Open multi-reflection White cell infrared spectroscopic analysis system

Abstract

The present invention provides an open multi-reflection White cell infrared spectroscopic analysis system applicable to gas detection in a smog chamber, which includes a smog chamber, a Fourier transform infrared spectrometer and an industrial control computer, a multi-reflection White cell, a mirror, a pipeline and a lifting device, etc. The multi-reflection White cell includes a main mirror member, a secondary mirror member, a secondary mirror adjustment member, an incident and an exit parabolic mirror adjustment member, etc. The coupling methods between the spectrometer and the smog chamber mainly include an incident method, an exit method and a spectrometer installation method. In the incident method, by adjusting the plane mirror in the sample chamber, the modulated light is converged and incident on the smog chamber at a specific angle; in the exit method, through the turning of multiple plane mirrors, the exit light is guided back to the optical axis of the sample chamber; in the connection method, it is hermetically connected through a plane mirror mounting table and the smog chamber, and the spectrometer is hermetically connected to the mounting table through a pipeline; the spectrometer is mounted on a platform, and a lifting adjustment device is placed on the platform to ensure that the optical axis of the spectrometer is aligned with the optical axis of the smog chamber.

Description

Technical Field

[0001] The present invention belongs to the field of detection of atmospheric environmental gases, and particularly relates to an open multi-reflection White cell infrared spectroscopic analysis system. Background Art

[0002] A smog chamber, short for a photochemical smog chamber, is a device for studying the formation mechanism of photochemical smog and an important tool for simulating atmospheric photochemical reactions. Smog chamber experiments can simulate physical and chemical processes in a nearly real atmospheric environment under isolated complex source emission intensities and meteorological conditions, thereby ensuring strict boundary constraint conditions for model simulations. Through closed experiments of smog chamber experiments and model simulations, complex physical and chemical processes and mechanisms occurring in the atmosphere can be revealed, and thus a scientific basis can be provided for reasonable control countermeasures. A smog chamber is an essential scientific device for evaluating and constructing atmospheric chemical reaction mechanisms and obtaining accurate parameters for the formation mechanism of secondary aerosols. Infrared spectroscopic analysis technology is usually used for characterizing, identifying, and quantitatively analyzing various gaseous components and is an important method for component analysis.

[0003] Fourier transform infrared spectroscopy (FTIR) technology is one of the important methods for detecting atmospheric trace gas components and concentrations. According to the Lambert-Beer law, when the detection CV value is constant, the detectable gas concentration value is inversely proportional to the absorption optical path. This means that when detecting trace gases with relatively low concentrations, an absorption optical path of dozens or even hundreds of meters is required, and it is difficult for ordinary optical detection systems to meet this requirement. Therefore, a multi-reflection White cell is introduced, and through the multi-reflection principle of the White cell, the absorption optical path is increased in a limited space. Summary of the Invention

[0004] To overcome the technical problems that the optical-mechanical structure of the current closed cavity gas absorption cell is fixed, resulting in a fixed maximum effective optical path, and it cannot provide a longer effective optical path, higher detection sensitivity, and accuracy, the present invention provides an open multi-reflection White cell infrared spectroscopic analysis system to increase the maximum effective optical path and lower the detection limit of polluted gases, which is beneficial to improving the detection sensitivity and accuracy of the gas spectroscopic analysis system, and is particularly suitable for the gas spectroscopic analysis system of a smog chamber and the field gas detection system.

[0005] The multi-reflection White cell in the present invention is composed of three spherical concave mirrors with the same radius of curvature. Two concave mirrors B and C with smaller apertures are placed at one end of the White cell, and one concave mirror A with a larger aperture is placed at the other end of the White cell. The light source is incident on the concave mirror B from one side of the concave mirror A and is at a certain distance, and the concave mirrors B and C are symmetrically arranged with respect to the center of curvature of A. By adjusting the angles of the two small mirrors and the position and angle of the incident light, the light can be reflected back and forth multiple times in the White cell, thereby obtaining a larger optical path.

[0006] Introducing a multi-reflection White cell is one of the most effective methods to increase the absorption optical path and lower the detection limit of Fourier transform infrared spectrometers, and it makes the whole system more sensitive and accurate. The system mainly consists of a smog chamber, a Fourier transform infrared spectrometer and an industrial control computer, a multi-reflection White cell, a plane mirror and peripheral devices, etc. Among them, the spectral range of the FTIR spectrometer is 650 - 6500 cm -1 , and the maximum spectral resolution is 0.5 cm -1 , the spectral measurement speed is faster than 2 scan / s@cm -1 , and the spectral signal-to-noise ratio ≥ 45000:1 (peak-to-peak). The multi-reflection White cell mainly consists of structures such as a primary mirror component, a secondary mirror component, a secondary mirror adjustment component, an incident parabolic mirror adjustment component and an exit parabolic mirror adjustment component. The concave mirror uses infrared quartz glass, which has high infrared transmittance performance, and the transmittance is as high as more than 85%, and its application wavelength range is 260 - 3500 nm. A DM-25L differential micrometer is used in the adjustment mechanism. The DM-25L differential micrometer can provide sub-micron-level positioning and a 25-mm coarse adjustment stroke, with a sensitivity of 0.1 μm. It is the first actuator in the DM-L series that can lock the coarse adjustment stroke and the fine adjustment stroke through a single knob. Using the DM-25L differential micrometer greatly improves the adjustment accuracy, and also ensures the balance of the locking mechanism, facilitating the accurate and stable adjustment of the inclination of the secondary mirror, which plays an important role in the overall adjustment of the White cell, provides a more accurate adjustment mechanism for the entire multi-reflection White cell system, and also provides a more effective and convenient method and means for increasing the absorption optical path and lowering the detection limit of the Fourier transform infrared spectrometer.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] An open multi-reflection White cell infrared spectroscopic analysis system, comprising a smog chamber, a Fourier transform infrared spectrometer and an industrial control computer, a multi-reflection White cell and a plane mirror; the multi-reflection White cell comprises a primary mirror component, a secondary mirror component, a secondary mirror adjustment component, an incident parabolic mirror adjustment component and an exit parabolic mirror adjustment component;

[0009] The flat mirror mounting table is hermetically connected to the smoke chamber, and the Fourier transform infrared spectrometer is hermetically connected to the flat mirror mounting table through a pipeline. The Fourier transform infrared spectrometer is mounted on a platform, and a lifting and adjusting device is placed on the platform to ensure that the optical axis of the Fourier transform infrared spectrometer is aligned with the optical axis of the smoke chamber; the light outlet of the smoke chamber can transmit infrared light and is hermetically connected; the internal infrared light source in the Fourier transform infrared spectrometer emits an infrared beam that is collimated by a collimating mirror. By adjusting the flat mirror in the sample chamber, the modulated light converges and enters the smoke chamber at a specific angle, and then is reflected by the incident parabolic mirror, so that the modulated light converges and enters the multi-reflection White cell at a specific angle; the internal optical path of the multi-reflection White cell is realized by three spherical concave mirrors with the same radius of curvature. Among them, the large spherical concave mirror is mounted on the main mirror member and fixed by a snap; the two small spherical concave mirrors are mounted on the secondary mirror member and fixed with glue; when the modulated light is reflected multiple times, it leaves the smoke chamber through the exit parabolic mirror at the light outlet, and then is turned by multiple flat mirrors to guide the outgoing light back to the optical axis of the sample chamber and finally returns to the Fourier transform infrared spectrometer.

[0010] Further, a HeNe laser is used for optical path calibration; the laser beam enters the multi-reflection White cell along the optical axis of the modulated infrared beam of the Fourier transform infrared spectrometer through a reflecting mirror, and a parallel beam is generated through a collimating mirror for the initial positioning of the three spherical concave mirrors; after the initial alignment, the focusing mirror is adjusted to make the laser focus on the surface of the large spherical concave mirror. Then, by observing the laser spot at the aperture of the light outlet, the true situation of the beam aberration can be understood.

[0011] Further, the lens material of the spherical concave mirror is selected as infrared fused silica, and silver films are coated on all three spherical concave mirrors. The reflectivity of the coated spherical concave mirror to mid-infrared light reaches more than 98%.

[0012] Further, the multiple reflections of the internal optical path of the multi-reflection White cell are realized by a secondary mirror adjusting member; the secondary mirror adjusting member uses a concave sphere cut out on an intermediate plate, and then a corresponding positioning sphere is set. By combining the front plate and the screw pair, the adjustment of the two small spherical concave mirrors is jointly realized.

[0013] Further, a DM-25L differential micrometer is used as the screw pair to adjust the tilt angle; the sensitivity of the DM-25L differential micrometer is 0.1μm and it has a locking mechanism.

[0014] Beneficial effects:

[0015] In existing multi-reflection White cell infrared spectroscopy analysis systems, most use a closed-chamber White cell or an open optical path as a means to increase the optical path. However, the basic optical path of a closed-chamber White cell is fixed, and the adjustable range of the optical path is limited, unable to meet the requirements for a larger optical path. For an open optical path, an infrared light source needs to be installed several hundred meters away, requiring a larger experimental space. In the open White cell of the present invention, the basic optical path can be adjusted with the positions of the primary mirror and secondary mirror components, thereby achieving a larger adjustment of the optical path. A larger optical path can be realized in a limited space, which can greatly improve the lower limit of the detection concentration of the spectrometer. Moreover, a DM-25L differential micrometer is applied in the secondary mirror structure, greatly improving the adjustment accuracy, ensuring the balance of the locking mechanism, and facilitating the accurate and stable adjustment of the inclination of the secondary mirror. The optical path of this system is easy to align, and can maintain a small alignment error even under harsh environmental conditions. Also, this system is easy to set up and calibrate, and can operate even under harsh environmental conditions. Description of the Drawings

[0016] Figure 1 is a schematic diagram of the open multi-reflection White cell infrared spectroscopy analysis system of the present invention;

[0017] Figure 2 is a schematic diagram of the structural principle of the White cell;

[0018] Figure 3 is a schematic diagram of the internal structure of the smoke chamber;

[0019] Figure 4 is a schematic diagram of the primary mirror component;

[0020] Figure 5 is a schematic diagram of the secondary mirror component;

[0021] Figure 6 is a schematic diagram of the parabolic mirror adjustment component;

[0022] Figure 7 is a schematic diagram of the DM-25L differential micrometer.

[0023] Figure 3 In it: 1. Smoke chamber; 2. Primary mirror component; 3. Secondary mirror component; 4. Parabolic mirror adjustment component; 5. Thread pair;

[0024] Figure 4 In it: 4. Parabolic mirror adjustment component; 6. Large spherical concave mirror; 7. Snap fastener;

[0025] Figures 5 - 6 In it: 5. Thread pair; 8. Small spherical concave mirror; 9. Front plate; 10. Intermediate plate; 11. Positioning sphere; 12. Parabolic mirror probe; 13. Parabolic mirror probe positioning sphere; 14. Parabolic mirror probe intermediate plate; 15. Spring washer; 16. Socket head cap screw. Detailed Embodiments

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0027] As Figure 1 shown, an open multi-reflection White cell infrared spectroscopy analysis system of the present invention mainly includes a smoke chamber 1, a Fourier transform infrared spectrometer and an industrial control computer, a multi-reflection White cell, a plane mirror, a pipeline and a lifting device.

[0028] As Figure 3 , 4 , 5, and 6 shown, the multi-reflection White cell mainly includes a primary mirror member 2, a secondary mirror member 3, a secondary mirror adjustment member, a parabolic mirror adjustment member 4, etc. The parabolic mirror adjustment member 4 includes an incident parabolic mirror adjustment member and an exit parabolic mirror adjustment member. Among them, the parabolic mirror adjustment member 4 places a plane mirror on the parabolic mirror probe 12, cuts out a concave spherical shape on the middle plate 14 of the parabolic mirror probe, and then designs a corresponding parabolic mirror probe positioning sphere 13. The inner hexagon socket head screw 16 is used in cooperation with the spring washer 15 to hold down the middle plate 14 of the parabolic mirror probe to achieve 360° adjustment of the plane mirror. When the internal infrared light source in the Fourier transform infrared spectrometer emits an infrared beam, it is collimated by a collimating mirror, and then the plane mirror in the sample chamber is adjusted so that the modulated light converges and enters the smoke chamber 1 at a specific angle, and then is reflected by the incident parabolic mirror, and the modulated light converges and enters the multi-reflection White cell at a specific angle.

[0029] The present invention uses a HeNe laser for optical path calibration; the laser beam enters the multi-reflection White cell along the optical axis of the modulated infrared beam of the Fourier transform infrared spectrometer through a reflecting mirror, and a parallel beam is generated through a collimating mirror for the initial positioning of the three spherical concave mirrors; after the initial alignment, the focusing mirror is adjusted to make the laser focus on the surface of the large mirror, and then, by observing the laser spot at the light exit aperture, the true situation of the beam aberration is understood.

[0030] As Figure 2As shown in the figure, the internal optical path of the multi-reflection White cell is mainly realized by three spherical concave mirrors with the same radius of curvature. Among them, the large spherical concave mirror 6 is installed on the main mirror component 2 and fixed by a buckle 7. The fixing method of the buckle 7 makes the lens easy to disassemble and convenient for maintenance. Moreover, by replacing lenses of different apertures, the base length can be changed to adapt to different installation spaces and meet different optical path requirements. The two small spherical concave mirrors 8 are installed on the secondary mirror component 3 and fixed by glue. Silver films are coated on the surfaces of the three spherical concave mirrors. Silver has relatively stable physical and chemical properties and a very high reflectivity. It has a mid-infrared reflectivity of more than 98%, which can withstand mechanical cleaning better than gold films and is the most commonly used coating in this wavelength range. When the incident light enters the smoke chamber 1 and then enters the multi-reflection White cell through the incident parabolic mirror, the pitching angle and rolling angle of the two small spherical concave mirrors 8 are adjusted by the adjusting component in the secondary mirror component 3 to meet the requirements of the number of reflections and achieve the required optical path. Then, it leaves the smoke chamber through the exit parabolic mirror at the exit port, and then passes through multiple plane mirrors to deflect the outgoing light back to the optical axis of the sample chamber and return to the spectrometer to receive and detect the interference information. Finally, the collected interferogram is sent to the industrial control computer. The industrial control computer converts the interferogram into a spectrum through Fourier transform, and thus obtains the absorption spectrum of the entire measurement area. The absorption spectrum contains the concentration information of the gas to be measured.

[0031] As Figure 3 shown, the multi-reflection White cell is placed inside the smoke chamber 1. Since the multi-reflection White cell in the present invention is open, the main mirror component 2 and the secondary mirror component 3 of the multi-reflection White cell are respectively placed on the cement bases at both ends of the smoke chamber 1. The Fourier transform infrared spectrometer is outside the smoke chamber 1 and mounted on a platform. An elevation adjustment device is placed on the platform to ensure that the optical axis of the Fourier transform infrared spectrometer is aligned with the optical axis of the smoke chamber 1. The plane mirror mounting table is hermetically connected to the smoke chamber 1, and the Fourier transform infrared spectrometer is hermetically connected to the mounting table through a pipeline. The exit port of the smoke chamber 1 can transmit infrared light and requires a hermetic connection.

[0032] The incident end component includes an infrared light source and a collimating mirror that refracts and transforms the divergent light beam of the light source into a parallel beam. The exit end component includes a focusing mirror that refracts and transforms the outgoing parallel beam into an outgoing light spot, and a reflecting mirror that is optically connected to the Fourier transform infrared spectrometer. The two small spherical concave mirrors 8 of the multi-reflection White cell inside the smoke chamber 1 have the same structural dimensions and are installed on the secondary mirror component 3 at one end of the smoke chamber 1, while a large spherical concave mirror 6 is installed on the main mirror component 2 at the other end. The incident light entering the smoke chamber 1 is reflected multiple times in the three spherical concave mirrors and then exits the smoke chamber 1.

[0033] When selecting the material for the concave mirror, the lens material is selected as infrared quartz glass. In ordinary glass (such as Na2SiO3, CaSiO3, SiO2, or Na2O·CaO·6SiO2), in addition to SiO2, there are also some mixtures such as Na2SiO3, CaSiO3, and Na2O·CaO·6SiO2. Quartz glass is made mainly from pure quartz as the raw material, and its composition is only SiO2. It is an excellent basic material, and quartz glass sheets have many excellent physical and chemical properties. ① High temperature resistance: The melting point temperature of quartz glass is about 1730 °C; ② Corrosion resistance: Except for hydrofluoric acid, quartz glass hardly reacts chemically with other acid substances. Since the detection environment may contain SO2, CO2, H2S, HCl, nitrogen oxides, etc., which are likely to produce substances with certain acidity, the application of quartz glass can effectively protect the mirror surface. Its acid resistance is 30 times that of ceramics and 150 times that of stainless steel. Especially its chemical stability at high temperatures is unparalleled by any other engineering material; ③ Good thermal stability: The thermal expansion coefficient of the applicable glass is extremely small, with excellent thermal shock resistance, capable of withstanding drastic temperature changes, reducing the impact of temperature changes on the concave mirror, and thus reducing the deviation of the optical path; ④ Good light transmission performance: Quartz glass sheets have good light transmission performance in the entire spectral band from ultraviolet to infrared, and the visible light transmittance is above 93%; ⑤ Good electrical insulation performance: The resistance value of quartz glass is equivalent to 10,000 times that of ordinary glass, and it is an excellent electrical insulation material, with good electrical properties even at room temperature.

[0034] The apertures of the three spherical concave mirrors can be set according to actual requirements. For example, if designing a White cell with an incident beam diameter of 28 mm, a base length of 4.5 m, and a maximum allowable optical path of 270 m, the theoretical number of reflections of the White cell is 60 times, and the actual number of reflections is 50 times. The light enters the White cell at an inclination of 0.95°. The inclination angles of the two small spherical concave mirrors in the secondary mirror mechanism 3 are 1.61° and 1.5° respectively. Therefore, the adjustment accuracy of the inclination angles of the two small spherical concave mirrors should reach at least 0.01°. In the present invention, the adjustment of the two small spherical concave mirrors is completed through the secondary mirror adjustment member. The secondary mirror adjustment member mainly uses a concave sphere cut out on the middle plate 10, and then designs a corresponding positioning sphere 11. By combining the front plate 9 and the thread pair 5, the adjustment of the two small spherical concave mirrors is jointly realized.

[0035] Considering that when installing spherical concave mirrors with different apertures in the system, the required adjustment accuracy is also different, it is necessary to select or design different thread pairs to meet the corresponding adjustment accuracy requirements. Since the adjustment accuracy of this embodiment needs to reach below 0.01°, in the present invention, a DM-25L differential micrometer is used as the thread pair to adjust the inclination angle, as Figure 7 shown. Among them Figure 7Among them, A represents the coarse adjustment travel range of DM-25L, B represents the length of DM-25L, and C represents the distance from the adjustable knob to the bottom of DM-25L.

[0036] Since the sensitivity of the DM-25L differential micrometer is 0.1μm, the aperture of the small mirror of the White cell designed in the present invention is about 200mm. Through calculation, the DM-25L differential micrometer can make the adjustment accuracy of the secondary mirror reach below 0.01°, meeting the design requirements. Applying the DM-25L differential micrometer not only greatly improves the adjustment accuracy, but also it has a novel locking mechanism that clamps the non-threaded part of the screw from all sides. This stress-balanced design ensures the balance of the locking mechanism, facilitating the precise and stable adjustment of the inclination of the secondary mirror, which plays an important role in the overall adjustment of the White cell.

[0037] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An open multi-reflection White cell infrared spectroscopy analysis system, characterized in that: It includes a smog chamber, a Fourier transform infrared spectrometer, an industrial control computer, a multi-reflection White cell, and a plane mirror; the multi-reflection White cell includes a primary mirror member, a secondary mirror member, a secondary mirror adjustment member, an incident parabolic mirror adjustment member, and an exit parabolic mirror adjustment member; The plane mirror mounting table is hermetically connected to the smog chamber, and the Fourier transform infrared spectrometer is hermetically connected to the plane mirror mounting table through a pipeline. The Fourier transform infrared spectrometer is mounted on a platform, and a lifting adjustment device is placed on the platform to ensure that the optical axis of the Fourier transform infrared spectrometer is aligned with the optical axis of the smog chamber; the light outlet of the smog chamber can transmit infrared light and is hermetically connected; the internal infrared light source in the Fourier transform infrared spectrometer emits an infrared beam that is collimated by a collimating mirror. By adjusting the plane mirror in the sample chamber, the modulated light is converged and incident on the smog chamber at a specific angle, and then reflected by the incident parabolic mirror, so that the modulated light is converged and incident on the multi-reflection White cell at a specific angle; The internal optical path of the multi-reflection White cell is realized by three spherical concave mirrors with the same radius of curvature. Among them, the large spherical concave mirror is mounted on the primary mirror member and fixed by a snap fastener; the two small spherical concave mirrors are mounted on the secondary mirror member and fixed with glue; when the modulated light is reflected multiple times, it leaves the smog chamber through the exit parabolic mirror at the light outlet, and then turns through multiple plane mirrors to guide the outgoing light back to the optical axis of the sample chamber and finally returns to the Fourier transform infrared spectrometer; A HeNe laser is used for optical path calibration; A DM-25L differential micrometer is used as a screw pair to adjust the tilt angle; The multiple reflections of the internal optical path of the multi-reflection White cell are realized by the secondary mirror adjustment member; the secondary mirror adjustment member uses a concave sphere cut out on an intermediate plate and then sets a corresponding positioning sphere, and uses the combination of the front plate and the screw pair to jointly realize the adjustment of the two small spherical concave mirrors.

2. An open multi-reflection White cell infrared spectroscopic analysis system according to claim 1, characterized in that: The laser beam enters the multi-reflection White cell along the optical axis of the modulated infrared beam of the Fourier transform infrared spectrometer through a mirror, and a parallel beam is generated through a collimating mirror for the initial positioning of the three spherical concave mirrors; after the initial alignment, the focusing mirror is adjusted to focus the laser on the surface of the large spherical concave mirror. Then, by observing the laser spot at the aperture of the light outlet, the true situation of the beam distortion can be understood.

3. An open multi-reflection White cell infrared spectroscopic analysis system according to claim 1, characterized in that: The lens material of the spherical concave mirror is selected as infrared quartz glass, and silver films are coated on all three spherical concave mirrors. The reflectivity of the coated spherical concave mirror to mid-infrared band light reaches more than 98%.

4. An open multi-reflection White cell infrared spectroscopy analysis system according to claim 1, characterized in that: The sensitivity of the DM-25L differential micrometer is 0.1μm and it has a locking mechanism.

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