A gas concentration detection device

Abstract

The utility model provides a kind of gas concentration detection device, belong to gas detection field, including laser frequency relay, first optical frequency comb, second optical frequency comb, the output end of laser frequency relay is connected to the input end of first beam splitter, the output end of first beam splitter is divided into two ways, one way is connected to the input end of second beam splitter, another way is connected to the input end of third beam splitter, the output end of first optical frequency comb is connected to the input end of second beam splitter, the output end of second optical frequency comb is connected to the input end of third beam splitter, the output end of second beam splitter is divided into two ways, the output end of third beam splitter is divided into two ways, using laser frequency relay provides laser frequency reference for two optical frequency combs, utilizes the time resolution characteristics of double optical frequency comb and the in-situ real-time non-invasive measurement advantage of laser absorption spectroscopy technology, simple structure, flexible operation.

Description

Technical Field

[0001] This utility model relates to the field of gas detection technology, and in particular to a gas concentration detection device. Background Technology

[0002] In fields such as environmental monitoring, industrial safety, climate research, and air pollution analysis, trace gas concentration detection not only helps in understanding air quality but also effectively prevents leaks or pollution incidents of toxic and harmful gases. For example, carbon dioxide, carbon monoxide, nitrogen oxides, volatile organic compounds, and ozone are all gases that require strict monitoring. Therefore, trace gas concentration detection has a profound impact on health, the environment, and climate change.

[0003] Traditional gas detection methods include gas chromatography and chemical analysis. Gas chromatography is a dynamic method that separates mixtures of gases (or vapors), offering high precision and the ability to detect multiple components. However, it involves complex instruments, is difficult to operate, has a long response time, and requires sample pretreatment. Chemical analysis can sample, analyze, and detect gas samples, but it measures only a single gas and is susceptible to interference from gaseous components with similar chemical properties, making it unsuitable for real-time, accurate detection of ethylene. Currently, laser absorption spectroscopy offers advantages such as high selectivity and sensitivity for trace gas detection, enabling in-situ, real-time, non-invasive measurements without any sample pretreatment, making it the optimal choice for online gas detection devices.

[0004] However, traditional laser absorption spectroscopy generally uses tunable semiconductor lasers as the laser source, requiring sawtooth wave signals to adjust the temperature and current of the semiconductor laser to ensure continuous variation of the laser output frequency. This results in existing equipment requiring a certain measurement cycle and is unable to achieve time-resolved measurements. In existing technologies, dual optical frequency combs possess time-resolved characteristics. When using dual optical frequency combs for gas detection, two infrared optical combs with different repetition frequencies are used to achieve high-speed, ultra-wideband spectral measurements through optical heterodyne beat frequency modulation. The difference in repetition frequencies between the two infrared optical combs directly affects the accuracy of gas detection. Existing technologies typically use electro-optic modulation of the dual optical combs to adjust the repetition frequency difference, but this results in low bandwidth and complex operation. Utility Model Content

[0005] The technical problem to be solved by this invention is how to design a simple and flexible dual-optical frequency comb gas detection device.

[0006] This utility model solves the above-mentioned technical problems through the following technical solution: A gas concentration detection device, comprising a laser frequency repeater, a first optical frequency comb, a second optical frequency comb, a first beam splitter, a second beam splitter, a first detector, a third beam splitter, a second detector, and a beam combiner. The output end of the laser frequency repeater is connected to the input end of the first beam splitter. The output end of the first beam splitter is divided into two paths, one connected to the input end of the second beam splitter and the other connected to the input end of the third beam splitter. The output end of the first optical frequency comb is connected to the input end of the second beam splitter, and the output end of the second optical frequency comb is connected to the input end of the third beam splitter. The output end of the second beam splitter is divided into two paths, one connected to the input end of the first detector and the other connected to the input end of the beam combiner. The output end of the first detector is connected to the first optical frequency comb through a first PID controller. The output end of the third beam splitter is divided into two paths, one connected to the input end of the second detector and the other connected to the input end of the beam combiner. The output end of the second detector is connected to the second optical frequency comb through a second PID controller. The output end of the beam combiner is connected to a gas absorption cell.

[0007] Preferably, the detection device further includes an optical fiber collimator, and the output end of the combiner is connected to the gas absorption cell via the optical fiber collimator.

[0008] Preferably, the detection device further includes a focusing lens, a third detector, a data acquisition card, and a data processor. The output end of the gas absorption cell is connected to the third detector through the focusing lens, the third detector is electrically connected to the data acquisition card, and the data acquisition card is electrically connected to the data processor.

[0009] Preferably, the laser frequency repeater is a single-frequency laser.

[0010] Preferably, the first beam splitter is a 50 / 50 beam splitter.

[0011] Preferably, both the second and third beam splitters are 99 / 1 beam splitters.

[0012] Preferably, both the first PID controller and the second PID controller are lock-in amplifiers.

[0013] Preferably, the gas absorption cell is a long optical path gas absorption cell with a multi-channel Herriot type structure. The cavity of the gas absorption cell is a cylindrical hollow glass, and the two sides of the cavity are equipped with reflectors with the same diameter as the cavity. The cavity has an air inlet and an air outlet.

[0014] Preferably, the focusing lens is perpendicular to the spatial light output from the gas absorption cell.

[0015] Preferably, the data processor has a built-in concentration inversion system, which includes a Fourier transform program, a bandpass filter window, a peak extraction program, a normalization program, an absorbance calculation program, a linear function fitting program, and a gas concentration inversion program.

[0016] The advantages of this invention are as follows: The gas concentration detection device of this invention uses a laser frequency repeater to provide a laser frequency reference for two optical frequency combs. The laser output from the laser frequency repeater is coupled with the light source output from the two optical frequency combs respectively, obtaining the relative frequency between the laser frequency repeater and the first optical frequency comb, and the relative frequency between the laser frequency repeater and the second optical frequency comb. By changing the two relative frequencies, dual optical frequency combs with different repetition rate differences can be output to meet the detection requirements of different gases. This invention combines dual optical frequency comb generation and laser absorption spectroscopy technology, utilizing the time resolution characteristics of dual optical frequency combs and the in-situ real-time non-invasive measurement advantages of laser absorption spectroscopy technology. Compared with electro-optic modulation, the dual optical frequency comb gas detection device of this invention has a simple structure, fewer parts, and flexible operation, reducing the difficulty of operating the equipment, improving the practicality of the equipment, and making it suitable for widespread promotion. Attached Figure Description

[0017] Figure 1 A schematic diagram of the gas concentration detection device provided in an embodiment of this utility model;

[0018] Figure 2 A simulated optical path diagram of the 7-ring gas absorption cell in the gas concentration detection device provided in this embodiment of the utility model;

[0019] Figure 3 The absorbance fitting result diagram of the gas concentration detection device provided in the embodiment of this utility model;

[0020] In the figure: 1 Laser frequency repeater, 2 First optical frequency comb, 3 Second optical frequency comb, 4 First beam splitter, 5 Second beam splitter, 6 First detector, 7 First PID controller, 8 Third beam splitter, 9 Second detector, 10 Second PID controller, 11 Beam combiner, 12 Fiber collimator, 13 Gas absorption cell, 14 Focusing lens, 15 Third detector, 16 Acquisition card, 17 Data processor. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this utility model clearer, the technical solutions of this utility model are described clearly and completely below with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without creative effort are within the scope of protection of this utility model.

[0022] like Figure 1 As shown, this embodiment provides a gas concentration detection device, including a laser frequency repeater 1, a first optical frequency comb 2, a second optical frequency comb 3, a first beam splitter 4, a second beam splitter 5, a first detector 6, a first PID controller 7, a third beam splitter 8, a second detector 9, a second PID controller 10, a beam combiner 11, an optical fiber collimator 12, a gas absorption cell 13, a focusing lens 14, a third detector 15, a data acquisition card 16, and a data processor 17. The output of the laser frequency repeater 1 is connected to the input of the first beam splitter 4. The output of the first beam splitter 4 is split into two paths, one connected to the input of the second beam splitter 5 and the other connected to the input of the third beam splitter 8. The output of the first optical frequency comb 2 is connected to the input of the second beam splitter 5, and the output of the second optical frequency comb 3 is connected to the input of the second beam splitter 5. The output of the second beam splitter 5 is split into two paths: one path is connected to the input of the first detector 6, and the other path is connected to the input of the beam combiner 11. The output of the first detector 6 is connected to the first optical frequency comb 2 through the first PID controller 7. The output of the third beam splitter 8 is split into two paths: one path is connected to the input of the second detector 9, and the other path is connected to the input of the beam combiner 11. The output of the second detector 9 is connected to the second optical frequency comb 3 through the second PID controller 10. The output of the beam combiner 11 is connected to the gas absorption cell 13 through the fiber collimator 12. The output of the gas absorption cell 13 is connected to the third detector 15 through the focusing lens 14. The third detector 15 is electrically connected to the acquisition card 16, and the acquisition card 16 is electrically connected to the data processor 17.

[0023] Laser frequency repeater 1 uses a single-frequency laser. The center wavelength of the laser source is selected according to the gas to be measured. For example, if the gas to be measured is acetylene, a laser source with a center wavelength of 1531nm is selected.

[0024] The first beam splitter 4 is a 50 / 50 beam splitter, used to split the input light source into two identical light signals. The second beam splitter 5 and the third beam splitter 8 are both 99 / 1 beam splitters, used to split the input light source into two light signals of 99% and 1% respectively.

[0025] Both the first PID controller 7 and the second PID controller 10 are servo-locked control systems, and can be equipped with lock-in amplifiers.

[0026] Gas absorption cell 13 is a long-path gas absorption cell, employing a multi-channel Herriot type structure with a base length of 0.113m. The multi-channel gas cell extends the interaction length between light and gas molecules, enabling the acquisition of highly sensitive gas absorption spectra. A cylindrical hollow glass cavity with a wall thickness of 1mm is used. Two 6mm diameter circular holes are cut into one side of the cavity to serve as the inlet and outlet for the optical path cell. Two reflectors with a reflectivity of 99.99% and a diameter matching the cavity are glued to both sides of the cavity to ensure airtightness meets measurement requirements. By adjusting the incident light on one side of the reflectors, the laser is reflected multiple times on the two reflector surfaces, ultimately presenting seven identical light rings, such as... Figure 2 As shown. The gas absorption cell 13 outputs spatial light, and the focusing lens 14 is placed perpendicular to the spatial light.

[0027] The data processor 17 has a built-in concentration inversion system, which includes a Fourier transform program, a bandpass filter window, a peak extraction program, a normalization program, an absorbance calculation program, a linear function fitting program, and a gas concentration inversion program.

[0028] The gas concentration detection device of this invention uses a laser frequency repeater 1 to provide a laser frequency reference for two optical frequency combs. The laser output from the laser frequency repeater 1 is coupled with the light sources output from the two optical frequency combs respectively, to obtain the relative frequencies of the laser frequency repeater 1 and the first optical frequency comb 2, and the relative frequencies of the laser frequency repeater 1 and the second optical frequency comb 3. By changing the two relative frequencies, dual optical frequency combs with different repetition rate differences can be output to meet the detection requirements of different gases. This invention combines dual optical frequency comb generation and laser absorption spectroscopy technology, utilizing the time resolution characteristics of dual optical frequency combs and the in-situ real-time non-invasive measurement advantages of laser absorption spectroscopy technology. Compared with electro-optic modulation, the dual optical frequency comb gas detection device of this invention has a simple structure, fewer parts, and flexible operation, reducing the difficulty of operating the equipment, improving the practicality of the equipment, and making it suitable for widespread promotion.

[0029] Working principle: Taking acetylene as the gas to be tested as an example, the working principle of the gas concentration detection device of this utility model will be introduced:

[0030] In practical work, two sets of time-domain data need to be collected. Pure nitrogen is introduced into the gas absorption tank 13, and a set of time-domain signals is collected as the background signal for mixed gas detection. The inlet and outlet of the gas absorption tank 13 are connected to the gas distribution system, and the gas flow rate is controlled by a mass flow meter. A mixed gas of acetylene and nitrogen is simultaneously introduced into the gas absorption tank, and the prepared acetylene content is 200 ppm. During the measurement process, to ensure the laser's absorption line aligns with that of acetylene, the system uses a laser source with a center wavelength of 1531nm as laser frequency repeater 1. Laser frequency repeater 1 provides a laser frequency reference for the two optical frequency combs. The first beam splitter 4 splits the laser into two beams. One beam is coupled to the light source output from the first optical frequency comb 2 at the second beam splitter 5. The second beam splitter 5 splits the coupled optical signal into two paths, extracting 1% of the light to enter the first detector 6 to extract the error signal. The error signal is input to the first PID controller 7 to lock the relative frequency between laser frequency repeater 1 and the first optical frequency comb 2. The relative frequency between laser frequency repeater 1 and the first optical frequency comb 2 is 250001490.75Hz. The other laser signal split from the first beam splitter 4 is coupled to the light source output from the second optical frequency comb 3 at the third beam splitter 8. The third beam splitter 8 splits the coupled optical signal into two paths, extracting 1% of the light to enter the second detector 9 to extract the error signal. The error signal is input to the second PID controller 10 to lock the relative frequency between laser frequency repeater 1 and the second optical frequency comb 3. The relative frequency between laser frequency repeater 1 and second optical frequency comb 3 is 250000972.5 Hz. 99% of the light split from second beam splitter 5 and 99% of the light split from third beam splitter 8 are input together into beam combiner 11 for coupling, outputting a dual-comb light source with a repetition rate difference of 518.25 Hz. By changing the two relative frequencies, dual optical frequency combs with different repetition rate differences can be output. The dual-comb light source is input into fiber collimator 12 for laser collimation and focusing. The collimated and focused light source is input into gas absorption cell 13 to interact with the mixed gas. After some light is absorbed by the gas to be tested, the weak light signal output from the gas absorption cell 13 is spatial light. After being focused and collimated by the focusing lens 14, it is received by the third detector 15 and converted into an electrical signal. This electrical signal is pre-amplified and then used for time-domain data acquisition via the acquisition card 15. The acquired data is input to the data processor 17 for data processing. First, the data undergoes Fourier transform, bandpass filtering, peak extraction, and normalization preprocessing. According to Lambert-Beer's law, the transmittance of the laser light passing through the gas absorption cell 13 is... It can be represented as

[0031] (1)

[0032] In formula (1), The intensity of the transmitted light. The intensity of the incident light. The spectral absorbance is influenced by spectral line intensity, line shape function, total pressure, gas volume concentration, and effective path length. Therefore, the spectral absorbance can be obtained by calculating the preprocessed signals of the two sets of data using formula (1). .

[0033] When the gas being tested has weak absorption of light, the transmittance is... It can be represented as

[0034] (2)

[0035] In formula (2), The absorption rate of the absorption spectral line for incident photons varies with temperature, and its unit is _____. , The line shape function of the spectral lines. It represents the total pressure of a gas, and its unit is atmospheric pressure (atm). The volume concentration of the gas. The effective absorption path length is measured in centimeters (cm).

[0036] Absorbance by integrated spectrum The integral absorption area of ​​the target gas can be calculated. Due to linear functions satisfy ,therefore It can be simplified to:

[0037] (3)

[0038] Once the gas pressure and effective absorption path length are determined, the concentration of the gas to be measured can be calculated by measuring the integral absorption area. According to formula (4), the expression for the concentration of the target gas is:

[0039] (4)

[0040] In the formula, and These represent the pressure and temperature measured in the actual measurements. For the Loschmidt constant, at standard temperature =273.15K and standard pressure Under the condition of 1 atm, The value is 2.6875 × 10 19 molecules / cm 3Therefore, given the thermodynamic temperature T = 296.15 K, absorption length L = 15.09 m, and absorption intensity S of the corresponding line-type spectral line obtained from the HITRAN database, the concentration of acetylene in the mixed gas can be calculated by fitting the measurement results using the Voigt line-type function and inverting the calculation using formula (4). .

[0041] The above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A gas concentration detection device, characterized in that: The system includes a laser frequency repeater (1), a first optical frequency comb (2), a second optical frequency comb (3), a first beam splitter (4), a second beam splitter (5), a first detector (6), a third beam splitter (8), a second detector (9), and a beam combiner (11). The output of the laser frequency repeater (1) is connected to the input of the first beam splitter (4). The output of the first beam splitter (4) is split into two paths, one connected to the input of the second beam splitter (5) and the other connected to the input of the third beam splitter (8). The output of the first optical frequency comb (2) is connected to the input of the second beam splitter (5), and the output of the second optical frequency comb (3) is connected to... The input of the third beam splitter (8) and the output of the second beam splitter (5) are split into two paths, one path is connected to the input of the first detector (6) and the other path is connected to the input of the beam combiner (11). The output of the first detector (6) is connected to the first optical frequency comb (2) through the first PID controller (7). The output of the third beam splitter (8) is split into two paths, one path is connected to the input of the second detector (9) and the other path is connected to the input of the beam combiner (11). The output of the second detector (9) is connected to the second optical frequency comb (3) through the second PID controller (10). The output of the beam combiner (11) is connected to the gas absorption cell (13).

2. The gas concentration detection device according to claim 1, characterized in that: The detection device also includes an optical fiber collimator (12), and the output end of the combiner (11) is connected to the gas absorption cell (13) through the optical fiber collimator (12).

3. The gas concentration detection device according to claim 1, characterized in that: The detection device also includes a focusing lens (14), a third detector (15), and a data acquisition card (16). The output end of the gas absorption cell (13) is connected to the third detector (15) through the focusing lens (14), and the third detector (15) is electrically connected to the data acquisition card (16).

4. The gas concentration detection device according to claim 1, characterized in that: The laser frequency repeater (1) is a single-frequency laser.

5. The gas concentration detection device according to claim 1, characterized in that: The first beam splitter (4) is a 50 / 50 beam splitter.

6. The gas concentration detection device according to claim 1, characterized in that: The second beam splitter (5) and the third beam splitter (8) are both 99 / 1 beam splitters.

7. The gas concentration detection device according to claim 1, characterized in that: Both the first PID controller (7) and the second PID controller (10) are lock-in amplifiers.

8. The gas concentration detection device according to claim 1, characterized in that: The gas absorption cell (13) is a long optical path gas absorption cell with a multi-channel Herriot type structure. The cavity of the gas absorption cell (13) is a cylindrical hollow glass. The two sides of the cavity are equipped with reflectors with the same diameter as the cavity. The cavity has an air inlet and an air outlet.

9. The gas concentration detection device according to claim 3, characterized in that: The focusing lens (14) is perpendicular to the spatial light output from the gas absorption cell (13).

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