Multi-pass cell cavity structure capable of realizing rapid double-point calibration of single-concentration standard gas

Abstract

The invention relates to a multi-pass cell cavity structure capable of realizing single-concentration standard gas rapid double-point calibration, which is characterized by comprising a laser device, a cavity mirror I with an entrance port, a cavity mirror II with an entrance port, a reflecting mirror and a detector, and the laser device, the reflecting mirror and the detector are positioned on the outer side of the cavity mirror I; the first cavity mirror and the second cavity mirror are oppositely arranged, a double-face cavity mirror is arranged between the first cavity mirror and the second cavity mirror, emitted light of the laser enters the light cavity between the first cavity mirror and the second cavity mirror from the incidence port according to the incidence angle designed by the multi-pass cell, goes back and forth in the light cavity for multiple times and then is emitted out from the incidence port, and emitted emergent light enters the detector through the reflecting mirror. The detector is used for measuring laser intensity changes. The multi-pass cell cavity is ingenious in structure, double-point calibration based on single-concentration standard gas can be achieved through the additionally-arranged double-face cavity mirror, the calibration frequency can be reduced, the calibration rate can be increased, then the standard gas for calibration can be saved subsequently, the use cost can be reduced, and the use experience can be enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of optical detection, in particular to a multi-pass cell cavity structure capable of rapid double-point calibration with single-concentration standard gas. Background Art

[0002] Multi-pass cell technology is a method used in the field of optical detection to increase the interaction distance between the light beam and the gas sample, thereby improving the detection sensitivity. It is mainly composed of a specific number of reflectors. When the laser beam passes through the peripheral optical path and enters the multi-pass cell, it is constrained to reflect back and forth between the reflectors for multiple times before being emitted from the incident port to the outside of the cell, achieving an optical path of several meters to tens of meters. Multi-pass cell technology combined with tunable semiconductor laser absorption spectroscopy (TDLAS) technology has been widely used in many fields due to its advantages such as high sensitivity, high selectivity and rapid response, such as environmental monitoring, for air quality detection and greenhouse gas detection; for example, combustion efficiency evaluation and pollutant emission monitoring in combustion diagnosis; for example, respiratory gas analysis and blood gas analysis in medical diagnosis; for example, reaction process gas monitoring and leak monitoring in industrial control; for example, greenhouse gas management and soil gas analysis in agriculture. With the continuous advancement of technology, the application potential in more fields will be further explored.

[0003] The advantages of multi-pass cell technology mainly include: 1. Effectively increase the absorption optical path, and increase the optical path from a limited length of ten to tens of centimeters to several meters or even tens of meters, thereby improving the sensitivity of detecting gas; 2. Miniaturization and portability, suitable for on-site rapid monitoring and mobile monitoring; 3. The high-reflection cavity mirror of the multi-pass cell generally adopts metal film, which can be compatible with a wide range of wavelength response of 0.6-20 microns; 4. Flexible structural design, including White type, Herriott type, Chernin type, etc., can flexibly select the structural design according to application requirements.

[0004] However, the laser source of the multi-pass cell technology usually adopts off-axis incidence (off-axis incidence refers to the situation where the central axis of the light or optical element is not on the same straight line). The laser is reflected multiple times in the cavity. In order to ensure the performance and stability of the optical system and avoid interference problems caused by the overlap of light spots, it is required that the light spots on the cavity mirrors do not overlap as much as possible. This causes a slight change in the laser light path when the optomechanical structure is deformed or stress is released due to temperature, causing the light spots on the cavity mirrors to interfere or hit the side wall of the multi-pass cell, increasing the interference noise, and ultimately causing the long-term stability of the gas analyzer based on the multi-pass cell to be poor. Generally, high-precision temperature and pressure control can be used to solve part of the deformation of the optomechanical structure, but the impact caused by stress release cannot be completely eliminated.

[0005] At present, in practical applications, the effect of sensor drift on gas monitoring is generally reduced by increasing the calibration frequency. However, high-frequency calibration has the following disadvantages: 1. Calibration requires at least two high-precision calibration gases of different concentrations. High-frequency calibration consumes a large amount of calibration gas, which increases the user's cost; 2. The calibration process requires waiting for the calibration gas in the cavity to be replaced, which generally takes more than half an hour, resulting in a decrease in the effective data rate of the analyzer, affecting the user experience. Summary of the invention

[0006] In order to overcome the defects in the above-mentioned prior art, the object of the present invention is to provide a multi-pass cell cavity structure that can quickly perform dual-point calibration with single-concentration standard gas. The multi-pass cell cavity structure is ingenious. By adding a double-sided cavity mirror, dual-point concentration calibration based on single-concentration standard gas can be achieved, which can reduce the number of calibrations and increase the calibration rate, thereby saving the standard gas used for calibration, reducing the cost of use, and enhancing the user experience.

[0007] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme: a multi-pass cell cavity structure that can be used for rapid dual-point calibration with single-concentration standard gas, comprising a laser, a spherical cavity mirror 1 with an incident port, a spherical cavity mirror 2, a double-sided cavity mirror, a reflector and a detector, wherein the laser, the reflector and the detector are located on the outside of the spherical cavity mirror 1, the spherical cavity mirror 1 and the spherical cavity mirror 2 are arranged opposite to each other, and the double-sided cavity mirror is located between the spherical cavity mirror 1 and the spherical cavity mirror 2. The emitted light of the laser is emitted from the incident port into the optical cavity between the spherical cavity mirror 1 and the spherical cavity mirror 2 according to the incident angle designed by the multi-pass cell, and travels back and forth in the optical cavity for multiple times before being emitted from the incident port. The emitted light is emitted through the reflector and enters the detector, and the detector is used to measure the change in laser light intensity.

[0008] As a preferred solution of the present invention, there is one double-sided cavity mirror.

[0009] As a preferred embodiment of the present invention, the size of the incident angle is determined by the distance between the spherical cavity mirror 1 and the spherical cavity mirror 2, the size of the spherical cavity mirror 1, and the size of the spherical cavity mirror 2.

[0010] As a preferred solution of the present invention, the double-sided cavity mirror is located in the middle of the spherical cavity mirror 1 and the spherical cavity mirror 2 on the optical axis.

[0011] As a preferred solution of the present invention, the incident port is a circular hole structure.

[0012] As a preferred solution of the present invention, the incident port is arranged close to the edge of the spherical cavity mirror 1.

[0013] As a preferred solution of the present invention, the double-sided cavity mirror is a double-sided reflecting mirror, and the spherical cavity mirror 1 and the spherical cavity mirror 2 are both single-sided reflecting mirrors.

[0014] As a preferred solution of the present invention, the double-sided cavity mirror is circular or rectangular.

[0015] As a preferred solution of the present invention, the area of ​​the double-sided cavity mirror is larger than the area of ​​the light spot at any position in the cavity formed between the spherical cavity mirror 1 and the spherical cavity mirror 2.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: the multi-pass cell cavity structure of the present invention can be used for rapid double-point calibration with single-concentration calibration gas. The multi-pass cell cavity structure is ingenious. By adding a double-sided cavity mirror between spherical cavity mirror 1 and spherical cavity mirror 2, the existing optical path can be quickly doubled by the presence or absence of the double-sided cavity mirror. According to the Beer-Lambert law, under weak absorption conditions, it is approximately considered that the optical path and the absorption intensity are proportional. The absorption under the condition of 2 times the optical path is used as the high / low concentration calibration point, and the concentration calibration point under the original condition of 1 times the optical path is used to form a two-point calibration, thereby reducing the number of calibrations and increasing the calibration rate, and then subsequently being able to save calibration gas, reduce the cost of use, and enhance the user experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of a Herriott-type multi-pass pool device in the prior art; Figure 2 It is a partial structural schematic diagram of a multi-pass cell cavity structure capable of rapid dual-point calibration with single-concentration standard gas in the present invention; Figure 3 Schematic diagram of a light spot in which a double-sided cavity mirror is inserted to increase the number of reflections in the present invention; Figure 4 It is a schematic diagram of the structure of the traditional Herriott-type multi-pass cell absorption spectroscopy technology device used in Example 1; Figure 5 Schematic diagram of the light spot on the cavity mirror of the traditional Herriott multi-pass cell absorption spectroscopy technology used in Example 1; Figure 6 It is a structural schematic diagram of the multi-pass cell cavity structure of the present invention applied in Example 1; Figure 7 Schematic diagram of the light spot on the cavity mirror using the multi-pass cell cavity structure of the present invention in Example 1; Figure 8 It is a schematic diagram of the structure of the conventional Herriott-type multi-pass cell absorption spectroscopy technology device used in Example 2; Fig. 9Schematic diagram of the light spot on the cavity mirror of the traditional Herriott multi-pass cell absorption spectroscopy technology used in Example 2; Fig.10 It is a structural schematic diagram of the multi-pass cell cavity structure of the present invention used in Example 2; Fig.11 Schematic diagram of the light spot on the cavity mirror using the multi-pass cell cavity structure of the present invention in Example 2.

[0018] Figure numerals: 1. Laser; 2. Spherical cavity mirror 1; 2-1. Incident port; 3. Spherical cavity mirror 2; 4. Reflector; 5. Detector; 6. Double-sided cavity mirror. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is described below by the specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0020] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limitations on the present invention.

[0021] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0022] In the prior art, the effect of sensor drift on gas monitoring is generally reduced by increasing the calibration frequency. However, high-frequency calibration has the following main disadvantages: 1. Calibration requires at least two high-precision calibration gases of different concentrations, and high-frequency calibration consumes a large amount of calibration gas, increasing the user's cost; 2. The calibration process requires waiting for the calibration gas in the cavity to be replaced, which generally takes more than half an hour, resulting in a decrease in the effective data rate of the analyzer, affecting the user experience.

[0023] In order to solve the above technical problems, the present invention provides a multi-pass cell cavity structure that can quickly calibrate two points with a single concentration standard gas, which is based on the traditional Herriott type multi-pass cell device. Figure 1As shown, the conventional Herriott-type multi-pass cell device comprises a laser 1, a spherical cavity mirror 1 2 with an incident port 2-1, a spherical cavity mirror 2 3, a reflector 4 and a detector 5. The laser 1, the reflector 4 and the detector 5 are all arranged outside the spherical cavity mirror 1 2. In this embodiment, the spherical cavity mirror 1 2 and the spherical cavity mirror 2 3 are arranged opposite to each other and a double-sided cavity mirror 6 is arranged between the spherical cavity mirror 1 2 and the spherical cavity mirror 2 3. The double-sided cavity mirror 6 is located at the middle position between the spherical cavity mirror 1 2 and the spherical cavity mirror 2 3. Specifically, the distance between the spherical cavity mirror 1 2 and the spherical cavity mirror 2 3 can be designed and determined as needed. The double-sided cavity mirror 6 is a double-sided reflector. By adding a double-sided reflector between the spherical cavity mirror 1 2 and the spherical cavity mirror 2 3, the existing optical path is quickly doubled. According to the Beer-Lambert law, under weak absorption conditions, it is approximately assumed that the optical path and absorption intensity are proportional. The absorption at 2 times the optical path is used as the high / low concentration calibration point, and the concentration calibration point at the original 1 times the optical path is used to form a two-point calibration, thereby reducing the number of calibrations and increasing the calibration rate. This will subsequently save calibration gas, reduce usage costs, and enhance the user experience.

[0024] The emitted light of the above-mentioned laser 1 is incident from the above-mentioned incident port 2-1 into the optical cavity between the above-mentioned spherical cavity mirror 1 2 and the above-mentioned spherical cavity mirror 2 3 according to the incident angle designed by the multi-pass cell, and travels back and forth in the optical cavity for many times before being emitted from the above-mentioned incident port 2-1. The emitted light passes through the above-mentioned reflector 4 and enters the above-mentioned detector 5. The above-mentioned detector 5 is used to measure the change of laser light intensity. According to the beer-lambert law, the change of light intensity is positively correlated with the concentration of the gas, and then the concentration of the gas is calculated.

[0025] Among them, the purpose of setting the spherical cavity mirror 2-3 without a hole is to increase the number of laser reflections. The spherical cavity mirror 2 with the incident port 2-1 not only makes the laser reflection times more, but the incident port 2-1 also has the function of emission, that is, the laser needs to enter from the incident port 2-1, and after reflection, it is emitted from the incident port 2-1.

[0026] In the Herriott-type multi-pass cell design, the incident angle is related to the distance between the spherical cavity mirror 1 2 and the spherical cavity mirror 2 3 , the size of the spherical cavity mirror 1 2 , the size of the spherical cavity mirror 2 3 , the size of the double-sided cavity mirror 6 , and the number of round trips of the outgoing light.

[0027] The design parameters of the multi-pass cell cavity structure in the present invention mainly include the number of reflected light spots of a single lens N, the interval between two adjacent reflected light spots on the same cavity mirror is K, and according to the traditional multi-pass cell technology design theory, the angle between the two light spots is: In optics, cavity mirror curvature is usually used to describe the geometric characteristics of laser cavity mirrors, which has an important influence on the reflection, focusing and transmission characteristics of laser beams. The curvature of the cavity mirror designed in the present invention is R, according to the formula It can be found that the distance between the two cavity mirrors, namely the spherical cavity mirror 1 2 and the spherical cavity mirror 2 3, is d, and the corresponding optical path is approximately: In the present invention, the incident position and direction of the laser 1 are defined as parameters. The laser is incident at the incident port 2-1 of the cavity mirror with holes, i.e., the spherical cavity mirror 2, and its position coordinates are , the position coordinates of the outgoing light after n reflections are According to Herriott's existing theory, the calculation formula is: In the present invention, a small double-sided reflector, namely, double-sided cavity mirror 6, is added at the middle of the spherical cavity mirror 1 2 and the spherical cavity mirror 2 3. The position of the double-sided cavity mirror 6 just blocks one of the light paths. The shape of the double-sided cavity mirror 6 can be circular or square. The area of ​​the double-sided cavity mirror 6 needs to be larger than the area of ​​the light spot at any position in the cavity, and it cannot block the light spot on the adjacent light path. The specific position of the double-sided cavity mirror 6 needs to block any light path. Taking the Hth light as an example, according to the above formula, the coordinates of the center position of the double-sided cavity mirror 6 can be obtained as : The inserted double-sided cavity mirror 6 will change the original optical path, and there are two situations. In one case, when K=2, the inserted double-sided reflector, i.e., the double-sided cavity mirror 6, will be located at the intersection of the two optical paths, which will cause the optical path to be 1 / 2 of the original, i.e., the optical path is half of the original, L=Nd; in the other case, when K≠2, the double-sided reflector, i.e., the double-sided cavity mirror 6, has only one optical path, which will double the number of reflections, and add a light spot between the two adjacent light spots on the cavity mirror, as shown below Figure 3 As shown, the optical path will eventually be doubled, that is, L=4Nd.

[0028] In laser absorption spectroscopy, under weak absorption conditions, the absorption It can be approximately expressed as: Among them, P represents pressure; L is the absorption path; X is the gas concentration; S is the absorption line intensity; Ф is the absorption line function, so when L increases or decreases, other parameters remain unchanged, the absorption The same changes also occur.

[0029] In practical applications, gas analyzers based on multi-pass cell absorption spectroscopy display concentration C and absorption The relationship between them is: Therefore, when the optical path length becomes 1 / 2L or 2L, according to the above formula, the concentration becomes: According to the above formula, a gas analyzer based on a multi-pass cell can obtain the display value 1 / 2C or 2C of 1 / 2X or 2X standard gas by inserting a small double-sided reflector when a constant single concentration X standard gas is introduced. In this way, two sets of standard gas concentrations and display values ​​can be obtained, namely [X, C], [1 / 2X, 1 / 2C] or [X, C], [2X, 2C]. The analyzer can then be calibrated linearly at two points, thereby reducing the number of calibrations and increasing the calibration rate.

[0030] Implementation Cases: The implementation examples mainly include two cases: K≠2 and K=2. The following examples are presented with N=5, k=1 and k=2, the cavity mirror diameter is selected to be 50.8mm, and the cavity mirror curvature is fixed to 1000mm.

[0031] Example 1: Design and simulate Herriott multi-pass cell, N is 5, K is 1, d is 190.98mm, and the optical path is about Nd=1.910m. Application Figure 4 The conventional Herriott multi-pass cell absorption spectroscopy device shown in FIG. 1 has a light spot on the spherical cavity mirror 2 as shown in FIG. Figure 5 shown.

[0032] When a double-sided reflector is inserted, Figure 6 In the multi-pass cell cavity structure, the number of reflected light spots on a single cavity mirror doubles to 10, and the optical path is about 3.820m, which is twice the original one, so that the standard gas concentration and 2 times concentration double-point calibration can be achieved. The light spot on the spherical cavity mirror 23 is shown as follows: Figure 7 shown.

[0033] Example 2: Design and build a traditional Herriott multi-pass cell, design N to 5, K to 2, d to 690.983mm, optical path to about 6.910m, application such as Figure 8The conventional Herriott multi-pass cell absorption spectroscopy device shown in FIG. 1 has a light spot on the spherical cavity mirror 2 as shown in FIG. Fig. 9 shown.

[0034] When a double-sided reflector is inserted, Fig.10 When the multi-pass cell cavity structure is used, the optical path becomes half of the original one, that is, 3.455m, and the double-point calibration of the standard gas concentration and 1 / 2 standard gas concentration can be realized. The light spot on the spherical cavity mirror 23 is shown as follows Fig.11 shown.

[0035] The multi-pass cell cavity structure of the present invention can realize rapid double-point calibration with single-concentration standard gas. Through the new multi-pass cell optical design, the optical path in the cavity can be quickly reduced or doubled. According to the principle of laser weak absorption spectroscopy, the concentration of the gas to be measured can be approximately reduced or increased by 1 time. That is, the device can realize double-point linear calibration with single-concentration standard gas, which can save standard gas and reduce the use cost.

[0036] Traditional multi-concentration calibration requires waiting for the replacement time of the standard gas. Depending on the size of the cavity, each time a standard gas is introduced, it takes more than ten minutes to half an hour for the replacement and stabilization time. The present invention does not require the replacement of the standard gas, and through a reasonable optical-mechanical structure, a double-sided reflector can be quickly inserted. The two-point concentration can be obtained in a very short time for calibration, which greatly improves the data efficiency of the analyzer.

[0037] The present invention discloses a multi-pass cell cavity structure that can be used for rapid dual-point calibration with single-concentration standard gas. The multi-pass cell cavity structure is ingenious. By adding a double-sided cavity mirror between spherical cavity mirror 1 and spherical cavity mirror 2, the existing optical path can be changed to 1 / 2 or 2 times of the original. According to the Beer-Lambert law, under weak absorption conditions, it is approximately considered that the optical path and the absorption intensity are proportional. The absorption under 1 / 2 or 2 times the optical path is used as the low / high concentration calibration point, and the concentration calibration point under the original 1 times the optical path is used to form a two-point calibration, thereby reducing the number of calibrations and increasing the calibration rate. In addition, the calibration gas used can be saved in the future, reducing the use cost and enhancing the user experience.

[0038] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention; therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

[0039] Although the following terms are frequently used in this article: 1, laser; 2, spherical cavity mirror 1; 2-1, incident port; 3, spherical cavity mirror 2; 4, reflector; 5, detector; 6, double-sided cavity mirror, etc., the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. A multi-pass cell chamber structure capable of rapid dual-point calibration with single-concentration standard gas, characterized in that: The invention comprises a laser (1), a spherical cavity mirror (2) with an incident port (2-1), a spherical cavity mirror (3), a double-sided cavity mirror (6), a reflector (4) and a detector (5). The laser (1), the reflector (4) and the detector (5) are located outside the spherical cavity mirror (2). The spherical cavity mirror (2) and the spherical cavity mirror (3) are arranged opposite to each other. The double-sided cavity mirror (6) is located between the spherical cavity mirror (2) and the spherical cavity mirror (3). The emitted light of the laser (1) is incident from the incident port (2-1) into the optical cavity between the spherical cavity mirror (2) and the spherical cavity mirror (3) according to the incident angle designed by the multi-pass cell, and travels back and forth in the optical cavity for multiple times before being emitted from the incident port (2-1). The emitted light passes through the reflector (4) and enters the detector (5). The detector (5) is used to measure the change of laser light intensity.

2. The multi-pass cell chamber structure capable of rapid dual-point calibration with single-concentration standard gas according to claim 1, characterized in that: The double-sided cavity mirror (6) is one.

3. The multi-pass cell chamber structure capable of rapid dual-point calibration with single-concentration standard gas according to claim 1, characterized in that: The size of the incident angle is determined by the distance between the spherical cavity mirror 1 (2) and the spherical cavity mirror 2 (3), the size of the spherical cavity mirror 1 (2), and the size of the spherical cavity mirror 2 (3).

4. The multi-pass cell chamber structure capable of rapid dual-point calibration with single-concentration standard gas according to claim 1, characterized in that: The double-sided cavity mirror (6) is located on the optical axis in the middle of the spherical cavity mirror 1 (2) and the spherical cavity mirror 2 (3).

5. The multi-pass cell chamber structure capable of rapid dual-point calibration with single-concentration standard gas according to claim 1, characterized in that: The incident port (2-1) is a circular hole structure.

6. The multi-pass cell chamber structure capable of rapid dual-point calibration with single-concentration standard gas according to claim 5, characterized in that: The incident port (2-1) is arranged close to the edge of the spherical cavity mirror 1 (2).

7. The multi-pass cell chamber structure capable of rapid dual-point calibration with single-concentration standard gas according to claim 1, characterized in that: The double-sided cavity mirror (6) is a double-sided reflecting mirror, and the spherical cavity mirror 1 (2) and the spherical cavity mirror 2 (3) are both single-sided reflecting mirrors.

8. The multi-pass cell chamber structure capable of rapid dual-point calibration with single-concentration standard gas according to claim 7, characterized in that: The double-sided cavity mirror (6) is circular or rectangular.

9. The multi-pass cell chamber structure capable of rapid dual-point calibration with single-concentration standard gas according to claim 7, characterized in that: The area of ​​the double-sided cavity mirror (6) is larger than the area of ​​the light spot at any position in the cavity formed between the spherical cavity mirror 1 (2) and the spherical cavity mirror 2 (3).

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