Gas absorption spectrometer

Abstract

We provide a cavity ring-down spectrometer that enables accurate measurement of extremely low-temperature samples. [Solution] The gas absorption spectrometer is a gas absorption spectrometer for measuring a sample gas and comprises a resonator 100A including at least two mirrors, a laser light source that emits laser light for irradiating the resonator 100A, and a photodetector for detecting the light extracted from the resonator. The resonator includes an inner chamber 1A that houses the mirrors 21 and 22 and forms a measurement space 15 into which the sample gas is introduced, an outer chamber 3A disposed outside the inner chamber 1A for vacuum insulation of the measurement space 15 from the outside, and a cooler 9 disposed within the outer chamber 3A, spaced apart from the inner chamber 1A, and having an internal space through which a refrigerant flows.

Description

Technical Field

[0001] The present disclosure relates to a gas absorption spectroscopic apparatus for determining the concentration of a target component in a gas using cavity ring-down absorption spectroscopy (CRDS), which is a type of gas absorption spectroscopy.

Background Art

[0002] As one of the gas absorption spectroscopies, cavity ring-down spectroscopy (CRDS) is known. CRDS is a spectroscopic technique for highly sensitively determining the concentration of a target component contained in a sample gas by increasing the effective optical path length for light absorption by the sample gas using a resonator (cavity) configured to include highly reflective mirrors.

[0003] Non-Patent Document 1 discloses CRDS for measuring radioactive carbon isotope 14 C. 14 Since 14 C is the only long half-life radionuclide among the isotopes of elements, 14 environmental and / or biological tracing is possible by measuring 13 C. However, at room temperature, 12 the absorption intensity of 13 CO2 is about two to three orders of magnitude smaller than the absorption intensity of 12 CO2, 14 CO2. As will be described later, at extremely low temperatures (about -100°C), 14 the absorption intensities of 13 CO2 and 12 CO2 decrease to the same level as 14 CO2. Therefore, in order to measure 14 CO2, it is necessary to cool the sample gas to an extremely low temperature (about -100°C) to reduce the absorption intensities of 13 CO2 and 12 CO2. As a method for reducing the sample gas to an extremely low temperature, a method of bringing a cooler into contact with the resonator is known.

Prior Art Documents

Non-Patent Documents

[0004] [Non-Patent Document 1] Development of a cavity ring-down spectrometer for radiocarbon isotopes (14C), Kazune Mano, Shimadzu Review, Vol. 78, Nos. 3-4, 2021. [Overview of the project] [Problems that the invention aims to solve]

[0005] However, if the cooler is placed in contact with the resonator, vibrations from the refrigerant flowing through the cooler are transmitted to the resonator, reducing the accuracy of the measurement.

[0006] This invention was made to solve these problems, and its objective is to provide a cavity ring-down spectrometer that can accurately measure extremely low-temperature samples. [Means for solving the problem]

[0007] The gas absorption spectrometer according to this disclosure is a gas absorption spectrometer for measuring a sample gas and comprises a resonator including at least two mirrors, a laser light source that emits laser light for irradiating the resonator, and a photodetector for detecting the light extracted from the resonator. The resonator includes an inner chamber that houses the mirrors and forms a measurement space into which the sample gas is introduced, an outer chamber disposed outside the inner chamber for vacuum insulating the measurement space from the outside, and a cooler disposed within the outer chamber, spaced apart from the inner chamber, and having an internal space through which a coolant flows. [Effects of the Invention]

[0008] According to this disclosure, a cavity ring-down spectrometer capable of accurately measuring extremely low-temperature samples can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] This diagram schematically shows the configuration of a gas absorption spectrometer. [Figure 2]It is a conceptual diagram for explaining the mode frequency. [Figure 3] It is a diagram for explaining the temperature dependence of the absorption intensity of interfering gases near the 14CO2 absorption peak. [Figure 4] It is a diagram showing the configuration of the resonator according to the comparative example. [Figure 5] It is a diagram showing the configuration of the resonator according to Embodiment 1. [Figure 6] It is a diagram showing the configuration of the resonator according to Embodiment 2. [Figure 7] It is a diagram showing the configuration of the resonator according to Embodiment 3. [Figure 8] It is a diagram showing the configuration of the resonator according to Embodiment 4. [Figure 9] It is a diagram showing the configuration of the resonator according to Embodiment 5. [Figure 10] It is a diagram showing the configuration of the resonator according to Embodiment 6. [Figure 11] It is a diagram showing the configuration of the resonator according to Embodiment 7. [Figure 12] It is an example of the joint according to Embodiment 7. [Figure 13] It is an example of the joint according to Embodiment 7. [Figure 14] It is a diagram showing the configuration of the resonator according to Modification 1.

Mode for Carrying Out the Invention

[0010] Hereinafter, the present embodiment will be described in detail with reference to the drawings. In the following, the same or corresponding parts in the drawings are denoted by the same reference numerals and their description will not be repeated.

[0011] <Configuration of the Gas Absorption Spectrometer> FIG. 1 is a diagram schematically showing the configuration of a gas absorption spectrometer 1000 according to the present embodiment. The gas absorption spectrometer 1000 is configured to be able to measure the light absorption by the target component contained in the sample gas by cavity ring-down spectroscopy (CRDS).

[0012] The gas absorption spectrometer 1000 comprises a laser light source 83, an AOM (Acousto-Optic Modulator) 94, a resonator 100A, a photodetector 86, and a controller 80.

[0013] The laser light source 83 emits laser light to irradiate the resonator 100A. The laser light source 83 is configured to vary the oscillation frequency of the laser light according to commands from the controller 80. Specifically, the laser light source 83 includes a distributed feedback type quantum cascade laser (QCL) 831 and a laser driver 832. The QCL 831 has a center oscillation wavenumber of, for example, 2200 cm⁻¹. -1 It emits laser light of approximately 4.5 μm wavelength. The laser driver 832 supplies drive current to QCL831 according to commands from the controller 80. By changing the drive current to QCL831, the oscillation wavenumber of QCL831 can be changed to 0.2 cm². -1 It can be swept to a certain extent.

[0014] The AOM84 is located in the optical path between the laser light source 83 and the resonator 100A. The AOM84 is an optical switch (switch) that rapidly switches between irradiating and blocking laser light from the laser light source 83 to the resonator 100A according to a command from the controller 80. When an ON command for irradiating light is applied from the controller 80, the AOM84 enters an ON state, outputting laser light from the laser light source 83 to the resonator 100A. When an OFF command for blocking light is applied from the controller 80, the AOM84 enters an OFF state, not outputting laser light from the laser light source 83 to the resonator 100A.

[0015] Next, the configuration for CRDS measurement of the sample gas in the resonator 100A will be described. The resonator 100A is located in the optical path between the AOM 84 and the photodetector 86. The resonator 100A includes a container (inner chamber 1A, described later) in which the sample gas is sealed and which forms the measurement space 15, an introduction pipe 41 for introducing the sample gas into the resonator 100A before the start of measurement, and an exhaust pipe 42 for discharging the sample gas outside the resonator 100A after the end of measurement. An introduction valve 411 is provided in the introduction pipe 41. An exhaust valve 412 is provided in the exhaust pipe 42. The opening and closing of the introduction valve 411 and the exhaust valve 412 can also be controlled by the controller 80.

[0016] The resonator 100A includes at least two mirrors. In the example shown in Figure 1, a pair of mirrors 21 and 22 are installed inside the resonator 100A. The mirrors 21 and 22 are positioned opposite each other inside the resonator 100A so that light reflects between them. Each of the mirrors 21 and 22 has at least one concave surface to facilitate the meeting of the stability requirements for the resonator 100A. In addition, each of the mirrors 21 and 22 has a high reflectivity (for example, about 99.9%) so that the amount of light leaking out of the resonator 100A is extremely small. The resonator length of the resonator 100A (distance between the mirrors 21 and 22 in the optical axis AX direction) is, for example, about 450 mm. Note that the number of mirrors placed inside the resonator 100A is not limited to two, but may be three or more. In other words, it may be a resonator in which mirrors are arranged so that light reflects between them, or it may be a resonator in which mirrors are arranged in a ring shape so that light reflects in one direction.

[0017] Piezoelectric elements (not shown) are placed on mirrors 21 and / or 22. The piezoelectric elements drive mirrors 21 and / or 22, which constitute the resonator 100A, according to commands from the controller 80, thereby displacing mirrors 21 and / or 22 in the direction of the optical axis. This allows the resonator length of the resonator 100A to be changed. Therefore, the resonator length can be varied to match the laser wavenumber, or the laser wavenumber can be swept to match the resonator length.

[0018] In this embodiment, the sample gas in the resonator 100A is cooled by the cooler 9. The configuration for this cooling will be described later.

[0019] The photodetector 86 detects the light extracted from the resonator 100A. The photodetector 86 is a photodetector such as a photodiode or an image sensor. The photodetector 86 detects the weak light extracted from the resonator 100A as the output light of the resonator 100A and outputs a signal (detection signal) indicating the detection result to the controller 80. For example, a liquid nitrogen-cooled InSb (indium antimony) detector can be used as the photodetector 86.

[0020] The controller 80 includes a processor 81 such as a CPU (Central Processing Unit) or FPGA (Field-Programmable Gate Array), memory 82 such as ROM (Read Only Memory) and RAM (Random Access Memory), and input / output ports (not shown).

[0021] The controller 80 is a control device that measures the target component in the sample gas inside the resonator 100A using the output signal from the photodetector 86. The controller 80 also controls each component of the gas absorption spectrometer 1000. Specifically, the controller 80 outputs commands to the laser driver 832 for scanning the oscillation frequency of the laser light, and outputs the aforementioned ON or OFF signals to the AOM 84. The controller 80 outputs commands to the introduction valve 411 for introducing the sample gas into the resonator 100A, and outputs commands to the discharge valve 412 for discharging the sample gas outside the resonator 100A. The controller 80 applies a voltage to the piezoelectric element 43 to displace the mirror 22. The controller 80 also performs various data processing operations to calculate the concentration (absolute concentration) of the target component contained in the sample gas based on the detection signal from the photodetector 86.

[0022] The controller 80 may be configured by dividing it into two or more units for each function. For example, the controller 80 may be divided into a unit that controls each device and a unit that performs various data processing.

[0023] <Measurement principle using cavity ring-down spectroscopy (CRDS)> This section briefly explains the measurement principle of cavity ring-down absorption spectroscopy in the gas absorption spectrometer 1000. Generally, a resonator has resonance conditions under which resonance occurs when the frequency of the light irradiated onto the resonator is a specific frequency. Hereinafter, the frequency of the laser light irradiated onto the resonator 100A will be referred to as the "laser frequency," and the frequency of light in which resonance can occur in the resonator 100A will be referred to as the "mode frequency."

[0024] Figure 2 is a conceptual diagram illustrating mode frequencies. As shown in Figure 2, multiple mode frequencies exist at predetermined frequency intervals. Hereafter, the interval between two adjacent mode frequencies will be referred to as the "free spectral range" (FSR).

[0025] If the laser frequency does not match any of the mode frequencies, no light power is stored in the resonator 100A. On the other hand, if the laser frequency matches any of the mode frequencies, light power is stored in the resonator 100A.

[0026] The controller 80 determines whether sufficient laser power has been stored in the resonator 100A based on the output signal of the photodetector 86 (the output light from the resonator 100A). When the output light from the resonator 100A reaches a predetermined threshold, the controller 80 determines that sufficient laser power has been stored in the resonator 100A and outputs an off signal to the AOM 84. As a result, the light input to the resonator 100A is blocked by the AOM 84. The light stored in the resonator 100A then travels back and forth between mirror 21 and mirror 22 many times (usually several thousand to tens of thousands of times). As this light travels back and forth between mirrors 21 and 22, it is gradually attenuated due to losses from reflection leakage between mirrors 21 and 22 and absorption by the target component in the sample gas. Therefore, the output light from the resonator 100A leaking from mirror 22 is gradually attenuated. In CRDS, the effective optical path length (the distance the light travels through the sample gas) is increased using a resonator 100A, allowing for the detection of even extremely small amounts of light absorption by the target component.

[0027] The controller 80 acquires the output signal of the photodetector 86 after the light input to the resonator 100A is blocked by the AOM 84 as a "ring-down signal," and calculates the decay time constant of the acquired ring-down signal as the "ring-down time." From the calculated ring-down time, the controller 80 calculates the concentration of the target component contained in the sample gas.

[0028] The controller 80 acquires the output signal of the photodetector 86 at intervals of, for example, 0.2 μsec, and calculates the ring-down time from the acquired output signal of the photodetector 86. When there are no gas components that absorb laser light inside the resonator 100A, the ring-down time becomes the decay time constant of the resonator 100A and is therefore approximately a constant value. On the other hand, when there are gas components that absorb laser light inside the resonator 100A, the ring-down time becomes a value that fluctuates depending on the concentration of the gas components. This point can be used to quantify the concentration of the target component.

[0029] < 14 Measurement of C> Radiocarbon isotopes are the only radioactive nuclides with a long half-life among the isotopes of elements. 14 C is used as an environmental tracer. For example, in organic resources 14 By measuring the relative abundance of carbon (C), it is possible to determine whether the organic resource in question is derived from plant-based biomass or from fossil fuels. 14 C is also used as a biotracer. In drug development, a portion of the carbon in a compound is used. 14 When a compound labeled with 1C is administered to a living organism, it accumulates in its blood, urine, feces, and organs. 14 By measuring the concentration of C, the in vivo dynamics of the administered compound can be analyzed.

[0030] however, 14 The isotopic ratio of C is very low. Therefore, 14 To measure C, it is necessary to distinguish it from other carbon isotopes. 14 C needs to be detected with high sensitivity.

[0031] Laser absorption spectroscopy utilizes the fact that different isotopes in a molecule absorb different wavelengths of infrared light, allowing for the analysis of isotopic molecules. In CRDS (Critical Laser Deposition Spectroscopy), sensitivity is improved by increasing the effective optical path length using an optical resonator.

[0032] Even higher sensitivity 14To detect C, it is useful to cool the sample gas. At room temperature, 14 The absorption intensity of CO2 is due to the presence of interfering gases. 12 CO2, 13 Although the absorption intensity is about 2 to 3 orders of magnitude smaller than that of CO2, by cooling the sample gas, 12 CO2, 13 This can reduce the absorption intensity of CO2.

[0033] Figure 3 shows 14 This figure illustrates the temperature dependence of the interfering gas absorption intensity near the CO2 absorption peak. In Figure 3, the horizontal axis represents temperature, and the vertical axis represents the gas absorption intensity. Refer to Figure 3. 14 When CO2 is cooled to extremely low temperatures (-100°C), 14 The CO2 absorption intensity is, 12 CO2, 13 It can be seen that the absorption intensity is close to that of CO2. In this way, by cooling the sample gas, it becomes possible to measure it under conditions different from room temperature.

[0034] <Comparative Example> Figure 4 shows the configuration of the resonator 100P in a comparative example. In resonator 100P, the sample gas is measured within the inner chamber unit 10P. The sample gas is cooled by directly contacting the cooler 9 with the inner chamber unit 10P. However, in resonator 100P, vibrations of the refrigerant flowing within the cooler 9 are transmitted to the inner chamber unit 10P, which can affect CRDS measurement. Specifically, vibrations of the mirrors 21 and 22 of the inner chamber unit 10P can degrade the accuracy of CRDS measurement.

[0035] <Embodiment 1> Figure 5 shows the configuration of the resonator 100A according to Embodiment 1. The resonator 100A includes an inner chamber unit 10A, an outer chamber unit 30, an inlet pipe 41, an outlet pipe 42, and a cooler 9.

[0036] The inner chamber unit 10A includes the inner chamber 1A, mirrors 21 and 22, and window material 19.

[0037] The inner chamber 1A houses the mirrors 21 and 22 and forms a measurement space 15 into which the sample gas is introduced. The inner chamber 1A includes a mirror holding portion 11A in which the mirrors 21 and 22 are installed, and a cooling portion 12A between the mirror holding portions 11A. The inner chamber 1A is, for example, a cylindrical member. The inner chamber unit 10A is sealed by the window material 19 sealing the opening of the inner chamber 1A.

[0038] The outer chamber unit 30 includes an outer chamber 3 and a window material 39. The outer chamber 3 is located outside the inner chamber 1A and vacuum-insulates the measurement space 15 from the outside. The outer chamber 3 is, for example, a cylindrical member. The window material 39 seals the opening of the outer chamber 3, thereby sealing the inside of the outer chamber unit 30.

[0039] The inner chamber unit 10A and the outer chamber unit 30 are arranged such that the window material 39, window material 19, and mirrors 21 and 22 are located on the optical axis AX connecting the laser light source 83 and the photodetector 86. Laser light emitted from the laser light source 83 enters the inner chamber unit 10A located inside the outer chamber unit 30, is reflected by the mirrors 21 and 22, and then detected by the photodetector 86.

[0040] The cooler 9 includes a cooler body 99. The cooler body 99 has an internal space through which the refrigerant flows. In one embodiment, the refrigerant cooled by the refrigerant cooling unit 92 is supplied to the cooler body 99 via piping 91. The cooler body 99 and the piping 91 and / or the refrigerant cooling unit 92 may be configured as a single unit. Note that the refrigerant cooling unit 92 is omitted from the description in the following figures.

[0041] The cooler 9 is positioned within the outer chamber 3, spaced apart from the inner chamber 1A. This allows the cooler 9 to cool the inner chamber 1A by radiation, thereby cooling the sample gas within the inner chamber 1A. Preferably, the cooler 9 is positioned opposite the cooling portion 12A of the inner chamber 1A. Since the inner chamber 1A and the cooler 9 are not in contact, vibrations of the cooler 9 caused by the flow of refrigerant are not transmitted to the inner chamber 1A. This makes it possible to cool the sample gas without degrading the measurement accuracy of the resonator 100A. Therefore, using the resonator 100A, it is possible to accurately measure extremely low-temperature samples.

[0042] Next, we will describe additional configurations for Embodiment 1. The cooler 9 may further include a cooling block 95, as shown in the example in Figure 5. The cooling block 95 is a component for improving the cooling efficiency by radiation within the inner chamber 1A by the cooler body 99. The cooling block 95 is installed between the inner chamber 1A and the cooler body 99, preferably between the cooling portion 12A and the cooler body 99, spaced apart from the inner chamber 1A. It is preferable that the cooling block 95 is positioned so that a part of it is in contact with the cooler body 99. The area of ​​the surface of the cooling block 95 facing the inner chamber 1A (indicated by reference numeral 950 in Figure 5) is larger than the area of ​​the surface of the cooler body 99 facing the inner chamber 1A (indicated by reference numeral 990 in Figure 5).

[0043] When the cooling block 95 is present, the inner chamber 1A can be cooled more efficiently than when the cooling block 95 is absent. Furthermore, since the inner chamber 1A and the cooling block 95 are not in contact, vibrations of the cooling block 95 caused by the flow of refrigerant through the cooler body 99 are not transmitted into the inner chamber 1A. Therefore, by using the cooling block 95 in addition to the cooler body 99, the cooling efficiency of the sample gas can be improved while maintaining the measurement accuracy of the resonator 100A.

[0044] Preferably, the cooler 9 is positioned to surround the inner chamber 1A. Specifically, for example, the cooler 9 itself may be formed as a cylindrical member surrounding the inner chamber 1A, or a cylindrical member formed to surround the inner chamber 1A may be used. With this configuration, the outer circumference of the inner chamber 1A is widely opposite to the cooler 9, so the cooling efficiency can be improved.

[0045] By forming the cooling block 95 from a material with high thermal conductivity, it becomes easier to lower the temperature of the cooling block 95. An example of a material with high thermal conductivity is metal, and a more specific example is copper.

[0046] Furthermore, by forming the inner chamber 1A with a material that has high emissivity, the inner chamber 1A can be efficiently cooled. More specifically, it is preferable to form the cooling portion 12A within the inner chamber 1A, which corresponds to most of the measurement space 15 where the sample gas is present, with a material that has an emissivity higher than a predetermined value. More specifically, it is preferable to form the cooling portion 12A with a material that has an emissivity higher than 0.8. In this case, a sufficient radiation effect can be expected. Materials with an emissivity higher than 0.8 include, for example, quartz glass, anodized aluminum, anodized aluminum painted white or black, and quartz glass.

[0047] Furthermore, by forming the inner chamber 1A with a material that has a low coefficient of thermal expansion, the change in resonator length is reduced even when the inner chamber 1A is cooled. More specifically, it is preferable to form the cooling portion 12A within the inner chamber 1A, which corresponds to most of the resonator length, with a material that has a low coefficient of thermal expansion. This stabilizes the resonator length with respect to temperature changes. The material with a low coefficient of thermal expansion is, more specifically, a material with a lower coefficient of thermal expansion than metals, such as quartz glass.

[0048] Based on the above, by forming the inner chamber 1A from quartz glass, the inner chamber 1A can be cooled efficiently, and the change in resonator length due to cooling can be reduced.

[0049] Based on the above, the resonator 100A according to Embodiment 1 provides a cavity ring-down spectrometer that can accurately measure extremely low-temperature samples.

[0050] <Use of thermal conductive materials that do not transmit vibrations> Next, embodiments further including a heat conductive material positioned between the inner chamber and the cooler to mediate heat conduction between the inner chamber and the cooler will be described. In these embodiments, the heat conductive material is such that, even when in contact with both the cooler and the inner chamber, vibrations from the cooler are not easily transmitted to the inner chamber, or are almost not transmitted at all. More specifically, even if the portion of the heat conductive material in contact with the cooler vibrates, vibrations are not easily transmitted to the portion of the heat conductive material in contact with the inner chamber, or are almost not transmitted at all. In other words, the portion of the heat conductive material in contact with the cooler and the portion in contact with the inner chamber are configured so that they do not move in conjunction. Examples of heat conductive materials include, for example, a gas (Embodiment 4), a liquid, or a highly flexible solid. A highly flexible solid is, for example, a solid formed in the shape of wool (Embodiment 2) or a solid formed in the shape of a strap (Embodiment 3). Naturally, it is preferable to use a material with high thermal conductivity as the heat conductive material.

[0051] <Embodiment 2> Figure 6 shows the configuration of the resonator 100B according to Embodiment 2. The resonator 100B includes wool 51B in addition to the configuration of the resonator 100A. The wool 51B is placed between the inner chamber 1B and the cooler 9, and more specifically, connects the inner chamber 1C and the cooler 9. The wool 51B corresponds to one embodiment of a "thermal conductive material". The wool 51B is preferably made of a material with high thermal conductivity, such as a metal such as copper. According to Embodiment 2, the inner chamber 1B can be cooled not only by radiation from the cooler 9 but also by heat conduction from the wool 51B. Therefore, the cooling efficiency of the inner chamber 1B can be improved while suppressing the transmission of vibrations from the cooler 9 to the inner chamber 1B. Preferably, the thermal conductivity of the wool 51B is 100 W / m·K or higher. In other words, preferably, the wool 51B is made of a material with a thermal conductivity of 100 W / m·K or higher (for example, diamond, copper, gold, aluminum, brass). This configuration allows for efficient cooling.

[0052] <Embodiment 3> Figure 7 shows the configuration of the resonator 100C according to Embodiment 3. The resonator 100C includes a thermal strap 51C in addition to the configuration of the resonator 100A. The thermal strap 51C is placed between the inner chamber 1C and the cooler 9, and more specifically, connects the inner chamber 1C and the cooler 9. The thermal strap 51C corresponds to one embodiment of the "thermal conductive material". The thermal strap 51C is preferably made of a material with high thermal conductivity, such as copper, aluminum, indium, or gold. According to Embodiment 3, the inner chamber 1C can be cooled not only by radiation from the cooler 9 but also by heat conduction from the thermal strap 51C. Therefore, the cooling efficiency of the inner chamber 1C can be improved while suppressing the transmission of vibrations from the cooler 9 to the inner chamber 1C. Preferably, the thermal conductivity of the thermal strap 51C is 100 W / m·K or higher. In other words, preferably, the thermal strap 51C is made of a material with a thermal conductivity of 100 W / m·K or higher (for example, diamond, copper, gold, aluminum, or brass). With this configuration, efficient cooling is possible.

[0053] <Embodiment 4> Figure 8 shows the configuration of the resonator 100D according to Embodiment 4. The resonator 100D includes a cooling block 95D in place of the cooling block 95 of the resonator 100A. The cooling block 95D is a housing that is arranged to accommodate the inner chamber unit 10D inside. The cooling block 95D seals the inside of the cooling block 95D.

[0054] The space 35D between the outer chamber 3 and the cooling block 95D is evacuated. This vacuum-insulates the cooling block 95D from the outside.

[0055] The space 55D between the cooling block 95D and the inner chamber unit 10D is filled with a cooling gas (hereinafter also referred to as "cooling gas") which is a gas that mediates heat conduction between the inner chamber 1D and the cooler 9. The cooling gas corresponds to one embodiment of the "heat conductive material". One embodiment of the cooling gas is nitrogen (N2) gas. The cooling gas absorbs heat from the cooler 9 and absorbs heat from the inner chamber 1D while convecting in the space 55D. As described above, according to Embodiment 4, the inner chamber 1D can be cooled not only by radiation from the cooler 9 but also by heat conduction by the convecting cooling gas. Therefore, the cooling efficiency of the inner chamber 1D can be improved while suppressing the transmission of vibrations from the cooler 9 to the inner chamber 1D.

[0056] Furthermore, since the cooling gas and cooling block 95D are located on the optical axis AX of the laser beam, it is preferable that they be made of materials that do not interfere with the measurement of the sample gas.

[0057] As with the resonator 100D, by filling the inner chamber unit 10D with gas not only inside but also around it, the risk of sample gas leaking out of the inner chamber unit 10D (sample gas leakage) is reduced due to the pressure difference between the inside and outside of the inner chamber unit 10D. The leak rate is proportional to the pressure difference between the inside and outside of the inner chamber unit 10D. Therefore, it is preferable to fill the cooling gas so that the atmospheric pressure in space 55D is approximately the same as the atmospheric pressure inside the inner chamber unit 10D. In one embodiment, for example, the cooling gas is filled so that the atmospheric pressure in space 55D is about 1 to 10 times the atmospheric pressure inside the inner chamber unit 10D.

[0058] Even if the radiant cooling of the cooler shown in Embodiment 1 does not provide sufficient cooling, and / or if the heat transfer rate is slow and the temperature control accuracy is insufficient with such radiant cooling, the use of a heat conductive material as shown in Embodiments 2 to 4 allows for heat conduction between the inner chamber and the cooler without transmitting vibrations. This enables sufficient cooling of the inner chamber and improves temperature control accuracy by increasing the heat transfer rate. More specifically, even if the temperature reached by radiation alone cannot be stabilized due to thermal disturbances or losses, the temperature can be stabilized by using a heat conductive material.

[0059] <Use of an inner chamber formed from multiple types of materials> Next, an embodiment including an inner chamber formed from two or more materials having different properties will be described.

[0060] <Embodiment 5> Figure 9 shows the configuration of the resonator 100E according to Embodiment 5. The resonator 100E includes an inner chamber 1E instead of the inner chamber 1A of the resonator 100A.

[0061] The mirror holding portion 11E of the inner chamber 1E is preferably made of a material with low thermal conductivity, and more specifically, a material with lower thermal conductivity than metal. This makes it more difficult for the mirrors 21 and 22 to cool down. In one embodiment, the mirror holding portion 11E is made of quartz glass.

[0062] In the example shown in Figure 9, the mirror holding portion 11E and the cooling portion 12E are connected by laser welding. Laser welding allows for a linear connection between the mirror holding portion 11E and the cooling portion 12E, thus reducing the connection area and improving the heat insulation effect. This makes it more difficult for the mirror holding portion 11E and the mirrors 21 and 22 to cool down. The cooling portion 12E is formed from a material (for example, metal) that can be laser welded to quartz glass. In one embodiment, the cooling portion 12E is formed from Kovar metal.

[0063] As described above, due to both the low thermal conductivity of the mirror holding portion 11E and the low thermal conductivity of the line contact between the cooling portion 12E and the mirror holding portion 11E, the mirrors 21 and 22 are not easily cooled even when the cooling portion 12E is cooled. Because the mirrors 21 and 22 are not easily cooled, condensation on the surface of the mirrors 21 and 22 due to cooling is less likely to occur. In addition, the risk of failure of the piezoelectric elements (not shown) placed on the mirrors 21 and 22 to adjust the resonator length due to cooling can be reduced.

[0064] <Embodiment 6> Figure 10 shows the configuration of the resonator 100F according to Embodiment 6. The resonator 100F includes an inner chamber 1F instead of the inner chamber 1A of the resonator 100A.

[0065] The inner chamber 1F includes a mirror holding portion 11F, a cooling portion 12F, and a welded bellows 13F. The welded bellows 13F connects the mirror holding portion 11F and the cooling portion 12F. By using the welded bellows 13F, heat conduction between the mirror holding portion 11F and the cooling portion 12F can be reduced. Furthermore, changes in the position of the mirror holding portion 11F due to the contraction of the cooling portion 12F can also be reduced. In this specification, a component that connects the mirror holding portion 11F and the cooling portion 12F, such as the welded bellows 13F, is also referred to as a "joint."

[0066] As described above, the welded bellows 13F of the resonator 100F, like the laser welding of the resonator 100E, can suppress heat conduction and reduce the effects of thermal shrinkage. Therefore, in the resonator 100F as well, the mirrors 21 and 22 are less likely to cool, thus reducing the likelihood of condensation on the surfaces of the mirrors 21 and 22. In addition, the risk of failure of the piezoelectric elements (not shown) placed on the mirrors 21 and 22 to adjust the resonator length due to cooling can be reduced. The welded bellows 13F may be a molded bellows or a softer bellows.

[0067] Preferably, within the outer chamber 3, the position of the mirror holding portion 11F in the resonator 100F is fixed with a material that has a low coefficient of expansion, thereby further improving the stability of the resonator length against temperature changes.

[0068] The cooling portion 12F is preferably made of a material with high cooling efficiency and high emissivity, for example, aluminum that has undergone black anodizing. The mirror holding portion 11F is made of, for example, Invar alloy.

[0069] <Uses joints made from a combination of multiple types of materials> Next, an embodiment will be described in which a joint made of two or more materials having different properties is used. More specifically, by connecting the mirror holding portion and the cooling portion of the inner chamber with a joint that combines a "material with a thermal conductivity of 1 or less" and a "material with high elasticity," the resonator length can be stabilized and the thermal conductivity can be reduced.

[0070] <Embodiment 7> Figure 11 shows the configuration of the resonator 100G according to Embodiment 7. The resonator 100G includes an inner chamber 1G in place of the inner chamber 1A of the resonator 100A. The inner chamber 1G includes a mirror holding portion 11G, a cooling portion 12G, and a joint 13G. The joint 13G includes a heat insulating member 131G and an expansion / contraction member 132G.

[0071] In Embodiment 7, by using a joint that combines the thermal insulation member 131G and the expansion member 132G, vibration and displacement of the mirrors 21 and 22 can be reduced compared to using a joint with only the thermal insulation member 131G, and the resonance length can be kept stable. Furthermore, compared to using a joint with only the expansion member 132G, problems such as condensation due to cooling of the mirrors 21 and 22 can be reduced.

[0072] Figures 12 and 13 show an example of the joint 13G according to Embodiment 7. Figure 12 discloses a joint 13G' formed by joining together an insulating member 131G and an expansion member 132G that are formed independently. With this configuration, it is easy to reuse the insulating member 131G and the expansion member 132G individually for other purposes, or to change the combination of the types of insulating member 131G and expansion member 132G.

[0073] Figure 13 discloses a joint 13G'' in which a thermal insulation member 131G and an expansion / contraction member 132G are integrally formed. With this configuration, the effort required to join and use separate thermal insulation members 131G and separate expansion / contraction members 132G in the resonator 100G of Figure 11 can be eliminated.

[0074] The support members 133G to 137G in Figures 12 and 13 support the thermal insulation member 131G and / or the expansion member 132G. The support members 133G to 137G have a hole formed in the center for the laser beam to pass through, or are made of a material that transmits laser beam. The support members 133G to 137G are, for example, metal flanges.

[0075] The thermal insulation member 131G is made of a material with a thermal conductivity of 1 or less. An example of a material for the insulating member 131G is glass, which has low thermal conductivity and is easily bonded to metals. An example of such glass is Kovar glass, which has a coefficient of thermal expansion similar to that of Kovar metal. The insulating member 131G is, for example, a glass flange.

[0076] Another example of a material for the thermal insulation member 131G is rubber. The thermal insulation member 131G is, for example, a rubber tube. Since it is difficult to form the rubber tube and the welded bellows as a single unit, it is appropriate to form them as separate parts, as shown in Figure 12. In this case, the rubber tube is connected to a flange (one of the support members 133G to 135G) with a hose clamp or the like.

[0077] The expandable member 132G is formed from a highly expandable material. An example of the expandable member 132G is a welded bellows. By using such a welded bellows, as described above, heat conduction from the cooling portion 12G to the mirror holding portion 11G can be suppressed, and the change in the position of the mirror holding portion 11G due to the thermal contraction of the cooling portion 12G can be reduced. The welded bellows may be a molded bellows or a softer bellows.

[0078] In one embodiment, the joint 13G is arranged such that the heat insulating member 131G is located on the mirror holding portion 11G side and the expansion member 132G is located on the cooling portion 12G side. In particular, if the expansion member 132G is a welded bellows, the heat insulating effect of the welded bellows itself prevents it from being cooled as much as if the heat insulating member 131G were located on the mirror holding portion 11G side. This reduces deterioration of the rubber due to cooling, for example, if the heat insulating member 131G is made of rubber.

[0079] <Example 1> Furthermore, the joints shown in Figures 12 and 13 can be used in other resonators as well, and by using them, it is possible to reduce vibration transmission to mirrors 21 and 22 and suppress the cooling of mirrors 21 and 22.

[0080] Figure 14 shows the configuration of the resonator 100H according to Modification 1. The resonator 100H according to Modification 1 includes a cooling plate 53H in addition to the configuration of the resonator 100G. The cooling plate 53H is, for example, a copper plate. In the resonator 100H, vibrations from the cooler 9 are more easily transmitted to the cooling section 12G than from the resonator 100G, but the coupling 13G mitigates conduction to the mirrors 21 and 22. Also, in the resonator 100H, the cooling section 12G is more easily cooled than from the resonator 100G, but the coupling 13G mitigates the cooling of the mirrors 21 and 22.

[0081] An example of an expansion / contraction member 132G included in the joint 13G is a welded bellows, as described above. By using this welded bellows, heat conduction from the cooling portion 12G to the mirror holding portion 11G is suppressed, the change in position of the mirror holding portion 11G due to thermal contraction of the cooling portion 12G is reduced, and the transmission of vibrations of the cooler 9 to the mirror holding portion 11G is reduced. The welded bellows may be a molded bellows or a softer bellows. From the viewpoint of suppressing vibrations to the mirrors 21 and 22, it is preferable that the spring constant of the welded bellows is 70 N / mm or less in the axial direction.

[0082] Based on the characteristics of the gas to be detected and the cooler 9, if it is considered that the measurement will not be hindered even if the cooling plate 53H is used, the resonator 100H can be used for measurement. Furthermore, when using the resonator 100H, if the cooling portion 12G is sufficiently cooled by heat conduction by the cooling plate 53H alone, there is no need to provide a cooling block to improve the cooling efficiency by radiation.

[0083] The configurations of the embodiments and modifications described above can be combined as appropriate, provided there are no inhibiting factors. For example, by using the heat conductive material shown in Embodiments 2 to 4 and the inner chamber formed of multiple types of members shown in Embodiments 5 to 7 in combination, it is possible to enhance the cooling effect of the cooling portion of the inner chamber, reduce changes in the resonator length due to cooling of the cooling portion, and reduce the risk of condensation due to cooling of the mirror holding portion.

[0084] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0085] [Aspect] Those skilled in the art will understand that the embodiments and their modifications described above are specific examples of the following embodiments.

[0086] (Section 1) The gas absorption spectrometer according to the present disclosure is a gas absorption spectrometer for measuring a sample gas, comprising: a resonator including at least two mirrors; a laser light source emitting laser light for irradiating the resonator; and a photodetector for detecting light extracted from the resonator. The resonator includes an inner chamber housing the mirrors and forming a measurement space into which the sample gas is introduced; an outer chamber disposed outside the inner chamber for vacuum insulating the measurement space from the outside; and a cooler disposed within the outer chamber, spaced apart from the inner chamber, and having an internal space through which a coolant flows.

[0087] In the gas absorption spectrometer described in paragraph 1, the inner chamber and the cooler are not in contact, so vibrations of the cooler caused by the flow of refrigerant through the cooler are not transmitted to the inner chamber. This makes it possible to cool the sample gas without degrading the measurement accuracy of the resonator. Therefore, by using a resonator, it is possible to accurately measure extremely low-temperature samples.

[0088] (Section 2) In the gas absorption spectrometer described in Section 1, the cooler is arranged to surround the inner chamber.

[0089] In the gas absorption spectrometer described in paragraph 2, the outer circumference of the inner chamber is wide and faces the cooler, thus improving cooling efficiency.

[0090] (3) The gas absorption spectrometer described in paragraph 1 or 2 further comprises a heat conductive material disposed between the inner chamber and the cooler, which mediates heat conduction between the inner chamber and the cooler.

[0091] In the gas absorption spectrometer described in paragraph 3, even if sufficient cooling cannot be expected by cooling by radiation of the cooler, and / or if the heat transfer rate is slow and the temperature control accuracy is insufficient with said cooling by radiation, sufficient cooling can be achieved and the heat transfer rate can be increased and the temperature control accuracy can be improved by using a heat conductive material.

[0092] (Section 4) In the gas absorption spectrometer described in Section 3, the thermal conductive material is in the form of wool.

[0093] In the gas absorption spectrometer described in paragraph 4, it is possible to improve the cooling efficiency of the inner chamber while suppressing the transmission of vibrations from the cooler to the inner chamber.

[0094] (Item 5) In the gas absorption spectrometer described in Item 4, the thermal conductivity of the thermal conductive material is 100 W / m·K or higher.

[0095] The gas absorption spectrometer described in Section 5 allows for efficient cooling. (Section 6) In the gas absorption spectrometer described in Section 3, the thermal conductive material is in the shape of a strap.

[0096] In the gas absorption spectrometer described in Section 6, it is possible to improve the cooling efficiency of the inner chamber while suppressing the transmission of vibrations from the cooler to the inner chamber.

[0097] (Section 7) In the gas absorption spectrometer described in Section 6, the thermal conductivity of the thermal conductive material is 100 W / m·K or higher.

[0098] The gas absorption spectrometer described in paragraph 7 allows for efficient cooling. (Section 8) In the gas absorption spectrometer described in Section 3, the thermal conductive material includes a cooling gas.

[0099] In the gas absorption spectrometer described in Section 8, it is possible to improve the cooling efficiency of the inner chamber while suppressing the transmission of vibrations from the cooler to the inner chamber.

[0100] (Section 9) In the gas absorption spectrometer described in any one of Sections 1 to 3, the inner chamber has a mirror holding portion on which a mirror is installed and a cooling portion between the mirror holding portions. The cooling portion is made of a material with an emissivity higher than a predetermined value.

[0101] In the gas absorption spectrometer described in paragraph 9, the inner chamber 1A can be cooled efficiently.

[0102] (Item 10) In the gas absorption spectrometer described in Item 9, the predetermined value is 0.8. In the gas absorption spectrometer described in Section 10, a sufficient radiation effect can be expected.

[0103] (Section 11) In the gas absorption spectrometer described in any one of Sections 1 to 3 and Sections 9 to 10, the inner chamber has a mirror holding portion on which a mirror is installed and a cooling portion between the mirror holding portions. The cooling portion is made of a material with a lower coefficient of thermal expansion than that of a metal.

[0104] In the gas absorption spectrometer described in paragraph 11, the resonator length is stable with respect to temperature changes.

[0105] (Section 12) In the gas absorption spectrometer described in any one of Sections 1 to 3 or 9 to 11, the inner chamber has a mirror holding portion on which a mirror is installed and a cooling portion between the mirror holding portions. The mirror holding portion is made of a material with a thermal conductivity lower than that of a metal.

[0106] In the gas absorption spectrometer described in paragraph 12, the mirror becomes difficult to cool. (Section 13) In the gas absorption spectrometer described in any one of Sections 1 to 3 or 9 to 12, the inner chamber has a mirror-holding section in which a mirror is installed and a cooling section between the mirror-holding sections. The mirror-holding section and the cooling section are connected by a welded bellows.

[0107] In the gas absorption spectrometer described in paragraph 13, the mirror becomes difficult to cool. (Section 14) In the gas absorption spectrometer described in any one of Sections 1 to 3 or 9 to 12, the inner chamber has a mirror-holding section in which a mirror is installed and a cooling section between the mirror-holding sections. The mirror-holding section and the cooling section are connected by laser welding.

[0108] In the gas absorption spectrometer described in paragraph 14, the mirror becomes difficult to cool. (Section 15) In the gas absorption spectrometer described in any one of Sections 1 to 3 or 9 to 12, the inner chamber has a mirror holding section in which mirrors are installed and a cooling section between the mirrors. The mirror holding section and the cooling section are connected by a joint combining an expansion / contraction member and a material with a thermal conductivity of 1 W / m·K or less.

[0109] In the gas absorption spectrometer described in Section 15, mirror vibration and displacement can be reduced, and the resonance length can be kept stable. Problems such as condensation caused by the cooling of the mirror can be reduced. [Explanation of Symbols]

[0110] 1 Inner chamber, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1P Inner chamber, 3 Outer chamber, 9 Cooler, 10, 10A, 10D, 10P Inner chamber unit, 11A, 11E, 11F, 11G Mirror holding part, 12A, 12E, 12F, 12G, 12H Cooling part, 13F Welded bellows, 13G Fitting, 15 Measurement space, 19, 39 Window material, 21, 22 Mirror, 30 Outer chamber unit, 35D, 55D Space, 41 Inlet pipe, 42 Outlet pipe, 43 Piezo element, 51B Wool, 51C Thermal strap, 53H Cooling plate, 80 Controller, 81 Processor, 82 Memory, 83 Laser light source, 84 AOM, 86 Photodetector, 91 Piping, 92 Refrigerant cooling section, 95, 95D Cooling block, 99 Cooler body, 100A, 100B, 100C, 100D, 100E, 100F, 100G, 100H, 100P Resonator, 131G Insulating member, 132G Expandable member, 133G, 135G, 137G Support member, 411 Inlet valve, 412 Outlet valve, 831 QCL, 832 Laser driver, 1000 Gas absorption spectrometer, AX Optical axis.

Claims

1. A gas absorption spectrometer for measuring sample gases, A resonator containing at least two mirrors, A laser light source that emits laser light for irradiating the aforementioned resonator, The system includes a photodetector that detects light extracted from the resonator, The aforementioned resonator is An inner chamber that houses the mirror and forms a measurement space into which the sample gas is introduced, An outer chamber is provided, which is located outside the inner chamber and vacuum-insulates the measurement space from the outside. A gas absorption spectrometer comprising a cooler positioned within the outer chamber, spaced apart from the inner chamber, and having an internal space through which a refrigerant flows.

2. The gas absorption spectrometer according to claim 1, wherein the cooler is arranged to cover the periphery of the inner chamber.

3. The gas absorption spectrometer according to claim 1 or 2, further comprising a heat conductive material disposed between the inner chamber and the cooler, which mediates heat conduction between the inner chamber and the cooler.

4. The gas absorption spectrometer according to claim 3, wherein the heat conductive material is in the form of wool.

5. The gas absorption spectrometer according to claim 4, wherein the thermal conductivity of the heat-conducting material is 100 W / m·K or more.

6. The gas absorption spectrometer according to claim 3, wherein the heat conductive material is in the shape of a strap.

7. The gas absorption spectrometer according to claim 6, wherein the thermal conductivity of the heat-conducting material is 100 W / m·K or more.

8. The gas absorption spectrometer according to claim 3, wherein the heat conductive material includes a cooling gas.

9. The inner chamber has a mirror holding portion on which the mirror is installed, and a cooling portion between the mirror holding portions. The gas absorption spectrometer according to claim 1 or 2, wherein the cooling portion is formed of a material with an emissivity higher than a predetermined value.

10. The gas absorption spectrometer according to claim 9, wherein the predetermined value is 0.

8.

11. The inner chamber has a mirror holding portion on which the mirror is installed, and a cooling portion between the mirror holding portions. The gas absorption spectrometer according to claim 1 or 2, wherein the cooling portion is formed of a material with a lower coefficient of thermal expansion than that of a metal.

12. The inner chamber has a mirror holding portion on which the mirror is installed, and a cooling portion between the mirror holding portions. The gas absorption spectrometer according to claim 1 or 2, wherein the mirror holding portion is formed of a material with lower thermal conductivity than metal.

13. The inner chamber has a mirror holding portion on which the mirror is installed, and a cooling portion between the mirror holding portions. The gas absorption spectrometer according to claim 1 or 2, wherein the mirror holding portion and the cooling portion are connected by a welded bellows.

14. The inner chamber has a mirror holding portion on which the mirror is installed, and a cooling portion between the mirror holding portions. The gas absorption spectrometer according to claim 1 or 2, wherein the mirror holding portion and the cooling portion are connected by laser welding.

15. The inner chamber has a mirror holding portion on which the mirror is installed and a cooling portion between the mirrors. The gas absorption spectrometer according to claim 1 or 2, wherein the mirror holding portion and the cooling portion are connected by a joint combining an expandable member and a material with a thermal conductivity of 1 W / m·K or less.

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