Device and method for measuring radius and refractive index of suspended single droplet

Abstract

The invention discloses a device and a method for measuring the radius and the refractive index of a suspended single droplet, and belongs to the field of aerosol droplet spectral analysis. The technical problems that an existing optical tweezers stimulated Raman method is weak in signal, and the radius and the refractive index of PM2.5-scale liquid drops cannot be measured are solved. The device comprises a single-droplet suspension sample cell, a micro-droplet pumping system, an atmosphere control system, an optical trap system, an optical signal detection system, an optical imaging system and an LED light beam shaping system, wherein the LED light beam shaping system is communicated with the light trap system, and the light trap system is respectively communicated with the single-droplet suspension sample pool, the optical signal detection system and the optical imaging system; and the single-droplet suspension sample pool is respectively communicated with the microdroplet pumping system and the atmosphere control system. According to the invention, the suspended single liquid drop is lightened by using the LED, the radius and refractive index data of the liquid drop are accurately obtained according to the stimulated elastic scattering signal, and a key parameterization measurement scheme is provided for revealing the aerosol generation mechanism in the atmospheric fine particulate matter pollution prevention and control process.

Description

Technical Field

[0001] The invention relates to the technical field of aerosol droplet spectrum analysis and detection, and in particular to a device and method for measuring the radius and refractive index of a suspended single droplet. Background Art

[0002] PM 2.5 The formation mechanism is complex, the chemical components are numerous, and the key physical and chemical parameters are lacking. 2.5 Aerosols are a major form of pollution. There is a lack of reliable experimental data on the saturated vapor pressure of semi-volatile organic compounds, the rate constant of trace gas conversion to particulate matter, the molecular diffusion coefficient of the high viscosity state, the critical conditions for phase separation, etc. The optical tweezers single droplet suspension technology combined with stimulated Raman measurement can measure the radius and refractive index data of aerosol droplets in real-time, in situ, and dynamically under the real environmental conditions of the atmosphere, and then deduce a variety of physical and chemical parameters of aerosols. Laser optical tweezers suspend a single droplet, and spontaneous Raman peaks of water molecule stretching vibrations are generated between 3000-3700 wavenumbers. Certain specific wavelengths will form standing waves and output a set of whispering gallery modes, also known as stimulated Raman spectra. According to the position of this set of stimulated Raman peaks and based on the Mie scattering theory, the radius and refractive index of the droplet can be determined. It is an accurate direct measurement method that has been used to measure a variety of physical and chemical parameters of atmospheric aerosols.

[0003] The existing optical tweezers suspending single droplets combined with stimulated Raman measurement still have several limitations. The first is that the spontaneous Raman signal of the droplet is weak, which is 6 to 8 orders of magnitude lower than the elastic scattering signal, making it difficult to measure high-quality spectra. The second is that this method is suitable for the measurement of droplets with a radius of 4 to 10 μm, which belongs to the cloud droplet size range. If the droplet radius is less than 2 μm, the number of stimulated Raman peaks at 3000 to 3700 wavenumbers (half-peak width ~ 25 nm) will be less than 4 groups, and the Raman signal is also very weak, which makes it difficult to accurately fit the droplet radius.

[0004] The existing spontaneous-stimulated Raman measurement method is based on the whispering gallery mode formed by droplets and coherent lasers. When measuring aerosol droplets close to the real atmospheric environment, when the droplet radius is as low as 1 μm, the spontaneous Raman and stimulated Raman signal-to-noise ratios of the measured spectra are low, and the peak intensity and peak position of the stimulated Raman peak are not obvious at this time. In addition, this method detects the stimulated Raman peak of water in the droplets, which is about 620~670 cm -1 The peak shift changes within the spectrum, so the spectral detection range is limited.

[0005] The above reasons result in low spectral quality when measuring droplets with a radius as low as 1 μm, limited spectral measurement width, unclear peak intensity and peak position, and low accuracy of the results of Mie scattering inversion and fitting. Summary of the invention

[0006] In view of the above analysis, the present invention aims to provide a device and method for measuring the radius and refractive index of a suspended single droplet, so as to solve the problems of weak signal and poor sensitivity to PM in the existing stimulated Raman method of optical tweezers. 2.5 The technical problem is that it is impossible to measure the radius and refractive index of a large droplet.

[0007] The purpose of the present invention is mainly achieved through the following technical solutions: On the one hand, the present invention provides a device for measuring the radius and refractive index of a suspended single droplet, the device comprising a single droplet suspension sample pool, a droplet pumping system, an atmosphere control system, a light trap system, an optical signal detection system, an optical imaging system, and an LED beam shaping system; The LED beam shaping system is connected to the light trap system, and the light trap system is respectively connected to the single droplet suspension sample pool, the optical signal detection system and the optical imaging system; at the same time, the single droplet suspension sample pool is respectively connected to the droplet pumping system and the atmosphere control system.

[0008] In one possible design, a droplet pumping system is used to pump the aerosol into aerosol droplets and pump them into a single droplet suspension sample cell.

[0009] In one possible design, the light trap system includes a laser, a first semi-transparent and semi-reflective mirror, a beam expander, a second semi-transparent and semi-reflective mirror, a microscope objective, a third semi-transparent and semi-reflective mirror, and a reflector; An optical trap system is used to capture single droplets and suspend them.

[0010] In one possible design, a laser is used to emit a laser beam, which is split after passing through a first semi-transparent and semi-reflective mirror, a beam expander and a second semi-transparent and semi-reflective mirror. The upward laser beam is focused by a microscope objective to form a light trap to capture a single droplet; the downward laser beam is split by a third semi-transparent and semi-reflective mirror and input into an optical signal detection system and then enters an optical imaging system after changing direction through a reflector.

[0011] In one possible design, an LED beam shaping system includes an LED light source; The LED beam shaping system can shape the divergent light of its LED light source into parallel light. The parallel light enters the light trap system and can couple with the laser beam emitted by the laser. After coupling, it is focused on the suspended single droplet in the sample pool through the microscope objective to provide the back-stimulated elastic scattering signal of the droplet. The radius and refractive index of the droplet are directly measured based on the LED stimulated signal. The LED illuminates the suspended droplet and collects its stimulated elastic scattering signal, which is not limited to the stimulated scattering signal collection method of various other methods of backscattering.

[0012] In a possible design, the optical signal detection system includes a spectrometer, a spectral CCD detector and a data processing unit, and the spectrometer is connected to the spectral CCD detector and the data processing unit respectively.

[0013] In one possible design, the optical imaging system includes a lens and an imaging CCD; The lens is connected to the imaging CCD; after the light beam is focused by the lens, the droplet signal is focused onto the imaging CCD, and the macroscopic morphology of the suspended droplets is observed through the imaging CCD.

[0014] In one possible design, the atmosphere control system includes a gas generating device, a pressure reducing valve and a mass flow meter; the gas generating device, the pressure reducing valve and the mass flow meter are connected in sequence.

[0015] On the other hand, the present invention also provides a method for measuring the radius and refractive index of a suspended single droplet, using the above-mentioned device for measuring the radius and refractive index of a suspended single droplet, the method comprising the following steps: Step 1: Pumping the aerosol into the single droplet suspension sample pool using a droplet pumping system; Step 2: At the same time, the light trap system and the atmosphere control system are turned on, and the laser emitted by the light trap system is used as a capture beam to capture a single droplet of the aerosol in the single droplet suspension sample pool and suspend it; at the same time, the required gas is introduced into the single droplet suspension sample pool through the atmosphere control system; Step 3: Turn on the LED beam shaping system and use the LED beam shaping system to obtain stimulated elastic scattering signals of the droplets.

[0016] Furthermore, in step 1, the diameter of a single droplet is ≤2.5 μm.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: (1) The present invention utilizes LED light sources to autonomously change or combine elastic scattering wavelength ranges, and can simultaneously measure the spontaneous and stimulated elastic scattering peak changes of droplets of specific chemical components in a wider wavelength range, thereby obtaining the real-time changes in droplet component concentration and droplet radius.

[0018] (2) The existing measurement method is not limited to the spontaneous and stimulated Raman peak position changes of water in a single droplet. When a droplet with a larger radius forms a whispering gallery mode with the laser, the number of stimulated Raman peaks of water in the droplet tends to 4 to 5 groups of peaks, but the number of stimulated Raman peaks of water measured by a droplet with a smaller radius tends to 1 to 2 groups of peaks, which greatly affects the accuracy of the Mie scattering theory inversion of the droplet radius. The present invention not only broadens the spectral acquisition range, but also the whispering gallery mode of elastic scattering, i.e., stimulated elastic scattering peaks, has the advantages of large number and high intensity. Therefore, clearer fitting parameters can be obtained in subsequent inversion calculations.

[0019] (3) The present invention uses the optical tweezers device to suspend aerosol droplets of micron-submicron size, and utilizes the resonance peak of the stimulated elastic scattering whispering gallery mode, namely the stimulated elastic scattering peak (the displacement trajectory of the peak is obtained by identifying the stimulated elastic scattering peak, and then the radius r and refractive index are inverted). The peak intensity is 6 to 8 orders of magnitude higher than that of stimulated Raman scattering, and has a higher signal-to-noise ratio. The change of droplet radius (i.e., dr / dt, the real-time change of radius over time) obtained by Mie theory inversion and fitting is clear and has high accuracy. Therefore, the method of measuring droplet radius and refractive index by stimulated elastic scattering can effectively overcome the problem of low subsequent inversion and fitting accuracy caused by the small radius of micron-submicron droplets, poor optical signals and poor spectral signal-to-noise ratio of stimulated Raman.

[0020] (4) The present invention uses the stimulated elastic scattering signal of the suspended droplet to measure its radius and refractive index, breaking through the limitations of the existing technology and achieving PM 2.5 Accurate measurement of the physical and chemical parameters of droplets of different sizes. According to the actual needs of the experiment, LED light sources of different wavelengths can be selected to illuminate the suspended droplets. The elastic scattering signal is very strong, which solves the problem of weak spontaneous Raman signals. The LED light source has a wide spectral peak range (half-peak width ~50nm). Even for droplets with a radius less than 2μm, more groups of stimulated elastic scattering peaks can appear, which can achieve accurate measurement of the radius.

[0021] (5) The present invention provides a new concept and method with high sensitivity and high accuracy for measuring atmospheric aerosol droplets of micron-submicron size.

[0022] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the embodiments of the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components; Figure 1 It is a schematic diagram of the composition of the device for measuring the droplet radius and the refractive index of the present invention; Figure 2 The morphology of the suspended single droplet in Example 2 in the microscopic imaging camera; Figure 3 is a stimulated elastic scattering spectrum of a single droplet suspended in Example 2; Figure 4is a graph showing the relationship between the peak displacement trajectory of the stimulated elastic scattering peak of a suspended single droplet in Example 2 and time; Figure 5 The displacement trajectory of the stimulated Raman peak of a suspended single droplet in Example 2 changes with time; Figure 6 The relationship between the radius of the ammonium chloride droplet and the time variation is measured by the stimulated elastic scattering method of Comparative Example 1; Figure 7 The relationship between the radius of the ammonium chloride droplet and the time variation is measured by the stimulated Raman scattering method of Comparative Example 1; Figure 8 The lower limit value of the radius of the ammonium chloride droplet measured by the stimulated elastic scattering method of Comparative Example 2; Fig. 9 The lower limit value of the radius of the ammonium chloride droplet measured by the stimulated Raman scattering method of Comparative Example 2; Fig.10 The peak shift and peak intensity change of the droplet with a radius of 2.9-2.5 μm were measured by stimulated elastic scattering of Comparative Example 4; Fig.11 The peak shift and peak intensity change of the droplet with a radius of 2.9-2.5 μm were measured by stimulated Raman scattering of Comparative Example 4; Fig.12 The peak shift and peak intensity changes of the droplets with a radius of 2.5-1.5 μm were measured by stimulated elastic scattering of Comparative Example 3; Fig.13 The peak shift and peak intensity change of the droplet with radius 2.9-1.7 μm were measured by stimulated Raman scattering of Comparative Example 3; Fig.14 It is a schematic diagram of the composition of the LED beam shaping system; Fig.15 It is a schematic diagram of the sample pool structure of the present invention; FIG. 16 ( a ) is a structural discrete diagram of the droplet beam device of the present invention; FIG16( b ) shows apertures of different diameters according to the present invention; FIG16 ( c ) shows washers of different diameters according to the present invention; Fig.17 is a cross-sectional view of the droplet beam device of the present invention; Fig.18 It is a schematic diagram of the monodisperse action principle of the droplet beam device of the present invention.

[0024] Reference numerals: 1- single droplet suspension sample pool; 101- sample pool body; 102- illumination light source; 1021- outer ring wall; 1022- inner ring wall; 1023- single droplet inlet; 1024- gas inlet; 1025- gas outlet; 2- droplet pumping system; 0201- aerosol generator; 2031- pipeline; 2032- aperture; 2033- gasket; 2034- clamp; 2035- threaded cover; 3- atmosphere control system; 301- gas generator; 302- pressure reducing valve; 303- flow meter; 4- light Trap system; 401-laser; 402-first semi-transparent and semi-reflective mirror; 403-beam expander; 404-microscope objective; 405-second semi-transparent and semi-reflective mirror; 406-third semi-transparent and semi-reflective mirror; 407-reflector; 5-optical signal detection system; 501-spectrometer; 502-spectral CCD detector; 503-data processing unit; 6-optical imaging system; 601-imaging CCD; 602-lens; 7-LED beam shaping system; 701-LED light source; 702-aperture group; 703-lens group. DETAILED DESCRIPTION

[0025] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0026] In one aspect, the present invention provides a device for measuring the radius and refractive index of a suspended single droplet, such as Figure 1 As shown, the measuring device includes a single droplet suspension sample pool 1 (optical tweezers device), a droplet pumping system 2, an atmosphere control system 3, a light trap system 4, an optical signal detection system 5, an optical imaging system 6 and an LED beam shaping system 7; wherein the LED beam shaping system 7 is connected to the light trap system 4, and the light trap system 4 is respectively connected to the single droplet suspension sample pool 1, the optical signal detection system 5 and the optical imaging system 6; in addition, the single droplet suspension sample pool 1 is respectively connected to the droplet pumping system 2 and the atmosphere control system 3.

[0027] Specifically, in the above-mentioned measuring device, the single droplet suspension sample pool 1 is a container for aerosol droplets to be suspended, which is an independent container that can pass background gas and reaction gas and has a specific humidity; the droplet pumping system 2 is used to pump aerosols of specific components into aerosol droplets and pump them into the single droplet suspension sample pool 1.

[0028] The single droplet suspension sample pool 1 comprises a sample pool body 101, such as Fig.15 As shown, The sample pool body 101 includes a concentric outer annular wall 1021 and an inner annular wall 1022, and a connecting portion is provided between the outer annular wall 1021 and the inner annular wall 1022, and the connecting portion is used to connect the outer annular wall 1021 and the partial side walls of the inner annular wall 1022, and a single droplet inlet 1023 is provided on the connecting portion that penetrates the outer annular wall 1021 and the inner annular wall 1022; the outer annular wall 1021 and the inner annular wall 1022 are each provided with a plurality of gas inlets 1024 and gas outlets 1025 that penetrate the annular walls and are arranged at intervals, and the gas inlet 1024 and gas outlet 1025 on the outer annular wall 1021 are staggered with the gas inlet 1024 and gas outlet 1025 on the inner annular wall 1022.

[0029] Specifically, the single droplet inlet 1023 , the gas inlet 1024 and the gas outlet 1025 are all arranged radially. Moreover, the diameters of the gas inlet 1024 and the gas outlet 1025 are both smaller than the diameter of the single droplet inlet 1023 , and the diameter of the gas inlet 1024 is smaller than the diameter of the gas outlet 1025 .

[0030] Exemplarily, the diameter of the single droplet inlet 1023 is 3-4 times the diameter of the gas inlet 1024, and the diameter of the single droplet inlet 1023 is 2-2.5 times the diameter of the gas outlet 1025. For example, the diameter of the single droplet inlet 1023 is 3 mm, the diameter of the gas inlet 1024 is 1.0 mm, and the diameter of the gas outlet 1025 is 1.5 mm.

[0031] It should be noted that the outer annular wall 1021 is coaxially arranged with the inner annular wall 1022 and shares a bottom surface with the sample pool. In addition, the distance between the outer annular wall 1021 and the inner annular wall 1022 is 2-3 mm.

[0032] In a preferred embodiment, a quartz glass sheet (not shown) is disposed at the bottom of the sample cell body 101, and an anionic surfactant layer is disposed on the quartz glass sheet. The anionic surfactant reduces the surface tension of the spherical droplets, and makes the droplets at the bottom of the sample cell no longer deposit in a spherical form, but directly spread on the bottom of the sample cell, thereby avoiding the measurement error caused by the curved surface pressure caused by the curved surface structure of the droplets containing volatile chemical components at the bottom of the sample cell.

[0033] Exemplarily, the anionic surfactant layer has a thickness of 0.1-0.2 mm.

[0034] Exemplarily, the anionic surfactant is sodium fatty alcohol ether sulfate and / or sodium dodecyl sulfate.

[0035] It should be noted that the droplets deposited on the inner wall of the sample pool cannot be solved directly by applying anionic surfactants. This is because, in addition to the single droplet inlet 1023, the structure of the sample pool body 101 of the present invention also includes a gas inlet 1024 and a gas outlet 1025. If the anionic surfactant is applied to the inner wall surface, when the humidity in the sample pool body 101 increases, water molecules and the anionic surfactant will be emulsified on the inner wall of the sample pool body 101 to produce foam, which may cause pore blockage, and when the foam collides and accumulates to a certain weight, it will not be able to hang on the wall and will slide to the quartz glass sheet at the bottom of the sample pool. If it slides to the vicinity of the focusing position, it will cause a macroscopic morphological effect of suspended droplet imaging. If it slides to the focusing center position of the microscope objective 404, it will affect the refraction effect and cause the suspended droplets to fall.

[0036] Compared with the prior art, the sample pool structure of the present invention can make the gas enter and discharge the sample pool evenly, and ensure the stability of the gas pressure in the sample pool, thereby stabilizing the optical tweezers to suspend a single droplet, and reducing the contact between the droplet and the wall, thereby reducing the wall effect; and the diameter of the gas inlet and the diameter of the gas outlet are both smaller than the diameter of the single droplet inlet. When a single droplet is pumped into the sample pool from the single droplet inlet, the turbulent effect of the aerosol droplets in the sample pool can be generated and enhanced. The rapid and swirling airflow does not simply go from the inlet to the outlet, but approaches the center of the sample pool (i.e., the laser focusing center) by means of turbulent action. At the same time, the swirling effect can also increase the probability of the airflow outside the focusing center returning to the focus, thereby increasing its capture efficiency, and reducing the probability of aerosol droplets depositing on the inner wall of the sample pool, reducing the error influence of the wall effect on the measurement result.

[0037] The droplet pumping system 2 is used to pump the aerosol of specific components into aerosol droplets and pump them into the single droplet suspension sample pool 1.

[0038] The atmosphere control system 3 of the present invention includes a dry gas control device and a wet gas control device; both the dry gas control device and the wet gas control device include a gas generator 301, a pressure reducing valve 302 and a mass flow meter 303; wherein the gas generator 301, the pressure reducing valve 302 and the mass flow meter 303 are connected in sequence, and the working process is as follows: the gas cylinder of the gas generator 301 outputs the gas of the controlled flow through the pressure reducing valve 302, and the gas of the controlled flow then passes through the mass flow meter 303 to obtain the accurate gas mass and gas volume. In addition, the wet gas control device also includes a humidifying container.

[0039] The above-mentioned atmosphere control system 3 has the following functions: one is humidity control: controlling relative humidity by different ratios of dry and wet gases; the other is reaction gas control: the trace gas demand for each experimental condition is different, and the mass flow rate is converted into the ppm / ppb demand of the trace gas through its mass flow meter 303.

[0040] The droplet pumping system 3 of the present invention comprises an aerosol generator 0201, a stop valve (not shown in the figure) and a droplet beam device (not shown in the figure) which are connected in sequence, and the droplet beam device is connected to the sample pool 101. When the aerosol droplets pass through the droplet beam device, the droplet beam device changes the droplets from an aggregated state into a monodispersed single string of droplets which enter the sample pool one by one.

[0041] Exemplarily, as shown in FIG. 16( a ), the droplet beam device 303 includes a plurality of pipes 2031 with different inner diameters connected in sequence, and the inner diameters of the plurality of pipes 2031 gradually decrease along the aerosol flow direction.

[0042] Furthermore, as shown in Figure 16(b) and Figure 4 As shown, a plurality of apertures 2032 with different inner diameters are arranged inside the pipeline 2031, and the inner diameters of the plurality of apertures 2032 gradually decrease along the aerosol flow direction.

[0043] For example, Fig.17 As shown, along the flow direction of the aerosol droplets, three apertures with gradually decreasing inner diameters are sequentially arranged in the first pipeline, an aperture with a smaller inner diameter than the inner diameter of the second pipeline is arranged at the outlet of the second pipeline, and an aperture with a smaller inner diameter than the inner diameter of the third pipeline is arranged at the outlet of the third pipeline. This embodiment can gradually arrange the gathered droplets into a string and discharge them from the outlet, as shown in FIG. Fig.18 shown.

[0044] For example, the inner diameter of the aperture at the outlet of the third pipeline is greater than or equal to the diameter of a single droplet and less than the diameter of the single droplet × 2. That is, the aperture at the outlet of the third pipeline can only pass a single droplet at the same time, such as Fig.18 shown.

[0045] Exemplarily, the aperture is coaxially arranged with the pipeline, and a gasket 2033 is arranged between the aperture and the inner wall of the pipeline ( FIG. 16( c )).

[0046] Exemplarily, a clamp 2034 is provided at the inlet end of the first tube for fixing the tube and adjusting the tube to align with the light capture point in the sample pool 101 .

[0047] Exemplarily, a threaded cap 2035 with a central hole is provided at the outlet of the third pipeline. The threaded cap 2035 is used to protect the outlet of the third pipeline.

[0048] A stop valve is arranged between the aerosol generator and the droplet beam device of the present invention. When the droplets enter the droplet beam device, the stop valve can be closed and the environmental background gas can be introduced into the droplet beam device to dilute the droplets in the droplet beam device, thereby further promoting the droplet beam device to change the droplets from an aggregated state into a monodisperse single string of droplets that enter the sample pool one by one.

[0049] In the method of the present invention, after a single droplet is suspended by optical tweezers technology, dry gas and / or wet gas is introduced into the sample pool through a gas atmosphere control system to reduce the humidity in the sample pool to below the weathering point humidity of the chemical components in the droplet, so that the droplets on the inner wall of the sample pool are weathered and crystallized, and then the humidity in the sample pool is adjusted to the humidity required for the reaction. During the weathering and crystallization process, the volatile components in the droplets deposited on the wall have volatilized. When the ambient humidity is increased to the reaction humidity, the crystals on the wall adsorb water molecules in the environment to form a solid-liquid mixture. The liquid phase in the solid-liquid mixture is only the adsorbed water molecules, and no longer has the volatile organic components in the aerosol droplets. In this process, the volatile components in the single droplet suspended by the optical tweezers remain unchanged, thereby effectively avoiding the influence of the volatile components in the droplets deposited on the wall on the measurement of the single droplet suspended by the optical tweezers.

[0050] The light trap system 4 of the present invention includes a laser 401, a first semi-transparent and semi-reflective mirror 402, a beam expander 403, a second semi-transparent and semi-reflective mirror 405, a microscope objective lens 404, a third semi-transparent and semi-reflective mirror 406 and a reflector 407; its working process is: the laser 401 emits a laser beam, which first passes through the first semi-transparent and semi-reflective mirror 402, the first semi-transparent and semi-reflective mirror 402 is used to change the propagation angle of the laser beam, and reflects the downward light into a horizontal beam. The beam is expanded by the beam expander 403 to increase the diameter of the laser beam, and then the laser beam is passed through the second semi-transparent and semi-reflective mirror 405 to change the propagation angle of the laser beam, and the horizontal light is reflected into upward and downward beams. After the upward beam passes through the microscope objective lens 404, the laser beam is focused to form a light trap, and the formed light trap is used to capture droplets; the downward beam is split by the third semi-transparent and semi-reflective mirror 406 and input into the optical signal detection system 5 and enters the optical imaging system 6 after changing direction by the reflector 407.

[0051] In the above-mentioned optical signal detection system 5, it includes a spectrometer 501, a spectral CCD detector 502 and a data processing unit 503; the spectrometer 501 is connected to the spectral CCD detector 502 and the data processing unit 503 respectively; its working process is: the light beam is focused on the slit of the spectrometer 501, and then enters the spectrometer 501, the spectrometer 501 detects the light beam through the spectral CCD detector 502, and then returns to the spectrometer 501, and the spectrometer 501 transfers the signal to the data processing unit 503 after signal processing to output the spectrum through software.

[0052] It should be pointed out that the detectors used for spectral measurement include, in addition to the spectral CCD detector, other detectors; they are not listed one by one here.

[0053] In the above optical imaging system 6, it includes a lens 602 and an imaging CCD 601, and the lens 602 is connected to the imaging CCD 601; its working process is: after the light beam is focused by the lens 602, the droplet signal is focused on the imaging CCD 601, and then the macroscopic morphology of the suspended droplet (such as Figure 2 as shown).

[0054] The above-mentioned LED beam shaping system 7 includes an LED light source 701, an aperture group 702 and a lens group 703, and its function is to change the divergent light source of the LED light source 701 into a parallel light beam. The parallel light enters the light trap system 4 and can be coupled with the laser beam emitted by the laser 401. After coupling, it is focused on the single droplet suspended in the sample pool 1 through the microscope objective 404 to provide a back-stimulated elastic scattering signal of the droplet, and the radius and refractive index of the droplet are directly measured based on the LED stimulated signal.

[0055] Specifically, it is crucial to determine the uniformity of the beam profile over its propagation distance. The lens 602 is used to convert the LED non-uniform beam and profile emitted by the LED light source 701 into a circular profile and homogenize it. Since the LED laser without collimating optical elements has different divergence angles in the x-axis and y-axis, the aperture and lens group 703 are used to convert it into a circular profile to form a collimated, uniform, parallel beam with a small divergence angle. At the same time, the clear aperture of each lens 602 must be larger than the corresponding maximum beam width to avoid beam truncation. The relative position and distance between the aperture and the lens 602 in the LED beam shaping system 7 can be freely adjusted. Fig.14 As one of the methods, it is ultimately necessary to ensure that the divergence angle of the LED beam and the light spot divergence angle are smaller than those before beam shaping and the light spot is uniform.

[0056] When the above-mentioned measuring device is implemented, the droplet pumping system 2 pumps the aerosol of specific components into the single droplet suspension sample pool 1; the laser emitted by the light trap system 4 is used as a capture beam to capture a single droplet and suspend it in the single droplet suspension sample pool 1 by constructing a light trap; after the droplet is suspended, the required gas is introduced into the single droplet suspension sample pool 1 through the atmosphere control system 3; at the same time, the LED beam shaping system 7 is turned on, and the LED beam shaping system 7 shapes the divergent light of the LED light source 701 into parallel light through the aperture group 702 and the lens group 703, and the parallel light enters the light trap The system 4 is coupled with the laser beam emitted by the laser 401, and after coupling, it is focused on the single droplet suspension sample pool 1 through the microscope objective 40404 to obtain the stimulated elastic scattering signal of the droplet, and the stimulated elastic scattering signal is returned to the light trap system 4 in the form of backscattering, and then focused on the optical signal detection system 5 and the optical imaging system 6. The spectrometer 501 in the optical signal detection system 5 processes the obtained droplet optical signal (spectrum information) through its data processing unit 503, and can convert the spectrum information into droplet radius, droplet refractive index and droplet peak position information (such as Figure 6 and Figure 7 As shown); the optical imaging system 6 is used to focus the obtained droplet radius, droplet refractive index and droplet peak position information onto the imaging CCD601, and then the macroscopic morphology of the suspended droplet is viewed through the imaging CCD601. The real-time, in-situ change information of the radius and refractive index values ​​of the obtained single droplet of a specific component (the single droplet of a specific component refers to a configured droplet, including an ammonium sulfate droplet, an ammonium sulfate + ammonium hydrogen sulfate droplet or an ammonium chloride droplet) before and after the reaction is inverted, and then the droplet radius change rate dr / dt is obtained according to the measured red shift or blue shift of the stimulated Raman peak of the droplet, so as to achieve the measurement of the mass growth factor of the suspended droplet moisture absorption process, the saturated vapor pressure of the volatilization process, the diffusion coefficient of the mass transfer diffusion process, the critical humidity of the liquid-liquid phase separation process, and the rate constant of the chemical reaction kinetic process.

[0057] Compared with the prior art, the suspended droplets used in the measuring device of the present invention are droplets of aerosol size close to those in the real atmospheric environment (droplet size ≤ 2.5 μm). The radius of droplets in the real environment is smaller, and PM2.5 is a droplet with an equivalent diameter of 2.5 μm. This method can suspend smaller droplets close to the real atmospheric environment. The present invention utilizes the resonance peak of the stimulated elastic scattering whispering gallery mode, namely the stimulated elastic peak, whose peak intensity is significantly different from that of spontaneous elastic scattering. The stimulated elastic scattering signal of the measured single droplet has a good signal-to-noise ratio, and the droplet radius change obtained by Mie theory inversion and fitting is clear and has high accuracy. Therefore, the use of stimulated elastic scattering to measure the droplet radius and refractive index can effectively overcome the problem of low subsequent inversion and fitting accuracy caused by the small radius of micron-submicron droplets, poor optical signals, and poor spectral signal-to-noise ratio.

[0058] It should be pointed out that when collecting stimulated elastic scattering signals of suspended droplets illuminated by LEDs, the method is not limited to the backscattering collection method, but also includes various other stimulated scattering signal collection methods.

[0059] The present invention also provides a method for accurately measuring the radius and refractive index of a suspended single droplet, using the above-mentioned measuring device, and the measuring method comprises the following steps: Step 1, using a droplet pumping system 2 to pump aerosol of a specific component into a single droplet suspension sample pool 1; Step 2: At the same time, the light trap system 4 and the atmosphere control system 3 are turned on, and the laser emitted by the light trap system 4 is used as a capture beam to capture a single droplet of the aerosol in the single droplet suspension sample pool 1 and suspend it; at the same time, the required gas is introduced into the single droplet suspension sample pool 1 through the atmosphere control system 3; In the above step 2, the laser beam emitted by the laser 401 in the optical trap system 4 is focused by the microscope objective 40404 to construct an optical potential well with an optical gradient force. The light intensity in the optical potential well is distributed in a gradient, and the optical gradient force is used to stably capture and suspend a single aerosol droplet.

[0060] Compared with the prior art, the method of the present invention for accurately measuring the radius and refractive index of a suspended single droplet is a direct measurement method. The method can directly present the radius and refractive index results based on the Mie scattering theory according to the whispering gallery mode of the droplet stimulated elastic scattering.

[0061] In the above step 2, the laser 401 of the light trap system 4 is used to emit a laser beam, which is expanded by the first semi-transparent and semi-reflective mirror 402 and the beam expander 403 and then split into two upward and downward laser beams by the second semi-transparent and semi-reflective mirror 405. The upward laser beam passes through the microscope objective 40404 to construct a light trap, and the downward laser beam is split by the third semi-transparent and semi-reflective mirror 406 and input into the optical signal detection system 5 and enters the optical imaging system 6 after changing direction by the reflector 407.

[0062] The above laser light sources can be selected in different types according to the requirements, including solid laser 401, gas laser 401, semiconductor laser 401, dye laser 401, and optical fiber light source suitable for the requirements of optical tweezers suspending droplets.

[0063] In step 2, the atmosphere control system 3 passes the ambient gas and trace reaction gas through the pressure reducing valve 302 and the flow meter 30303 to simulate the real external atmospheric environment atmosphere and control the humidity of the suspended single droplet.

[0064] In step 2, the atmosphere control system 3 controls the ratio of dry gas, wet gas and reaction gas entering the single droplet suspension sample pool 1 to simulate the trace reaction gas environment and relative humidity (60%-90% RH) in the actual atmospheric environment, and records the humidity of the mixed gas ratio and the mass concentration of each gas in real time.

[0065] Step 3: Turn on the LED beam shaping system 7 or use the LED beam shaping system 7 to obtain stimulated elastic scattering signals of the droplets.

[0066] In the above step 3, alternatively, the LED beam shaping system 7 is turned on simultaneously when the light trap system 4 is turned on.

[0067] In the above step 3, after a single droplet is captured and suspended, the LED beam shaping system 7 is turned on. The LED beam shaping system 7 shapes the divergent light of the LED light source 701 into parallel light, which enters the light trap system 4 and couples with the laser beam emitted by the laser 401. The light is focused on the single droplet suspension sample pool 1 through the microscope objective 40404 to obtain the stimulated elastic scattering signal of the droplet. The stimulated elastic scattering signal returns to the light trap system 4 in a backscattering manner and is then focused on the spectrometer 501 of the optical signal detection system 5 (the spectrometer 501 can collect spectral data) and the optical imaging system 6. Under specific atmospheric conditions, the dynamic changes of the droplet radius and refractive index are obtained by inverting the stimulated elastic scattering whispering gallery mode through the Mie scattering theory.

[0068] In the above step 3, the LED light source 701 enters the inner cavity of the droplet as the incident light and generates total reflection to form a standing wave, namely, an optical whispering gallery mode (WGM) resonant cavity. After the LED light source 701 is totally reflected in the inner cavity of the droplet, a stimulated elastic scattering signal is formed at its specific wavelength, and its signal intensity is higher than that of the elastic scattering signal.

[0069] In the above step 3, the wavelength of the light source of the LED beam shaping system 7 covers a wide range, including ultraviolet light, blue light, green light, yellow light, red light, infrared light and white light, and the LED light source 701 is connected with the aperture group 702 and the lens group 703 and coupled with the light trap optical path. The optical axis of the LED light source 701 and the optical axis of the laser optical path are coaxially incident into the microscope objective 404, and the spot size and intensity can be adjusted autonomously according to specific needs.

[0070] Compared with the prior art, the present invention can obtain a high-quality stimulated elastic scattering spectrum by selecting the wavelength band of the LED light source at the top of the LED beam shaping system 7, and achieve the fine particles (PM 2.5 ) to accurately obtain its radius and refractive index information.

[0071] In the above step 3, the elastic scattering signal carried by the single droplet from the LED light source 701 generates a stimulated elastic scattering signal after forming a standing wave in the droplet using the whispering gallery mode. The radius and refractive index of the droplet can be inverted through the Mie scattering theory. The radius change rate dr / dt and the refractive index of the droplet of a specific component in a preset atmosphere are obtained through fitting. The mass growth factor of the droplet moisture absorption process, the saturated vapor pressure of the volatilization process, the diffusion coefficient of the mass transfer diffusion process, and the rate constant of the chemical reaction kinetics process are then calculated using the radius change rate dr / dt.

[0072] It should be noted that the optical imaging system 6 can simultaneously use the backscattered stimulated elastic scattering signal formed by the LED light source 701 together with the spectral signal detection system to complete the spectral detection and optical imaging of a single droplet.

[0073] The above-mentioned method for measuring stimulated elastic scattering of suspended droplets, in addition to using the above-mentioned device to perform backscattering measurement, also includes other methods and devices for collecting stimulated elastic scattering signals at any angle.

[0074] Compared with the existing technology, the suspended single droplet is inverted based on the whispering gallery mode of stimulated elastic scattering and the Mie scattering theory to obtain the real-time dynamic changes of the droplet radius and refractive index of a specific component. The real-time dynamic changes of the droplet radius and refractive index obtained can provide a real-time change reference for calculating the droplet dynamics and physical and chemical parameters, reducing experimental errors.

[0075] The measuring principle of the measuring method of the present invention is: using a single droplet suspension sample pool 1 (optical tweezers device) and a light trap system 4 to capture a single droplet, using an LED light source 701 to light up the suspended droplet and measuring the elastic scattering signal of the droplet LED, elastic scattering light of a specific wavelength forms a standing wave in the droplet, i.e., a whispering gallery mode, and a group of resonance peaks of the whispering gallery mode, i.e., stimulated elastic scattering peaks, can be obtained, which are superimposed on the elastic scattering peaks generated by the continuous LED light source. According to the position of the stimulated elastic scattering peak, the radius and refractive index of the droplet are calculated using Mie scattering theory. The optical tweezers device uses the gradient force of the laser to capture a single droplet containing different chemical components, and the single droplet and the surrounding atmosphere undergo a dynamic process of gas-particle distribution, gas-particle balance, and gas-particle conversion. The stimulated elastic scattering signal of the LED can provide radius and refractive index change information in real time and in situ, thereby realizing the measurement of parameters such as the mass growth factor of the suspended droplet moisture absorption process, the saturated vapor pressure of the volatilization process, the diffusion coefficient of the mass transfer diffusion process, the critical humidity of the liquid-liquid phase separation process, and the rate constant of the chemical reaction kinetic process.

[0076] In summary, the present invention uses the optical tweezers device to suspend aerosol droplets of micron-submicron size, and uses the resonance peak of the stimulated elastic scattering whispering gallery mode, namely the stimulated elastic scattering peak (the displacement trajectory of the peak is obtained by identifying the stimulated elastic scattering peak, and then the radius r and refractive index are inverted). Its peak intensity is 6 to 8 orders of magnitude higher than that of stimulated Raman scattering, and has a higher signal-to-noise ratio. The change of droplet radius (i.e., dr / dt, the real-time change of radius over time) obtained by Mie theory inversion and fitting is clear and has high accuracy. Therefore, the method of measuring droplet radius and refractive index by stimulated elastic scattering can effectively overcome the problem of low subsequent inversion and fitting accuracy caused by stimulated Raman due to the small radius of micron-submicron droplets, poor optical signals and poor spectral signal-to-noise ratio.

[0077] Compared with the prior art, the stimulated elastic scattering generated by the LED light of the present invention measures the stimulated elastic scattering signal of the droplet; when the droplet radius is very small, the traditional method cannot detect the light signal, but this method can still have a good light signal and can detect it. In addition, the method provided by the present invention can directly measure the important physical and chemical parameters of atmospheric aerosols (droplet radius and refractive index), can achieve accurate measurement and joint characterization of key physical and chemical parameters in the evolution process of atmospheric particulate matter, and provide a key parameterized measurement scheme for revealing the generation mechanism of aerosols in the process of atmospheric fine particulate matter pollution prevention and control.

[0078] The method for accurately measuring the radius and refractive index of a liquid droplet by using stimulated elastic scattering of the present invention is further described below by way of specific embodiments.

[0079] Example 1 This embodiment provides a stimulated elastic scattering method for accurately measuring a droplet radius and a refractive index, comprising the apparatus of embodiment 1, including: The droplet pumping system 2 pumps aerosols of specific components into the single droplet suspension sample pool 1. At this time, the laser beam emitted by the laser 401 in the optical trap system 4 is focused through the microscope objective 40404 to construct an optical potential well, and the optical gradient force is used to stably capture and suspend the aerosol single droplet. The atmosphere control system 3 controls the ambient gas and trace reaction gas through the pressure reducing valve 302 and the flow meter 30303 to simulate the real atmospheric environment atmosphere and control the humidity of the suspended single droplet.

[0080] The laser 401 of the light trap system 4 emits a laser beam, which is expanded by a semi-transparent and semi-reflective mirror 402 and a beam expander 403 and then split into two upper and lower laser beams by a semi-transparent and semi-reflective mirror 405. One of the laser beams passes through a microscope objective 40404 to construct a light trap, and the other laser beam is split again by a semi-transparent and semi-reflective mirror 406 and input into the optical signal detection system 5 respectively, and then changes direction by a reflector 407 and enters the optical imaging system 6.

[0081] The LED beam shaping system 7 shapes the divergent light of the LED light source 701 into parallel light that enters the light trap system 4 and couples with the laser beam. The light is focused on the single droplet suspension sample pool 1 through the microscope objective 40404 to obtain the stimulated elastic signal of the droplet, which is returned to the light trap system 4 in a backscattering manner and then focused on the optical signal detection system 5. The displacement change of the characteristic peak of the suspended single droplet is analyzed based on the signal data of stimulated elastic scattering, and then the numerical changes of the refractive index and radius of the droplet in the reaction process are obtained by inversion using the Mie scattering theory.

[0082] The atmosphere control system 3 simulates the trace reaction gas environment and relative humidity (60%-90% RH) in the actual atmospheric environment by controlling the ratio of dry gas, wet gas and reaction gas entering the single droplet suspension sample pool 1, and records the humidity of the mixed gas ratio and the mass concentration of each gas in real time.

[0083] During implementation, the droplet pumping system 3 pumps the aerosol into the sample pool 101 of the single droplet suspension system 1 in the form of a single droplet; the single droplet suspension system 1 includes the sample pool 101, such as Figure 2 As shown, the sample pool 101 includes a concentric outer annular wall 1021 and an inner annular wall 1022, and a connecting portion is provided between the outer annular wall 1021 and the inner annular wall 1022, and the connecting portion is used to connect partial side walls of the outer annular wall 1021 and the inner annular wall 1022, and a single droplet inlet 1023 penetrating the outer annular wall 1021 and the inner annular wall 1022 is provided on the connecting portion; the outer annular wall 1021 and the inner annular wall 1022 are each provided with a plurality of gas inlets 1024 and gas outlets 1025 penetrating the annular walls and arranged at intervals, and the gas inlet 1024 and gas outlet 1025 on the outer annular wall 1021 are staggered with the gas inlet 1024 and gas outlet 1025 on the inner annular wall 1022.

[0084] Specifically, the single droplet inlet 1023 , the gas inlet 1024 and the gas outlet 1025 are all arranged radially. Moreover, the diameters of the gas inlet 1024 and the gas outlet 1025 are both smaller than the diameter of the single droplet inlet 1023 , and the diameter of the gas inlet 1024 is smaller than the diameter of the gas outlet 1025 .

[0085] Figure 2 This is a morphology image of a suspended single droplet in Example 1 in a microscopic imaging camera, which illustrates that a single microdroplet is stably captured at the focus of the optical tweezers; Figure 3 This is the stimulated elastic spectrum of the suspended single droplet in Example 1.

[0086] Example 2 Method for detecting droplet radius and refractive index using stimulated elastic scattering ( Figure 4 ) and stimulated Raman scattering detection method ( Figure 5), there is a significant difference in the relationship between the characteristic peak displacement and time of the collected spectral data. Figure 4 The peak position shift can be clearly seen in Figure 5 Although there is a continuous linear change trend, a large number of noise points are still identified. This will lead to the inability to accurately calculate the dr / dt and droplet radius value in the subsequent numerical judgment of the droplet radius and refractive index based on Mie scattering inversion.

[0087] Comparative Example 1 By peak finding, the displacement trajectory of the characteristic peak position is obtained over time, and the linear relationship of the droplet radius dr / dt-t is obtained (such as Figure 6 and Figure 7 As shown in Figure 3), this set of data can determine the growth rate of the droplet radius, that is, the volatilization rate of ammonium chloride and the change value of the droplet radius during the reaction. Figure 6-7 By comparing the stimulated elasticity and stimulated Raman scattering in the data, it can be seen that, under the same environment with a relative humidity of 80%, the data points of stimulated elastic scattering dr / dt are continuous and dense, while the data points of stimulated Raman scattering dr / dt are discontinuous and sparse. This result may be due to the fact that when detecting the optical signal of the droplet, the elastic scattering spectrum bandwidth of the LED light source 701 can accommodate and highlight more stimulated elastic scattering resonance peaks, and the spontaneous Raman signal is 6-8 orders of magnitude lower than the stimulated elastic scattering signal. Therefore, the stimulated elastic scattering signal measured by the present invention may have better potential in the field of detecting physical and chemical parameters such as the radius and refractive index of atmospheric aerosol droplets.

[0088] Comparative Example 2 For droplets containing volatile components such as NH4Cl, the change in the droplet radius before and after the droplet volatilizes is screened by the refractive index range. The comparative proportions show that the optical signals detectable by the spectrometer 501CCD502 after NH4Cl volatilizes are measured by stimulated elastic scattering and stimulated Raman scattering respectively. The minimum droplet radius that can be detected after the droplet volatilizes is obtained by Mie scattering fitting inversion. Figure 8 and Fig. 9 As shown in the figure, the stimulated elastic scattering method can detect a minimum droplet radius of 1582.9 nm, while the stimulated Raman scattering method can detect a minimum droplet radius of 2523.0 nm. This result shows that the droplet radius detected by the stimulated elastic scattering method can exceed the detection limit of the original method.

[0089] Comparative Example 3 The stimulated signals of NH4Cl volatile component droplets with a radius of 2.9-2.5 μm were detected by stimulated elastic scattering and stimulated Raman scattering, and the peak position displacement trajectory and peak intensity were compared. Fig.10 and Fig.11As shown in the figure, the peak displacement trajectory of stimulated elastic scattering is obviously different from the background information, and compared with stimulated Raman scattering, both the peak intensity and peak displacement have obvious advantages. This result shows the advantages of stimulated elastic scattering with high intensity and good optical signal. The measurement results obtained after Mie scattering inversion are significantly improved compared with previous measurement methods.

[0090] Comparative Example 4 The stimulated signals of NH4Cl volatile component droplets with smaller radius were detected by stimulated elastic scattering and stimulated Raman scattering, and the peak position displacement trajectory and peak intensity were compared. Fig.12 and Fig.13 As shown, the displacement trajectory and peak intensity of the resonance peak can be better resolved, fitted and inverted to the radius and refractive index. Based on this, the minimum detectable droplet radius of NH4Cl obtained by stimulated elastic scattering fitting inversion is in the range of 2.5~1.5μm. Compared with the detection limit of 2.5 μm of stimulated Raman scattering, the method of directly measuring the droplet radius and refractive index by stimulated elastic scattering is better. Therefore, the droplet radius and refractive index directly measured by the stimulated elastic scattering method of the present invention can break through the detection limit of the original technology, that is, the detection range of the droplet radius and refractive index measured by the present invention is widened, and the error of the measurement result is small.

[0091] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A device for measuring the radius and refractive index of a suspended single droplet, characterized in that: It includes a single droplet suspension sample pool, a droplet pumping system, an atmosphere control system, a light trap system, an optical signal detection system, an optical imaging system, and an LED beam shaping system; The LED beam shaping system is connected to the light trap system, and the light trap system is respectively connected to the single droplet suspension sample pool, the optical signal detection system and the optical imaging system; at the same time, the single droplet suspension sample pool is respectively connected to the droplet pumping system and the atmosphere control system.

2. The device for measuring the radius and refractive index of a suspended single droplet according to claim 1, characterized in that: The droplet pumping system is used to pump the aerosol into aerosol droplets and pump the aerosol droplets into a single droplet suspension sample pool.

3. The device for measuring the radius and refractive index of a suspended single droplet according to claim 1, characterized in that: The light trap system comprises a laser, a first semi-transparent and semi-reflective mirror, a beam expander, a second semi-transparent and semi-reflective mirror, a microscope objective lens, a third semi-transparent and semi-reflective mirror and a reflector; The optical trap system is used to capture a single droplet and suspend it.

4. The device for measuring the radius and refractive index of a suspended single droplet according to claim 3, characterized in that: The laser is used to emit a laser beam, which is split after passing through a first semi-transparent and semi-reflective mirror, a beam expander, and a second semi-transparent and semi-reflective mirror. The upward laser beam is focused by the microscope objective lens to form a light trap to capture a single droplet; the downward laser beam is split by a third semi-transparent and semi-reflective mirror, and is respectively input into an optical signal detection system and enters an optical imaging system after changing direction through a reflector.

5. The device for measuring the radius and refractive index of a suspended single droplet according to claim 4, characterized in that: The LED beam shaping system comprises an LED light source; The LED beam shaping system can shape the divergent light of its LED light source into parallel light. The parallel light enters the light trap system and can be coupled with the laser beam emitted by the laser. After coupling, it is focused in the sample pool through the microscope objective to suspend a single droplet. The LED is illuminated to suspend the single droplet, and its stimulated elastic scattering signal is collected, which is not limited to the backscattering method, but also includes stimulated scattering signal collection methods at other angles.

6. The device for measuring the radius and refractive index of a suspended single droplet according to claim 1, characterized in that: The optical signal detection system comprises a spectrometer, a spectral CCD detector and a data processing unit, wherein the spectrometer is connected to the spectral CCD detector and the data processing unit respectively.

7. The device for measuring the radius and refractive index of a suspended single droplet according to claim 1, characterized in that: The optical imaging system includes a lens and an imaging CCD; The lens is connected to the imaging CCD; after the light beam is focused by the lens, the droplet signal is focused onto the imaging CCD, and the macroscopic morphology of the suspended droplet is observed through the imaging CCD.

8. The device for measuring the radius and refractive index of a suspended single droplet according to claim 1, characterized in that: The atmosphere control system comprises a gas generating device, a pressure reducing valve and a mass flow meter; the gas generating device, the pressure reducing valve and the mass flow meter are connected in sequence.

9. A method for measuring the radius and refractive index of a suspended single droplet, characterized in that: Using the device for measuring the radius and refractive index of a suspended single droplet according to any one of claims 1 to 8, the measuring method comprises the following steps: Step 1: Pumping the aerosol into the single droplet suspension sample pool using a droplet pumping system; Step 2: At the same time, the light trap system and the atmosphere control system are turned on, and the laser emitted by the light trap system is used as a capture beam to capture a single droplet of the aerosol in the single droplet suspension sample pool and suspend it; at the same time, the required gas is introduced into the single droplet suspension sample pool through the atmosphere control system; Step 3: Turn on the LED beam shaping system and use the LED beam shaping system to obtain stimulated elastic scattering signals of the droplets.

10. The method for measuring the radius and refractive index of a suspended single droplet according to claim 9, characterized in that: In step 1, the diameter of the single droplet is ≤2.5 μm.

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