Dual-path nitrous dioxide measurement system and method based on blue laser

Abstract

The present application relates to a kind of dual optical path nitrogen dioxide measurement system and method based on blue laser, using dual-wavelength laser cavity enhanced absorption spectroscopy technology, carries out NO2 absorption measurement under 405nm and 410nm wavelength, and combined with high reflectivity optical resonator, improve detection precision and sensitivity.Through dual-wavelength comparison method, using dual-wavelength absorption spectroscopy analysis, calculate absorbance difference, to effectively eliminate the influence of environmental factors on measurement accuracy, improve measurement reliability.Using more than 99.9% high reflectivity mirror, to realize high reflectivity optical resonator enhancement technology, laser is reflected in resonator multiple times, optical path is extended hundreds of times, improve NO2 absorption signal intensity, realize ppb grade ultra-low concentration measurement.Compared with traditional optical method, the system has lower cost, higher accuracy and stronger environmental adaptability, provides an efficient, stable solution for atmospheric pollution monitoring.

Description

Technical Field

[0001] This invention relates to the field of gas detection and environmental monitoring technology, and in particular to a dual-path nitrogen dioxide measurement system and method based on a blue laser. Background Technology

[0002] Nitrogen dioxide (NO2) is a significant component of air pollution, primarily originating from high-temperature combustion processes such as vehicle exhaust, coal-fired power plants, and industrial emissions. NO2 not only directly harms human health but also reacts with volatile organic compounds (VOCs) under sunlight to form photochemical smog, and further reacts with water vapor to generate acid rain, thus damaging the ecological environment.

[0003] Currently, NO2 detection methods mainly include chemical, electrochemical, and optical methods. Chemical methods, such as chemiluminescence, have high sensitivity but are susceptible to interference, and the equipment is expensive and complex to maintain. Electrochemical methods have the advantages of low cost and miniaturization, but the sensors have short lifespans, are easily affected by temperature and humidity, and have poor long-term stability. Optical methods, such as Differential Optical Absorption Spectroscopy (DOAS) and Cavity Ring-Down Spectroscopy (CRDS), have high sensitivity and real-time monitoring capabilities, but the equipment is complex, expensive, and has limited environmental adaptability.

[0004] Accurate measurement of nitrogen dioxide (NO2) is crucial in atmospheric environmental monitoring, industrial emission control, and vehicle exhaust detection. However, current NO2 measurement technologies still face the following challenges: First, measurement accuracy and sensitivity are limited. At low NO2 concentrations, the signal strength is insufficient, making it difficult for traditional methods to achieve high-precision detection, especially in ultra-low concentration monitoring at the ppb (parts per billion) level, where chemical and electrochemical methods have significant errors. Second, environmental interference is significant; existing methods are easily affected by temperature, humidity, and other gaseous components. For example, the response of electrochemical sensors is affected by changes in temperature and humidity, leading to drift in measurement data; chemical fluorescence methods are easily interfered with by substances such as ozone (O3), affecting detection stability; thirdly, the equipment is complex and costly. High-precision optical detection methods (such as CRDS and DOAS) require expensive optical components, precision-tuned lasers, and high-reflectivity optical cavities, resulting in high equipment costs. Moreover, the optical cavities are sensitive to vibration and are not suitable for portable or field monitoring; fourthly, the response speed and real-time monitoring capabilities are insufficient. Some traditional methods, such as colorimetry and chemical absorption methods, have problems such as long reaction times and complex operation steps, making it difficult to achieve rapid and continuous real-time monitoring.

[0005] However, current technologies also have limitations. The working principle of chemiluminescence can be summarized as the reaction of NO2 with ozone (O3) to produce excited-state NO2, which then releases fluorescence. The NO2 concentration is calculated by detecting the fluorescence intensity. However, chemiluminescence is greatly affected by humidity and background gases, requires additional removal of O3 interference, and the instrument is expensive and complex to maintain.

[0006] The working principle of electrochemical sensors is that NO2 undergoes a redox reaction on the electrode surface, generating a change in current, which is then used to calculate the concentration. However, these sensors have short lifespans, are easily affected by temperature and humidity, have poor long-term monitoring stability, and require frequent calibration.

[0007] Differential optical absorption spectroscopy (DOAS) utilizes the absorption characteristics of NO2 on ultraviolet-visible light to perform measurements at multiple wavelengths and removes background noise through a differential algorithm. This method is susceptible to background noise interference, requires high instrument accuracy, and the optical path is significantly affected by weather conditions during remote measurements.

[0008] Cavity ring-down spectroscopy (CRDS) uses a laser to undergo multiple reflections within a highly reflective optical cavity, measuring the light intensity decay time to calculate the absorption coefficient and thus invert the NO2 concentration. However, the equipment is expensive, requires extremely high precision in the optical cavity, and vibration can easily lead to measurement instability, making it difficult to achieve low-cost, portable applications. Summary of the Invention

[0009] To address the above issues, a dual-path nitrogen dioxide measurement system and method based on a blue laser is proposed.

[0010] The technical solution of this invention is as follows: a dual-path nitrogen dioxide measurement system based on a blue laser, comprising a laser source, an optical collimation system, a reflector, a beam splitter, an optical resonant cavity, a fiber optic spectrometer, and a data acquisition and processing module; the laser source comprises two single-wavelength lasers, one of which emits 405nm blue laser visible light, which, after passing through the optical collimation system, outputs parallel light that is reflected by the reflector and then passes through the beam splitter before entering a horizontally input black light-shielding tube; the other single-wavelength laser emits 410nm blue laser visible light, which, after passing through the optical collimation system, outputs parallel light that, after passing through the beam splitter, is partially reflected into the horizontally input black light-shielding tube, and the other part passes through the beam splitter into a vertically input black light-shielding tube. The light emitted from the horizontal black light-shielding tube is absorbed and enters the optical resonant cavity. There is a high-reflection mirror at both the input and output ends of the optical resonant cavity. The light is repeatedly reflected and resonated by the two high-reflection mirrors within the optical resonant cavity. The light emitted from the output high-reflection mirror of the optical resonant cavity passes through the horizontal output black light-shielding tube and enters the fiber optic spectrometer. The gas being measured is sent into the optical resonant cavity at the focal point of the input high-reflection mirror through a vent pipe. There is an exhaust gas outlet near the focal point of the output high-reflection mirror of the optical resonant cavity, which is connected to the atmosphere through an exhaust hood. The fiber optic spectrometer is connected to the computer through a fiber optic interface. The optical signal is transmitted to the computer in real time. The data acquisition and processing module in the computer analyzes the acquired spectral data in real time and finally calculates the concentration of nitrogen dioxide.

[0011] Preferably, the effective length of the optical resonant cavity is designed to be 76 cm to ensure that a sufficiently strong absorption signal can be measured in a low concentration of nitrogen dioxide gas.

[0012] Preferably, the optical resonant cavity consists of two high-reflectivity lenses, and the lens surfaces are coated with a precision coating process to ensure a smooth surface and a reflectivity of over 99.9%.

[0013] Preferably, the optical resonant cavity is made of polytetrafluoroethylene, which has low light absorption and good heat resistance.

[0014] Preferably, the fiber optic spectrometer is a DQ-Pro cooled fiber optic spectrometer, which captures the spectral changes after passing through nitrogen dioxide gas with a resolution of 0.1 nm. The CCD detector in the fiber optic spectrometer converts the optical signal into an electrical signal, which is then transmitted to a computer for data analysis.

[0015] Preferably, the software system in the computer automatically calibrates the spectral data and removes background noise before sending it to the data acquisition and processing module. The data acquisition and processing module performs real-time analysis on the acquired spectral data and finally calculates the concentration of nitrogen dioxide.

[0016] A dual-path nitrogen dioxide measurement method based on a blue laser is proposed. The method uses a dual-path nitrogen dioxide measurement system based on a blue laser to perform dual-wavelength absorption, and simultaneously measures the difference in absorbance at wavelengths of 405nm and 410nm. This effectively eliminates the influence of background light and other environmental factors. The relationship between absorbance and gas concentration is established using the Lambert-Beer law to obtain a high-precision nitrogen dioxide concentration.

[0017] Furthermore, the concentration of nitrogen dioxide is obtained as follows: the absorbance A is directly proportional to the gas concentration C, as shown in the formula: ,in, ε This is the absorption cross section for NO2 gas. C The concentration of NO2 gas. L The optical path length is L, which remains constant within the same cavity. By measuring the absorbance difference |A1-A2| at wavelengths of 405nm and 410nm, and combining this with the known absorption cross-section and optical path length, the system accurately calculates the gas concentration. The absorbance difference is represented by... To explain, in the formula I 1 and I The second signal is the optical signal acquired by the spectrometer at the receiving end at two wavelengths: 405nm and 410nm. I in1 and I in2 The signal is an optical signal collected by a spectrometer at two wavelengths, 405nm and 410nm, with zero gas introduced into the optical resonant cavity.

[0018] The beneficial effects of this invention are as follows: The dual-path nitrogen dioxide measurement system and method based on a blue laser utilizes dual-wavelength absorption analysis at 405nm and 410nm to improve anti-interference capabilities; it employs a high-reflectivity optical resonant cavity to enhance the optical path and improve detection sensitivity; and it optimizes the system structure to make it more compact and suitable for portable applications. Compared with traditional optical methods, this system offers lower cost, higher accuracy, and stronger environmental adaptability, providing an efficient and stable solution for air pollution monitoring. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the dual-path nitrogen dioxide measurement system based on a blue laser according to the present invention. Figure 2 This is a cross-sectional view of nitrogen dioxide absorption at the corresponding wavelength used in this invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0021] like Figure 1 The diagram shows the structure of the dual-path nitrogen dioxide measurement system based on a blue laser according to the present invention. The system includes a laser source, an optical collimation system, a reflector, a beam splitter, an optical resonant cavity, a fiber optic spectrometer, and a data acquisition and processing module. The laser source includes two single-wavelength lasers. One single-wavelength laser emits 405nm blue laser visible light. After passing through the optical collimation system, the output parallel light is reflected by a mirror and then passes through a beam splitter before entering a horizontal input black light-shielding tube. The other single-wavelength laser emits 410nm blue laser visible light. After passing through the optical collimation system, the output parallel light passes through a beam splitter. Part of the light is reflected into the horizontal input black light-shielding tube, and the other part passes through the beam splitter and enters a vertical black light-shielding tube where it is absorbed. The light emitted from the horizontal black light-shielding tube is incident on an optical resonant cavity. There is a high-reflection mirror at both the input and output ends of the optical resonant cavity. The light is repeatedly reflected and resonated by the two high-reflection mirrors within the optical resonant cavity. The light emitted from the output high-reflection mirror of the optical resonant cavity passes through the horizontal output black light-shielding tube and enters a fiber optic spectrometer. The gas being measured is delivered into the optical resonant cavity at the focal point of the input high-reflection mirror through a vent pipe. Near the focal point of the output high-reflection mirror of the optical resonant cavity, there is an exhaust outlet, which is connected to the atmosphere through an exhaust hood. The spectrometer is connected to the computer via a fiber optic interface. The optical signal is transmitted to the computer in real time. The data acquisition and processing module in the computer analyzes the acquired spectral data in real time and finally calculates the concentration of nitrogen dioxide.

[0022] The laser source module is one of the core components of this system, responsible for generating the laser beam for subsequent measurements. The experiment uses two single-wavelength lasers as the light source for the spatial path integral optical absorption spectroscopy system. Each single-wavelength laser and its driver can provide 405 / 410nm blue laser visible light, emitting stable, high-power blue laser light with a relatively smooth spectral line and no fine structure. Furthermore, the lasers have analog modulation capabilities; this invention uses a 50mW MLL-III laser manufactured by Changchun New Industries Optoelectronics Technology Co., Ltd. Each laser has an output power of 50mW, transmitted via optical fiber to ensure high brightness and stable beam output. The laser output beam exhibits excellent monochromaticity, with wavelength stability within ±0.1nm, which is crucial for long-term measurements. Fine adjustment of the laser output ensures that the beam transmission in the subsequent optical system is not interfered with by light source instability.

[0023] Laser wavelength and absorption characteristics: 405nm and 410nm are the absorption wavelengths of nitrogen dioxide molecules. In these two wavelength bands, nitrogen dioxide molecules can effectively absorb laser light energy, resulting in significant changes in light intensity. The absorption cross-section of nitrogen dioxide is very large at these wavelengths, thus providing a strong signal.

[0024] Stability and Temperature Control Design: To ensure stability during long-term experiments, the laser source is equipped with a temperature control system and a current regulation circuit. The temperature control system precisely regulates the laser's operating temperature, ensuring the stability of the laser wavelength. The laser's output power can be finely controlled through current regulation, avoiding errors caused by power fluctuations.

[0025] Optical collimation system: The laser beam passes through a collimation system, ensuring a highly consistent propagation direction. The function of the collimation system is to adjust the output laser beam into a perfectly parallel beam, preventing divergence or non-uniformity during propagation. This is crucial for enhancing the optical path length of the subsequent optical resonator.

[0026] A reflector is an optical element that operates based on the law of reflection and is used in this system. Reflectors can be classified into three types according to their shape: plane reflectors, spherical reflectors, and aspherical reflectors; and according to their degree of reflection, they can be classified into total reflection reflectors and semi-reflective reflectors (i.e., beam splitters). The 405nm blue laser reflector is a total reflection reflector, mounted using a 1-inch KCD1L-M1 30mm cage-type right-angle optical adjustment bracket. The KCD1L-M1 uses 4-40 screw holes to fix the cage rod and is compatible with 30mm cage systems and SM1 threaded components. It allows for pitch and yaw adjustment within a range of ±4°. Its bottom surface has M4 screw holes, and its top surface has M6 screw holes, which can be used to install extension rods.

[0027] The beam splitter is a semi-transparent, semi-reflective mirror, mounted on an SM series 45° mirror mount. This beam splitter uses a fixed 45° mount that can accommodate 0.5-inch, 1-inch, or 2-inch circular optical elements. It has two through-holes at 90° angles to each other, allowing for both transmission and reflection of the beam, making it ideal for beam splitting applications.

[0028] Beam splitters typically have a defined incident angle, usually 45°, which separates incident light into reflected and transmitted light. By splitting a beam of light into two, a neutral beam splitter ensures that, within a certain wavelength range, such as the visible light region, the reflected and transmitted light are neutral. A neutral beam splitter with a transmission-to-reflection ratio of 50:50 is most commonly used. The 410nm blue laser light selected in this invention is split using a neutral beam splitter. Simultaneously, the 405nm blue laser light, after passing through the reflecting mirror, also passes through the neutral beam splitter, which is a crucial part of the experimental system.

[0029] The optical resonant cavity is one of the key components of this system. It is a cavity in which light waves are reflected back and forth to provide light energy feedback.

[0030] Cavity Length and Optical Path Design: The effective length of the optical resonant cavity is designed to be 76 cm, and the cavity length is crucial for extending the optical path. A longer optical path increases the interaction time between the laser and nitrogen dioxide molecules, ensuring a sufficiently strong absorption signal can be measured even in low-concentration nitrogen dioxide gas. Furthermore, the cavity's structural design ensures that the light can pass through the gas sample with the maximum path length, thereby optimizing signal acquisition.

[0031] High-reflectivity lens design: The optical resonant cavity consists of two high-reflectivity lenses with a reflectivity exceeding 99.9%, ensuring that most of the laser beam is reflected within the cavity, thereby extending the optical path. The reflectivity of the lenses not only affects the signal intensity but also the resonance quality of the cavity. Therefore, the lens surfaces are coated with a precision coating process to ensure a smooth surface and avoid signal loss due to surface defects.

[0032] Material Selection and Optimization: Polytetrafluoroethylene (PTFE) was chosen as the material for the optical resonator, as it exhibits low light absorption and good heat resistance. The use of PTFE effectively reduces signal attenuation caused by the absorption of light beams by the optical resonator material itself, thus improving measurement accuracy.

[0033] Optical path gain: The laser beam is reflected multiple times within the cavity, and through optimized design of the reflected optical path, the optical path is significantly extended. Specifically, as the light passes through the resonant cavity, each reflection interacts with gas molecules, thereby enhancing the absorption signal. Theoretically, the more times the light is reflected, the greater the absorbance, thus improving the sensitivity of nitrogen dioxide concentration measurement.

[0034] Collimation system optimization: The collimation system consists of a set of high-precision optical lenses used to adjust the laser beam into a perfectly parallel beam. By adjusting the focal length of the lenses, the system ensures that the laser beam does not deflect or focus when entering the optical resonant cavity. The precise adjustment of the system ensures that the light propagates uniformly within the cavity and maximizes the interaction between the light and nitrogen dioxide molecules.

[0035] The fiber optic spectrometer module is a crucial component of this system for data acquisition and signal analysis. At its core is the DQ-Pro cooled fiber optic spectrometer, which boasts high resolution and extremely low background noise, enabling stable operation even under weak signal conditions.

[0036] Precision Measurement by the Spectrometer: The spectrometer can capture spectral changes after passing through nitrogen dioxide gas with a resolution of 0.1 nm. The spectrometer converts the light signal into an electrical signal using a CCD detector, which is then transmitted to a computer for data analysis. Because the absorption characteristics of nitrogen dioxide differ significantly at wavelengths of 405 nm and 410 nm, the spectrometer can accurately measure changes in absorbance, thus achieving high-precision concentration measurement.

[0037] Deeply Cooled CCD Detector: The spectrometer is equipped with a deeply cooled CCD detector, which has the advantage of reducing background noise and improving the signal-to-noise ratio. The detector's cooling temperature is 20°C below room temperature, which not only effectively reduces the influence of dark current but also improves measurement accuracy under low-light conditions.

[0038] Data transmission and processing: The spectrometer is connected to the computer via a fiber optic interface, and the optical signal is transmitted to the computer in real time. The software system can automatically calibrate the spectral data and remove background noise to ensure the high reliability of the acquired absorbance data.

[0039] The data acquisition and processing module analyzes the acquired spectral data in real time and ultimately calculates the concentration of nitrogen dioxide. This process relies on powerful data processing software that can accurately determine the gas concentration.

[0040] Real-time data acquisition and analysis: The system acquires spectral data in real time using U spectral-PLUS software and processes the data according to the dual-wavelength absorption method. The advantage of the dual-wavelength absorption method is that it can eliminate interference caused by ambient light or other gas components by comparing the difference in absorbance at wavelengths of 405nm and 410nm.

[0041] Data denoising and correction: During data analysis, the software system automatically removes noise and performs wavelength calibration. To improve analysis accuracy, the system incorporates environmental parameters (such as temperature and humidity) for error correction, thereby ensuring high accuracy of measurement results.

[0042] Concentration Inversion and Display: After data processing, the system can display the nitrogen dioxide concentration in real time on the computer screen in graphical form. Researchers can observe concentration changes, perform data analysis, and record data through the software interface. Simultaneously, the system also supports data storage and report generation, facilitating subsequent statistical analysis.

[0043] The system operates on the principle of light absorption between a laser beam and nitrogen dioxide (NO2) molecules. Nitrogen dioxide exhibits light absorption characteristics at specific wavelengths, which allows the system to accurately measure its concentration. The specific operating principle can be divided into several stages, each crucial for accurate measurement and system performance.

[0044] The system begins by the laser source module emitting blue laser light with wavelengths of 405nm and 410nm. The laser continuously emits laser light through a stable driving circuit, and a temperature control device ensures the stability of the output beam and the accuracy of the wavelength.

[0045] Laser selection: The laser source was chosen at wavelengths of 405nm and 410nm because nitrogen dioxide exhibits very significant absorption characteristics in these two wavelength bands. These wavelengths of laser light can be effectively absorbed by NO2 molecules, causing changes in light intensity and thus reflecting the concentration of NO2.

[0046] Beam Characteristics: The laser beam, output through a precisely controlled laser, exhibits high monochromaticity, meaning a single laser wavelength. This ensures that the light propagates without color mixing interference, guaranteeing high signal accuracy. The laser output power is 50mW, and the output is via optical fiber, ensuring sufficient brightness and stable transmission to the optical system.

[0047] Stability and wavelength control: The temperature and current of the laser affect its output wavelength. Therefore, the system is designed with temperature control and current regulation modules to ensure that the laser maintains a constant output wavelength and power during operation. This is the foundation for ensuring high-precision measurements.

[0048] After a laser beam is emitted from a laser source, it first passes through a collimation system. The collimation system ensures that the laser beam remains parallel during propagation, preventing scattering or divergence. This is crucial for the stable propagation of the beam within the optical resonant cavity.

[0049] How a collimation system works: A collimation system consists of multiple lenses, which are precisely designed to ensure that the laser beam remains perfectly parallel. This reduces any form of light scattering or deflection, ensuring that the optical path is not disturbed by non-uniform propagation in subsequent processes.

[0050] The function of the beam splitter: After collimation, the laser beam passes through the beam splitter, which separates the 405nm and 410nm beams and guides them into their respective paths. These two beams then enter the optical resonator separately for their respective optical enhancement processes. The beam splitter requires extremely high installation precision, as deviations from the beam-splitting angle can lead to optical path errors, thus affecting the final measurement results.

[0051] Two laser beams enter the optical resonant cavity and are reflected multiple times within the cavity, interacting with nitrogen dioxide molecules. The optical resonant cavity is designed to maximize the interaction time between the laser and the gas molecules.

[0052] Intracavity Reflection and Optical Path Enhancement: The optical resonant cavity is designed to be 76 cm long, allowing the light beam to be reflected multiple times within the cavity. Each reflection further enhances the interaction between the light and gas molecules. Through multiple reflections, the optical path is significantly increased, prolonging the contact time between the light and nitrogen dioxide molecules and enhancing the absorption effect.

[0053] The role of high-reflectivity lenses: High-reflectivity lenses (above 99.9%) within the cavity ensure that most of the laser beam can be continuously reflected and pass through the gas region within the cavity, further increasing the beam's penetration depth. The more times the light is reflected, the more fully the light interacts with the gas, enhancing the gas's ability to absorb light of specific wavelengths.

[0054] The light absorption effect of nitrogen dioxide: Nitrogen dioxide molecules can absorb light of specific wavelengths, especially in the 405nm and 410nm bands. The vibrational modes of nitrogen dioxide molecules match the frequency of light waves, thus they can effectively absorb laser beams of these wavelengths, leading to a decrease in beam intensity. By analyzing changes in light intensity, the system can calculate the concentration of nitrogen dioxide.

[0055] Optical path length and its impact on sensitivity: In the design, the length of the optical resonant cavity and the reflectivity of the lenses determine the number of light reflections. Prolonged interaction between light and gas molecules allows even low concentrations of nitrogen dioxide gas to induce sufficiently strong absorption signals, thereby improving measurement sensitivity. A longer optical path length results in greater signal attenuation, thus enabling the system to provide high-sensitivity measurements even in low-concentration gas environments.

[0056] The laser beam, enhanced by reflection, is transmitted through optical fiber to a fiber optic spectrometer for data acquisition. The spectrometer converts the acquired light intensity information into electrical signals, which are then transmitted to a computer for further processing.

[0057] Fiber optic transmission: Fiber optics, as a transmission medium, can effectively transmit optical signals and ensure signal stability. Compared to traditional beam transmission methods, fiber optic transmission has the advantage of reducing light scattering and signal attenuation, thus ensuring signal integrity.

[0058] How a spectrometer works: A fiber optic spectrometer converts light signals into electrical signals, and uses a CCD detector to capture changes in light intensity transmitted through nitrogen dioxide gas. These changes are then converted into digital signals by the spectrometer's processing circuitry and transmitted in real time to a computer for analysis.

[0059] Data Correction and Noise Suppression: Since environmental factors can interfere with the signal, the spectrometer has a built-in noise suppression function. During data transmission, the computer automatically performs data correction based on the experimental environment conditions, removing background noise and ensuring signal purity.

[0060] The system employs a dual-wavelength absorption method, calculating the concentration of nitrogen dioxide by comparing the absorbance difference at two wavelengths: 405 nm and 410 nm. This method effectively eliminates interference from ambient light, temperature, and humidity, providing more accurate concentration calculations.

[0061] Advantages of dual-wavelength absorption method: Nitrogen dioxide has different absorption characteristics at different wavelengths. By simultaneously measuring the difference in absorbance at wavelengths of 405nm and 410nm, the influence of background light and other environmental factors can be effectively eliminated, thereby improving the accuracy of concentration measurement.

[0062] Application of Lambert-Beer's Law: In dual-wavelength absorption methods, the system utilizes Lambert-Beer's Law to establish the relationship between absorbance and gas concentration. According to this law, absorbance (A) is directly proportional to gas concentration (C), as shown in the formula: ,in, ε The absorption cross section of NO2 gas is shown. The absorption cross section of NO2 gas can be obtained from Voigt 2002, 1000 mBar, 293 K, as shown in the nitrogen dioxide absorption cross section diagram for 400-415 nm (the complete range is 250-800 nm). Figure 2 As shown, the two black vertical lines represent the two laser wavelengths (405.339nm and 409.262nm) selected in this invention. Figure 2 The absorption cross section at wavelength 405.339 nm can be obtained from this. 1 = 6.941E-19 cm 2 ·molecule -1 Absorption cross section at wavelength 409.262 nm 2 = 5.855E-19 cm 2 ·molecule -1 It should be noted that the absorption cross-section of NO2 is mainly affected by temperature (223-293K) and total pressure (100-1000 mbar, with N2 as a buffer gas). C represents the NO2 gas concentration, and L represents the optical path length; L remains constant within the same cavity. By measuring the absorbance difference |A1-A2| at wavelengths of 405nm and 410nm, and combining this with the known absorption cross-section and optical path length, the system can accurately calculate the gas concentration. The absorbance difference can be represented by... To explain, in the formula I 1 and I The second signal is the optical signal acquired by the spectrometer at the receiving end at two wavelengths: 405nm and 410nm. I in1 and I in2 The signal is an optical signal collected by a spectrometer at two wavelengths, 405nm and 410nm, with zero gas introduced into the optical resonant cavity.

[0063] Concentration inversion: By calculating the difference in absorbance at two wavelengths, the system ultimately determines the concentration of nitrogen dioxide. This calculation process is automated; the system quickly outputs results based on real-time acquired spectral data, providing real-time monitoring and data display.

[0064] Computer software displays and analyzes the processed data, presenting real-time changes in nitrogen dioxide concentration.

[0065] Real-time monitoring: Researchers can monitor changes in nitrogen dioxide concentration in real time through the software interface. The data charts provided by the system can dynamically display the trend of concentration changes over time.

[0066] Data storage and report generation: The system not only supports real-time display but also stores measurement results in a database and automatically generates experimental reports. These reports include concentration measurements, experimental conditions, and data processing methods, facilitating subsequent analysis and archiving.

[0067] This invention employs dual-wavelength laser cavity enhanced absorption spectroscopy (IBBCEAS) technology to measure NO2 absorption at wavelengths of 405nm and 410nm, and combines it with a high-reflectivity optical resonant cavity to improve detection accuracy and sensitivity.

[0068] Most existing technologies use single-wavelength measurement. This invention uses a dual-wavelength comparison method, employing dual-wavelength absorption spectroscopy analysis (405nm and 410nm), to calculate the absorbance difference, thereby effectively eliminating the influence of environmental factors (such as changes in background light and interference from coexisting gases) on measurement accuracy and improving measurement reliability.

[0069] Using high reflectivity lenses of over 99.9% to achieve high reflectivity optical resonant cavity enhancement technology, the laser is reflected multiple times within the resonant cavity, extending the optical path by hundreds of times, increasing the intensity of NO2 absorption signal, and enabling ultra-low concentration measurement at the ppb level.

[0070] By using stable blue semiconductor lasers (405nm and 410nm) to replace traditional high-cost tunable lasers, the system has the advantages of low cost and miniaturization, while ensuring high spectral resolution.

[0071] By optimizing the optical design, the structure is made compact, reducing the system's sensitivity to vibration and improving its vibration resistance, making the device suitable for portable and field monitoring, unlike technologies such as CRDS which have stringent requirements for laboratory environments.

[0072] Due to the significant extension of the optical path (CRDS is usually a few meters, while the effective optical path of this invention can reach hundreds of meters), the detection sensitivity is improved. This invention can detect lower concentrations of NO2, with the lowest detection limit reaching the ppb level, which is superior to traditional electrochemical and colorimetric methods.

[0073] Dual-wavelength absorption spectroscopy analysis can effectively distinguish the true absorption signal of NO2 from environmental noise, improve data stability, enhance anti-interference ability, and reduce the influence of background gases, making it superior to single-wavelength DOAS or CRDS methods.

[0074] This method provides real-time monitoring with a fast response speed and a short system response time (on the order of seconds). It enables continuous and real-time monitoring and is suitable for applications such as atmospheric environmental monitoring and industrial emission monitoring, unlike colorimetric methods which require a long chemical reaction process.

[0075] The embodiments described above merely illustrate specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A dual-path nitrogen dioxide measurement system based on a blue laser, characterized in that, The system includes a laser source, an optical collimation system, a reflector, a beam splitter, an optical resonant cavity, a fiber optic spectrometer, and a data acquisition and processing module. The laser source comprises two single-wavelength lasers. One laser emits 405nm blue visible light, which, after passing through the optical collimation system, outputs parallel light that is reflected by the reflector and then passes through the beam splitter before entering a horizontally input black light-shielding tube. The other laser emits 410nm blue visible light, which, after passing through the optical collimation system, outputs parallel light that, after passing through the beam splitter, is partially reflected into the horizontally input black light-shielding tube, while the remaining portion passes through the beam splitter and enters a vertically input black light-shielding tube where it is absorbed. The light emitted from the horizontally input black light-shielding tube enters the vertically input black light-shielding tube. The optical resonant cavity has a high-reflection mirror at both its input and output ends. Light is repeatedly reflected and resonated by the two mirrors within the cavity. The light emitted from the output mirror passes through a horizontal black light-shielding tube and enters the fiber optic spectrometer. The gas being measured is fed into the optical resonant cavity through a vent pipe to the focal point of the input mirror. Near the focal point of the output mirror, there is an exhaust port that connects to the atmosphere via an exhaust hood. The fiber optic spectrometer is connected to a computer via a fiber optic interface, transmitting optical signals to the computer in real time. The data acquisition and processing module in the computer analyzes the acquired spectral data in real time and ultimately calculates the concentration of nitrogen dioxide.

2. The dual-path nitrogen dioxide measurement system based on a blue laser according to claim 1, characterized in that, The effective length of the optical resonant cavity is designed to be 76 cm to ensure that a sufficiently strong absorption signal can be measured in a low concentration of nitrogen dioxide gas.

3. The dual-path nitrogen dioxide measurement system based on a blue laser according to claim 1 or 2, characterized in that, The optical resonant cavity consists of two high-reflectivity lenses. The lens surfaces are coated with a precision coating process to ensure a smooth surface and a reflectivity of over 99.9%.

4. The dual-path nitrogen dioxide measurement system based on a blue laser according to claim 3, characterized in that, The optical resonant cavity is made of polytetrafluoroethylene, which has low light absorption and good heat resistance.

5. The dual-path nitrogen dioxide measurement system based on a blue laser according to claim 4, characterized in that, The fiber optic spectrometer used is the DQ-Pro cooled fiber optic spectrometer, which captures the spectral changes after passing through nitrogen dioxide gas with a resolution of 0.1 nm. The CCD detector in the fiber optic spectrometer converts the optical signal into an electrical signal, which is then transmitted to the computer for data analysis.

6. The dual-path nitrogen dioxide measurement system based on a blue laser according to claim 5, characterized in that, The computer's software system automatically calibrates the spectral data and removes background noise before sending it to the data acquisition and processing module. The data acquisition and processing module analyzes the acquired spectral data in real time and finally calculates the concentration of nitrogen dioxide.

7. A dual-path nitrogen dioxide measurement method based on a blue laser, characterized in that, The dual-path nitrogen dioxide measurement system based on a blue laser, as described in claim 5, is used to perform dual-wavelength absorption and simultaneously measure the difference in absorbance at wavelengths of 405nm and 410nm. This effectively eliminates the influence of background light and other environmental factors. The relationship between absorbance and gas concentration is established using the Lambert-Beer law to obtain a high-precision nitrogen dioxide concentration.

8. The dual-path nitrogen dioxide measurement method based on a blue laser according to claim 7, characterized in that, The concentration of nitrogen dioxide is obtained as follows: the absorbance A is directly proportional to the gas concentration C, as shown in the formula: ,in, ε This is the absorption cross section for NO2 gas. C The concentration of NO2 gas. L The optical path length is L, which remains constant within the same cavity. By measuring the absorbance difference |A1-A2| at wavelengths of 405 nm and 410 nm, and combining this with the known absorption system cross-section and optical path length, the system accurately calculates the gas concentration. The absorbance difference is represented by... To explain, in the formula I 1 and I The second signal is the optical signal acquired by the spectrometer at the receiving end at two wavelengths: 405nm and 410nm. I in1 and I in2 The signal is an optical signal collected by a spectrometer at two wavelengths, 405nm and 410nm, with zero gas introduced into the optical resonant cavity.

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