Hydroxyl radical online generation and reference check method, device and application

Abstract

The application belongs to the technical field of environmental monitoring, and discloses a hydrogen-oxygen radical online generation and reference checking method, device and application. The device comprises a laser light splitting unit, a laser collimation and focusing lens group, a laser incidence cavity, a reference cavity, a laser emission cavity and an atmospheric hydrogen-oxygen radical measurement cavity. The device can not only continuously and stably generate high-concentration hydrogen-oxygen radicals, but also can monitor the resonance fluorescence signal generated by the hydrogen-oxygen radicals in real time. The device has the advantages of high signal-to-noise ratio, low cost, good adaptability, stable and reliable operation, etc. As a key core component of a laser-induced fluorescence method radical measurement system, the device can be directly applied to wavelength monitoring and locking of a dye laser, and can be used for wavelength calibration of the dye laser instead of a wavelength meter.

Description

Technical Field

[0001] This invention belongs to the field of environmental monitoring technology, and in particular to a method, apparatus and application for online generation and reference inspection of hydroxyl radicals. Background Technology

[0002] Atmospheric oxidizing power, represented by hydroxyl radicals (OH radicals), determines the residence time and range of influence of primary pollutants (such as CH4, CO, VOCs, NO, etc.) in the atmosphere. It also drives the formation and transformation of secondary pollutants (such as ozone and secondary organic aerosols), making it a key factor in atmospheric environmental chemistry research and pollution control. Accurate in-situ measurement of atmospheric hydroxyl radicals is a crucial technical issue in atmospheric environmental science. Laser-induced fluorescence measurement, proposed in 1972, can measure the concentration of hydroxyl radicals in ambient air (Baardsen & Terhune, 1972). Laser-induced fluorescence technology has become the most widely used method for measuring atmospheric free radicals after 50 years of development. The measurement principle is as follows: an atmospheric sample is introduced through a Laval nozzle, and gas expansion allows the environmental sample to enter the fluorescence cavity under an ultra-low pressure of about 350 Pa. The ambient air sample is excited by a 308 nm high-frequency, low-pulse-energy dye laser, and the OH free radicals in the sample undergo electronic transitions and emit 308 nm fluorescence. Based on electronic gating technology combined with multi-channel plate photomultiplier tube detection technology, the effective resonant fluorescence photon signal emitted by the OH free radical transition is separated and detected from the excitation source. The intensity of the detected effective resonant fluorescence signal is proportional to the concentration of OH free radicals. The concentration of OH free radicals in the ambient air can be calculated by calibrating the OH free radical standard source generator. The atmospheric free radical laser-induced fluorescence detection method requires that the laser source emitted by the dye laser is always stable on the optimal excitation line (Q1(3) line) of OH free radicals to ensure the accuracy of the measurement results. Inside the fluorescent cavity, the optimal absorption line half-width of OH radicals to 308nm laser is about 1pm, while the wavelength temperature drift of dye lasers is generally around 2pm / ℃. At the same time, the stability of dye lasers is also affected by various factors such as humidity, dye, solvent, pump light, and tuning elements. Even small changes in laser wavelength will cause drastic changes in the excitation efficiency of OH radicals, leading to greater measurement uncertainty.

[0003] Therefore, developing and establishing a method and device for online generation and reference monitoring of hydroxyl radicals that can determine in real time whether the laser wavelength is on the optimal excitation line (Q1(3) line) of hydroxyl radicals and dynamically adjust the laser wavelength of the dye laser to ensure that the laser emitted by the dye laser is continuously and stably on the optimal excitation line (Q1(3) line) of OH radicals is the key to the accurate measurement of atmospheric OH radicals by laser-induced fluorescence method. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method, apparatus and application for online generation and reference inspection of hydroxyl radicals.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] A method for online generation and reference testing of hydroxyl radicals includes the following steps:

[0007] 1) The laser emitted from the dye laser is split by a laser beam splitting unit with a splitting ratio of 9:1. The split lasers are then introduced into the atmospheric hydrogen and oxygen free radical measurement cavity and the reference cavity, respectively.

[0008] 2) The hydroxyl radical generating unit (13) set in the reference chamber can continuously generate stable high concentrations, i.e., concentrations greater than 10. 10 molecule / cm 3 The OH radicals are excited by the laser and induce resonant fluorescence. The fluorescence intensity is detected by a fluorescence detection unit set in the reference cavity, and the laser energy is detected by a laser energy detector. The reference cavity normalized OH radical concentration signal is obtained by dividing the detected resonant fluorescence intensity by the laser energy, which is directly related to the laser wavelength.

[0009] 3) By monitoring whether the normalized OH radical concentration signal of the reference cavity is at its peak, it is possible to directly determine whether the wavelength of the dye laser is on the optimal excitation line of OH radicals. By dynamically adjusting the angle of the calibrator in the resonant cavity of the dye laser, the laser wavelength is automatically adjusted to ensure that the normalized OH radical concentration signal of the reference cavity is always at its peak, thereby ensuring that the wavelength of the dye laser is always at the optimal excitation position of OH radicals, thus ensuring the accuracy of laser-induced fluorescence detection of OH radicals.

[0010] An online hydroxyl radical generation and reference inspection device for implementing the method described above includes a laser beam splitting unit, a laser collimating and focusing lens group, a laser incident cavity, a reference cavity, a laser exit cavity, and an atmospheric hydroxyl radical measurement cavity. The laser beam splitting unit is connected to the laser collimating and focusing lens group, and the laser beam split by the laser beam splitting unit is input into the laser collimating and focusing lens group. The laser collimating and focusing lens group is fixedly mounted on the laser incident cavity. The laser incident cavity, reference cavity, and laser exit cavity are coaxially and tightly connected sequentially along the horizontal direction.

[0011] The laser beam splitting unit is positioned opposite an externally mounted dye laser. This unit splits the dye laser's output into two beams. One beam is transmitted via an optical fiber to an atmospheric hydroxyl radical measurement cavity, which measures the concentration of hydroxyl radicals in the atmosphere. The other beam is transmitted via another optical fiber to a laser collimating and focusing lens group. This group collimates and focuses the split laser beam before transmitting it to the laser incident cavity and adjusts the minimum circumscribed reference circle diameter of the laser spot. The laser incident cavity redirects the laser beam and ensures it enters from the center of the reference cavity. The reference cavity can continuously and stably generate high concentrations (greater than 10). 10 molecule / cm 3 The laser can induce OH free radicals to generate resonant fluorescence. The built-in fluorescence detection unit can continuously detect the intensity of the resonant fluorescence generated when OH free radicals are induced by laser. The laser emission cavity can split the emitted laser beam, collect the transmitted light after splitting, and detect the reflected light.

[0012] Furthermore, the laser beam splitting unit includes a beam splitter, a plano-convex mirror, a fiber optic interface adapter, and an optical fiber arranged sequentially from bottom to top. The beam splitter, plano-convex mirror, and fiber optic interface adapter are coaxially arranged. The beam splitter is positioned directly opposite the dye laser. The beam splitter can split the output laser of the dye laser into two paths, namely transmitted light and reflected light, with a splitting ratio of 9:1. The plano-convex mirror can collimate and focus the incident laser. The reflected light is focused by the plano-convex mirror and then enters the laser collimating and focusing lens group through the fiber optic interface adapter and the optical fiber. The transmitted light is transmitted to the atmospheric hydrogen and oxygen free radical measurement cavity through the optical fiber.

[0013] Furthermore, the beam splitter, plano-convex mirror, and fiber optic interface adapter are connected using a cage-like structure; or, the beam splitter is made of ultraviolet fused silica material with a diameter of 25.4 mm.

[0014] Alternatively, the plano-convex mirror is made of ultraviolet-fused silica and has a diameter of 25.4 mm;

[0015] Alternatively, the optical fiber is an SMA905 general-purpose ultraviolet silica fiber with a core diameter of 200 μm and a numerical aperture of 0.22 ± 0.02.

[0016] Alternatively, the emitted laser from the dye laser is positioned at a 45° angle to the plane of the beam splitter and is coaxial with the center of the beam splitter.

[0017] Alternatively, the beam splitter includes a light-facing surface and a back-light-facing surface. The light-facing surface is coated with a beam-splitting film, and the back-light-facing surface is coated with an anti-reflection film. This allows 10% of the energy emitted by the dye laser to be reflected in a 90-degree direction and enter the reference cavity, while 90% of the energy passes through the beam splitter and enters the atmospheric hydroxyl radical measurement cavity.

[0018] Alternatively, the lens sleeve is a universal male-to-female type, model CSA-48, with a thread specification of SM1, an outer diameter of 30.5mm, and a length of 48mm; the plano-convex lens is a universal optical plano-convex lens with a uniformly UV-coated surface and a diameter of 25.4mm; the adjustable aperture is a ring-driven universal male-to-female type, model GT-5701, with a thread specification of SM1, an adjustable minimum aperture of 1mm, and a maximum aperture of 12mm, used to adjust the laser spot size; the fiber optic interface adapter is an SM1-SMA universal type with a thread specification of SM1. External thread, interface specification is SMA; or, the plano-convex mirror of the laser collimator and focusing lens group is fixedly installed in the lens barrel by the SM1 pressure ring. The position of the plano-convex mirror is adjusted by adjusting the position of the pressure ring, so as to ensure that the incident laser is focused on the center hole of the adjustable aperture. The fiber optic interface adapter and the adjustable aperture are coaxially connected to the lens sleeve by the SM1 thread. By adjusting the aperture window diameter of the adjustable aperture, the size and energy of the laser spot can be finely adjusted, ultimately ensuring that the minimum outer reference circle diameter of the laser spot is 2.1±0.2mm and the spot energy is 2±0.2mw.

[0019] Furthermore, the laser incident cavity includes an incident cage cube, a total reflection mirror, and a three-axis adjustable platform. The total reflection mirror is disposed inside the incident cage cube, and the three-axis adjustable platform is connected to and disposed outside the incident cage cube. The laser output from the laser collimating and focusing lens group can be incident on the total reflection mirror, which can perform total reflection on the laser. The three-axis adjustable platform can adjust the position of the total reflection mirror to ensure that the incident laser and the plane angle of the total reflection mirror are 45° and that the incident laser passes through the center of the total reflection mirror, ensuring that the incident laser and the central axis of the reference cavity are coaxial.

[0020] Furthermore, the incident cage cube is a general-purpose optical element, model M2-4W, used in a 30mm cage structure, with through holes of 44.5mm diameter on both the upper and lower surfaces, and SM1 threaded holes on both side ends; the total reflection mirror has a diameter of 25.4mm, is a general-purpose ultraviolet single-wavelength reflector, model GCCH-101322, with a 308nm laser reflectivity greater than 99.5%; the three-axis adjustable platform is a general-purpose optical element, model LB30-C, capable of ±4° pitch and tilt adjustment and ±2mm height adjustment;

[0021] Furthermore, the reference cavity includes a reference cavity body, a window mirror, a hydroxyl radical generation unit, a fluorescence detection unit, a filter, and an inlet / outlet channel. The window mirror, filter, and inlet / outlet channel are all disposed inside the reference cavity body. A laser channel is arranged horizontally inside the reference cavity body, and the window mirror is disposed at both ends of the horizontal laser channel to ensure that the reference cavity body is sealed and that the laser is transmitted efficiently. The hydroxyl radical generation unit and the fluorescence detection unit are arranged vertically. The hydroxyl radical generation unit can continuously and stably generate OH radicals, and the fluorescence detection unit can detect fluorescence. The filter is disposed between the fluorescence detection unit and the reference cavity body. The inlet / outlet channel is coaxially disposed in the middle of the reference cavity body and orthogonal to the laser channel. The inlet / outlet channel can allow the required oxygen and water vapor to pass through.

[0022] The laser emitted from the incident laser cavity can enter the reference cavity body through the window mirror and exit the reference cavity body. At the same time, the ambient air is filtered, dried, purified and throttled, and then drawn into the reference cavity body by the vacuum pump through the inlet and outlet air channels. The hydroxyl radical generating unit can pyrolyze the air and stably generate a high concentration of OH radicals in the reference cavity body. The laser in the reference cavity body excites the OH radicals generated by the hydroxyl radical generating unit to produce resonance fluorescence. The resonance fluorescence is detected by the fluorescence detection unit after passing through the filter.

[0023] Furthermore, the reference cavity body is an aluminum cube with dimensions of 50mm (length) × 40mm (width) × 40mm (height). A laser channel with a diameter of 8mm is set at the center of the horizontal direction inside the reference cavity body. A fluorescence channel with a diameter of 10mm is set at the center of one side of the reference cavity body in the vertical direction to connect and install a fluorescence detection unit. A hydroxyl radical generator installation channel with a diameter of 10mm is set at 3mm directly below the center on the other side to connect and install a hydroxyl radical generator unit. An inlet and outlet channel with a diameter of 2mm is set at the center of the longitudinal direction. Both ends of the inlet and outlet channels can be connected to a 1 / 8NPT threaded interface.

[0024] Preferably, both the inner and outer surfaces of the reference cavity body are subjected to blackening oxidation treatment to reduce the impact of laser scattering;

[0025] Alternatively, an O-ring groove is provided on both sides of the laser channel and an O-ring is configured. A window mirror is placed on each O-ring and connected, fixed, and sealed by a pressure ring; or, the window mirror is made of ultraviolet fused silica glass coated with a UV film. It is a general-purpose optical element, model WG40530-UV, with a thickness of 3 mm, to increase the transmittance of the 308nm laser.

[0026] Alternatively, two small holes, each 2 mm deep and 1 mm in diameter, can be symmetrically set on the outer surfaces of both sides of the reference cavity body in the laser channel direction. These holes can be directly connected to the incident cage cube via pins to ensure that the incident laser cavity and the reference cavity body are coaxial.

[0027] Alternatively, the light-receiving surface of the fluorescence detection unit is provided with an O-ring groove and configured with an O-ring, and the O-ring and the filter are fixed together by connecting aluminum sheet;

[0028] Alternatively, the filter can be a narrow-bandpass interference filter with a center wavelength of 308nm, a bandwidth of 10nm, a thickness of 3mm, and a diameter of 25.4mm. This filter can efficiently and accurately select resonant fluorescence with a wavelength of 308±5nm to pass through, thereby improving the signal-to-noise ratio of OH resonant fluorescence detection.

[0029] Furthermore, the fluorescence detection unit includes a connecting aluminum sheet and a photomultiplier tube that are coaxially and sealed together. The photomultiplier tube is arranged vertically, and the lower bottom surface of the connecting aluminum sheet is disposed on the upper surface of the photomultiplier tube. The upper surface of the connecting aluminum sheet is sealed and connected to the reference cavity body, and a filter is disposed between the connecting aluminum sheet and the reference cavity body.

[0030] Furthermore, the connecting aluminum sheet and the photomultiplier tube are connected and sealed by an O-ring groove and a black O-ring. The connecting aluminum sheet is fixed to the bottom surface of the reference cavity body by screws and is also connected and sealed by a black O-ring.

[0031] Alternatively, the photomultiplier tube is a photon-counting general-purpose photomultiplier tube with a sensitivity greater than 90 μA / lm to a 308 nm fluorescent photocathode and a gain greater than 1 × 10⁻⁶. 6 The dark count is less than 50.

[0032] Furthermore, the hydroxyl radical generating unit includes a high-resistivity heating alloy wire, a high-temperature wire, a ceramic sleeve, and an aluminum alloy base. Both ends of the high-resistivity heating alloy wire are connected to the high-temperature wire. The aluminum alloy base has two vertical through holes. The lower part of the ceramic sleeve is coaxially installed in the through holes. The high-temperature wire is coaxially installed with the ceramic sleeve, and its upper part is installed inside the ceramic sleeve. The upper part of the high-temperature wire passes through the ceramic sleeve and the through holes, and its top end is connected to a constant current power supply. The aluminum alloy base is installed on the upper part of the reference cavity body, and the high-resistivity heating alloy wire is located inside the reference cavity body.

[0033] Furthermore, the high-resistivity heating alloy wire is made of iron-chromium-aluminum-nickel alloy, with iron, chromium, aluminum, and nickel contents of 67%, 25%, 5%, and 0.8%, respectively. It has a diameter of 0.35 mm and a resistance of 14.94 ohms / meter. During manufacturing and use, a 48 mm long iron-chromium-aluminum-nickel alloy wire can be cut, and the middle section can be bent into a spring shape. The spring's circular surface has a diameter of 2.0 mm, a height of 1.3 mm, and 3 turns. Both ends are connected and twisted together with a high-temperature wire. The high-temperature wire passes through a ceramic sleeve and then through an aluminum alloy base. The position of the spring in the middle section of the high-resistivity heating alloy wire is adjusted so that the spring's circular surface is perpendicular to the central axis of the inlet and outlet air channels, and its center is exactly on the central axis. It is then fixed with high-temperature sealant. The connected high-temperature wire is powered by a constant current power supply, together forming a hydroxyl radical generating unit.

[0034] Alternatively, the hydroxyl radical generating unit is fixed to the upper part of the reference cavity body by screws and sealed with O-rings; or, the outer surface of the aluminum alloy base is treated with black wire oxidation to reduce the influence of scattered light.

[0035] Furthermore, the air inlet and outlet channels include an air inlet end and an air outlet end, both of which are located on the reference chamber body. The air inlet end can input ambient air and is sequentially connected to a pipeline temperature, humidity, pressure and flow sensor, an adjustable needle valve, an activated carbon adsorption column, a drying tube and an ultrafine particulate filter. The air outlet end is connected to a vacuum pump, which is tightly connected to the reference chamber body through the air outlet end. The vacuum pump can ensure a negative pressure environment inside the reference chamber body and draw in ambient air connected to the air inlet end.

[0036] Furthermore, the hydroxyl radical generating unit is connected to a constant current power supply and is powered by the constant current power supply. The power supply current is constant at 2.55A, and the voltage is 3±0.05V. When the air intake flow rate is 1mL / min, the surface temperature of the middle section of the high resistance heating alloy wire 36 is 650±1℃.

[0037] Furthermore, the laser emission cavity includes an emission cage cube, a beam splitter, a three-axis adjustable platform, an adjustable aperture, a light collector, and a laser energy detector. The emission cage cube is arranged horizontally, and the emission cage cube, the light collector, and the incident cage cube are coaxially arranged horizontally. The emission cage cube and the laser energy detector are coaxially arranged vertically. One horizontal side of the emission cage cube is tightly connected to the reference cavity body. The light collector is connected to the other horizontal end of the emission cage cube via an adjustable aperture and is located outside. The laser energy detector is located in the vertical direction of the emission cage cube via another adjustable aperture. The beam splitter is fixed on the three-axis adjustable platform and is mounted on the emission cage cube. It can receive the laser emitted from the reference cavity, split the laser beam into transmitted light and reflected light. The transmitted light after beam splitting is directed to the light collector to prevent the laser from being reflected back to the reference cavity body and causing measurement interference. The reflected light is directed to the laser energy detector.

[0038] Furthermore, the emitted cage-like cube is a general-purpose optical element, model M2-4W, used in a 30mm cage structure. It has through holes with a diameter of 44.5mm on its upper and lower surfaces, and SM1 threaded holes at all four ends of its sides. The beam splitter of the laser emission cavity is made of ultraviolet fused silica, with a beam-splitting film on one side and an anti-reflection film on the other, and a diameter of 25.4mm. This allows 10% of the laser energy to be reflected at a 90-degree angle for detection by the laser energy detector, while 90% of the energy is collected by the light collector through the beam splitter. The three-axis adjustable platform of the laser emission cavity is a general-purpose optical element, model LB30-C, capable of ±4° pitch and tilt adjustment and ±2mm height adjustment. The laser emission... The adjustable aperture of the cavity is a ring-driven universal type, model GT-5701, with an SM1 thread specification. It has an adjustable minimum aperture of 1mm and a maximum aperture of 12mm, used to confirm the center position and spot shape of the laser beam. The light collector is a general-purpose optical element, model GZF-SM1-20, with an SM1 thread specification, used to collect the laser light transmitted through the beam splitter, preventing laser reflection back to the reference cavity body and causing measurement interference. The laser energy detector is a silicon photodiode integrated universal type, model PDA100UV, with an SM1 internal thread interface, capable of detecting the energy of light sources from 190nm to 1100nm, with a measurement range of 0-10mW and a resolution of 1nW.

[0039] Alternatively, the beam splitter of the laser emission cavity is connected to the emission cage cube via a circular optical element mounting base. Preferably, the circular optical element mounting base is model LFM1-B, used to install the beam splitter, and can be mounted on a three-axis adjustable platform by screws; or, the angle between the beam splitter of the laser emission cavity and the incident laser is 45°.

[0040] Furthermore, the device also includes a pump laser connected to the dye laser, the pump laser being able to provide the dye laser with a 532nm laser pulse source.

[0041] Furthermore, the device also includes a signal acquisition and software control unit, which is electrically connected to the reference cavity. The signal acquisition and software control unit can acquire in real time the reference cavity's inlet temperature, humidity, inlet flow rate, cavity pressure, resonant fluorescence signal intensity, laser energy signal, and the power supply voltage and current to the reference cavity. The signal acquisition and software control unit includes a temperature, humidity, pressure, and flow sensor, a signal acquisition card, and a computer, which are sequentially electrically connected. The temperature, humidity, pressure, and flow sensor is connected to the reference cavity. The signal acquisition card is also connected to the laser energy detector and the computer. The signal acquisition card can collect data from the temperature, humidity, pressure, and flow sensor and the laser energy detector, convert the data, and send it to the computer. The computer collects analog signals detected by temperature, humidity, pressure, and flow sensors via a signal acquisition card, and the data from the signal acquisition card is then acquired by the computer. The computer is also connected to a fluorescence detection unit, allowing it to adjust the output of the dye laser based on data from the fluorescence detection unit and the signal acquisition card. Furthermore, the computer is connected to the hydroxyl radical generation unit, the reference cavity, the constant current power supply, and the laser energy detector, enabling it to collect in real-time parameters affecting OH radical generation in the reference cavity, such as injection flow rate, inlet temperature, humidity, pressure within the reference cavity, OH radical supply current, voltage, incident laser intensity, and fluorescence signal intensity. Finally, the computer is also connected to the dye laser, allowing it to collect the emitted laser wavelength signal in real-time and output a signal to adjust the emitted laser wavelength.

[0042] The advantages and positive effects of this invention are as follows:

[0043] 1. The online generation and reference inspection device for hydroxyl radicals developed in this invention can not only continuously and stably generate high concentrations of OH radicals, but also monitor the resonance fluorescence signal generated by OH radicals in real time. It has the advantages of high signal-to-noise ratio, low cost, good adaptability, and stable and reliable operation, and can be widely used in the online measurement of atmospheric hydroxyl radicals by laser-induced fluorescence method.

[0044] 2. The hydroxyl radical generating unit developed in this invention utilizes an iron-chromium-aluminum-nickel heating wire that can catalytically dissociate low-concentration water vapor in ambient air at a relatively low temperature (650℃) to generate stable high-concentration OH radicals (concentration greater than 10). 10 molecule / cm 3 This enabled the generation of significant resonant fluorescence signals using low-energy excitation laser (2mW), significantly improving the system's signal-to-noise ratio and stability.

[0045] 3. The method and apparatus for generating OH radicals by thermal dissociation of ambient air sample developed in this invention only requires ambient air as the inlet medium and an inlet flow rate of only 1 mL / min. It has the advantages of simple system and low operating cost.

[0046] 4. The fluorescence detection unit developed in this invention significantly reduces the influence of laser scattering by misaligning it with the hydroxyl radical generation unit, breaking through the gating limitation of resonance fluorescence signal detection. This not only simplifies the system structure but also expands the application scenarios of this invention, and can meet the reference check for OH radical measurement using both resonance and non-resonance laser-induced fluorescence.

[0047] 5. The present invention also includes a signal acquisition and control unit, which acquires, records and controls all parameters that affect the concentration of OH radicals and the resonance fluorescence signal in the reference cavity in real time, ensuring the accuracy and reliability of the system.

[0048] 6. The method and apparatus of the present invention can realize real-time monitoring and dynamic adjustment of the laser wavelength of the dye laser, ensuring that the wavelength of the dye laser is always stable at the optimal excitation wavelength of OH radicals (Q1(3) line), thereby ensuring the accuracy of laser-induced fluorescence method for measuring OH radicals. As a key core component of the laser-induced fluorescence method for measuring radicals, it can not only be directly applied to the monitoring and locking of the wavelength of the dye laser, but also replace the wavelength meter for the calibration of the wavelength of the dye laser. It can be widely used in the in-situ measurement of OH radicals in the ambient atmosphere. Attached Figure Description

[0049] Figure 1 This is a schematic front view of the structural connection of the device of the present invention;

[0050] Figure 2 for Figure 1 A top view schematic diagram of a structural connection of the central reference cavity;

[0051] Figure 3 for Figure 1 A schematic front view of a structural connection of a OH radical generating unit;

[0052] Figure 4 This diagram shows the changes in fluorescence signals obtained by the atmospheric hydrogen and oxygen free radical measurement cavity and the reference cavity when the wavelength of the dye laser changes in this invention.

[0053] Figure reference numerals: 1. Laser beam splitter; 2. Beam splitter; 3. Plano-convex mirror; 4. Fiber optic interface adapter; 5. Fiber optic cable; 6. Adjustable aperture; 7. Incident cage cube; 8. Total reflection mirror; 9. Triaxial adjustable platform; 10. Reference cavity body; 11. Window mirror; 12. Hydroxyl radical generation unit; 13. Fluorescence detection unit; 14. Filter; 15. Connecting aluminum sheet; 16. Photomultiplier tube; 17. Inlet / outlet gas channel; 18. Outlet cage cube; 19. Light collector; 20. Laser energy detector; 21. Constant current power supply; 22. Temperature, humidity, pressure and flow sensor; 23. Signal acquisition card; 24. Computer; 25. Pump laser; 26. Dye laser; 27. Atmospheric hydroxyl radical measurement cavity; 28. Fluorescence channel; 31. Mounting channel; 32. Inlet end; 33. Outlet end; 34. Small hole; 35. High resistance heating alloy wire; 36. Ceramic sleeve; 37. High temperature wire; 38. Aluminum alloy base; 39. Laser channel; 40. Detailed Implementation

[0054] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0055] The various experimental operations involved in the specific embodiments are all conventional techniques in the field. For parts not specifically annotated in this document, those skilled in the art can refer to various commonly used reference books, scientific and technological documents or related instructions and manuals prior to the filing date of this invention to carry out the operations.

[0056] A method for online generation and reference testing of hydroxyl radicals includes the following steps:

[0057] 1) The laser emitted from the dye laser 27 is split by the laser beam splitting unit 1 at a ratio of 9:1. The split laser is then introduced into the atmospheric hydrogen and oxygen free radical measurement cavity 28 and the reference cavity, respectively.

[0058] 2) The hydroxyl radical generating unit 13 installed in the reference chamber can continuously and stably generate high concentrations (i.e., concentrations greater than 10). 10 molecule / cm 3 The laser excitation induces OH radicals to generate resonant fluorescence, and the fluorescence intensity is detected by the fluorescence detection unit 14 set in the reference cavity. The laser energy is detected by the laser energy detector 21. The reference cavity normalized OH radical concentration signal is obtained by dividing the detected resonant fluorescence intensity by the laser energy, which is directly related to the laser wavelength. When the laser wavelength changes, the reference cavity normalized OH radical concentration signal will also change significantly.

[0059] 3) By monitoring whether the OH radical concentration signal normalized by the reference cavity is at its peak, it is possible to directly determine whether the wavelength of the dye laser 27 is on the optimal excitation line (Q1(3) line) of OH radicals. By dynamically adjusting the angle of the calibrator in the resonant cavity of the dye laser 27, the laser wavelength is automatically adjusted to ensure that the OH radical concentration signal normalized by the reference cavity is always at its peak, thereby ensuring that the wavelength of the dye laser 27 is always at the optimal excitation position of OH radicals, thus ensuring the accuracy of laser-induced fluorescence detection of OH radicals.

[0060] An online hydroxyl radical generation and reference testing device for implementing the above method, such as... Figure 1 As shown, the device includes a laser beam splitting unit 1, a laser collimating and focusing lens group, a laser incident cavity, a reference cavity, a laser exit cavity, and an atmospheric hydrogen and oxygen free radical measurement cavity 28. The laser beam splitting unit 1 is connected to the laser collimating and focusing lens group (e.g., via optical fiber 5), and the laser beam split by the laser beam splitting unit 1 is fed into the laser collimating and focusing lens group. The laser collimating and focusing lens group is fixedly mounted on the laser incident cavity, and the laser incident cavity, reference cavity, and laser exit cavity are coaxially and tightly connected in sequence along the horizontal direction.

[0061] The laser beam splitting unit 1 is positioned opposite the externally mounted dye laser 27. The laser beam splitting unit 1 splits the output laser from the dye laser 27 into two beams. One beam is transmitted via an optical fiber 5 to an atmospheric hydroxyl radical measurement cavity 28, which measures the concentration of hydroxyl radicals in the atmosphere. The other beam is transmitted via another optical fiber 5 to a laser collimating and focusing lens group. This group collimates and focuses the split laser beam before transmitting it to the laser incident cavity and adjusts the minimum circumscribed reference circle diameter of the laser spot. The laser incident cavity redirects the laser beam and ensures it enters from the center of the reference cavity. The reference cavity can continuously and stably generate high concentrations (i.e., concentrations greater than 10). 10 molecule / cm 3 The laser can induce OH free radicals to generate resonant fluorescence. The built-in fluorescence detection unit 14 can continuously detect the intensity of the resonant fluorescence generated when OH free radicals are induced by laser. The laser emission cavity can split the emitted laser beam, collect the transmitted light after splitting, and detect the reflected light.

[0062] The laser beam splitting unit 1, laser collimating and focusing lens group, laser incident cavity, reference cavity and laser exit cavity of this device can be connected by a cage structure, which ensures that the laser passes through the central axis of the device and ensures the best excitation effect of the laser on OH free radicals.

[0063] In use, the dye laser 27 emits a laser beam that is split into two beams by the laser beam splitting unit 1. The transmitted laser beam is transmitted to the atmospheric hydroxyl radical measurement cavity 28 via the optical fiber 5. This is used to induce hydroxyl radicals in the ambient air sample and generate a resonance fluorescence signal, thereby measuring the concentration of hydroxyl radicals in the atmosphere. The reflected laser beam is sent to the reference cavity to induce a constant high concentration of hydroxyl radicals continuously generated by the hydroxyl radical generation unit in the reference cavity and generate a resonance fluorescence signal. The reference cavity normalized hydroxyl radical concentration signal is obtained by dividing the detected resonance fluorescence intensity by the laser energy in the reference cavity. By monitoring whether the reference cavity normalized hydroxyl radical concentration signal is at its peak, it is possible to directly determine whether the laser wavelength is on the optimal excitation line (Q1(3) line) of hydroxyl radicals. The laser wavelength of the dye laser 27 is dynamically adjusted to ensure that the laser emitted by the dye laser 27 is continuously and stably on the optimal excitation line (Q1(3) line) of hydroxyl radicals.

[0064] In this embodiment, as Figure 1 As shown, the laser beam splitting unit 1 includes a beam splitter 2, a plano-convex mirror 3, a fiber optic interface adapter 4, and an optical fiber 5 arranged sequentially from bottom to top. The beam splitter 2, plano-convex mirror 3, and fiber optic interface adapter 4 are coaxially arranged. The beam splitter 2 is positioned directly opposite the dye laser 27. The beam splitter 2 can split the output laser (i.e., incident laser) of the dye laser 27 into two paths: transmitted light and reflected light, with a splitting ratio of 9:1 (i.e., 90% transmitted light and 10% reflected light). The plano-convex mirror 3 can collimate and focus the incident laser. The reflected light, after being focused by the plano-convex mirror 3, enters the laser collimating and focusing lens group through the fiber optic interface adapter 4 and the optical fiber 5. The transmitted light is transmitted to the atmospheric hydroxyl radical measurement cavity 28 through the optical fiber 5. The beam splitter 2, plano-convex mirror 3, and fiber optic interface adapter 4 can be connected using a cage-like structure to ensure coaxial laser transmission. Preferably, the beam splitter 2 is made of ultraviolet fused silica material and has a diameter of 25.4 mm.

[0065] Alternatively, the plano-convex mirror 3 is made of ultraviolet-fused silica and has a diameter of 25.4 mm;

[0066] Alternatively, the optical fiber 5 is an SMA905 general-purpose ultraviolet quartz optical fiber 5 with a core diameter of 200um and a numerical aperture of 0.22 ± 0.02, which can realize efficient transmission of 200-450nm laser.

[0067] Alternatively, the emitted laser from the dye laser 27 is positioned at a 45° angle to the plane of the beam splitter 2 and is coaxial with the center of the beam splitter 2.

[0068] Alternatively, the beam splitter 2 includes a light-facing surface and a back-facing surface (not labeled in the figure). The light-facing surface is coated with a beam-splitting film (not shown in the figure), and the back-facing surface is coated with an anti-reflection film (not shown in the figure). This allows 10% of the energy of the emitted laser from the dye laser 27 to be reflected in a 90-degree direction into the reference cavity, while 90% of the energy passes through the beam splitter 2 into the atmospheric hydroxyl radical measurement cavity 28. This ensures that more laser light enters the measurement cavity and improves the sensitivity of atmospheric hydroxyl radical measurement.

[0069] Preferably, the laser beam splitting unit 1 further includes a cage-type right-angle optical adjustment frame, a cage-type XY translation adjustment frame, a cage-type mounting mirror frame, a cage-type coaxial system connecting rod, a rotating magnetic connecting rod bracket, a stainless steel connecting rod, and an optical platform breadboard (all not shown in the figure). The beam splitter 2 is fixedly mounted on the cage-type right-angle optical adjustment frame by a polytetrafluoroethylene set wire (not shown in the figure), and the plano-convex mirror 3 is fixedly mounted on the cage-type XY translation adjustment frame by an SM1 pressure ring (not shown in the figure). The fiber optic interface adapter 4 is directly screwed into and installed on the cage-type mounting mirror frame.

[0070] The cage-type right-angle optical adjustment frame, the cage-type XY translation adjustment frame, and the cage-type mounting frame are connected together by a cage-type coaxial system connecting rod; by adjusting the relative position of the cage-type XY translation adjustment frame and the cage-type mounting frame, it can be ensured that the incident laser can be focused to the center through hole of the fiber optic interface adapter 4 and the laser is led out through the fiber optic 5.

[0071] Alternatively, both the cage-type right-angle optical adjustment frame and the cage-type mounting frame have blind holes (not shown in the figure) at their bottoms. The two blind holes are screwed together with a stainless steel connecting rod and fixed on the breadboard of the optical platform by a rotating magnetic connecting rod bracket. The rotating magnetic connecting rod bracket is equipped with fixing screws (not shown in the figure). The height of the cage-type right-angle optical adjustment frame is adjusted by adjusting the insertion depth of the stainless steel connecting rod, and the position of the cage-type right-angle optical adjustment frame is adjusted by adjusting the fixed position of the magnetic connecting rod bracket on the optical platform, so as to ensure that the laser emitted from the dye laser 27 has a 45° angle with the plane of the beam splitter 2 and passes exactly through the center of the beam splitter 2.

[0072] Alternatively, the laser incident cavity and the laser exit cavity are respectively screwed together by a stainless steel connecting rod, and fixed on the breadboard of the optical platform by a rotating magnetic connecting rod bracket.

[0073] Preferably, the cage-type right-angle optical adjustment frame, cage-type XY translation adjustment frame, fiber optic interface adapter 4, cage-type mounting lens frame, fiber optic cable 5, cage-type coaxial system connector, rotating magnetic connector bracket, stainless steel connector, and optical platform breadboard are all general-purpose optical components, with models KCD1L-M1, CXY1-MCXY1-M, SM1-SMA, CSJ-25, SMA905 UV-VIS 200 / 220, PCM-S, CA-XC, PCA-A, and OHD2525, respectively.

[0074] In this embodiment, as Figure 1 As shown, the laser beam splitting unit 1 is connected to the laser collimating and focusing lens group via optical fiber 5, transmitting the laser output from the laser beam splitting unit 1 to the laser collimating and focusing lens group. The laser collimating and focusing lens group includes a lens sleeve 6, a plano-convex mirror 3, an optical fiber interface adapter 4, and an adjustable aperture 7. The lens sleeve 6 is arranged vertically, and the optical fiber interface adapter 4, the plano-convex mirror 3, and the adjustable aperture 7 are coaxially arranged from bottom to top inside the lens sleeve 6. The optical fiber interface adapter 4 can receive the laser output from the laser beam splitting unit 1. The plano-convex mirror 3 can focus and collimate the laser received by the optical fiber interface adapter 4 of the laser collimating and focusing lens group. The adjustable aperture 7 can fine-tune the size and energy of the laser spot output from the optical fiber interface adapter 4 to ensure that the size and energy of the laser spot meet the measurement requirements. In use, the fiber optic interface adapter 4 of the laser collimator and focusing lens group receives the laser output from the laser beam splitter 1 into the lens sleeve 6. After the laser is focused by the plano-convex lens 3, it enters the adjustable aperture 7. The adjustable aperture 7 finely adjusts the incident laser and then shoots the incident laser into the laser incident cavity, ensuring coaxial transmission of the laser.

[0075] Preferably, the lens sleeve 6 is a universal male-to-female type, model CSA-48, with a thread specification of SM1, an outer diameter of 30.5mm, and a length of 48mm; the plano-convex lens 3 is a universal optical plano-convex lens with a uniformly UV-coated surface and a diameter of 25.4mm; the adjustable aperture 7 is a ring-driven universal male-to-female type, model GT-5701, with a thread specification of SM1, an adjustable minimum aperture of 1mm, and a maximum aperture of 12mm, used to adjust the laser spot size; the fiber optic interface adapter 4 is an SM1-SMA universal type, with a thread specification of SM1 external thread and an interface specification of S... MA; or, the plano-convex mirror 3 of the laser collimating and focusing lens group is fixedly installed in the lens barrel by the SM1 pressure ring (not shown in the figure). The position of the plano-convex mirror 3 is adjusted by adjusting the position of the pressure ring, so as to ensure that the incident laser is focused on the center hole of the adjustable aperture 7. The fiber optic interface adapter 4 and the adjustable aperture 7 are coaxially connected to the lens sleeve 6 by the SM1 thread (not shown in the figure). By adjusting the aperture window diameter of the adjustable aperture 7, the size and energy of the laser spot can be finely adjusted, ultimately ensuring that the minimum outer reference circle diameter (roundness value) of the laser spot is 2.1±0.2mm and the spot energy is 2±0.2mw.

[0076] In this embodiment, as Figure 1 As shown, the laser incident cavity includes an incident cage cube 8, a total reflection mirror 9, and a three-axis adjustable platform 10. The total reflection mirror 9 is disposed inside the incident cage cube 8, and the three-axis adjustable platform 10 is connected to the total reflection mirror 9 and disposed outside the incident cage cube 8. The laser output from the laser collimating and focusing lens group can be incident on the total reflection mirror 9, which can perform total reflection on the laser. The three-axis adjustable platform 10 can adjust the position of the total reflection mirror 9 to ensure that the incident laser and the plane angle of the total reflection mirror 9 are 45° and that the incident laser passes through the center of the total reflection mirror 9, ensuring that the incident laser and the central axis of the reference cavity are coaxial. The incident cage cube 8, the total reflection mirror 9, and the three-axis adjustable platform 10 are all commonly used optical components, which are easy to connect and have good reliability and stability. The incident laser emitted from the laser collimation and focusing lens group is totally reflected by the total reflection mirror 9 and then enters the reference cavity body 11. By adjusting the three-axis adjustable platform 10, the reflected light from the total reflection mirror 9 can pass through the central axis of the reference cavity body 11.

[0077] Preferably, the incident cage cube 8 is a general-purpose optical element, model M2-4W, used for a 30mm cage structure, with through holes of 44.5mm diameter on both the upper and lower surfaces, and SM1 threaded holes at all four ends of the side; the total reflection mirror 9 has a diameter of 25.4mm, is a general-purpose ultraviolet single-wavelength reflector, model GCCH-101322, with a 308nm laser reflectivity greater than 99.5%; the three-axis adjustable platform 10 is a general-purpose optical element, model LB30-C, capable of ±4° pitch and tilt adjustment and ±2mm height adjustment;

[0078] Preferably, the laser incident cavity further includes a circular optical element mounting base, a lens sleeve 6 cover plate and a cubic cover plate, a cage-like cubic connector, a stainless steel connecting rod and a rotating magnetic connecting rod bracket (all not shown in the figure). The total reflection mirror 9 is mounted on the circular optical element mounting base and can be mounted on the three-axis adjustable platform 10 by screws. The incident cage-like cubic 8 can be connected to the reference cavity through the cage-like cubic connector, and the connection is quick. One side of the incident cage-like cubic 8 is coaxially mounted with the laser collimating and focusing lens group through an SM1 threaded interface, and the opposite side is sealed by the lens sleeve 6 cover plate. One side of the other pair of sides is fixed to the cage-like cubic connector by screws. It is coaxially fixed together with the reference cavity body 11, and its opposite side is sealed by the lens sleeve 6 cover plate; the upper surface can be directly inserted into the three-axis adjustable platform 10 with the total reflection mirror 9 fixed, the three-axis adjustable platform 10 can rotate 360°, and when adjusted to 45° with the incident laser, it is locked with M4 screws, and the lower surface is sealed by the cubic cover plate; the rotating magnetic rod bracket can be fixedly installed on the optical platform and fixedly connected to the stainless steel rod of the laser incident cavity, one end of the stainless steel rod is screwed together with the central blind hole of the cubic cover plate on the lower surface of the incident cage cube 8, and the other end is fixedly installed on the breadboard of the optical platform through the rotating magnetic rod bracket of the laser incident cavity. After the laser collimating and focusing lens assembly collimates and adjusts the circularity of the laser, it passes through the laser incident cavity and is redirected at a 90-degree angle by the total reflection mirror 9 before entering the reference cavity body 11. Adjusting the three adjustable nuts (X, Y, and height) of the three-axis adjustable platform 10 ensures that the incident laser passes perpendicularly through the reference cavity body 11 and is aligned with the central axis of the reference cavity body 11, making adjustment convenient and quick. Preferably, the circular optical element mounting base is model LFM1-B, the lens sleeve 6 cover plate is model CSL-P1 with an SM1 external thread, the cubic cover plate is model CSJ-T1A, the cage-type cubic connector is model M2-CX, and the rotating magnetic rod bracket is model CA-XC.

[0079] In this embodiment, as Figure 1As shown, the reference cavity includes a reference cavity body 11, a window mirror 12, a hydroxyl radical generating unit 13, a fluorescence detection unit 14, a filter 15, and an inlet / outlet channel 18. The window mirror 12, the filter 15, and the inlet / outlet channel 18 are all disposed inside the reference cavity body 11. A laser channel 40 is arranged horizontally inside the reference cavity body 11, and the window mirror 12 is disposed at both ends of the horizontal direction of the laser channel 40 to ensure that the reference cavity body 11 is sealed and that the laser is transmitted efficiently. The hydroxyl radical generating unit 13 and the fluorescence detection unit 14 are arranged vertically. The hydroxyl radical generating unit 13 can continuously and stably generate OH radicals, and the fluorescence detection unit 14 can detect fluorescence. The filter 15 is disposed between the fluorescence detection unit 14 and the reference cavity body 11. The inlet / outlet channel 18 is coaxially disposed in the middle of the reference cavity body 11 along the longitudinal direction and is orthogonal to the laser channel 40. The inlet / outlet channel 18 can introduce the required oxygen and water vapor.

[0080] The laser emitted from the incident laser cavity can enter and exit the reference cavity body 11 through the window mirror 12. Simultaneously, ambient air, after being filtered, dried, purified, and throttled, is drawn into the reference cavity body 11 through the inlet / outlet channel 18 by a vacuum pump. The hydroxyl radical generating unit 13 can pyrolyze the air, stably generating a high concentration of OH radicals within the reference cavity body 11. The laser within the reference cavity body 11 excites the OH radicals generated by the hydroxyl radical generating unit 13 to produce resonant fluorescence. This resonant fluorescence is detected by the fluorescence detection unit 14 after passing through the filter 15. The window mirror 12, the hydroxyl radical generating unit 13, the fluorescence detection unit 14, the filter 15, and the inlet / outlet channel 18 are respectively sealed and installed in three directions on the reference cavity body 11. The system is compact and reasonable, ensuring both stable hydroxyl radical generation and accurate and reliable resonant fluorescence detection results.

[0081] Better, such as Figure 2 As shown, the reference cavity body 11 is an aluminum cube with dimensions of 50mm (length) × 40mm (width) × 40mm (height). A laser channel 40 with a diameter of 8mm is arranged at the center of the horizontal direction inside the reference cavity body 11. A fluorescence channel 31 with a diameter of 10mm is arranged at the center of one side of the reference cavity body 11 along the vertical direction to connect and install the fluorescence detection unit 14. A hydroxyl radical generator unit 13 mounting channel 32 with a diameter of 10mm is arranged at 3mm directly below the center on the other side to connect and install the hydroxyl radical generator unit 13. An inlet and outlet gas channel 18 with a diameter of 2mm is arranged at the center of the longitudinal direction. Both ends of the inlet and outlet gas channel 18 can be connected to each other with a 1 / 8NPT threaded interface.

[0082] Preferably, both the inner and outer surfaces of the reference cavity body 11 are subjected to blackening oxidation treatment to reduce the impact of laser scattering;

[0083] Alternatively, an O-ring groove is provided on both sides of the laser channel 40 and an O-ring is configured. A window mirror 12 is placed on each O-ring and connected, fixed and sealed by a pressure ring (not shown in the figure); or, the window mirror 12 is made of ultraviolet fused silica glass and coated with a UV film. It is a general-purpose optical element, model WG40530-UV, with a thickness of 3 mm, to increase the transmittance of the 308nm laser.

[0084] Alternatively, two small holes 35, each 2 mm deep and 1 mm in diameter, can be symmetrically arranged on the outer surfaces of both sides of the reference cavity body 11 in the direction of the laser channel 40. These holes can be directly connected to the incident cage cube 8 via pins to ensure that the incident laser incident cavity and the reference cavity body 11 are coaxial.

[0085] Alternatively, the light-receiving surface of the fluorescence detection unit 14 is provided with an O-ring groove and configured with an O-ring, and the O-ring and the filter 15 are pressed and fixed by connecting aluminum sheet 16;

[0086] Alternatively, the filter 15 is a narrow-bandpass interference filter 15 with a center wavelength of 308nm, a bandwidth of 10nm, a thickness of 3mm, and a diameter of 25.4mm. It can efficiently and accurately select resonant fluorescence with a wavelength of 308±5nm to pass through, thereby improving the signal-to-noise ratio of OH resonant fluorescence detection.

[0087] In this embodiment, as Figure 1 As shown, the fluorescence detection unit 14 includes a connecting aluminum plate 16 and a photomultiplier tube 17 that are coaxially and sealed together. The photomultiplier tube 17 is arranged vertically. The bottom surface of the connecting aluminum plate 16 is disposed on the upper surface of the photomultiplier tube 17. The upper surface of the connecting aluminum plate 16 is sealed and connected to the reference cavity body 11. A filter 15 is disposed between the connecting aluminum plate 16 and the reference cavity body 11, which improves the connection strength and tightly fixes the filter 15, reduces the distance between the fluorescence detection unit 14 and the reference cavity, and improves the light collection effect.

[0088] Preferably, the connecting aluminum sheet 16 and the photomultiplier tube 17 are connected and sealed by an O-ring groove and a black O-ring (not shown in the figure). The connecting aluminum sheet 16 is fixed to the bottom surface of the reference cavity body 11 by screws and is connected and sealed by a black O-ring (not shown in the figure).

[0089] Alternatively, the photomultiplier tube 17 is a photon counting general-purpose photomultiplier tube 17 with a sensitivity greater than 90 uA / lm to a 308nm fluorescent photocathode and a gain greater than 1×10⁻⁶. 6 It has a dark count of less than 50 and a high signal-to-noise ratio for 308nm fluorescence.

[0090] In this embodiment, as Figure 1 and Figure 3As shown, the hydroxyl radical generating unit 13 includes a high-resistivity heating alloy wire 36, a high-temperature wire 38, a ceramic sleeve 37, and an aluminum alloy base 39. Both ends of the high-resistivity heating alloy wire 36 are connected to the high-temperature wire 38. The aluminum alloy base 39 has two vertically arranged base through holes (not labeled in the figure). The lower middle part of the ceramic sleeve 37 is coaxially installed in the base through holes. The high-temperature wire 38 is coaxially arranged with the ceramic sleeve 37, and its upper part is installed in the ceramic sleeve 37. The upper middle part of the high-temperature wire 38 passes through the ceramic sleeve 37 and the base through holes, and its top end is connected to the constant current power supply 22. The aluminum alloy base 39 is installed on the upper part of the reference cavity body 11, and the high-resistivity heating alloy wire 36 is arranged inside the reference cavity body 11. In use, the high-resistivity heating alloy wire 36 can be connected to the high-temperature wire 38 by hinge and insulated by the ceramic sleeve 37, ensuring that the high-temperature wire 38 safely supplies power to the high-resistivity heating alloy wire 36. The high-resistivity heating alloy wire 36, the high-temperature wire 38 and the ceramic sleeve 37 can be sealed and fixed to the through hole in the aluminum alloy base 39 with high-temperature sealant. The whole unit constitutes the hydroxyl radical generating unit 13 and is fixed on the reference cavity body 11. The unit has a compact structure, is safe and reliable, and ensures that the hydroxyl radical generating unit 13 stably generates high concentrations of hydroxyl radicals.

[0091] Preferably, the high-resistivity heating alloy wire 36 is made of iron-chromium-aluminum-nickel alloy, wherein the contents of iron, chromium, aluminum, and nickel are 67%, 25%, 5%, and 0.8%, respectively, with a diameter of 0.35 mm and a resistance of 14.94 ohms / meter. In manufacturing and use, a 48 mm long iron-chromium-aluminum-nickel alloy wire can be cut, and the middle section can be bent into a spring shape with a spring diameter of 2.0 mm, a height of 1.3 mm, and 3 turns. The two ends are then connected to the high-temperature wire 38 by twisting. Figure 3 As shown, the high-temperature wire 38 passes through the ceramic sleeve 37 and together through the aluminum alloy base 39. The position of the spring in the middle section of the high resistance heating alloy wire 36 is adjusted. When the circular surface of the spring is perpendicular to the central axis of the air inlet and outlet channel 18 and its center is exactly on the central axis, it is fixed by high-temperature sealant. The high-temperature wire 38 is powered by the constant current power supply 22, and together they form the hydroxyl radical generating unit 13.

[0092] Alternatively, the hydroxyl radical generating unit 13 is fixed to the upper part of the reference cavity body 11 by screws and sealed with O-rings; or, the outer surface of the aluminum alloy base 39 is treated with black wire oxidation to reduce the influence of scattered light.

[0093] Better, such as Figure 2As shown, the air inlet / outlet channel 18 includes an inlet end 33 and an outlet end 34, both of which are mounted on the reference chamber body 11. The inlet end 33 can input ambient air and is sequentially connected to a pipeline temperature, humidity, pressure, and flow sensor, an adjustable needle valve, an activated carbon adsorption column, a drying tube, and an ultrafine particulate filter (not shown in the figure). The ultrafine particulate filter can filter particulate matter, the drying tube can regulate the relative humidity of the incoming air and ensure stable incoming air humidity over a long period of time, the activated carbon adsorption column can remove interfering substances in the ambient air, the adjustable needle valve is used to precisely control the incoming air flow rate, and the temperature, humidity, pressure, and flow sensor 23 is used to monitor the incoming air temperature, humidity, and flow rate, as well as the pressure inside the reference chamber body 11 in real time. The outlet end 34 is connected to a vacuum pump (not shown in the figure), and the vacuum pump is tightly connected to the reference chamber body 11 through the outlet end 34. The vacuum pump can ensure a negative pressure environment inside the reference chamber body 11 and draw in ambient air connected to the inlet end.

[0094] Preferably, the inlet end 33 and outlet end 34 of the air inlet and outlet channels 18 are both connected to a 1 / 8 NPT internal thread interface, allowing the connection of the air inlet and outlet channels 18 using a 1 / 8 NPT external thread to 1 / 8 ferrule stainless steel fitting; the ultrafine particulate filter is a general-purpose type, model 9933-05-DQ, capable of filtering and removing particles with a diameter greater than 0.01 μm; the drying tube is a common color-changing silica gel drying tube, used to control the intake air humidity and ensure a stable relative humidity of 30% ± 2% over a long period; the activated carbon adsorption column is a common high-iodine-value coconut shell activated carbon purification tube, used to remove other species in the air that induce fluorescence near 308 nm. (e.g., naphthalene); the adjustable needle valve is a general-purpose type, model SS-34S6F, used to precisely control the inlet flow rate at 1.0 mL / min. The pipeline temperature, humidity, pressure, and flow sensors 23 are general-purpose types, with the temperature and humidity probe model SHT31-A, the pressure sensor model XGZP6847A, and the flow sensor model CAFS3000-100, used to monitor the inlet temperature, humidity, flow rate, and pressure inside the reference chamber body 11 in real time. Preferably, the vacuum pump is a backflow-proof oil-free vacuum pump, which is a general-purpose type. When the inlet flow rate is 1 mL / min, the pressure inside the reference chamber body 11 is below -99.6 kPa. Preferably, the gas paths at the inlet end 33 and the outlet end 34 are connected using 1 / 8-inch stainless steel tubing to prevent ambient light from entering the reference chamber body 11 and causing measurement errors.

[0095] Preferably, the hydroxyl radical generating unit 13 is connected to a constant current power supply 22, which controls the power supply current to be constant at 2.55A, while the voltage is 3±0.05V. When the air inlet flow rate is 1mL / min, the surface temperature of the middle section of the high-resistivity heating alloy wire 36 is 650±1℃. At this time, the oxygen and water vapor entering the reference chamber react on the high-temperature surface of the high-resistivity heating alloy wire 36 as follows:

[0096]

[0097]

[0098]

[0099]

[0100] Among them, the high-resistivity heating alloy wire 36 is an iron-chromium-aluminum-nickel alloy wire; the iron element in the iron-chromium-aluminum-nickel alloy wire acts as a catalyst, which can significantly improve the dissociation efficiency of water molecules, ensuring the generation of a high concentration of OH free radicals (greater than 10) at a relatively low temperature. 10 molecule / cm 3 This is crucial for improving the signal-to-noise ratio of the reference cavity, as it not only significantly reduces the background noise of the photomultiplier tube 17 but also significantly extends the lifespan of the reference cavity and improves system stability. To ensure that the hydroxyl radical generating unit 13 produces a stable concentration of OH radicals, it is necessary to ensure the stability of the power supply current, airflow rate, air humidity, air temperature, and internal pressure of the iron-chromium-nickel wire alloy.

[0101] In this embodiment, the laser emission cavity includes an emission cage cube 19, a beam splitter 2, a three-axis adjustable platform 10, an adjustable aperture 7, a light collector 20, and a laser energy detector 21. The emission cage cube 19 is arranged horizontally, and the emission cage cube 19, the light collector 20, and the incident cage cube 8 are coaxially arranged horizontally. The emission cage cube 19 and the laser energy detector 21 are coaxially arranged vertically. One horizontal side of the emission cage cube 19 is tightly connected to the reference cavity body 11. The light collector 20 is connected via a... An adjustable aperture 7 is connected and set on the outer side of the other horizontal end of the exit cage cube 19. The laser energy detector 21 is set in the vertical direction of the exit cage cube 19 through another adjustable aperture 7. The beam splitter 2 is fixed on the three-axis adjustable platform 10 and is installed on the exit cage cube 19. It can receive the laser emitted from the reference cavity, split the laser into transmitted light and reflected light. The transmitted light after splitting is sent to the light collector 20 to prevent the laser from being reflected back to the reference cavity body 11 and causing measurement interference. The reflected light is sent to the laser energy detector 21.

[0102] Preferably, the emission cage cube 19 is a general-purpose optical element, model M2-4W, used in a 30mm cage structure, with through holes of 44.5mm diameter on the upper and lower surfaces, and SM1 threaded holes at all four ends of the side; the beam splitter 2 of the laser emission cavity is made of ultraviolet fused silica, with a beam-splitting film on one side and an anti-reflection film on the other, with a diameter of 25.4mm, so that 10% of the laser energy is reflected to a 90-degree direction for detection by the laser energy detector 21, and 90% of the energy is collected by the light collector 20 through the beam splitter 2; the three-axis adjustable platform 10 of the laser emission cavity is a general-purpose optical element, model LB30-C, capable of ±4° pitch and tilt adjustment and ±2mm height adjustment; the laser emission... The adjustable aperture 7 of the cavity is a ring-driven universal type, model GT-5701, with an SM1 thread specification. It has an adjustable minimum aperture of 1mm and a maximum aperture of 12mm, and is used to confirm the center position and spot shape of the laser beam. The light collector 20 is a general-purpose optical element, model GZF-SM1-20, with an SM1 thread specification. It is used to collect the laser transmitted through the beam splitter 2 to prevent the laser from being reflected back to the reference cavity body 11 and causing measurement interference. The laser energy detector 21 is a silicon photodiode integrated universal type, model PDA100UV, with an SM1 internal thread interface. It can detect the energy of light sources from 190nm to 1100nm, with a measurement range of 0-10mW and a resolution of 1nW.

[0103] Alternatively, the beam splitter 2 of the laser emission cavity is connected to the emission cage cube 19 via a circular optical element mounting base (not shown in the figure). Preferably, the circular optical element mounting base is model LFM1-B, used to install the beam splitter 2, and can be mounted on the three-axis adjustable platform 10 by screws; or, the angle between the beam splitter 2 of the laser emission cavity and the incident laser is 45°.

[0104] Alternatively, the laser emission cavity may further include a lens sleeve 6 cover plate, a cubic cover plate, a cage-like cubic connector, a stainless steel connecting rod, and a rotating magnetic connecting rod bracket. The lens sleeve 6 cover plate, the cubic cover plate, and the cage-like cubic connector are all connected to the emission cage-like cubic 19. The lens sleeve 6 cover plate can seal one side of the emission cage-like cubic 19, and the cubic cover plate can seal the lower side of the emission cage-like cubic 19. The emission cage-like cubic 19 can be connected to the reference cavity body 11 through the cage-like cubic connector. The rotating magnetic connecting rod bracket is fixedly installed on the optical platform breadboard and a stainless steel connecting rod is fixedly installed thereon. One end of the stainless steel connecting rod is screwed together with the center of the cubic cover plate on the lower surface of the emission cage-like cubic 19, and the other end is fixedly installed on the optical platform breadboard through the rotating magnetic connecting rod bracket. Preferably, the lens sleeve 6 cover plate is model CSL-P1 with an SM1 external thread specification; the cubic cover plate is model CSJ-T1A; the cage-type cubic connector is model M2-CX; and the rotating magnetic rod bracket is model CA-XC.

[0105] In use, one horizontal side of the exit cage cube 19 is coaxially connected to the reference cavity body 11 via a cage cube connector, and the other horizontal side is directly connected to the adjustable aperture 7 via an SM1 thread. The light collector 20 is connected to the other end of the adjustable aperture 7 via an SM1 thread. The triaxial adjustable platform 10 of the incident cavity is adjusted. When the laser passes through the center hole of the adjustable aperture 7 in front of the light collector 20 and forms a circular spot of 2.1±0.2mm, it is confirmed that the laser passes through the central axis of the reference cavity body 11. In the Y-axis direction (fluorescence detection direction), one side of the exit cage cube 19 is directly sealed by the lens sleeve 6 cover plate, and the other side is connected to the adjustable aperture 7 via an SM1 thread. The laser energy detector 21 is connected to the other end of the adjustable aperture 7 via an SM1 thread.

[0106] The lower surface of the exit cage cube 19 is sealed by a cube cover plate, and the upper surface can be directly inserted into the three-axis adjustable platform 10, which is fixed to the beam splitter 2. The three-axis adjustable platform 10 can rotate 360° and be adjusted so that the beam splitter 2 is at a 45° angle to the incident laser. At this time, the circular laser spot passes exactly through the center hole of the adjustable aperture 7 in front of the laser energy detector 21, and the laser energy is monitored and recorded in real time by the laser energy detector 21. The reference cavity optical path adjustment is now complete, and the three-axis adjustable platform 10 is locked with M4 screws.

[0107] In this embodiment, the device further includes a signal acquisition and software control unit, which is electrically connected to the reference cavity. The signal acquisition and software control unit can acquire in real time the reference cavity's inlet temperature, humidity, inlet flow rate, cavity pressure, resonant fluorescence signal intensity, laser energy signal, and the voltage and current supplying the reference cavity. The signal acquisition and software control unit includes a temperature, humidity, pressure, and flow sensor 23, a signal acquisition card 24, and a computer 25. These are sequentially electrically connected. The temperature, humidity, pressure, and flow sensor 23 is connected to the reference cavity. The signal acquisition card 24 is also connected to the laser energy detector 21 and the computer 25. The signal acquisition card 24 can collect data from the temperature, humidity, pressure, and flow sensor 23 and the laser energy detector 21, convert the data, and send it to the computer 25. The analog signal detected by the temperature, humidity, pressure, and flow sensor 23 is... The data is acquired by the signal acquisition card 24 and then by the computer 25 (e.g., via serial port communication). The computer 25 is also connected to the fluorescence detection unit 14, and can adjust the output of the dye laser 27 based on the data from the fluorescence detection unit 14 and the signal acquisition card 24. The computer 25 is also electrically connected to the hydroxyl radical generation unit 13, the reference cavity body 11, the constant current power supply 22, and the laser energy detector 21 (e.g., via RS485 serial port communication), and can collect relevant parameters affecting the generation of OH radicals in the reference cavity in real time, such as the injection flow rate, inlet temperature, humidity, and pressure inside the reference cavity body 11, OH radical power supply current, voltage, incident laser intensity, and fluorescence signal intensity. The computer 25 is also connected to the dye laser 27 (e.g., via RS485 serial port), and can collect the emitted laser wavelength signal of the dye laser 27 in real time and output a signal to adjust the emitted laser wavelength of the dye laser 27.

[0108] In use, the signal acquisition and software control unit is used to acquire the inlet flow rate, temperature, humidity, pressure, fluorescence intensity of OH free radicals detected by the single-photon counting photomultiplier tube 17, 308nm laser energy detected by the laser energy detector 21, and power supply current and voltage of the hydroxyl radical generator unit 13 of the reference cavity. The signal acquisition card 24 and the computer 25 can monitor, record, and display the status and detection results of the reference cavity in real time through the standard 485 communication protocol. The signal acquisition card 24 is a general-purpose analog data acquisition card, model DAM3971, with 4 analog inputs and 2 analog outputs. It can simultaneously acquire the gas flow rate, temperature, pressure, humidity of the gas entering the reference cavity, as well as the power supply voltage and current of the iron-chromium-aluminum-nickel wire alloy, and read or control them through the computer.

[0109] In this embodiment, the device further includes a pump laser 26, which is connected to a dye laser 27. The pump laser 26 can provide a 532nm laser pulse source for the dye laser 27.

[0110] Preferably, the pump laser 26 is an Nd:YAG laser (BX60-2-L, Edgewave), and the dye laser 27 is a Sirah Credo-Dye-N. The pump laser 26 provides a 532nm laser pulse with an energy of approximately 5W, which excites an ethanol solution of DCM dye (4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran) in the dye pool of the dye laser 27. This dye emits light at 600-650 nm with an energy of approximately 200mW. A diffraction grating is used to select a single wavelength, which is then converted into a 308nm output laser with an energy of approximately 40mW using a barium β-borate (BBO) frequency-doubled crystal. The emitted laser is split by the laser beam splitting unit 1, and the reflected light enters the reference cavity to monitor in real time whether the wavelength of the emitted laser is on the optimal excitation line (Q1(3) line) of hydroxyl radicals and to make dynamic adjustments; the transmitted light enters the atmospheric hydroxyl radical measurement cavity 28 to measure the atmospheric hydroxyl radical concentration.

[0111] During operation, when the reference cavity is running normally, the incident laser beam passes along the central axis of the laser channel 40 of the reference cavity body 11, and the laser energy is detected by the laser energy detector 21 of the exit cavity. Purified and humidity-controlled ambient air passes through a high-resistivity heating alloy wire 36 at a constant flow rate of 1 mL / min. The high-resistivity heating alloy wire 36 is located 3 mm below the laser optical axis. The constant current power supply 22 provides a constant current to the high-resistivity heating alloy wire 36, causing it to heat up. The temperature near the spring surface stabilizes at 650℃±5℃. At this point, the high-resistivity heating alloy wire 36 pyrolyzes water vapor and oxygen, stably generating OH free radicals on its surface. When the OH free radicals come into contact with the 308nm laser beam, they generate 308nm resonant fluorescence. The filter 15 only allows 308±5nm light waves to pass through the fluorescence detection channel. The OH free radical resonant fluorescence signal is detected by the photomultiplier tube 17, and the incident laser energy is detected by the laser energy detector 21. The normalized OH radical concentration signal of the reference cavity is obtained by dividing the detected fluorescence signal intensity by the incident laser energy intensity. The normalized OH radical concentration signal of the reference cavity is directly related to the incident laser wavelength. When the incident laser is on the optimal excitation line (Q1(3) line) of OH radicals, the reference signal is the strongest; when the incident laser wavelength shifts, the normalized OH radical concentration signal of the reference cavity will also change significantly. By monitoring whether the normalized OH radical concentration signal of the reference cavity is at its peak, it is possible to directly determine whether the laser wavelength is on the optimal excitation line (Q1(3) line) of OH radicals. The laser wavelength is automatically adjusted by dynamically adjusting the angle of the calibrator in the resonant cavity of the dye laser 27, thereby ensuring that the normalized OH radical concentration signal of the reference cavity is always at its peak, thus ensuring that the output wavelength of the dye laser 27 is always at the optimal excitation position of OH radicals, thereby ensuring the accuracy of laser-induced fluorescence detection of OH radicals.

[0112] Therefore, based on the present invention, not only is an online OH radical generator provided, but also a simple, efficient, low-cost, stable and reliable wavelength reference inspection method for a 308nm dye laser 27 is provided, which can determine in real time whether the laser emitted from the dye laser 27 is at the optimal excitation position for OH radicals and make dynamic adjustments.

[0113] More specifically, one method of using the above-mentioned online hydroxyl radical generation and reference inspection device includes the following steps:

[0114] (1) A 30mm cage-type laser beam splitting unit 1 is composed of a cage-type right-angle optical adjustment frame, a cage-type XY translation adjustment frame, a cage-type mounting frame, a cage-type coaxial system connecting rod, a rotating magnetic connecting rod bracket, a stainless steel connecting rod, and an optical platform breadboard. The position of the rotating magnetic connecting rod bracket on the optical platform breadboard and the height of the stainless steel connecting rod inserted into the rotating magnetic connecting rod bracket are adjusted to ensure that the laser emitted from the dye laser 27 has a plane angle of 45° with the beam splitter 2 and passes exactly through the center of the beam splitter 2. After passing through the beam splitter 2, the laser emitted from the dye laser 27 is split into two beams. The transmitted light has a splitting ratio of 90% and enters the atmospheric hydrogen and oxygen free radical measurement cavity 28. The reflected light has a splitting ratio of 10% and is focused by the plano-convex mirror 3 and guided by the optical fiber 5 into the reference cavity lens sleeve 6.

[0115] (2) By adjusting the position of the plano-convex mirror 3 in the lens sleeve 6, the incident laser is focused onto the center of the adjustable aperture 7. The size of the incident laser spot and its energy are then finely adjusted by adjusting the window size of the adjustable aperture 7, ensuring that the roundness value of the minimum circumscribed reference circle diameter of the incident laser spot is 2.1±0.2mm and the spot energy is 2±0.2mw. The lens sleeve 6 is coaxially connected to the incident cage cube 8, and the adjusted laser is introduced into the incident cage cube 8.

[0116] (3) The incident cage cube 8 is coaxially connected to the reference cavity body 11 through the cage cube connector. The laser is reflected into the reference cavity body 11 through the total reflection mirror 9 in the incident cage cube 8. By adjusting the three-axis adjustable platform 10, it is ensured that the laser incident into the reference cavity body 11 passes through the window mirror 12 perpendicularly and is on the central axis. The unused surface of the incident cage cube 8 is covered and sealed by the lens sleeve 6 or the cube cover plate.

[0117] (4) The reference cavity body 11 is an aluminum cube with a length of 50 mm × width of 40 mm × height of 40 mm. It is coaxially connected with the incident cage cube 8 and the exit cage cube 19. A laser channel 40, a hydroxyl radical generation unit 13, a fluorescence detection unit 14 and an inlet / outlet gas channel 18 are respectively set in the horizontal, vertical and vertical directions.

[0118] (5) In the horizontal direction, the laser is adjusted by the incident cage cube 8, passes vertically through the window mirror 12 of the reference cavity body 11 and passes through the central axis. The laser emitted from the reference cavity body 11 is split into two beams by the beam splitter 2 in the exit cage cube 19. One beam is transmitted light and is collected by the light collector 20, and the other beam is reflected light and is detected by the laser energy detector 21.

[0119] (6) In the longitudinal direction, an inlet and outlet air channel 18 is set at the center of the reference chamber body 11, with the lower end being the inlet end 33, which is connected from far to near to an ultrafine particulate filter, a drying tube, an activated carbon adsorption column, an adjustable needle valve, and pipeline temperature, humidity, pressure, and flow sensors. The outlet end 34 is connected to an anti-backflow oil-free vacuum pump. By adjusting the adjustable needle valve, the ambient air inlet flow rate is ensured to be 1 mL / min, the humidity to be 30%±2%, and the pressure to be -99.8 kPa.

[0120] (7) In the vertical direction, a high-resistivity heating alloy wire 36 of the hydroxyl radical generating unit 13 is installed 3 mm directly below the center of the reference cavity body 11; the hydroxyl radical generating unit 13 is powered by a constant current power supply 22, and the power supply current is adjusted to 2.55A. At this time, the voltage is 3±0.05V, and the surface temperature of the spring circle in the middle section of the high-resistivity heating alloy wire 36 is 650±5℃. Oxygen and water vapor entering the reference cavity body 11 generate a high concentration (concentration greater than 10) on the high-temperature surface of the iron-chromium-aluminum-nickel wire alloy wire. 10 molecule / cm 3 The OH radical generation unit 13 can continuously generate a stable high concentration of OH radicals by maintaining the power supply current, air flow rate, air humidity and internal pressure of the iron-chromium-nickel wire alloy wire.

[0121] A fluorescence detection unit 14 is installed at the center of the bottom of the reference cavity body 11, and a 308nm narrowband filter 15 is installed between the fluorescence detection unit 14 and the reference cavity body 11. Laser excitation of OH free radicals in the reference cavity body 11 causes fluorescence reaction, and the generated 308nm resonance fluorescence is detected by photomultiplier tube 17 through the 308nm narrowband filter 15.

[0122] (8) The computer 25 collects the resonant fluorescence detection signal detected by the photomultiplier tube 17 and the laser energy signal detected by the laser energy detector 21. The normalized OH radical concentration signal of the reference cavity is obtained by dividing the detected resonant fluorescence intensity by the laser energy signal. At the same time, the inlet temperature, humidity, flow rate, pressure inside the reference cavity body 11 and the power supply current and voltage of the hydroxyl radical generation unit 13 are collected by the signal acquisition card 24 to determine the stable operation of the system. When the inlet flow rate, humidity and pressure inside the cavity are stable, the normalized OH radical concentration signal of the reference cavity is directly related to the incident laser wavelength. When the laser wavelength changes, the reference cavity normalized OH radical concentration signal also changes significantly. When the incident laser is on the optimal excitation line (Q1(3) line) of OH radicals, the reference cavity normalized OH radical concentration signal is at its peak. The laser wavelength is automatically adjusted by dynamically adjusting the angle of the calibrator in the resonant cavity of the dye laser 27 by the computer 25 to ensure that the reference cavity normalized OH radical concentration signal is always at its peak. This ensures that the output laser wavelength of the dye laser 27 is always at the optimal excitation position of OH radicals, thereby ensuring the accuracy of laser-induced fluorescence detection of OH radicals.

[0123] like Figure 4 As shown, an application example of the present invention is illustrated. The dye laser 27 emits laser light in 0.001 nm steps, each step lasting 12 seconds, automatically adjusting from 616.315 nm to 616.363 nm. After passing through a frequency doubling crystal, the actual emitted laser wavelength is adjusted in steps from 308.158 nm to 308.182 nm. The emitted laser light passes through laser beam splitting unit 1 and enters both the atmospheric hydroxyl radical measurement cavity 28 and the reference cavity. The atmospheric hydroxyl radical measurement cavity 28 is connected to an OH radical standard source, and the concentration of OH radicals generated by the standard source is 10. 8 molecule / cm 3 The OH radicals generated by the hydroxyl radical generating unit 13 in the reference cavity are 10 8 molecule / cm 3Lasers induce OH radicals in the atmospheric hydroxyl radical measurement cavity 28 and the reference cavity, respectively, generating resonance fluorescence which is then detected. Using the wavelength of the laser emitted from the dye laser 27 as the abscissa and the resonance fluorescence intensity detected by the atmospheric hydroxyl radical measurement cavity 28 and the reference cavity as the ordinate, it was found that the fluorescence signals detected by the atmospheric hydroxyl radical measurement cavity 28 and the reference cavity completely overlapped, and three typical absorption spectral lines of OH radicals were obtained near 308 nm. The first peak was the most significant, representing the (Q1(3) line), which is the optimal excitation line for OH radicals. In actual measurement, this invention allows for real-time determination of the optimal excitation position (Q1(3) line) for OH radicals when the dye laser 27 is emitted, providing a simple, efficient, low-cost, and stable reference inspection method for the dye laser 27.

[0124] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for on-line generation of hydroxyl radicals and reference check, characterized in that: It comprises the following steps: 1) the output laser of the dye laser (27) is split by the laser light splitting unit (1), the splitting ratio is 9:1, and the split laser is introduced into the atmospheric hydrogen oxygen radical measuring cavity (28) and the reference cavity respectively; 2) The hydrogen and oxygen radical generating unit (13) arranged in the reference cavity can continuously and stably generate high concentration, i.e. concentration greater than 10 10 molecule / cm 3 hydrogen and oxygen radicals and induce resonance fluorescence under laser excitation, the fluorescence intensity is detected by the fluorescence detection unit (14) arranged in the reference cavity, and the laser energy is detected by the laser energy detector (21); the detected resonance fluorescence intensity is divided by the detected laser energy to obtain the reference cavity normalized OH radical concentration signal, which is directly related to the laser wavelength; 3) whether the wavelength of the dye laser (27) is on the best excitation line of the OH radical can be directly judged by monitoring whether the normalized OH radical concentration signal of the reference cavity is at the peak value, the laser wavelength is automatically adjusted by dynamically adjusting the angle of the calibrator in the dye laser (27) resonant cavity, the normalized OH radical concentration signal of the reference cavity is always at the peak value, thereby ensuring that the wavelength of the dye laser (27) is always at the best excitation position of the OH radical, and the accuracy of laser-induced fluorescence detection of OH radical is ensured; An air inlet and outlet channel (18) is arranged in the reference cavity; The hydroxyl radical generating unit (13) comprises a high-resistance electric heating alloy wire (36), a high-temperature electric wire (38), a ceramic sleeve (37) and an aluminum alloy base (39), both ends of the high-resistance electric heating alloy wire (36) are connected with the high-temperature electric wire (38) and are fixed on the aluminum alloy base (39) through the ceramic sleeve (37) and sealing glue; the hydroxyl radical generating unit (13) is connected with a constant current power supply (22) and is controlled to supply power through the constant current power supply (22), the constant current is 2.55 A, the voltage is 3±0.05 V, when the air inlet flow is 1 mL / min, the surface temperature of the middle section of the high-resistance electric heating alloy wire (36) is 650±1℃, when the environment air is input into the air inlet channel, the high-concentration OH free radicals with the concentration greater than 10 10 molecule / cm 3 are continuously and stably generated on the surface of the high-resistance electric heating alloy wire.

2. A hydroxyl radical on-line generation and reference check device for carrying out the method according to claim 1, characterized in that it comprises: The device comprises a laser light splitting unit (1), a laser collimation and focusing lens group, a laser incidence cavity, a reference cavity, a laser emission cavity and an atmospheric hydrogen oxygen radical measuring cavity (28), the laser light splitting unit (1) is connected with the laser collimation and focusing lens group; the laser collimation and focusing lens group is fixedly arranged on the laser incidence cavity, and the laser incidence cavity, the reference cavity and the laser emission cavity are coaxially and closely connected in sequence along the horizontal direction; The laser light splitting unit (1) is arranged opposite to an externally arranged dye laser (27), the laser light splitting unit (1) can split the output laser light of the dye laser (27) into two beams, one beam is transmitted to an atmospheric hydrogen oxygen free radical measuring cavity (28) through an optical fiber (5), the atmospheric hydrogen oxygen free radical measuring cavity (28) can measure the hydrogen oxygen free radical concentration of the atmosphere, the other beam is transmitted to a laser collimation and focusing lens group through another optical fiber (5); the laser collimation and focusing lens group can collimate and focus the split laser light and then transmit it to a laser incidence cavity and adjust the minimum circumscribed reference circle diameter of the laser spot; the laser incidence cavity can turn the laser light and ensure that the laser light is incident from the center position of the reference cavity; the reference cavity can continuously and stably generate high concentration, i.e. concentration greater than 10 10 molecule / cm 3 OH free radicals and can perform laser-induced OH free radical generation resonance fluorescence, and through the built-in fluorescence detection unit (14), the resonance fluorescence intensity generated when the laser-induced OH free radicals are continuously detected; the laser light emission cavity can split the emitted laser light, collect the transmitted light after splitting, and detect the reflected light.

3. The apparatus of claim 2, wherein: The laser light splitting unit (1) comprises a light splitting mirror (2), a plano-convex mirror (3), a fiber interface adapter (4) and a fiber (5) arranged in sequence from bottom to top, the light splitting mirror (2), the plano-convex mirror (3) and the fiber interface adapter (4) are coaxially arranged, the light splitting mirror (2) is arranged opposite to the dye laser (27), the light splitting mirror (2) can split the output laser of the dye laser (27) into two paths, i.e. transmitted light and reflected light, the splitting ratio is 9:1, and the plano-convex mirror (3) can collimate and focus the incident laser; after the reflected light is condensed by the plano-convex mirror (3), it is shot into the laser collimation and focusing lens group through the fiber interface adapter (4) and the fiber (5), and the transmitted light is transmitted to the atmospheric hydrogen oxygen radical measuring cavity (28) through the fiber (5).

4. The apparatus of claim 2, wherein: The laser light splitting unit (1) is connected by the fiber (5) to transmit the laser output by the laser light splitting unit (1) to the laser collimation and focusing lens group; the laser collimation and focusing lens group comprises a lens sleeve (6), the plano-convex mirror (3), the fiber interface adapter (4) and an adjustable diaphragm (7); the lens sleeve (6) is arranged along the vertical direction, and the fiber interface adapter (4), the plano-convex mirror (3) and the adjustable diaphragm (7) are coaxially arranged in sequence from bottom to top in the lens sleeve (6); the fiber interface adapter (4) can receive the laser output by the laser light splitting unit (1), the plano-convex mirror (3) can focus and collimate the received laser, and the adjustable diaphragm (7) can adjust the size and energy of the laser spot output by the fiber interface adapter (4).

5. The apparatus of claim 2, wherein: The laser incidence cavity comprises an incidence cage cube (8), a total reflection mirror (9) and a three-axis adjustable platform (10), the total reflection mirror (9) is arranged inside the incidence cage cube (8), and the three-axis adjustable platform (10) is arranged in connection with the total reflection mirror (9) and outside the incidence cage cube (8); laser output by laser collimation and focusing lens group can be incident on the total reflection mirror (9), the total reflection mirror (9) can perform total reflection operation on the laser, and the three-axis adjustable platform (10) can adjust the position of the total reflection mirror (9), so that the incidence laser and the total reflection mirror (9) plane angle is 45° and can pass through the center of the total reflection mirror (9), and the incidence laser and the reference cavity central axis are coaxially arranged.

6. The apparatus of claim 2, wherein: The reference cavity comprises a reference cavity main body (11), a window mirror (12), a hydrogen-oxygen radical generating unit (13), a fluorescence detection unit (14), a filter (15) and an air inlet and outlet channel (18), the window mirror (12), the filter (15) and the air inlet and outlet channel (18) are arranged inside the reference cavity main body (11), a laser channel (40) is arranged in the reference cavity main body (11) in the horizontal direction, the window mirror (12) is arranged at the horizontal two ends of the laser channel (40), so that the reference cavity main body (11) is sealed and laser is efficiently transmitted; the hydrogen-oxygen radical generating unit (13) and the fluorescence detection unit (14) are arranged in the vertical direction, the hydrogen-oxygen radical generating unit (13) can stably generate OH radicals, the fluorescence detection unit (14) can detect fluorescence generated by laser-induced OH radicals, the filter (15) is arranged between the fluorescence detection unit (14) and the reference cavity main body (11), and can filter stray light signals; the air inlet and outlet channel (18) is coaxially arranged in the middle of the reference cavity main body (11) in the longitudinal direction, and is arranged in perpendicular to the laser channel (40), and can pass in oxygen and water vapor required for generating hydrogen-oxygen radicals.

7. The apparatus of claim 2, wherein: The laser incidence cavity comprises an incidence cage cube (8), a total reflection mirror (9) and a three-axis adjustable platform (10), the total reflection mirror (9) is arranged inside the incidence cage cube (8), and the three-axis adjustable platform (10) is arranged in connection with the total reflection mirror (9) and outside the incidence cage cube (8); laser output by laser collimation and focusing lens group can be incident on the total reflection mirror (9), the total reflection mirror (9) can perform total reflection operation on the laser, and the three-axis adjustable platform (10) can adjust the position of the total reflection mirror (9), so that the incidence laser and the total reflection mirror (9) plane angle is 45° and can pass through the center of the total reflection mirror (9), and the incidence laser and the reference cavity central axis are coaxially arranged. The laser incidence cavity comprises an incidence cage cube (8), a total reflection mirror (9) and a three-axis adjustable platform (10), the total reflection mirror (9) is arranged inside the incidence cage cube (8), and the three-axis adjustable platform (10) is arranged in connection with the total reflection mirror (9) and outside the incidence cage cube (8); laser output by laser collimation and focusing lens group can be incident on the total reflection mirror (9), the total reflection mirror (9) can perform total reflection operation on the laser, and the three-axis adjustable platform (10) can adjust the position of the total reflection mirror (9), so that the incidence laser and the total reflection mirror (9) plane angle is 45° and can pass through the center of the total reflection mirror (9), and the incidence laser and the reference cavity central axis are coaxially arranged.

8. The device of any one of claims 2 to 7, wherein: The device also comprises a signal acquisition and software control unit, which can acquire the reference cavity inlet temperature, humidity, inlet flow rate, cavity pressure, resonance fluorescence signal intensity, laser energy signal in real time, and set the reference cavity power supply current or voltage and control the dye laser exit laser wavelength.

9. The apparatus of claim 8, wherein: The device can automatically stabilize the generation of constant high concentration OH free radicals and introduce laser, excite the generated OH free radicals to produce resonance fluorescence signal, automatically judge whether the dye laser (27) output laser wavelength is on the optimal excitation Q1(3) line of OH free radicals by real-time automatic checking of the ratio of resonance fluorescence signal intensity to laser energy, and dynamically adjust the dye laser (27) exit laser wavelength, so as to ensure that the reference cavity normalized OH free radical concentration signal is always at the peak, and then realize the dye laser wavelength monitoring and locking.

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