Infrared microscope

Abstract

To provide an infrared microscope capable of performing measurement with higher spatial resolution than the conventional one.SOLUTION: The infrared microscope comprises: a light source 10 for emitting infrared light repeatedly increasing and decreasing intensity; an irradiation side target element 22 to be irradiated with infrared light on a sample; a light condensing side target element 26 for condensing infrared light transmitting through or reflected from the sample; a spectroscopic part 30 for spectroscopically processing the condensed infrared light; a detector 40 for detecting the infrared light; and a signal processing part 50 for lock-in detecting the detected signal with a reference signal synchronizing with intensity change of the infrared light to obtain infrared spectrum of the sample. The light source 10 has an emission surface of 0.1 μm or more and 20 μm or less, and an outlet including a light source side condensing element 12 for condensing infrared light. The light source side condensing element 12 and the irradiation side target element 22 form an image of the emission surface of the light source 10 on the sample.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to infrared microscopes, and in particular to improvements in the spatial resolution thereof. [Background technology]

[0002] Fourier transform infrared microscopes are available as devices for infrared spectroscopic analysis of minute regions of a sample. For example, in the infrared microscope disclosed in Patent Document 1 below, infrared light from a light source is converted into interference waves by an interferometer, and then a spot is formed in a minute region of the sample by a Cassegrain mirror located above the sample. The infrared light reflected from the minute region is focused by the same Cassegrain mirror, and then a microscopic aperture allows only the reflected infrared light from the measurement site to pass through and be detected by a detector. A signal processing unit, such as a computer, can perform a Fourier transform on the detection signal from the detector to obtain the absorption spectrum of the measurement site. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-103814 [Patent Document 2] International Publication No. 2019 / 176705 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand for infrared microscopes to be able to measure absorption spectra in even smaller microscopic regions, that is, to have even higher spatial resolution. A typical concept of spatial resolution is the Rayleigh criterion, according to which the spatial resolution (Δd) due to the diffraction limit is defined by the formula Δd = 1.22λ / 2ns in θ. (Here, λ is the wavelength of infrared light, n is the refractive index of the medium between the sample and the objective, and θ is the maximum angle with respect to the optical axis of the light ray incident on the sample from the objective.) However, because standard conventional infrared microscopes use light from a light source in the wavelength range of about 2 to 15 μm and a size of several mm or more, their spatial resolution is said to be at most about 10 μm, which does not reach the diffraction limit. The object of the present invention is to provide an infrared microscope that enables measurements with a spatial resolution higher than conventional spatial resolutions. [Means for solving the problem]

[0005] Conventional infrared light sources use blackbody radiation sources such as halogen lamps or high-intensity ceramic light sources. However, because these light sources are macroscopic (several millimeters or more), the infrared light transmitted through or reflected by the sample is typically blocked with a mask to limit the spot area. However, further reducing the measurement area drastically reduces measurement accuracy, and the inventors believed this was the reason why the spatial resolution of infrared microscopes does not fully reach the diffraction limit of light. Therefore, they focused on the light source using a nanocarbon material (herein referred to as a nanocarbon light source) disclosed in Patent Document 2, whose light-emitting surface is on the order of micrometers or less. In other words, by using such a tiny nanocarbon light source to directly form an image of the light source on the sample, the infrared light spot area on the sample can be further reduced. Of course, due to the limitations of light diffraction, it is not possible to form an image of the same size on the sample when the size of the light-emitting surface of a nanocarbon light source is, for example, 1 μm. However, without using a mask, the light source image on the sample can be brought close to the size of the diffraction limit of light, thereby achieving spatial resolution approaching the diffraction limit without reducing measurement accuracy. On the other hand, the light from the source with a 1 μm light-emitting surface is very weak, and direct formation of the light source image at the sample position is significantly affected by background radiation at room temperature. In order to selectively detect the light from the source from the background radiation, it is necessary to periodically increase and decrease the emission intensity of the light from the source, i.e., to perform so-called pulse lighting.

[0006] That is, the infrared microscope according to the present invention comprises: a light source (10) that emits infrared light whose intensity repeatedly increases and decreases; an illumination-side objective element (22) that irradiates the sample with infrared light from the light source; A sample placement unit (24); a light-collecting objective element (26) that collects infrared light transmitted through or reflected by the sample; a spectroscopic unit (30) that performs spectroscopic processing of the infrared light collected by the light-collection-side objective element; a detector (40) for detecting the spectrally processed infrared light; a signal processing unit (50) that performs lock-in detection using a reference signal that is synchronized with a change in the intensity of the infrared light with respect to the detection signal of the detector to acquire an infrared spectrum of the sample; An infrared microscope comprising: The light source (10) has a light-emitting surface with a size of 0.1 μm or more and 20 μm or less, A light source-side focusing element (12) that focuses infrared light is provided at the exit of the light source (10), and an image of the light emitting surface of the light source (10) is formed on the sample by the light source-side focusing element (12) and the illumination-side objective element (22).

[0007] In this document, the light source (10) refers to a light source for high spatial resolution measurements, which will be described later.

[0008] The infrared microscope of the present invention includes a light source (10) having a light-emitting surface measuring "0.1 μm or more and 20 μm or less," a light-source-side focusing element (12) that focuses infrared light from the light source, and an illumination-side objective element (22) that illuminates the infrared light onto a sample. The extremely weak infrared light from the tiny light-emitting surface of the light source (10) is efficiently focused by the light-source-side focusing element (12), and the light-source-side focusing element (12) and the illumination-side objective element (22) cause the extremely weak infrared light to illuminate a measurement area on the sample with high precision. The image (spot area) of the tiny light-emitting surface formed in this way can be made to approach the size of the diffraction limit of light. Furthermore, the spectroscopic section (30) is placed behind the sample, rather than at the exit of the light source, and performs post-spectroscopic processing of the transmitted or reflected light from the sample. This means that an image of the light source is formed directly on the sample without passing through the spectroscopic section (30), thereby suppressing the intrusion of stray light into the spot area of ​​the sample. As a result, the infrared microscope of the present invention can perform measurements with low stray light and with extremely high spatial resolution approaching the diffraction limit.

[0009] Furthermore, the infrared microscope according to the present invention comprises: An infrared microscope comprising: a microscopic measurement unit (20) that performs transmission or reflection measurement of a minute area of ​​a sample using infrared light for high spatial resolution or low spatial resolution; an optical path switching unit (60) that switches between an optical path (61) for high spatial resolution and an optical path (62) for low spatial resolution; and a spectroscopic unit (30) that is connected to the microscopic measurement unit via the optical path switching unit, The microscopic measurement unit (20) is connected to a high spatial resolution light source (10) that supplies infrared light for high spatial resolution to the microscopic measurement unit, and a low spatial resolution detector (70) that detects infrared light for low spatial resolution that has passed through or reflected from a minute region of the sample in the microscopic measurement unit, the spectroscopic unit (30) is provided to be able to perform spectroscopic processing of high spatial resolution infrared light transmitted through or reflected by a minute region of the sample in the microscopic measurement unit (20) and low spatial resolution infrared light from a low spatial resolution light source (80) connected to the spectroscopic unit; the high spatial resolution optical path (61) is formed so that after the high spatial resolution infrared light from the high spatial resolution light source (10) passes through or is reflected by a minute region of the sample in the microscopic measurement unit (20), the infrared light is guided to the spectroscopic unit (30), and the high spatial resolution infrared light that has been spectrally processed by the spectroscopic unit (30) is guided to a high spatial resolution detector (40) connected to the optical path switching unit (60); The low spatial resolution optical path (62) is formed so that the low spatial resolution infrared light from the low spatial resolution light source (80) is spectroscopically processed in the spectroscopic section (30) and then guided to the microscopic measurement section (20), and in the microscopic measurement section (20), the low spatial resolution infrared light is transmitted through or reflected by a minute region of the sample and detected by the low spatial resolution detector (70).

[0010] As described above, the infrared light for high spatial resolution travels along the optical path for high spatial resolution (61) in the order of "10 → 20 → 61 → 30 → 40," directly irradiating the sample and then undergoing post-spectroscopic processing. On the other hand, the infrared light for low spatial resolution travels along the optical path for low spatial resolution (62) in the order of "80 → 30 → 62 → 20 → 70," pre-spectroscopic processing, and then irradiating the sample.

[0011] According to the above-described configuration of the infrared microscope, a single infrared microscope includes both a high spatial resolution light source (10) and a low spatial resolution light source (80), both a high spatial resolution detector (40) and a low spatial resolution detector (70), and an optical path switching unit (60) between the microscopic measurement unit (20) and the spectroscopic unit (30). This allows the microscope to switch between the high spatial resolution optical path (61) and the low spatial resolution optical path (62) as needed, enabling selective execution of both high spatial resolution and low spatial resolution measurements. This allows the user to appropriately select between analysis of a relatively large measurement area using low spatial resolution measurement and analysis of a minute area using high spatial resolution measurement, depending on the size of the sample, i.e., the size of the desired measurement range, and to switch between measurements with different spatial resolutions while the sample is still placed in the sample mounting unit.

[0012] Furthermore, for example, it is possible to perform low spatial resolution measurements using an existing infrared microscope, and to perform high spatial resolution measurements using an infrared microscope using the above-mentioned light source of a micro-light-emitting surface, making it possible to achieve compatibility between a microscopic optical system for high spatial resolution approaching the diffraction limit of light and an existing microscopic optical system.

[0013] The microscopic measurement unit (20) preferably has an irradiation-side objective element (22) that forms a spot of infrared light in a minute area on the sample, a sample placement unit (24), and a collection-side objective element (26) that collects the infrared light that has passed through or reflected from the minute area of ​​the sample.

[0014] The high spatial resolution light source (10) has an emission surface with a size of 0.1 μm or more and 20 μm or less, and a light source side focusing element (12) for focusing infrared light is provided at the exit of the high spatial resolution light source (10), and an image of the emission surface of the high spatial resolution light source (10) is preferably formed on the sample by the light source side focusing element (12) and the illumination side objective element (22).

[0015] In addition, a microscope aperture (21) may be provided between the high spatial resolution light source (10) and the illumination side objective element (22) to block the infrared light from the high spatial resolution light source (10) with the microscope aperture (21), thereby changing the size of the image of the light-emitting surface formed on the sample.

[0016] When performing transmission measurement, the microscopic measurement unit (20) Infrared light for high spatial resolution is guided through the illumination-side objective element (22), the sample placement section (24), and the collection-side objective element (26) in this order; It is preferable that the infrared light for low spatial resolution is guided through the light-collection-side objective element (26), the sample placement portion (24), and the illumination-side objective element (22) in this order.

[0017] In addition, a microscope aperture (21) may be provided between the light source (10) and the illumination-side objective element (22) to block the infrared light from the light source (10) with the microscope aperture (21), thereby changing the size of the image of the light-emitting surface formed on the sample.

[0018] Preferably, the light source side condensing element (12) and the illumination side objective element (22) are each made up of a Cassegrain mirror.

[0019] Preferably, the illumination-side objective element (22) is a Cassegrain mirror that also functions as a collection-side objective element (26) that collects infrared light reflected from the sample.

[0020] The illumination-side objective element (22) may be a Cassegrain mirror that also functions as a collection-side objective element (26) that collects infrared light reflected from the sample, and the Cassegrain mirror may have an ATR crystal (28) for total reflection measurement.

[0021] The spectroscopic unit 30 may include an interferometer 32 that forms an interference wave of infrared light, or may include a dispersive prism or a diffraction grating. In the case of the interferometer 32, the signal processing unit 50 performs Fourier transform processing after lock-in detection. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram illustrating the overall configuration of an infrared microscope according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a microscopic optical system for high spatial resolution in the infrared microscope. [Figure 3] FIG. 2 is a diagram showing a microscopic optical system for low spatial resolution in the infrared microscope. [Figure 4] 3A to 3C are diagrams showing variations in the configuration of the microscopic measurement unit in the infrared microscope. [Figure 5] FIG. 1 is a diagram showing the overall configuration of an infrared microscope according to a second embodiment of the present invention. [Figure 6] FIG. 10 is a diagram showing the overall configuration of an infrared microscope according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An infrared microscope according to a first embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 shows an overall configuration diagram of an infrared microscope according to a first embodiment.

[0024] The infrared microscope is capable of selectively switching between a microscopic optical system for high spatial resolution and a microscopic optical system for low spatial resolution, and is composed of three parts: a microscopic measurement unit 20, an optical path switching unit 60, and a spectroscopic unit 30.

[0025] The microscopic measurement unit 20 is a unit that performs transmission or reflection measurement of a minute area of ​​a sample using infrared light for high or low spatial resolution. The optical path switching unit 60 is configured to be able to switch between an optical path 61 for high spatial resolution and an optical path 62 for low spatial resolution. The spectroscopic unit 30 is a unit that performs spectroscopic processing of the infrared light for high and low spatial resolution, and is connected to the microscopic measurement unit 20 via the optical path switching unit 60.

[0026] Each part will be explained in detail. <Microscopic Measurement Section> The microscopic measurement unit 20 includes a nanocarbon light source 10 that emits infrared light for high spatial resolution, a light source side Cassegrain mirror 12 (corresponding to a light source side focusing element) that focuses the infrared light at the exit of the nanocarbon light source 10, an illumination side Cassegrain mirror 22 (corresponding to an illumination side objective element) that forms a spot of the focused infrared light on the sample, a sample mounting unit 24 on which the sample is placed, a focusing side Cassegrain mirror 26 (corresponding to a focusing side objective element) that focuses light transmitted through the sample, various reflecting mirrors for forming an optical path, and a mid-band MCT detector 70 used for low spatial resolution measurements.

[0027] The nanocarbon light source 10 has a light-emitting surface of approximately 1 μm square formed on the surface of a substrate using a nanocarbon material as a light-emitting material, and emits infrared light whose intensity repeatedly increases and decreases from the light-emitting surface. For example, it is preferable to use one that emits pulsed light with a periodic intensity change of 100 Hz or more, preferably 1000 Hz or more. The size of the light-emitting surface is preferably 0.1 μm or more and 20 μm or less, and preferably 1 μm or more and 5 μm or less. Furthermore, it is preferable that the size of the light-emitting surface be equal to or less than the measurement wavelength of the infrared microscope. The size of the light-emitting surface is, for example, the diameter if it is circular, the length of one side if it is square, or the length of the long side if it is rectangular.

[0028] The light source side Cassegrain mirror 12 is provided at a position close to the minute light emitting surface of the nanocarbon light source 10, and efficiently collects infrared light for high spatial resolution from the light emitting surface.

[0029] The switching mirror 14 is located above the sample and reflects downward the infrared light coming horizontally from the light source-side Cassegrain mirror 12. The switching mirror 14 is also provided so that the angle of the reflecting surface can be changed, and in low spatial resolution measurements, the low spatial resolution infrared light coming from below is reflected horizontally on the opposite side from the light source-side Cassegrain mirror 12 and directed to the mid-band MCT detector 70 via the two parabolic mirrors 11 and 13. In this way, the switching mirror 14 can select either the nanocarbon light source 10 or the mid-band MCT detector 70 for the microscopic measurement unit 20.

[0030] The irradiation-side Cassegrain mirror 22 and the collection-side Cassegrain mirror 26 are arranged at positions symmetrical above and below the sample in the sample placement section 24 .

[0031] -Transmission and reflection measurements using infrared light for high spatial resolution In transmission measurement, the illumination-side Cassegrain mirror 22 forms a spot of infrared light from above in a small area on the sample, and the collection-side Cassegrain mirror 26 collects the infrared light that has transmitted through the spot area. The collected infrared light is reflected by the lower plane mirror 15, parabolic mirror 16, and transmission / reflection switching mirror 17 in that order, and is guided to the optical path switching unit 60. In reflection measurement, the illumination-side Cassegrain mirror 22 functions both to form a spot of infrared light in a minute area on the sample and as a collection-side Cassegrain mirror to collect the infrared light reflected from the spot area. The infrared light collected by the illumination-side Cassegrain mirror 22 is reflected by the upper plane mirror 18, parabolic mirror 19, and transmission / reflection switching mirror 17, in that order, and is guided to the optical path switching unit 60. The transmission / reflection switching mirror 17 has a structure similar to that of the switching mirror 14, and is a plane mirror with reflective surfaces on both sides that can be rotated 90 degrees. It can select either the infrared light from the lower parabolic mirror 16 or the infrared light from the upper parabolic mirror 19 and reflect it in the direction of the optical path switching unit 60.

[0032] - Transmission and reflection measurements using infrared light for low spatial resolution In low spatial resolution measurements, infrared light for low spatial resolution is supplied from the optical path switching unit 60 to the microscopic measurement unit 20, and the infrared light travels along an optical path in the opposite direction to that in the high spatial resolution measurements described above. That is, in transmission measurements, the infrared light from the optical path switching unit 60 is reflected in this order by the transmission / reflection switching mirror 17 (facing downward), the parabolic mirror 16, and the plane mirror 15, before entering the collection-side Cassegrain mirror 26 from below and irradiating the sample. The light transmitted through the sample is collected by the illumination-side Cassegrain mirror 22, reflected by the upper switching mirror 14, and directed to the mid-band MCT detector 70. In reflection measurement, infrared light from the optical path switching unit 60 is reflected in this order by the transmission / reflection switching mirror 17 (facing upward), the parabolic mirror 19, and the plane mirror 18, and enters the illumination-side Cassegrain mirror 22 from above, irradiating the sample. The light reflected from the sample is collected by the illumination-side Cassegrain mirror 22, reflected by the upper switching mirror 14, and guided to the mid-band MCT detector 70.

[0033] Infrared microscopes often use Cassegrain mirrors with magnifications of approximately 8x to 32x, but in this embodiment, it is preferable to use Cassegrain mirrors with the same magnification so that the total magnification of the light source-side Cassegrain mirror 12 at the exit of the nanocarbon light source 10 and the irradiation-side Cassegrain mirror 22 immediately before the sample is 1x. However, the total magnification of these Cassegrain mirrors 12 and 22 should be selected from the range of 0.5x to 2x, and preferably 1x. The magnification of each Cassegrain mirror should be selected from the range of 8x to 64x, and preferably from the range of 15x to 32x.

[0034] Note that, on a cross section perpendicular to the optical axis connecting the switching mirror 14 and the illumination-side Cassegrain mirror 22, the plane mirror 18 is arranged in half of the area divided by a boundary line passing through the optical axis, and is not arranged in the other half of the area; in this sense, it is called a half mirror. In other words, infrared light traveling from the switching mirror 14 toward the illumination-side Cassegrain mirror 22 passes through the space where the half mirror is not located and enters the illumination-side Cassegrain mirror 22. On the other hand, the infrared light reflected from the sample and collected by the illumination-side Cassegrain mirror 22 travels toward the area where the half mirror is located, and is reflected by the half mirror before traveling toward the parabolic mirror 19. Instead of the plane mirror 18 that splits light spatially in this way, a half mirror that splits light intensity-wise (for example, one that transmits half of the intensity of incident light and reflects the other half) may be used.

[0035] <Spectroscopy section> The optical path switching unit 60 will be described later, and the spectroscopic unit 30 will be described first. The spectroscopic unit 30 includes a Michelson interferometer 32, various reflecting mirrors for forming an optical path, and a built-in (or externally connected) high-brightness ceramic light source 80 for low spatial resolution. The spectroscopic unit 30 has an input part IP that receives infrared light from the outside, and an output part OP that outputs infrared light after spectroscopic processing.

[0036] The high-spatial-resolution infrared light from the optical path switching unit 60 enters the input section IP, reflects off the plane mirror 33 and the parabolic mirror 34, and is directed to the entrance aperture 32a of the Michelson interferometer 32. Between the parabolic mirror 34 and the entrance aperture 32a, there is a switching mirror 35 with a movable reflective surface. For high-spatial-resolution measurements, the reflective surface is positioned so as not to obstruct the optical path. For low-spatial-resolution measurements, the low-spatial-resolution infrared light from the high-brightness ceramic light source 80 is focused by the ellipsoidal mirror 36, reflected by the reflective surface of the switching mirror 35 located on the optical path, and directed to the entrance aperture 32a. In this way, the switching mirror 35 can select either the high-spatial-resolution infrared light from the optical path switching unit 60 or the low-spatial-resolution infrared light from the high-brightness ceramic light source 80 and input it to the Michelson interferometer 32. The Michelson interferometer 32 then performs spectral processing of the input infrared light.

[0037] The entrance diameter of the opening of the entrance aperture 32a is selected according to the resolution of the spectrum to be measured. Therefore, the entrance aperture 32a can function for both high-spatial resolution and low-spatial resolution measurements. However, during low-spatial resolution measurements, the size of the element surface of the downstream microscopic aperture 21 or MCT detector 70 functions in the same way as the entrance aperture 32a, so measurements can be performed without using the entrance aperture 32a within the range of spectral resolution commonly used in normal microscopic measurements. Furthermore, during high-spatial resolution measurements, the light source size itself is so small that the same effect as the restriction imposed by the opening of the entrance aperture 32a can be obtained, so measurements can also be performed without using the entrance aperture 32a.

[0038] The Michelson interferometer 32 includes an entrance aperture 32a that limits the angle of incidence of the incident light, a collimator mirror 32b that collects the infrared light from the entrance aperture 32a and converts it into parallel light, a beam splitter 32c that splits the parallel light into two beams, a fixed mirror 32d that reflects one of the split beams at a fixed position, and a movable mirror 32e that reflects the other split beam while changing its distance from the beam splitter 32c.The reflected light from the fixed mirror 32d and the movable mirror 32e are recombined by the beam splitter 32c to become an infrared interference wave corresponding to the optical path difference between the two split beams, and is output from the output portion OP of the spectroscopic section 30.

[0039] <Optical path switching section> The optical path switching unit 60 includes various reflecting mirrors for forming an optical path 61 for high spatial resolution and an optical path 62 for low spatial resolution, and a narrowband MCT detector 40 for high spatial resolution with high speed response.

[0040] In the optical path of the infrared light from the output portion OP of the spectroscopic unit 30, there is a switching mirror 63 having a movable parabolic surface, and in high spatial resolution measurement, the infrared light for high spatial resolution from the spectroscopic unit 30 is collected by the parabolic surface of the switching mirror 63 on the optical path and detected by the narrowband MCT detector 40. In low spatial resolution measurement, the parabolic surface of the switching mirror 63 is positioned so as not to obstruct the optical path, and the infrared light for low spatial resolution passes through the switching mirror 63, is reflected by the plane mirror 64, and is guided to the switching mirror 65 on the optical path of the infrared light for high spatial resolution from the microscopic measurement unit 20.

[0041] The switching mirror 65 has a movable reflecting surface, and in high spatial resolution measurement, the reflecting surface is positioned so as not to obstruct the optical path, and the high spatial resolution infrared light from the microscopic measurement unit 20 passes through the switching mirror 65 and travels straight to the input portion IP of the spectroscopic unit 30. In low spatial resolution measurement, the reflecting surface of the switching mirror 65 is located on the optical path, and the low spatial resolution infrared light from the plane mirror 64 is reflected by the reflecting surface and guided to the microscopic measurement unit 20.

[0042] The optical path switching unit 60 can form an optical path 61 for high spatial resolution by positioning the two switching mirrors 63, 65 on the high spatial resolution side, and conversely, forms an optical path 62 for low spatial resolution by positioning the two switching mirrors 63, 65 on the low spatial resolution side. In other words, the optical path switching unit 60 can selectively switch the optical path connecting the microscopic measurement unit 20 and the spectroscopic unit 30 to either the optical path 61 for high spatial resolution or the optical path 62 for low spatial resolution.

[0043] In this embodiment, many switching mirrors (14, 17, 35, 63, 65) are used, and their operations are performed by electric actuators or the like, and are automatically controlled by the drive control unit of the infrared microscope.

[0044] Figure 2 shows a simplified view of the high spatial resolution microscope optical system for transmission measurements compared to Figure 1. High spatial resolution infrared light travels along a high spatial resolution optical path 61 in the following order: nanocarbon light source 10 → switching mirror (high spatial resolution side) 14 → illumination-side Cassegrain mirror 22 → sample → collection-side Cassegrain mirror 26 → plane mirror 15 → parabolic mirror 16 → switching mirror (transmission side) 17 → plane mirror 33 → parabolic mirror 34 → Michelson interferometer 32 → switching mirror (high spatial resolution side) 63 → narrowband MCT detector 40. In this microscope optical system, extremely weak infrared light from nanocarbon light source 10 directly illuminates the sample in the microscope measurement unit 20, and the extremely weak infrared light that transmits through the sample is then post-spectroscopically processed in the spectroscopic unit 30.

[0045] Figure 3 shows the low-spatial-resolution microscope optical system for transmission measurements, similar to Figure 2. The low-spatial-resolution infrared light travels along low-spatial-resolution optical path 62 in the following order: high-brightness ceramic light source 80 → ellipsoidal mirror 36 → switching mirror (low spatial resolution side) 35 → Michelson interferometer 32 → plane mirror 64 → switching mirror (low spatial resolution side) 65 → switching mirror (transmission side) 17 → parabolic mirror 16 → plane mirror 15 → collection-side Cassegrain mirror 26 → sample → illumination-side Cassegrain mirror 22 → microscope aperture 21 → switching mirror (low spatial resolution side) 14 → parabolic mirror 11 → parabolic mirror 13 → mid-band MCT detector 70. In this microscope optical system, macro-infrared light with a beam cross section of several millimeters square from high-brightness ceramic light source 80 is pre-spectroscopically processed in spectroscopic unit 30 and then irradiates the sample in microscopic measurement unit 20.

[0046] Note that Figure 3 shows a microscope aperture 21 between the switching mirror 14 and the plane mirror (half mirror) 18, but this microscope aperture 21 is also set in the optical path for high-spatial-resolution measurements. The opening of the microscope aperture 21 is sized to accommodate the macro-infrared light used in low-spatial-resolution measurements, so it functions as an aperture to adjust the spatial resolution for macro-infrared light. However, for high-spatial-resolution measurements, the size of the light source 10 determines the illumination size of the sample, so the aperture function is unnecessary. While the microscope aperture 21 is omitted in the microscope optical system shown in Figure 2, the microscope aperture 21 may be used to adjust the illumination size for light source 10 with a size of 0.5 μm or larger. For example, a mechanism may be provided that allows for variable selection of the size of the image of the light-emitting surface formed on the sample, using multiple microscope apertures 21 with different aperture sizes or a microscope aperture 21 with a variable aperture size.

[0047] 1, the signal processing unit 50 for high spatial resolution measurements includes a light source driver 52 that pulses the nanocarbon light source 10 at a frequency of, for example, 3 kHz, a preamplifier 54 that amplifies the detection signal from the narrowband MCT detector 40, a lock-in amplifier 56 that uses the frequency signal of the nanocarbon light source 10 as a reference signal to detect a signal synchronized with the reference signal from the detection signal from the preamplifier 54, and a computer 58 that performs Fourier transform processing on the lock-in detected signal to calculate absorption spectrum information. Thus, in high spatial resolution measurements, double modulation photometry is possible by pulsed lighting of the nanocarbon light source 10 and post-spectroscopic processing in the Michelson interferometer 32. On the other hand, in low spatial resolution measurements, constant intensity infrared light from a high-intensity ceramic light source 80 is converted into an interference wave by a Michelson interferometer 32 and then irradiated onto the sample, so that modulation photometry using the interference wave is performed.

[0048] The effects of the infrared microscope of this embodiment will be described. (1) In high-spatial-resolution measurements, Cassegrain mirrors 12 and 22 are placed between the nanocarbon light source 10 and the sample, allowing extremely weak infrared light from a small light-emitting surface to be efficiently focused with a high NA (numerical aperture) and irradiated onto the sample. Furthermore, the coaxial optical system illumination of the Cassegrain mirrors 12 and 22 allows a one-to-one image of the small light-emitting surface to be formed on the sample. With coaxial optical system illumination, the light source image is formed on the sample without the intervention of an off-axis aspherical (parabolic or ellipsoidal) mirror, resulting in very little distortion of the light source image and enabling measurement with low stray light. In this embodiment, a Michelson interferometer 32 is placed behind the sample and performs post-spectrometry on the transmitted or reflected light from the sample. Therefore, the image of the nanocarbon light source 10 is formed directly on the sample without the intervention of the Michelson interferometer 32. This prevents the image from being affected by aberrations such as the aspherical mirror of the Michelson interferometer, and also suppresses the intrusion of stray light into the spot area of ​​the sample, enabling low-stray-light measurement. In this way, in high spatial resolution measurements, by using a light source that is sufficiently small, such as 1 / 3 to 1 / 10 of the measurement wavelength, the image of the tiny light-emitting surface formed on the sample can be made to approach the size of the diffraction limit of light.

[0049] (2) In general, infrared microscopes handle weak infrared light, which requires high-sensitivity measurement, so they need to irradiate the sample with infrared light whose intensity changes periodically. The infrared light sources of conventional infrared microscopes have a large heat capacity due to their size, making them unsuitable for high-speed flashing. For this reason, the sample was irradiated with interference waves of infrared light formed by a Michelson interferometer (pre-spectroscopic processing). In contrast, the nanocarbon light source 10 has a small light-emitting volume, exhibits high response to on / off operations, and is capable of high-frequency pulsed illumination. Therefore, in high-spatial resolution measurements using the infrared microscope of this embodiment, even in post-spectroscopic processing, the detection signal of extremely weak infrared light from the narrowband MCT detector 40 is lock-in detected as a reference signal synchronized with the frequency signal of the light source 10, allowing for high-sensitivity measurements (e.g., separation from background radiation at room temperature). As a result, the infrared microscope of the present invention can perform high spatial resolution measurements with low stray light and with extremely high spatial resolution approaching the diffraction limit.

[0050] (3) Furthermore, the configuration of the infrared microscope of this embodiment makes it possible to appropriately switch between the high spatial resolution optical path 61 and the low spatial resolution optical path 62, and to selectively perform both high spatial resolution measurement and low spatial resolution measurement (for example, measurement using an existing infrared microscope). This allows the user to appropriately select between analysis of a relatively large measurement area using low spatial resolution measurement and analysis of a minute area using high spatial resolution measurement, depending on the size of the sample, i.e., the size of the desired measurement range, and to switch between measurements with different spatial resolutions while the sample is still placed on the sample mounting unit 24.

[0051] (4) Furthermore, as shown in Figure 4, the microscopic measurement unit 20 can perform high spatial resolution measurements by appropriately selecting one of three measurement modes (transmission, reflection, and total reflection). In the transmission measurement mode of Figure 4(A), Cassegrain mirrors 22 and 26 are used, which are symmetrically placed above and below the sample. In the reflection measurement mode of Figure 4(B), the Cassegrain mirror 22 above the sample is used. In the total reflection measurement mode of Figure 4(C), the high-magnification, high-numerical-aperture Cassegrain mirror 22 with an ATR crystal 28 for total reflection measurement is used.

[0052] (5) For example, when measuring a sample sandwiched between high-refractive-index window plates, irradiation of the sample with macro-sized infrared light source light is susceptible to the effects of stray light due to multiple reflections between the two window plates. In contrast, in high-spatial-resolution measurements, where the illumination size of the light source light is the same as the size of the measurement spot on the sample, the spot area on the sample is very small, so the effects of stray light due to multiple reflections can be suppressed.

[0053] (6) The nanocarbon light source 10 does not come too close to the sample, and there is no risk of the sample being damaged by the light and heat of the nanocarbon light source 10.

[0054] Figure 5 is a diagram showing the configuration of an infrared microscope according to a second embodiment of the present invention, and is a simplified illustration of the configuration of an infrared microscope dedicated to reflectance measurement. The upper side of Figure 5 shows an optical system for high spatial resolution, and the lower side shows an optical system for low spatial resolution. A feature of this microscope is that a high-brightness ceramic light source 80 is incorporated into the optical path 62 for low spatial resolution.

[0055] FIG. 6 is a diagram illustrating the configuration of an infrared microscope according to a third embodiment of the present invention, showing a simplified configuration of an infrared microscope dedicated to transmission measurements. The upper side of FIG. 6 is an optical system for high spatial resolution, and the lower side is an optical system for low spatial resolution. As with FIG. 5, a feature of the infrared microscope is that a high-brightness ceramic light source 80 is incorporated into the optical path 62 for low spatial resolution. Another feature of the infrared microscope of FIG. 6 is that, in high-spatial resolution measurements, extremely weak infrared light from a nanocarbon light source 10 illuminates the sample from below, and, in low-spatial resolution measurements, infrared light from a Michelson interferometer 32 illuminates the sample from below.

[0056] The following shows typical examples of combinations of light source and detector for two spatial resolution measurements. Note that the use of the detectors described here is not limited to these, and any detector that can satisfy the sensitivity and frequency response requirements in the measurement wavelength (wavenumber) range can be used. <For high spatial resolution> Nanocarbon Light Source Narrowband MCT detector (wavenumber range: 5000-750 cm -1 , wavelength range 2.0~13.3μm) <For low spatial resolution> High-intensity ceramic light source (or halogen lamp) Mid-band MCT detector (wavenumber range: 7800-600 cm -1 , wavelength range 1.3~16.7μm)

[0057] In the above embodiment, the spectroscopic unit 30 includes the Michelson interferometer 32 that forms an interference wave of infrared light. However, the spectroscopic unit 30 may include a dispersive prism or diffraction grating and output wavelength-dispersed infrared light. In this case, the signal processing unit 50 acquires the absorption spectrum by performing lock-in detection of the detection signal for each dispersed wavelength.

[0058] In the above embodiment, Cassegrain mirrors 12, 22, and 26 are used in microscopic measurement unit 20, but an objective lens can also be used instead of a Cassegrain mirror. However, since visible light for observing the sample is generally also introduced into an infrared microscope, and there are few high-quality, inexpensive lenses that transmit both the visible light for observation and the infrared light for measurement, and since lenses are prone to chromatic aberration problems when a wide infrared wavelength band is used, a Cassegrain mirror, which is a reflective focusing type, is preferable for infrared microscopes. [Explanation of symbols]

[0059] 10 Nanocarbon light source (light source for high spatial resolution) 12 Cassegrain mirror on the light source side (light source side focusing element) 20 Microscopic Measurement Unit 22 Cassegrain mirror on the illumination side (objective element on the illumination side) 24 Sample installation area 26 Focusing Cassegrain mirror (focusing objective element) 28 ATR Crystal 30 Spectroscopic section 32 Michelson interferometer 40 Narrowband MCT detector (detector for high spatial resolution) 50 Signal processing section 60 Optical path switching section 61 Optical path for high spatial resolution 62 Optical path for low spatial resolution 70 Mid-band MCT detector (detector for low spatial resolution) 80 High-brightness ceramic light source (light source for low spatial resolution)

Claims

1. a light source that emits infrared light whose intensity repeatedly increases and decreases; an illumination-side objective element that illuminates the sample with infrared light from the light source; A sample placement unit; a collecting-side objective element that collects infrared light transmitted through or reflected by the sample; a spectroscopic unit that performs spectroscopic processing on the infrared light collected by the light-collection-side objective element; a detector for detecting the spectrally processed infrared light; a signal processing unit that performs lock-in detection using a reference signal that is synchronized with a change in the intensity of the infrared light relative to the detection signal of the detector to acquire an infrared spectrum of the sample; An infrared microscope comprising: The light source has a light emitting surface with a size of 0.1 μm or more and 20 μm or less, An infrared microscope characterized in that a light source-side focusing element that focuses infrared light is provided at the exit of the light source, and an image of the light emitting surface of the light source is formed on the sample by the light source-side focusing element and the illumination-side objective element.

2. An infrared microscope comprising: a microscopic measurement unit that performs transmission or reflection measurement of a minute area of ​​a sample using infrared light for high spatial resolution or low spatial resolution; an optical path switching unit that switches between an optical path for high spatial resolution and an optical path for low spatial resolution; and a spectroscopic unit that is connected to the microscopic measurement unit via the optical path switching unit, a high spatial resolution light source that supplies high spatial resolution infrared light to the microscopic measurement unit, and a low spatial resolution detector that detects low spatial resolution infrared light that has passed through or reflected from a minute region of the sample in the microscopic measurement unit, are connected to the microscopic measurement unit; the spectroscopic unit is provided to be able to perform spectroscopic processing of high spatial resolution infrared light transmitted through or reflected by a minute region of the sample in the microscopic measurement unit and low spatial resolution infrared light from a low spatial resolution light source connected to the spectroscopic unit; the high spatial resolution optical path is formed so that after high spatial resolution infrared light from the high spatial resolution light source is transmitted through or reflected by a minute region of the sample in the microscopic measurement unit, the infrared light is guided to the spectroscopic unit, and the high spatial resolution infrared light that has been spectrally processed by the spectroscopic unit is guided to a high spatial resolution detector connected to the optical path switching unit; The low spatial resolution optical path is formed so that the low spatial resolution infrared light from the low spatial resolution light source is spectroscopically processed in the spectroscopic section, and then the infrared light is guided to the microscopic measurement section, and in the microscopic measurement section, the low spatial resolution infrared light is transmitted through or reflected by a minute region of the sample and detected by the low spatial resolution detector, characterized in that the infrared microscope.

3. 3. The infrared microscope according to claim 2, The infrared microscope is characterized in that the microscopic measurement unit has an illumination-side objective element that irradiates a minute area on the sample with infrared light, a sample placement unit, and a collection-side objective element that collects infrared light that has passed through or reflected from the minute area on the sample.

4. 4. The infrared microscope according to claim 3, The high spatial resolution light source has an emitting surface of 0.1 μm or more and 20 μm or less in size, and a light source side focusing element that focuses infrared light is provided at the exit of the high spatial resolution light source, and an image of the emitting surface of the high spatial resolution light source is formed on the sample by the light source side focusing element and the illumination side objective element.

5. 5. The infrared microscope according to claim 3, wherein a microscopic aperture is provided between the high spatial resolution light source and the illumination side objective element, An infrared microscope characterized in that the infrared light from the high spatial resolution light source is blocked by the microscope aperture, thereby changing the size of the image of the light emitting surface formed on the sample.

6. 5. The infrared microscope according to claim 3 or 4, When performing transmission measurement, the microscopic measurement unit Infrared light for high spatial resolution is guided through the irradiation-side objective element, the sample placement unit, and the collection-side objective element in this order; An infrared microscope characterized in that it is configured to guide infrared light for low spatial resolution through the light-collecting side objective element, the sample placement section, and the illumination side objective element in this order.

7. 2. The infrared microscope according to claim 1, wherein a microscopic aperture is provided between the light source and the illumination-side objective element, An infrared microscope characterized in that the infrared light from the light source is blocked by the microscope aperture, thereby changing the size of the image of the light-emitting surface formed on the sample.

8. 5. The infrared microscope according to claim 1, 10. An infrared microscope, wherein the light source side focusing element and the illumination side objective element are each composed of a Cassegrain mirror.

9. 4. The infrared microscope according to claim 1, 10. An infrared microscope, wherein the illumination-side objective element is a Cassegrain mirror that also serves as a collection-side objective element for collecting infrared light reflected from a sample.

10. 4. The infrared microscope according to claim 1, An infrared microscope characterized in that the illumination-side objective element is a Cassegrain mirror that also functions as a collection-side objective element that collects infrared light reflected from the sample, and the Cassegrain mirror has an ATR crystal for total reflection measurement.

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