriate infrared element is always selected, high-sensitivity measurements (improved S / N) are possible even without sufficient measurement know-how.

[0021] It is also preferable that the sample stage is configured to be movable in a direction perpendicular to the central axis of the detection-side objective mirror, and that the infrared microscope detects the infrared light by sequentially changing the measurement area on the sample where the infrared light is focused by moving the stage, and acquires spectral data for each measurement area, thereby performing mapping measurement of a predetermined range of the sample.

[0022] Alternatively, the infrared microscope preferably includes a detection-side scanning mirror arranged on the optical path from the detection-side objective mirror to the aperture, the detection-side scanning mirror being configured so that the orientation of the reflective surface can be changed, and since the reflective surface is variable with respect to the incident direction of the infrared light from the detection-side objective mirror, it is possible to change the measurement area on the sample detected by the detector, and the infrared microscope preferably detects infrared light from the measurement area on the sample that is sequentially changed by the detection-side scanning mirror and acquires spectral data for each measurement area, thereby performing mapping measurements of a predetermined range of the sample.

[0023] Here, the infrared microscope comprises a light output means for outputting infrared light for irradiating a sample, an irradiation-side scanning mirror for guiding the infrared light from the light output means to the sample, and an irradiation-side objective mirror for collecting the infrared light from the irradiation-side scanning mirror and irradiating a predetermined irradiation area on the sample, and it is preferable that the irradiation-side scanning mirror is configured so that the orientation of its reflecting surface can be changed, and that the reflecting surface is variable with respect to the incident direction of the infrared light from the light output means, so that the irradiation area of ​​the infrared light on the sample can be sequentially changed to match the measurement area.

[0024] Alternatively, the detection-side objective mirror is provided with a high-refractive index crystal element for contacting the sample, and infrared light supplied to the detection-side objective mirror, which also serves as an illumination-side objective mirror, is focused on the crystal element and illuminates a minute site within the contact surface with the sample at an incident angle equal to or greater than the critical angle; the infrared microscope further comprises a detection-side scanning mirror provided on the optical path from the detection-side objective mirror to the aperture; the detection-side scanning mirror is configured so that the orientation of its reflective surface can be changed, and since the reflective surface is variable with respect to the incident direction of the infrared light from the detection-side objective mirror, it is possible to change the measurement area in the minute site within the contact surface detected by the detector; and it is preferable that the infrared microscope detects infrared light from the measurement area in the minute site within the contact surface that is sequentially changed by the detection-side scanning mirror, and acquires spectral data for each measurement area, thereby performing mapping measurement of the minute site within the contact surface.

[0025] Here, the infrared microscope comprises a light output means for outputting infrared light for irradiating a sample, and an illumination-side scanning mirror for guiding the infrared light from the light output means to the detection-side objective mirror, and it is preferable that the illumination-side scanning mirror is configured so that the orientation of the reflective surface can be changed, and that since the reflective surface is variable with respect to the incident direction of the infrared light from the light output means, it is possible to sequentially change the irradiation area of ​​the infrared light at a small location within the contact surface to match the measurement area.

[0026] 1 is a diagram illustrating the overall configuration of a microscopy system configured by connecting an FTIR to an infrared microscope according to one embodiment of the present invention. (A) to (C) are diagrams illustrating variations in the layout of a plurality of infrared elements used in the detector of the infrared microscope. (A) and (B) are diagrams illustrating an example of the operation of a collecting mirror in front of the detector of the infrared microscope. (A) and (B) are diagrams illustrating changes in the position of the aperture opening image associated with the operation of the collecting mirror in FIG. 3. (B) are diagrams illustrating another example of the operation of the collecting mirror in front of the detector of the infrared microscope. (C) are diagrams illustrating a holding structure for fine-adjusting the attitude of the collecting mirror. (D) are diagrams illustrating an example of a method for automatically switching infrared elements. (D) are diagrams illustrating another example of a method for automatically switching infrared elements. (D) and (B) are diagrams illustrating the relationship between the size of the infrared element of the detector and the size of the aperture opening image formed on the infrared element.

[0027] An embodiment of an infrared microscope according to the present invention will now be described with reference to the drawings. Fig. 1 is a diagram showing the overall configuration of a microscopy system configured by connecting an infrared microscope 10 according to this embodiment to a Fourier transform infrared spectrophotometer (hereinafter referred to as FTIR) 20. The FTIR 20 incorporates an infrared light source and a Michelson interferometer, and supplies an interference wave of infrared light output from the interferometer to the infrared microscope 10, and corresponds to the light output means of the present invention.

[0028] The infrared microscope 10 is composed of a microscope optical section 30, an aperture 40, a focusing mirror 50 in front of the detector, a focusing mirror drive section (referred to here as a mirror mount 60), a detector 70, and various reflecting mirrors. The microscope optical section 30 is a section that performs transmission, reflection, or total reflection measurement of a minute region of a sample using infrared light.

[0029] First, the optical system for transmission measurement shown in FIG. 1 will be described. The switching mirror 12 guides infrared light from the FTIR 20 to the optical path for transmission measurement (the order is reflecting mirror 14, transmission measurement mirror 16, and lower Cassegrain mirror 18). The lower Cassegrain mirror 18 (corresponding to the illumination-side objective mirror) focuses the infrared light reflected from the transmission measurement mirror 16 and illuminates a predetermined area of ​​the sample placed on the sample stage 22 from below. The light transmitted through the sample is extracted and focused by the upper Cassegrain mirror 24 (corresponding to the detection-side objective mirror) and reflected by the detection-side scanning mirror 26 above. An aperture 40 is placed at the imaging position behind the upper Cassegrain mirror 24 to filter out light (such as stray light) generated from areas other than the measurement area on the sample and detect only the light transmitted through the desired measurement area. The light passing through the opening of the aperture 40 is focused again by the reflecting mirror 28 and the focusing mirror 50 in front of the detector, and irradiates the infrared elements 76, 78 of the detector 70 located at the confocal point of the aperture 40, where it is converted into an electrical signal and Fourier transformed in the signal processing means to produce an infrared spectrum.

[0030] The magnification of each Cassegrain mirror can be selected from a range of 4 to 100x, preferably from a range of 15 to 32x. The opening size of the aperture 40 indicates the size of the measurement area on the sample. Even if the aperture is the same, the size of the measurement area on the sample varies depending on the magnification of the upper Cassegrain mirror 24 to be combined. Even if the magnification of the upper Cassegrain mirror 24 is fixed, it is preferable to configure the opening size and shape to be changeable so that the measurement area on the sample can be adjusted. For example, multiple apertures with different shapes and opening sizes can be prepared, and the desired shape and opening size can be selected and used depending on the measurement conditions. An aperture equipped with a mechanism for changing the opening shape and size can also be used.

[0031] Next, the optical system for reflectance measurement will be described. The reflective surface of the switching mirror 12 is rotated 90 degrees so that the switching mirror 12 guides infrared light to the optical path for reflectance measurement (reflecting mirror 32, reflectance measurement mirror 34, and upper Cassegrain mirror 24). The upper Cassegrain mirror 24 functions to irradiate a predetermined area of ​​the sample from above with infrared light (function of the illumination-side objective mirror) and to extract and collect the light reflected from the sample (function of the detection-side objective mirror). The reflectance measurement mirror 34 is located in half of the area divided by a boundary line passing through the optical axis on a cross section perpendicular to the optical axis connecting the upper Cassegrain mirror 24 and the detection-side scanning mirror 26, and is not located in the other half. Therefore, it is also called a half mirror. In other words, in reflectance measurement, infrared light from the reflecting mirror 32 reflects off the reflectance measurement mirror 34 and travels toward the upper Cassegrain mirror 24, irradiating the sample. The infrared light reflected from the sample and collected by the upper Cassegrain mirror 24 then passes through the space where the reflection measurement mirror 34 is not located and proceeds to the detection-side scanning mirror 26. The formation of the optical path after the detection-side scanning mirror 26 and the signal processing after the detector 70 are the same as in the transmission measurement.

[0032] The optical system for total reflection measurement will now be described. The upper Cassegrain mirror 24 is switched to an upper Cassegrain mirror equipped with a high-refractive-index crystal element (ATR prism), bringing the ATR prism into contact with the sample. Infrared light is guided to the optical path for reflection measurement and supplied to the upper Cassegrain mirror equipped with an ATR prism. The infrared light passes through the ATR prism of the upper Cassegrain mirror and irradiates a minute area within the contact surface with the sample at an incident angle equal to or greater than the critical angle. The total reflected light from the sample passes through the ATR prism, is collected again by the upper Cassegrain mirror, and is sent to the detection-side scanning mirror 26.

[0033] The following describes mapping measurement of a predetermined area on a sample using the infrared microscope 10 configured as described above. The infrared microscope 10 enables spectrum measurement at high magnification, but when it is desired to capture the entire sample to be measured, mapping measurement is performed to capture the entire sample or a specific area in a unified manner.

[0034] The first method is mapping measurement involving the operation of the sample stage 22, which has an electronically controlled automatic stage. In this method, the sample is placed on the automatic stage of the sample stage 22, and the measurement area on the sample is changed in sequence by moving the automatic stage. Spectral data is acquired for each measurement area, and mapping data for a predetermined range of the sample is created.

[0035] In the second method, the sample stage 22 is fixed, and the detection-side scanning mirror 26 is operated to sequentially change the measurement area on the sample, acquire spectral data for each measurement area, and create mapping data for a predetermined range of the sample. In this embodiment, the switching mirror 12, which switches between transmission measurement and reflection measurement as described above, also serves as the illumination-side scanning mirror. In other words, the switching mirror 12 has both the function of switching between transmission measurement and reflection measurement by rotating the reflective surface 90 degrees, and the scanning function of sequentially moving the illumination area on the sample by minutely controlling the orientation of the reflective surface with a controller in each 90-degree rotation position (both transmission measurement and reflection measurement).

[0036] The orientation of the reflective surface of the detection-side scan mirror 26 is adjusted so that only light from a specific measurement area on the sample is directed toward the opening of the aperture 40. By controlling the orientation of the reflective surface of this detection-side scan mirror 26 with a controller, the measurement area on the sample can be moved to match the opening of the aperture 40. The orientation of the reflective surface of the switching mirror (illumination-side scan mirror) 12 is changed to move the irradiation area on the sample, and at the same time, the orientation of the reflective surface of the detection-side scan mirror 26 is also changed so that the measurement area moves in the same way as the irradiation area. By repeating spectrum measurements for all of these moved positions of the measurement area and irradiation area, two-dimensional mapping measurement of a certain range on the sample can be performed.

[0037] As described above, by synchronizing the operation of the switching mirror (illumination-side scanning mirror) 12 with the operation of the detection-side scanning mirror 26, when a wider XY plane range (here, the mounting surface of the sample stage is referred to as the XY plane) is set as the mapping measurement range, it is possible to acquire spectral data with high energy values ​​throughout the entire mapping measurement range. In other words, two-dimensional mapping measurement based on high-quality spectral data acquired over a wider XY plane range becomes possible.

[0038] Even when the switching mirror (illumination-side scanning mirror) 12 is fixed and only the detection-side scanning mirror 26 is operated, spectral data with a relatively high energy value can be acquired within a certain range of the X-Y plane near the center of the illumination light, making it possible to perform two-dimensional mapping measurement.

[0039] Even when an upper Cassegrain mirror with an ATR prism is used instead of the upper Cassegrain mirror 24 to measure the total reflection of a sample, two-dimensional mapping measurement can be performed without moving the sample stage 22 by using the detection-side scanning mirror 26 or by using both the detection-side scanning mirror 26 and the switching mirror (illumination-side scanning mirror) 12. That is, in total reflection measurement, the measurement area in a minute area within the contact surface between the ATR prism and the sample is sequentially changed by the operation of the detection-side scanning mirror 26. Furthermore, by adding the operation of the switching mirror (illumination-side scanning mirror) 12, the irradiation area in a minute area within the contact surface between the ATR prism and the sample is sequentially changed to match the measurement area.

[0040] Next, the detector 70 and its peripheral optical system, which are characteristic of this embodiment, will be described.

[0041] The detector 70 is, for example, a semiconductor detector such as an MCT detector or an InGaAs detector. Generally, semiconductor detectors are susceptible to thermal fluctuations and must be kept at a low temperature to maintain high-sensitivity measurements. In this embodiment, a detector element holder 74 is provided on the side of a container (Dewar 72) that contains a refrigerant such as liquid nitrogen, and multiple infrared elements 76 to 79 are closely attached to the vertical surface of the detector element holder 74 in a layout such as that shown in Figures 2(A) to 2(C), allowing the infrared elements 76 to 79 to be used while maintained at a low temperature.

[0042] The multiple infrared elements 76-79 constituting the detector 70 are squares with sides measuring 5-500 μm and differing in size. For example, in the layout of FIG. 2A, the large-sized infrared element 76 has a side length of 200-300 μm, and the small-sized infrared element 78 has a side length of 50-100 μm. The two infrared elements 76, 78 are arranged horizontally (e.g., parallel to the axis of incidence of infrared light on the reflector 28) at intervals of 50 μm-10 mm. Similarly, in the layout of FIG. 2B, three infrared elements 76-78 of large, medium, and small sizes are arranged horizontally. Similarly, in the layout of FIG. 2C, four infrared elements 76-79 of large, medium, small, and minute sizes are arranged two-dimensionally in the horizontal and vertical directions (e.g., perpendicular to the axis of incidence of infrared light on the reflector 28). In all layouts, the intervals between adjacent infrared elements 76 to 79 are 50 μm to 10 mm in both the horizontal and vertical directions, and the elements themselves and the intervals between the elements are small.

[0043] The infrared light that passes through the opening of aperture 40 is converted into a parallel beam by reflecting mirror 28 (parabolic mirror) and travels toward collecting mirror 50 (parabolic mirror) in front of the detector. Note that the infrared light that passes through the opening of aperture 40 may also be configured to be directly received by collecting mirror 50 in front of the detector (in this case, an ellipsoidal mirror is used).

[0044] FIG. 3 shows an example of a mechanism for switching between the infrared elements 76 and 78.

[0045] The positional relationship between the collecting mirror 50 in front of the detector and the small infrared element 78 is that of a paraboloid and its focal point, as shown by the dashed line in Figure 3, and the parallel light beam incident on the paraboloid of the collecting mirror 50 is collected on the small infrared element 78 located at the focal point of the paraboloid. The position of the small infrared element 78 is also confocal with the opening of the aperture 40, and an image of the opening of the aperture 40 is formed on the small infrared element 78 (see Figure 4(A)). For convenience of explanation, it is assumed here that the parallel light beam of infrared light in Figure 3 is horizontal, and that the plane defined by this parallel light beam and the focal point of the paraboloid is also horizontal.

[0046] The collecting mirror 50 in front of the detector is held by a mirror mount 60 with an actuator, and an external computer 80 connected to this mirror mount 60 by wire or wirelessly remotely controls the actuator, thereby changing the tilt of the parabolic surface of the collecting mirror 50. This mirror mount 60 with an actuator corresponds to the collecting mirror drive unit of the present invention. Known actuators can be used, such as a piezoelectric actuator, a DC motor with a rotary encoder, an ultrasonic vibrator, or a stepping motor.

[0047] In FIG. 3 , the mirror mount 60 tilts the focusing mirror 50 by a small angle about a vertical axis (an axis perpendicular to the plane of the paper in FIG. 3 ), thereby changing the angle of incidence of the parallel light on the focusing mirror 50, and the focusing position of the parallel light beam by the focusing mirror 50 can be shifted slightly (for example, by 500 μm or less) in the horizontal direction from the position of the small-sized infrared element 78, as shown by the solid line in FIG. 3 .

[0048] Therefore, by arranging the two infrared elements 76, 78 so that the position of the large-sized infrared element 76 is the focusing position after tilting the focusing mirror 50, it becomes possible to switch between the infrared elements 76, 78 by driving the mirror mount 60. This switching causes the opening image of the aperture 40 to be formed on the large-sized infrared element 76 as well. Figure 4(B) shows the state in which the opening image is formed on the large-sized infrared element 76 when the opening size of the aperture 40 is increased and the mirror mount 60 is driven to switch the focusing position to the large-sized infrared element 76. Note that the example in Figure 3 is suitable when the spacing between adjacent infrared elements is small (e.g., 500 μm or less), particularly when the spacing is 50 μm to 150 μm.

[0049] FIG. 5 shows another example of a mechanism for switching between the infrared elements 76 and 78. In FIG.

[0050] When the spacing between adjacent infrared elements is relatively large (e.g., greater than 500 μm), the angle of the focusing mirror 50 must be changed significantly, causing the focusing position of the infrared light to deviate significantly from the focus of the parabolic surface, resulting in poor focusing performance. Therefore, as shown in the switching mechanism of FIG. 5 , it is preferable to translate the focusing mirror 50 along the optical axis of the parallel light beam without changing its orientation. Because the angle of incidence of the parallel light beam on the focusing mirror 50 does not change before and after the translation, the focusing position of the infrared light remains at the focus of the parabolic surface, maintaining focusing performance. This is particularly suitable when the spacing between the infrared elements is 2 mm or more, preferably 3 mm or more.

[0051] The parallel movement of the focusing mirror 50 can be achieved by using a mirror mount 60 with an actuator, as in FIG.

[0052] When multiple infrared elements of different sizes are arranged two-dimensionally, it is preferable to use a mirror mount 60 that has both the function of tilting and the function of translating the collecting mirror 50. Alternatively, it is preferable to use a mirror mount 60 that is configured to be able to translate the collecting mirror 50 along the incident axis of the infrared light and to be able to rotate the collecting mirror 50 around the incident axis of the infrared light. Alternatively, it is preferable to use a mirror mount 60 that is configured to be able to change the angle of incidence of infrared light on the collecting mirror 50 and to be able to rotate the collecting mirror around the incident axis of the infrared light.

[0053] Since the movements of the focusing mirror 50 in these examples all require small movements, by using the mirror mount 60, it is possible to quickly and accurately align the aperture image of the infrared light with the respective positions of multiple infrared elements of different sizes arranged one-dimensionally or two-dimensionally on the detector 70.

[0054] Furthermore, the size of the infrared element attached to detector 70 is very small, ranging from 5 to 500 μm. Therefore, when assembling infrared microscope 10, fine adjustment is required to accurately position the tiny infrared element at the focus of the parabolic surface of collecting mirror 50. Therefore, Figure 6 shows a holding structure for finely adjusting the attitude of collecting mirror 50, in which collecting mirror 50 is suspended together with mirror mount 60.

[0055] 6 has a wall plate 44 standing on one end of a horizontally placed base plate 42 and two supports 46, 48 standing on the other end, with a top plate 52 supported by the wall plate 44 and the two supports 46, 48. A mirror mount 60 is attached to the underside of the top plate 52, and in this way, the focusing mirror 50 is suspended below the top plate 52.

[0056] Although fine adjustment of the attitude of collecting mirror 50 is usually performed using a screw provided on the back surface of collecting mirror 50 to hold collecting mirror 50 to the movable portion of mirror mount 60, fine adjustment of the attitude may also be performed by, for example, using adjustment screw 54 connecting top plate 52 to wall plate 44 and adjustment screws 55, 56 connecting top plate 52 to two supports 46, 48, respectively, and adjusting the tightening of adjustment screws 54 to 56. Adjustment may also be performed using an adjustment screw (not shown) provided on the back surface of collecting mirror 50.

[0057] Next, a method for automatically selecting an optimum infrared element from a plurality of infrared elements 76, 78 of different sizes attached to the detector 70 using the computer 80 will be described.

[0058] The first method is to select an infrared element according to the opening size of the aperture 40. For example, 400 to 900 μm ２ A threshold value is set in the range of 1 μm to 30 μm, and if the opening area of ​​the aperture 40 is larger than the threshold, the large-sized infrared element 76 is selected; if it is equal to or smaller than the threshold, the small-sized infrared element 78 is selected. If the opening is square, the threshold value can be set in the range of 20 to 30 μm, and the length of one side of the opening can be compared with the threshold. That is, the computer 80 connected to the mirror mount 60 recognizes information about the opening size of the aperture 40, compares it with the threshold, determines the infrared element of the size to be selected, and controls the mirror mount 60 to switch to the determined infrared element. The threshold value can be set by measuring a reference sample with different opening sizes for each infrared element, comparing the S / N ratios of the large-sized infrared element 76 and the small-sized infrared element 78 for each opening size, and then setting the threshold to the opening size at which the S / N ratios are approximately the same.

[0059] The second method involves selecting an infrared element based on the amount of light received by the detector 70, i.e., the light energy value. The detector gain is adjusted in advance so that the energy value E is 25,000 when the entire infrared element is illuminated by light (for example, when the light spot focused on a square element forms an inscribed circle). A graph showing the relationship between the opening size of the aperture 40 and the energy value E, as shown in FIG. 7 , is obtained for each infrared element. The computer 80 sets a threshold value, for example, in the range of 1,000 to 3,000, and switches to the small-sized infrared element 78 when the energy value E information for the currently selected large-sized infrared element 76 is smaller than the threshold value. As a result, the large-sized infrared element 76 is selected for aperture sizes A and B, and the small-sized infrared element 78 is selected for aperture sizes C and D.

[0060] The third method, like the second method, utilizes the light energy value E. However, in this case, the infrared element is switched depending on the linearity range of each infrared element (the aperture size range in which the relationship between the aperture size of the aperture 40 and the energy value E is linear). With actual infrared elements, the range in which the relationship between the aperture size of the aperture 40 and the energy value E is linear is limited, as shown in FIG. 8 . Therefore, the computer 80 acquires and stores, for each infrared element, information on the aperture size range in which the infrared light energy value is linear, measured in advance for each aperture size of the aperture 40 in the absence of a sample. An infrared element of optimal size may then be selected based on the information on the current aperture size of the aperture 40 and the information on the aperture size range in which linearity is exhibited. For example, if a small-sized infrared element 78 is currently being used, an excessively large aperture size will saturate the detection capability, making linearity impossible. Therefore, the infrared element may be switched to a large-sized infrared element 76 just before linearity is no longer attainable. Conversely, if large-sized infrared element 76 is currently being used, an excessively small aperture size will increase noise and make it impossible to obtain linearity, so before linearity is no longer obtainable, the system switches to small-sized infrared element 78. In Figure 8, for aperture sizes C and D, the small-sized infrared element is selected because it is within a range in which the small-sized infrared element exhibits linearity, and for aperture sizes A and B, the large-sized infrared element is selected because it is within a range in which the large-sized infrared element exhibits linearity.

[0061] In addition to these three methods, the computer 80 may select an infrared element of an optimum size using, for example, both the aperture size information and the energy value E information.

[0062] Furthermore, when a sample is on the stage, there may be a situation where the aperture size is relatively large but the energy value E is small. For example, this may occur when the reflectance of the sample is low during reflection measurement. In this case, even if the aperture size is larger than the threshold value in the first method, the small-sized infrared element 78 is selected. This is because measurement using the large-sized infrared element 76 may result in increased noise and an unsatisfactory spectrum. Using the small-sized infrared element 78 only obtains information from the central portion of the focused spot of infrared light, but it can provide measurements with a better S / N ratio than the large-sized infrared element 76.

[0063] According to this embodiment, it is possible to automatically switch to an infrared element of an optimal size depending on the measurement conditions (such as the size of the sample, the opening size of the aperture 40, or the amount of light received by the detector 70), making it possible to perform different types of measurements simultaneously. For example, it is possible to perform both a measurement that obtains a large amount of received light (bright measurement) and a highly sensitive measurement of a minute area, and also a measurement that receives a small amount of received light but has a good S / N ratio. It is also possible to perform measurements with a wide dynamic range (largely changing the area of ​​the measurement area).

[0064] Since the movement of the focusing mirror 50 by the mirror mount 60 is only a small distance, the switching of the infrared element can be completed in a short time, and as a result, a series of measurements involving the selective use of multiple infrared elements can be performed seamlessly. In addition, by always selecting the appropriate infrared element, high-sensitivity measurements (improved S / N) are possible even without sufficient measurement know-how.

[0065] 10 Infrared microscope 12 Switchable mirror also serving as illumination-side scanning mirror 16 Transmission measurement mirror 18 Lower Cassegrain mirror (illumination-side objective mirror) 20 FTIR (light output means) 22 Sample stage 24 Upper Cassegrain mirror (illumination-side objective mirror, detection-side objective mirror) 26 Detection-side scanning mirror 34 Reflection measurement mirror 40 Aperture 50 Collecting mirror 60 Mirror mount (collecting mirror drive unit) 70 Detector 72 Dewar 74 Detecting element holder 76, 77, 78, 79 Infrared element 80 Computer

Claims

1. An infrared microscope comprising: a sample stage on which a sample is placed; a detection-side objective mirror that focuses infrared light from the sample; an aperture located at the position of the sample image formed by the detection-side objective mirror; a focusing mirror that focuses infrared light that has passed through the opening of the aperture; a focusing mirror drive unit that moves the focusing mirror; and a detector that detects the infrared light focused by the focusing mirror, wherein the aperture is selected from a plurality of apertures with different opening sizes or shapes, or is configured with an opening with a variable size or shape; the detector has a detection element holder and a plurality of infrared elements placed on the surface of the detection element holder, the plurality of infrared elements being different sizes and arranged at intervals of 10 mm or less; and the focusing mirror drive unit is configured to move the focusing mirror so that the position of the aperture image formed by the focusing mirror coincides with the respective positions of the plurality of infrared elements.

2. An infrared microscope according to claim 1, wherein said focusing mirror drive section is configured to vary the angle of incidence of infrared light onto said focusing mirror.

3. An infrared microscope according to claim 1, wherein said focusing mirror drive unit is configured to be able to translate said focusing mirror along the axis of incidence of infrared light.

4. An infrared microscope according to claim 1, further comprising a computer connected to the focusing mirror drive unit, wherein the computer is configured to select an infrared element of an optimal size based on information on the opening size of the aperture provided at the position of the sample image, information on the energy value of the infrared light received by the detector, or both, and to control the focusing mirror drive unit so that the focusing mirror focuses the infrared light onto the selected infrared element.

5. An infrared microscope according to claim 1, further comprising a computer connected to the focusing mirror drive unit, wherein the computer acquires and stores, for each infrared element, information on the aperture size range in which the infrared light energy value measured in advance for each aperture opening size by the detector in the absence of a sample exhibits linearity, and is configured to select an infrared element of an optimal size based on the information on the aperture opening size of the aperture provided at the position of the sample image and the information on the aperture size range in which the linearity is exhibited, and to control the focusing mirror drive unit so that the focusing mirror focuses the infrared light onto the selected infrared element.

6. An infrared microscope according to any one of claims 1 to 5, characterized in that the sample stage is configured to be movable in a direction perpendicular to the central axis of the detection side objective mirror, and the infrared microscope detects the infrared light by sequentially changing the measurement area on the sample where the infrared light is focused by moving the stage, and acquires spectral data for each measurement area, thereby performing mapping measurements of a predetermined range of the sample.

7. An infrared microscope according to any one of claims 1 to 5, characterized in that it comprises a detection-side scanning mirror arranged on the optical path from the detection-side objective mirror to the aperture, the detection-side scanning mirror being configured so that the orientation of the reflective surface can be changed, and the reflective surface being variable with respect to the incident direction of infrared light from the detection-side objective mirror, making it possible to change the measurement area on the sample detected by the detector, and the infrared microscope detects infrared light from the measurement area on the sample that is sequentially changed by the detection-side scanning mirror, and acquires spectral data for each measurement area, thereby performing mapping measurements of a predetermined range of the sample.

8. An infrared microscope according to claim 7, comprising: a light output means for outputting infrared light for irradiating a sample; an irradiation-side scanning mirror for guiding the infrared light from said light output means to the sample; and an irradiation-side objective mirror for focusing the infrared light from said irradiation-side scanning mirror to irradiate a predetermined irradiation area on the sample, wherein said irradiation-side scanning mirror is configured so that the orientation of its reflecting surface can be changed, and since said reflecting surface is variable with respect to the incident direction of the infrared light from said light output means, it is possible to sequentially change the irradiation area of ​​the infrared light on the sample to match the measurement area.

9. The detection-side objective mirror is provided with a high-refractive index crystal element for contacting the sample, and is configured so that infrared light supplied to the detection-side objective mirror, which also serves as the illumination-side objective mirror, is focused on the crystal element and irradiates a minute area within the contact surface with the sample at an angle of incidence equal to or greater than the critical angle; the infrared microscope further comprises a detection-side scanning mirror provided on the optical path from the detection-side objective mirror to the aperture; the detection-side scanning mirror is configured so that the orientation of its reflective surface can be changed, and because the reflective surface is variable with respect to the incident direction of the infrared light from the detection-side objective mirror, it is possible to change the measurement area in the minute area within the contact surface detected by the detector; and the infrared microscope according to any one of claims 1 to 5, detects infrared light from the measurement area in the minute area within the contact surface that is sequentially changed by the detection-side scanning mirror, and acquires spectral data for each measurement area, thereby performing mapping measurements of the minute area within the contact surface.

10. An infrared microscope as described in claim 9, comprising: a light output means for outputting infrared light for irradiating a sample; and an illumination-side scanning mirror for guiding the infrared light from said light output means to said detection-side objective mirror, wherein said illumination-side scanning mirror is configured so that the orientation of its reflective surface can be changed, and since said reflective surface is variable with respect to the incident direction of the infrared light from said light output means, it is possible to sequentially change the irradiation area of ​​the infrared light at a minute location within said contact surface to match the measurement area.

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