A multi-pass cell cavity structure capable of quickly calibrating two points with a single-concentration standard gas

Abstract

The present invention relates to a multi-pass cell cavity structure capable of quickly performing double-point calibration with a single-concentration calibration gas, which includes a laser, a first cavity mirror with an incident port, a second cavity mirror, a reflector, and a detector. The laser, the reflector, and the detector are located outside the first cavity mirror. The first cavity mirror and the second cavity mirror are arranged opposite to each other, and a double-sided cavity mirror is provided between the first cavity mirror and the second cavity mirror. The emitted light of the laser enters the optical cavity between the first cavity mirror and the second cavity mirror from the incident port according to the incident angle designed by the multi-pass cell, and travels back and forth multiple times in the optical cavity and then exits from the incident port. The emitted light that exits is directed into the detector through the reflector, and the detector is used to measure the change in laser light intensity. This multi-pass cell cavity structure is ingenious. By adding the double-sided cavity mirror, double-point calibration can be achieved based on a single-concentration calibration gas, which can reduce the number of calibration times, improve the calibration rate, and subsequently save the calibration gas used, reduce the usage cost, and enhance the usage experience.

Description

Technical Field

[0001] The present invention relates to the technical field of optical detection, and specifically to a multi-pass cell cavity structure capable of quickly double-point calibrating a single-concentration standard gas. Background Art

[0002] The multi-pass cell technology is a method used in the field of optical detection to increase the interaction distance between a light beam and a gas sample, thereby improving the detection sensitivity. It mainly consists of a specific number of mirrors. When a laser beam is incident into the multi-pass cell through the peripheral optical path, it is constrained to reflect back and forth between the mirrors multiple times and then exits the cell from the entrance to achieve an optical path of several meters to dozens of meters. The multi-pass cell technology combined with tunable diode laser absorption spectroscopy (TDLAS) has been widely applied in many fields due to its advantages such as high sensitivity, high selectivity, and fast response. For example, in environmental monitoring, it is used for air quality detection and greenhouse gas detection; for example, in combustion diagnostics, it is used for combustion efficiency evaluation and pollutant emission monitoring; for example, in medical diagnostics, it is used for respiratory gas analysis and blood gas analysis; for example, in industrial control, it is used for monitoring process gases and leakage detection; for example, in agriculture, it is used for greenhouse gas management and soil gas analysis, etc. With the continuous progress of technology, its application potential in more fields will be further explored.

[0003] The advantages of the multi-pass cell technology mainly include: 1. Effectively increasing the absorption optical path, which can increase the optical path from more than ten to dozens of centimeters to several meters or even dozens of meters, thereby improving the sensitivity of detecting gases; 2. Miniaturization and portability, suitable for on-site rapid monitoring and mobile monitoring; 3. The high-reflection cavity mirrors of the multi-pass cell generally use metal films, which can be compatible with a wide range of wavelength responses from 0.6 to 20 microns; 4. Flexible structure design, including White type, Herriott type, Chernin type, etc., and the structure design can be flexibly selected 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 axes of light rays or optical elements are not on the same straight line). The laser reflects multiple times in the cavity. To ensure the performance and stability of the optical system and avoid interference problems caused by spot coincidence, it is required that the spots on the cavity mirrors do not coincide as much as possible. This leads to when the optomechanical structure deforms or stress is released due to temperature effects, it causes slight changes in the laser optical path, resulting in interference of the spots on the cavity mirrors or hitting the side walls of the multi-pass cell, increasing the interference noise, and ultimately causing poor long-term stability of the gas analyzer based on the multi-pass cell. Generally, part of the deformation of the optomechanical structure can be solved by high-precision temperature and pressure control, but the influence caused by stress release cannot be completely eliminated.

[0005] Currently, in practical applications, generally increasing the calibration frequency is adopted to reduce the impact of sensor drift on gas monitoring. However, high-frequency calibration mainly has the following disadvantages: 1. Calibration requires at least two different concentrations of high-precision calibration gases. High-frequency calibration consumes a large amount of calibration gases, increasing the user's usage cost; 2. The calibration process requires waiting for the replacement of the calibration gas in the cavity, generally taking more than half an hour, resulting in a decrease in the effective data rate of the analyzer and affecting the user experience. Summary of the Invention

[0006] In order to overcome the above defects in the prior art, the invention purpose of the present invention is to provide a multi-pass cell cavity structure capable of quickly double-point calibrating with a single concentration of calibration gas. The multi-pass cell cavity structure is ingenious. By adding a double-sided cavity mirror, double-point concentration calibration based on a single concentration of calibration gas can be realized, which can reduce the calibration times, improve the calibration rate, and then save the calibration gas used subsequently, reduce the usage cost, and enhance the user experience.

[0007] In order to achieve the above invention purpose, the present invention adopts the following technical solutions: A multi-pass cell cavity structure capable of quickly double-point calibrating with a single concentration of calibration gas, including a laser, a spherical mirror one with an incident port, a spherical mirror two, a double-sided cavity mirror, a reflecting mirror, and a detector. The laser, the reflecting mirror, and the detector are located outside the spherical mirror one. The spherical mirror one and the spherical mirror two are arranged opposite to each other. The double-sided cavity mirror is located between the spherical mirror one and the spherical mirror two. The emitted light of the laser enters the optical cavity between the spherical mirror one and the spherical mirror two from the incident port according to the incident angle designed by the multi-pass cell, travels back and forth in the optical cavity multiple times, and then exits from the incident port. The emitted light after exiting passes through the reflecting mirror 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 solution of the present invention, the magnitude of the incident angle is determined by the distance between the spherical mirror one and the spherical mirror two, the size of the spherical mirror one, and the size of the spherical mirror two.

[0010] As a preferred solution of the present invention, the double-sided cavity mirror is located at the exact middle position between the spherical mirror one and the spherical mirror two 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 mirror one.

[0013] As a preferred embodiment of the present invention, the double-sided mirror is a double-sided reflector, and the first spherical mirror and the second spherical mirror are both single-sided reflectors.

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

[0015] As a preferred embodiment of the present invention, the area of the double-sided mirror is larger than the area of the light spot at any position within the cavity formed between the first spherical mirror and the second spherical mirror.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: A multi-pass cell cavity structure capable of quickly double-point calibration with a single-concentration standard gas in the present invention has a clever structure. By adding a double-sided mirror between the first spherical mirror and the second spherical mirror, the existing optical path can be quickly doubled with or without this double-sided mirror. According to the Beer-Lambert law, under weak absorption conditions, it is approximately considered that the optical path is proportional to the absorption intensity. Taking the absorption in the case of double optical path as the high / low concentration calibration points, and combining them with the concentration calibration points in the case of the original single optical path for two-point calibration, thus reducing the calibration times, improving the calibration rate, and then saving the standard gas used for calibration, reducing the use cost, and enhancing the user experience in the subsequent process. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic structural diagram of a Herriott-type multi-pass cell device in the prior art;

[0018] Figure 2 is a partial schematic structural diagram of a multi-pass cell cavity structure capable of quickly double-point calibration with a single-concentration standard gas in the present invention;

[0019] Figure 3 is a schematic diagram of the light spot for increasing the number of reflections by inserting a double-sided mirror in the present invention;

[0020] Figure 4 is a schematic structural diagram of a traditional Herriott-type multi-pass cell absorption spectroscopy technology device applied in Example 1;

[0021] Figure 5 is a schematic diagram of the light spot situation on the mirror of a traditional Herriott-type multi-pass cell absorption spectroscopy technology applied in Example 1;

[0022] Figure 6 is a schematic structural diagram of the multi-pass cell cavity structure of the present invention applied in Example 1;

[0023] Figure 7 is a schematic diagram of the light spot situation on the mirror of the multi-pass cell cavity structure of the present invention applied in Example 1;

[0024] Figure 8 Schematic structural diagram of a traditional Herriott-type multi-pass cell absorption spectroscopy technology device applied in Example 2;

[0025] Figure 9 Schematic diagram of the light spot situation on the cavity mirror of the traditional Herriott-type multi-pass cell absorption spectroscopy technology applied in Example 2;

[0026] Figure 10 Schematic structural diagram of the multi-pass cell cavity structure of the present invention applied in Example 2;

[0027] Figure 11 Schematic diagram of the light spot situation on the cavity mirror of the multi-pass cell cavity structure of the present invention applied in Example 2.

[0028] Reference numerals: 1, laser; 2, first spherical cavity mirror; 2-1, incident port; 3, second spherical cavity mirror; 4, reflecting mirror; 5, detector; 6, double-sided cavity mirror. Detailed implementation manners

[0029] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be described below through specific embodiments shown in the drawings. However, it should be understood that these descriptions are merely exemplary and do not limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0030] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0031] The embodiments of the present invention will be described in detail below with reference to the drawings.

[0032] In the prior art, generally, increasing the calibration frequency is adopted to reduce the influence of sensor drift on gas monitoring. However, the high-frequency calibration mainly has the following disadvantages: 1. Calibration requires at least two different concentrations of high-precision calibration gases, and high-frequency calibration consumes a large amount of calibration gases, increasing the user's usage cost; 2. The calibration process requires waiting for the replacement of the calibration gas in the cavity, generally taking more than half an hour, resulting in a reduction in the effective data rate of the analyzer and affecting the user experience.

[0033] To solve the above technical problems, the present invention provides a multi-pass cell cavity structure capable of quickly performing double-point calibration with a single-concentration calibration gas, which is based on a traditional Herriott-type multi-pass cell device. AsFigure 1 As shown in the figure, the traditional Herriott-type multi-pass cell device includes a laser 1, a spherical mirror 1 with an incident port 2-1, a spherical mirror 2 3, a reflector 4, and a detector 5. The above-mentioned laser 1, the above-mentioned reflector 4, and the above-mentioned detector 5 are all arranged outside the above-mentioned spherical mirror 1. In this embodiment, the spherical mirror 1 and the spherical mirror 2 3 are arranged opposite to each other, and a double-sided mirror 6 is provided between the spherical mirror 1 and the spherical mirror 2 3. The double-sided mirror 6 is located at the middle position between the spherical mirror 1 and the spherical mirror 2 3. Specifically, the distance between the spherical mirror 1 and the spherical mirror 2 3 can be designed and determined as required. The double-sided mirror 6 is a double-sided reflector. By adding a double-sided reflector between the spherical mirror 1 and the spherical mirror 2 3, the existing optical path is quickly doubled. According to the Beer-Lambert law, under weak absorption conditions, it is approximately considered that the optical path is proportional to the absorption intensity. The absorption in the case of a 2-fold optical path is used as the high / low concentration calibration point, and it forms a two-point calibration with the concentration calibration point in the case of the original 1-fold optical path, thereby reducing the calibration times, improving the calibration rate, and then saving the calibration gas used later, reducing the use cost, and enhancing the use experience.

[0034] The emitted light of the above-mentioned laser 1 enters the optical cavity between the spherical mirror 1 and the spherical mirror 2 3 from the above-mentioned incident port 2-1 according to the incident angle designed by the multi-pass cell, and travels back and forth in the optical cavity multiple times and then exits from the above-mentioned incident port 2-1. The emitted light exits and 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 in laser light intensity. According to the beer-lambert law, the change in light intensity is positively correlated with the concentration of the gas, and then the concentration of the gas is calculated.

[0035] Among them, the purpose of setting the spherical mirror 2 3 without holes is to increase the number of laser reflections. In addition to making the number of laser reflections more, the incident port 2-1 on the spherical mirror 1 with the incident port 2-1 also has the function of emitting, that is, the laser needs to enter from the incident port 2-1, and after reflection, it exits from the incident port 2-1.

[0036] In the Herriott-type multi-pass cell design, the incident angle is related to the distance between the spherical mirror 1 and the spherical mirror 2 3, the size of the spherical mirror 1, the size of the spherical mirror 2 3, the size of the double-sided mirror 6, and the number of round trips of the emitted light.

[0037] The design parameters of the multi-pass cell cavity structure in the present invention mainly include the number of reflected light spots N of a single lens, and the interval K between two adjacent reflected light spots on the same mirror. According to the traditional multi-pass cell technology design theory, the angle between two light spots is:

[0038] θ = kπ / N

[0039] In optics, the curvature of a cavity mirror is usually used to describe the geometric characteristics of a laser cavity mirror, which has an important influence on the reflection, focusing, and transmission characteristics of a laser beam. In the present invention, the curvature of the designed cavity mirror is R. According to the formula

[0040] d = R·(1 - cos(θ))

[0041] the distance d between the two cavity mirrors, namely the above-mentioned spherical cavity mirror 2 and the above-mentioned spherical cavity mirror 3, can be obtained, and the corresponding optical path is approximately:

[0042] L = Nd

[0043] 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, namely the spherical cavity mirror 2, and its position coordinates are (x0, y0, x′0, y′0). After n reflections, the position coordinates of the outgoing light ray are (x n , y n , x′ n , y′ n ). According to the existing Herriott theory, the calculation formula is obtained as:

[0044] x n = x0·cos nθ

[0045] y n = x0·sin nθ

[0046]

[0047] In the present invention, by adding a small double-sided mirror, namely the double-sided cavity mirror 6, at the middle position between the above-mentioned spherical cavity mirror 2 and the above-mentioned spherical cavity mirror 3, the position of the double-sided cavity mirror 6 just blocks one of the optical 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 inside the cavity and cannot block the light spots on adjacent optical paths. The specific position of the above-mentioned double-sided cavity mirror 6 needs to block any one of the optical paths. Taking the Hth light ray as an example, according to the above formula, the coordinates of the center position of the inserted double-sided cavity mirror 6 can be obtained as (H x , H y ):

[0048]

[0049] The inserted double-sided mirror 6 will change the original optical path, and there are the following two situations. In one situation, when K = 2, the inserted double-sided mirror, that is, the double-sided 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, that is, the optical path is half of the original, L = Nd. In the other situation, when K ≠ 2, there is only one optical path at the position of the double-sided mirror, that is, the double-sided mirror 6, which will increase the number of reflections by one time, and add a spot between the two originally adjacent spots on the mirror. As follows Figure 3 As shown, it will finally double the optical path, that is, L = 4Nd.

[0050] In laser absorption spectroscopy, under weak absorption conditions, the absorption α can be approximately expressed as:

[0051] α = PLXSφ

[0052] Where P represents pressure; L is the absorption optical path; X is the gas concentration; S is the absorption line intensity; Ф is the absorption line shape function. Therefore, when L increases or decreases and other parameters remain unchanged, the absorption α also changes in the same way.

[0053] In practical applications, the relationship between the displayed concentration C and the absorption α of a gas analyzer based on a multi-pass cell absorption spectrum is:

[0054] C = ρα

[0055] Therefore, when the optical path becomes 1 / 2L or 2L, according to the above formula, the concentration becomes:

[0056] 1 / 2C = 1 / 2ρPLXSφ

[0057] 2C = ρPLXSφ

[0058] According to the above formula, a gas analyzer based on a multi-pass cell can, when introducing a constant single-concentration X standard gas, obtain the displayed values 1 / 2C or 2C of 1 / 2X or 2X standard gas by inserting a small double-sided mirror. In this way, two sets of standard gas concentrations and displayed values, namely [X, C], [1 / 2X, 1 / 2C] or [X, C], [2X, 2C], can be obtained, and the analyzer can be calibrated linearly at two points, thereby reducing the number of calibrations and improving the calibration rate.

[0059] Implementation cases:

[0060] The implementation examples mainly include two situations of K ≠ 2 and K = 2. The following examples show with N being 5, k = 1 and k = 2, and the mirror diameter is selected as 50.8 mm, and the mirror curvature is fixed at 1000 mm.

[0061] Example 1: Design and simulate a Herriott multi-pass cell. When N = 5 and K = 1, d = 190.98 mm can be obtained, and the optical path is approximately Nd = 1.910 m. Apply the traditional Herriott-type multi-pass cell absorption spectroscopy technology device as shown in Figure 4 . The spot situation on the spherical mirror 2 is as shown in Figure 5 .

[0062] When inserting a double-sided mirror, that is, adopting the multi-pass cell cavity structure in Figure 6 , the number of reflected spots on a single mirror doubles to 10, and the optical path is approximately 3.820 m, which becomes twice the original. Thus, dual-point calibration of the standard gas concentration and twice the concentration can be achieved. The spot situation on the spherical mirror 3 is as shown in Figure 7 .

[0063] Example 2: Design and build a traditional Herriott multi-pass cell. Design N = 5 and K = 2, d = 690.983 mm, and the optical path is approximately 6.910 m. Apply the traditional Herriott-type multi-pass cell absorption spectroscopy technology device as shown in Figure 8 . The spot situation on the spherical mirror 2 is as shown in Figure 9 .

[0064] When inserting a double-sided mirror, that is, adopting the multi-pass cell cavity structure in Figure 10 , the optical path becomes half of the original, which is 3.455 m. Dual-point calibration of the standard gas concentration and 1 / 2 of the standard gas concentration can be achieved. The spot situation on the spherical mirror 3 is as shown in Figure 11 .

[0065] A multi-pass cell cavity structure capable of rapid dual-point calibration with a single-concentration standard gas in the present invention can rapidly reduce or double the optical path inside the cavity through a new multi-pass cell optical design. According to the principle of laser weak absorption spectroscopy, it can be approximated that the concentration of the gas to be measured is reduced or increased by 1 time, that is, dual-point linear calibration can be achieved with a single-concentration standard gas by this device, which can save the standard gas and reduce the use cost.

[0066] Traditional multi-concentration calibration requires the replacement time of the standard gas. According to the size of the cavity, it takes more than ten minutes to half an hour for each introduction of a standard gas to reach a stable replacement time. The present invention does not require replacing the standard gas, and the double-sided mirror can be quickly inserted through a reasonable optomechanical structure, and two-point concentrations can be obtained for calibration in a very short time, greatly improving the data efficiency of the analyzer.

[0067] A multi-pass cell cavity structure capable of quickly performing double-point calibration with a single-concentration calibration gas in the present invention. This multi-pass cell cavity structure is ingenious. By adding a double-sided mirror between the first spherical mirror and the second spherical mirror, the existing optical path can be changed to 1 / 2 times or 2 times the original. According to the Beer-Lambert law, under weak absorption conditions, it is approximately considered that the optical path is proportional to the absorption intensity. The absorption in the case of 1 / 2 or 2 times the optical path is used as the low / high concentration calibration point, and together with the concentration calibration point in the case of 1 times the original optical path, it forms a two-point calibration, thereby reducing the calibration times, increasing the calibration rate, and subsequently being able to save the calibration gas used, reduce the usage cost, and enhance the usage experience.

[0068] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can 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 these embodiments shown herein, but rather will conform to the widest scope consistent with the principles and novel features disclosed herein.

[0069] Although the terms such as 1. laser; 2. the first spherical mirror; 2-1. incident port; 3. the second spherical mirror; 4. reflector; 5. detector; 6. double-sided mirror and other terms are used more in the drawings herein, the possibility of using other terms is not excluded. These terms are only used 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 cavity structure capable of quickly calibrating two points with a single-concentration calibration gas, characterized in that: It includes a laser (1), a first spherical cavity mirror (2) with an incident port (2-1), a second 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 first spherical cavity mirror (2). The first spherical cavity mirror (2) and the second spherical cavity mirror (3) are arranged oppositely. The double-sided cavity mirror (6) is a double-sided reflector and is located between the first spherical cavity mirror (2) and the second 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 first spherical cavity mirror (2) and the second spherical cavity mirror (3) according to the incident angle designed by the multi-pass cell, and travels back and forth in the optical cavity multiple times and then exits from the incident port (2-1). The emitted light after exiting passes through the reflector (4) and enters the detector (5); 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 optical cavity and cannot block the light spots on adjacent optical paths; the detector (5) is used to measure the change in laser light intensity.

2. The multi-pass cell cavity structure capable of quickly performing double-point calibration with a single-concentration calibration gas according to claim 1, wherein: There is one double-sided cavity mirror (6).

3. The multi-pass cell cavity structure capable of quickly calibrating two points with a single-concentration calibration gas according to claim 1, wherein: The magnitude of the incident angle is determined by the distance between the first spherical cavity mirror (2) and the second spherical cavity mirror (3), the size of the first spherical cavity mirror (2), and the size of the second spherical cavity mirror (3).

4. A multi-pass cell cavity structure capable of quickly performing double-point calibration with a single-concentration calibration gas according to claim 1, characterized in that: The double-sided cavity mirror (6) is located at the exact middle position between the first spherical cavity mirror (2) and the second spherical cavity mirror (3) on the optical axis.

5. A multi-pass cell cavity structure capable of quickly performing double-point calibration with a single-concentration calibration gas according to claim 1, characterized in that: The incident port (2-1) has a circular hole structure.

6. A multi-pass cell cavity structure capable of quickly performing double-point calibration with a single-concentration calibration gas according to claim 5, characterized in that: The incident port (2-1) is arranged close to the edge of the first spherical cavity mirror (2).

7. A multi-pass cell cavity structure capable of quickly performing double-point calibration with a single-concentration calibration gas according to claim 1, characterized in that: Both the first spherical cavity mirror (2) and the second spherical cavity mirror (3) are single-sided reflectors.

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

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