Particle counter

Abstract

The utility model discloses a particle counter, which relates to the technical field of gas detection and is characterized in that a pumping source is arranged on the outer side of a laser resonant cavity, a laser crystal is arranged in the laser resonant cavity, first-wavelength laser emitted by the pumping source enters the laser resonant cavity, and the laser crystal is irradiated by the first-wavelength laser to form second-wavelength laser; the second wavelength laser forms optical oscillation in the laser resonant cavity, the aerosol generating device provides aerosol airflow into the laser resonant cavity, the aerosol airflow passes through a light beam of the second wavelength laser, and the photoelectric detection device detects a scattered light signal of aerosol particles. The counter can realize detection of dust particles with the particle size of 0.1 micron, and has the advantages of low power consumption, portability and high detection precision.

Description

Technical Field

[0001] The utility model relates to the technical field of gas detection, in particular to a particle counter. Background Art

[0002] At present, particle counters using lasers are relatively mature in detecting particles with a diameter greater than 0.3 microns, and can accurately detect the concentration of particles with a diameter greater than 0.3 microns. For particles with a diameter less than 0.3 microns, since the intensity of scattered light from particles is proportional to the sixth power of the particle diameter, the intensity of scattered light is very weak, and since Rayleigh scattering in the air will form noise as background light, a laser beam with a larger energy and a suitable beam shape is required to detect particles with a diameter less than 0.3 microns. Generally, the laser power is required to reach more than 40 watts, and the use of high-power lasers will result in high electrical power and high heat generation.

[0003] The above information disclosed in the background technology is only used to increase the understanding of the background technology of the present application, and therefore, it may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0004] In view of the problems pointed out in the background technology, the utility model provides a particle counter, which can detect dust particles with a particle size of 0.1 micron and has the advantages of low power consumption, portability and high detection accuracy.

[0005] In order to achieve the above-mentioned utility model purpose, the utility model adopts the following technical solutions:

[0006] In some embodiments, a particle counter is provided, comprising:

[0007] a pump source configured to emit laser light of a first wavelength;

[0008] A laser resonant cavity, wherein the laser light of the first wavelength emitted by the pump source enters the laser resonant cavity;

[0009] A laser crystal, which is disposed in the laser resonant cavity, and the laser crystal is configured to be irradiated by the first wavelength laser to form a second wavelength laser, and the second wavelength laser forms an optical oscillation in the laser resonant cavity;

[0010] an aerosol generating device, configured to provide an aerosol gas flow into the laser resonant cavity, wherein the aerosol gas flow passes through the light beam of the second wavelength laser;

[0011] A photoelectric detection device is configured to detect scattered light signals of aerosol particles.

[0012] In some embodiments, the laser crystal is a Pr:YLF crystal;

[0013] The wavelength range of the first wavelength laser emitted by the pump source is [400, 700] nm;

[0014] The wavelength range of the second wavelength laser generated by the Pr:YLF crystal is [500, 700] nm.

[0015] In some embodiments, the wavelength range of the first wavelength laser emitted by the pump source is [430, 490] nm.

[0016] In some embodiments, the wavelength range of the first wavelength laser emitted by the pump source is [439, 449] nm or [464, 474] nm or [474, 484] nm.

[0017] In some embodiments, the wavelength range of the second wavelength laser generated by the Pr:YLF crystal is [638, 642] nm or [521, 525] nm.

[0018] In some embodiments, the laser crystal is a ruby ​​crystal;

[0019] The wavelength range of the first wavelength laser emitted by the pump source is [390, 450] nm;

[0020] The wavelength range of the second wavelength laser generated by the ruby ​​crystal is [600,750] nm.

[0021] In some embodiments, the particle counter includes a first reflector and a second reflector arranged at an interval, the laser resonant cavity is formed between the first reflector and the second reflector, the pump source is located outside the laser resonant cavity, the first wavelength laser emitted by the pump source enters the laser resonant cavity through the first reflector and / or the second reflector, and the second wavelength laser forms light oscillation between the first reflector and the second reflector.

[0022] In some embodiments, the reflectivity of the first reflector to the second wavelength laser is not less than 95%;

[0023] The reflectivity of the second reflector to the second wavelength laser is not less than 95%.

[0024] In some embodiments, the transmittance of the first wavelength laser emitted by the pump source to the first wavelength laser through the first reflector and / or the second reflector is not less than 80%.

[0025] In some embodiments, the particle counter includes a reflector;

[0026] The laser crystal is provided with an optical coating on a side surface facing the pump source, the laser resonant cavity is formed between the optical coating and the reflector, the pump source is located outside the laser resonant cavity, the first wavelength laser emitted by the pump source enters the laser resonant cavity through the optical coating and / or the reflector, and the second wavelength laser forms an optical oscillation between the optical coating and the reflector.

[0027] In some embodiments, the pump source is a laser diode.

[0028] In some embodiments, the photoelectric detection device includes a first photoelectric detection module, which is configured to detect scattered light signals of particles with a particle size of 0.1-0.3 microns.

[0029] In some embodiments, the first photoelectric detection module includes a first photodetector and a first scattered light collection system, the first scattered light collection system uses a lens to collect scattered light signals, and the first photodetector uses a photodiode array.

[0030] In some embodiments, the photoelectric detection device includes a second photoelectric detection module, which is configured to detect scattered light signals of particles with a particle size greater than 0.3 microns.

[0031] In some embodiments, the second photoelectric detection module includes a second photodetector and a second scattered light collection system, the second scattered light collection system uses a Mankin mirror or a double concave mirror to collect scattered light signals, and the second photodetector uses a single pixel detector.

[0032] Compared with the prior art, the advantages and positive effects of the utility model are:

[0033] The particle counter disclosed in the present application utilizes the cooperation of a pump source, a laser crystal and related optical paths, adopts a low-energy pump source outside the laser resonant cavity, utilizes the laser crystal to obtain a higher-power laser in the laser resonant cavity, and utilizes the high-power laser source in the cavity to realize particle detection of 0.1-0.3 micron particle size, and at the same time has the advantages of low power consumption, portability, and high detection accuracy.

[0034] After reading the specific embodiments of the present invention in conjunction with the accompanying drawings, other features and advantages of the present invention will become more clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0036] Figure 1 is a schematic diagram of a particle counter according to some embodiments;

[0037] Figure 2 is the absorption cross section of the Pr:YLF crystal according to some embodiments;

[0038] Figure 3 is the emission cross section of a Pr:YLF crystal according to some embodiments;

[0039] Figure 4 is a schematic diagram of a response spectrum of a silicon photodiode according to some embodiments;

[0040] Figure 5 is a schematic diagram of a lens assembly according to some embodiments;

[0041] Figure 6 is a schematic diagram of an aperture according to some embodiments;

[0042] Figure 7 is another principle schematic diagram of a particle counter according to some embodiments;

[0043] Reference numerals:

[0044] 10. Pump source; 11. First wavelength laser;

[0045] 21. a first reflector; 22. a second reflector;

[0046] 30. Laser crystal; 31. Second wavelength laser; 32. Optical coating;

[0047] 41. aerosol nozzle; 42. aerosol outlet; 43. aerosol airflow;

[0048] 50. First photoelectric detection module; 51. First photoelectric detector; 52. First scattered light collection system; 53. Lens group; 54. Convex lens; 55. Diaphragm;

[0049] 60. Second photoelectric detection module; 61. Second photoelectric detector; 62. Second scattered light collection system;

[0050] 70. A third photodetector. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0052] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0053] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0054] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0055] In the present utility model, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0056] The disclosure below provides many different embodiments or examples for realizing different structures of the utility model. In order to simplify the disclosure of the utility model, the components and settings of specific examples are described below. Of course, they are merely examples, and the purpose is not to limit the utility model. In addition, the utility model may repeat reference numbers and / or reference letters in different examples, and such repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the utility model provides various specific examples of processes and materials, but those of ordinary skill in the art may be aware of the application of other processes and / or the use of other materials.

[0057] In some embodiments, a particle counter is provided to achieve at least the technical effects of low power consumption, portability, and high detection accuracy. The particle counter can detect not only particles with a particle size of 0.3 microns or more, but also particles with a particle size of 0.1-0.3 microns.

[0058] In the prior art, particle counters using lasers can detect the concentration of particles larger than 0.3 microns, but cannot detect particles with a particle size of 0.1-0.3 microns. The core technical difficulty that restricts the detection of particles with a particle size of 0.1-0.3 microns by existing particle counters is the inability to obtain the high-power laser light source required to detect particles with a particle size of 0.1-0.3 microns.

[0059] In instruments for detecting particles with a diameter greater than 0.3 microns, semiconductor laser diodes are generally used as light sources. Semiconductor laser diodes have the advantages of low cost, small size, and light weight.

[0060] However, when detecting particles with a diameter of 0.1-0.3 microns, the scattered light intensity is very weak because it is approximately proportional to the sixth power of the particle size. This requires a higher power light source, and laser diodes with an output power of only watts are obviously unable to meet the detection needs.

[0061] When detecting dust particles with a particle size of 0.1-0.3 microns, the Rayleigh scattering power generated by the air cannot be ignored because the particle size is very small and the scattered light is very weak. In addition, since the Rayleigh scattering in the air will form noise as background light, the signal-to-noise ratio of the scattered light signal will drop significantly. Since the noise formed by Rayleigh scattering is proportional to the square root of the Rayleigh scattering intensity, and the scattered light signal of the dust particles is proportional to the incident light power, if the laser power is increased to n times the original, the signal-to-noise ratio of the scattered light signal will increase by the square root of n times.

[0062] For example, when using a 640nm wavelength laser, the laser power must be above 40 watts to effectively detect particles with a diameter of 0.1 micron. Using a high-power laser diode means higher electrical power and higher heat generation, making it difficult to make a portable detection instrument.

[0063] To sum up, due to the current technological limitations of laser diodes, it is impossible to obtain a high-power laser light source that can be used to detect 0.1-0.3 micron particles using laser diodes alone.

[0064] In view of the above technical background, this embodiment proposes a particle counter, referring to Figure 1 , creatively utilizing the pump source 10, the laser crystal 30 and the related optical paths to obtain a high-power laser light source, realizing particle detection with a particle size of 0.1-0.3 microns, and at the same time having the advantages of low power consumption, portability, and high detection accuracy.

[0065] Specifically, the particle counter includes a pump source 10, which is configured to emit a first wavelength laser 11. The light spot of the light source generated by the pump source 10 is linear and can produce a sheet-shaped light beam, which is suitable for the particle size detection of dust particles.

[0066] In a specific embodiment, the pump source 10 is a laser diode, which has low cost, small size, and light weight, and is conducive to the compactness of the overall structure and convenient design.

[0067] The particle counter comprises a laser resonant cavity. The laser resonant cavity is a steady-state internal resonant cavity. A first wavelength laser 11 emitted by a pump source 10 enters the laser resonant cavity.

[0068] The particle counter includes a laser crystal 30 disposed in a laser resonant cavity. The laser crystal 30 is configured to be irradiated by a first wavelength laser 11 to form a second wavelength laser 31 , and the second wavelength laser 31 forms optical oscillation in the laser resonant cavity.

[0069] In other words, the first wavelength laser 11 entering the laser resonant cavity is focused on the laser crystal 30 , and the laser crystal 30 is irradiated to form the second wavelength laser 31 .

[0070] The cavity mirror forming the laser resonant cavity has a high reflectivity for the second wavelength laser 31. Because the laser resonant cavity is a steady-state cavity, it has a low intracavity loss, and the second wavelength laser 31 has a high intensity in the cavity. The second wavelength laser 31 is reflected a high number of times in the laser resonant cavity, making full use of the reflected signal generated by the light energy, and the light energy utilization rate is high.

[0071] That is to say, by using a low-energy pump source 10 outside the laser resonant cavity, a higher-power laser can be obtained in the laser resonant cavity. In this way, the high-power laser source in the cavity can be used to detect particles with a diameter of 0.1-0.3 microns.

[0072] When particle detection is performed inside the laser resonant cavity, the photosensitive area can obtain extremely high energy density compared to detection outside the cavity.

[0073] The particle counter comprises an aerosol generating device, which is configured to provide an aerosol gas flow 43 into the laser resonance cavity, and the aerosol gas flow 43 passes through the light beam of the second wavelength laser 31 .

[0074] The specific structure of the aerosol generating device can refer to the prior art, and will not be elaborated in this embodiment. The aerosol generating device includes an aerosol nozzle 41 and an aerosol outlet 42. The aerosol airflow 43 flowing out of the aerosol nozzle 41 passes through the beam of the second wavelength laser 31 at a certain speed. When the aerosol particles pass through the laser beam, the laser is scattered, and the aerosol particles flow out from the aerosol outlet 42.

[0075] The particle counter includes a photoelectric detection device configured to detect scattered light signals of aerosol particles.

[0076] Since the light beam of the second wavelength laser 31 in the laser resonant cavity has a higher power, the aerosol particles passing through the second wavelength laser beam can produce stronger scattered light. When detecting particles with a particle size of 0.1-0.3 microns, although the particle size is small and the scattering is relatively weak, the particle signal can also be detected due to the high power of the laser beam, thereby realizing the detection of 0.1-0.3 micron particles and meeting the needs of small particle size detection.

[0077] In some embodiments, the laser crystal 30 is a Pr:YLF crystal. The theoretical analysis of the selection of the Pr:YLF crystal is as follows:

[0078] Particle scattering has the following characteristics: (1) The intensity of scattered light is proportional to the intensity of incident light; (2) The intensity of scattered light is approximately proportional to the sixth power of the particle size; (3) The intensity of scattered light is approximately inversely proportional to the fourth power of the wavelength of the incident light.

[0079] That is to say, the scattering signal of a 0.1 micron particle is only about 1 / 700 of that of a 0.3 micron particle. In order to detect the scattering signal of small-size particles, the power of the incident laser should be increased on the one hand, and light with a shorter wavelength should be used as much as possible on the other hand.

[0080] The detection capability of a particle counter is also related to the response spectrum of the detector used to detect scattered light. The detector includes photomultiplier tubes, silicon photodiodes, and photodiodes made of materials such as gallium arsenide. The response spectrum of commonly used silicon photodiodes is as follows: Figure 4 As shown. As a commonly used photoelectric detection device, silicon photodiode has the advantages of small dark current and large dynamic range, but its response spectrum is mainly in the range of 0.6-1 micron. Therefore, the wavelength of the light source is required to be optimal in this range.

[0081] The detection capability of small particle scattering signals is also affected by the photoelectric detection device. The commonly used silicon photoelectric detection device has the advantages of small dark current and large dynamic range, but it has a high response mainly in the wavelength range of 0.6-1 micron, so the wavelength of the laser should be selected within this range.

[0082] Lasers also have a characteristic that the optical power in the resonant cavity is much higher than the output power outside the cavity, and the ratio of the output power to the optical power in the cavity is approximately the transmittance of the output cavity mirror. In other words, if a cavity mirror with a reflectivity of 99.99% is used, the generated laser will continuously reflect back and forth in the resonant cavity, and only 0.001% of the light will be projected out. Therefore, the power in the cavity is 10,000 times the output power. Therefore, if dust particles are detected in the cavity, the detection capability will be greatly improved.

[0083] Based on the above considerations, we use a laser diode as the pump source 10, a Pr:YLF crystal as the laser crystal 30, and a high-reflectivity resonant mirror for detection in the laser resonant cavity, which can achieve the detection of 0.1-micron dust particles.

[0084] Pr:YLF crystal has a special step-level structure. The stimulated absorption cross section of Pr:YLF crystal at each wavelength is as follows: Figure 2 As shown in Figure 3 shown.

[0085] Figure 2 Curve a and curve b are the absorption cross sections of Pr:YLF crystal for pump light of different polarization directions. The larger the absorption cross section, the higher the absorption rate. As can be seen from the figure, the crystal absorbs pump light of 430-490nm, among which there are three absorption peaks at 444nm, 469nm and 479nm, and the absorption cross section is relatively large. When the wavelength of the pump light is these three wavelengths, the efficiency of generating the second wavelength laser is the highest.

[0086] Based on this, the particle counter in this case uses a laser diode capable of emitting a first wavelength laser in the wavelength range of [439, 449] nm as a pump source 10, which can output an optical power of about 5 W and has a relatively low price.

[0087] Figure 3 Curve c and curve d are the emission cross sections of Pr:YLF crystal in different polarization directions. The larger the emission cross section, the higher the emissivity. As can be seen from the figure, Pr:YLF has emission peaks at 479, 523, 640, 604, 607, 698, and 721nm. Since the emission peak and absorption peak of 479 coincide, it is not suitable for generating lasers of this wavelength. 640nm has a higher emission cross section and is most suitable for generating lasers of this wavelength, while 523nm is second. Due to the low absorption rate of other wavelengths, the pump light conversion efficiency is low. Unless there is a special requirement, it is not suitable for generating lasers.

[0088] In summary, within the visible light band, Pr:YLF crystals can produce a variety of different transition wavelengths, covering a wide range and with a large emission cross section. Laser output can be achieved in the six visible light bands of near infrared (720 nm), red light (695 nm), red light (639 nm), orange light (607 nm), green light (522 nm), and blue light (479 nm). Therefore, Pr:YLF crystals are ideal working media for obtaining visible light band lasers.

[0089] Among them, the blue light band (479 nm) belongs to the quasi-three-level process, and the other five bands are typical four-level processes. Figure 2 It can be seen that the region with stronger gain in the emission spectrum of the Pr:YLF crystal is located in the 640nm band, while the absorption rate at 444nm has a higher absorption rate.

[0090] Based on the above analysis, the particle counter in this case uses a laser diode that can emit a first wavelength laser in the wavelength range of [439, 449] nm as the pump light source of the Pr:YLF crystal. The Pr:YLF crystal stimulates radiation to form a second wavelength laser in the wavelength range of [638, 642] nm, which has great advantages in technology and cost. The Pr:YLF crystal uses a second wavelength laser of [638, 642] nm to take into account the scattered light intensity and the spectral response characteristics of the photoelectric detection device, and is very suitable as the light source of the laser particle counter.

[0091] Combined with the above analysis, in some embodiments, a pump source 10 capable of emitting light in the wavelength range of [400,700] nm is used as the light source of the Pr:YLF crystal, and the Pr:YLF crystal is stimulated to radiate light in the wavelength range of [500,700] nm to detect particles in the resonant cavity.

[0092] That is, the wavelength range of the first wavelength laser emitted by the pump source 10 is [400, 700] nm, and the wavelength range of the second wavelength laser 31 generated by the Pr:YLF crystal is [500, 700] nm.

[0093] Furthermore, it can be seen from the above that the Pr:YLF crystal absorbs pump light of 430-490 nm, so a pump source 10 capable of emitting light in the wavelength range of [430, 490] nm is used as the light source of the Pr:YLF crystal. That is, the wavelength range of the first wavelength laser 11 emitted by the pump source 10 is [430, 490] nm.

[0094] Furthermore, it can be seen from the above that the Pr:YLF crystal absorbs pump light of 430-490nm, among which there are three absorption peaks at 444nm, 469nm and 479nm, and the absorption cross section is relatively large. When the wavelength of the pump light is these three wavelengths, the efficiency of generating the second wavelength laser is the highest. Therefore, a pump source 10 capable of emitting a wavelength range of [439, 449]nm or [464, 474]nm or [474, 484]nm is used as the light source of the Pr:YLF crystal.

[0095] That is to say, the wavelength interval of the first wavelength laser 11 emitted by the pump source 10 is [439, 449] nm or [464, 474] nm or [474, 484] nm.

[0096] Furthermore, it can be seen from the above that the Pr:YLF crystal has a higher emission cross-section at 640nm, which is most suitable for generating lasers of this wavelength, while 523nm is second. Other wavelengths have low absorption rates, so the pump light conversion efficiency is low. Based on this, the wavelength range of the second wavelength laser generated by the Pr:YLF crystal is set to [638, 642]nm or [521, 525]nm.

[0097] In some embodiments, reference Figure 1 The particle counter includes a first reflector 21 and a second reflector 22, which are arranged at intervals along the irradiation direction of the first wavelength laser 11. A laser resonant cavity is formed between the first reflector 21 and the second reflector 22.

[0098] The pump source 10 is located outside the laser resonant cavity. The first wavelength laser 11 emitted by the pump source 10 enters the laser resonant cavity through the first reflector 21 and / or the second reflector 22 .

[0099] In other words, in some embodiments, one pump source 10 is provided, and the pump source 10 is located on a side of the first reflector 21 away from the laser resonant cavity, and the first wavelength laser 11 emitted by the pump source 10 enters the laser resonant cavity through the first reflector 21 .

[0100] When this structure is adopted, the first reflector 21 has a high transmittance to the first wavelength laser 11 , so as to ensure that the first wavelength laser 11 enters the laser resonance cavity as much as possible.

[0101] In other embodiments, one pump source 10 is provided, and the pump source 10 is located on a side of the second reflector 22 away from the laser resonant cavity, and the first wavelength laser 11 emitted by the pump source 10 enters the laser resonant cavity through the second reflector 22 .

[0102] When this structure is adopted, the second reflector 22 has a high transmittance to the first wavelength laser 11, so as to ensure that the first wavelength laser 11 enters the laser resonance cavity as much as possible.

[0103] In some other embodiments, two pump sources 10 are provided, one of which is located on the side of the first reflector 21 away from the laser resonant cavity, and the first wavelength laser 11 emitted by the pump source 10 enters the laser resonant cavity through the first reflector 21; the other pump source 10 is located on the side of the second reflector 22 away from the laser resonant cavity, and the first wavelength laser 11 emitted by the pump source 10 enters the laser resonant cavity through the second reflector 22.

[0104] When this structure is adopted, the first reflector 21 and the second reflector 22 both have high transmittance to the first wavelength laser 11 , so as to ensure that the first wavelength laser 11 enters the laser resonant cavity as much as possible.

[0105] The first reflector 21 and the second reflector 22 have a high reflectivity for the second wavelength laser 31. Because the laser resonant cavity is a steady-state cavity, it has a low intracavity loss, and the second wavelength laser 31 has a high intensity in the cavity. The second wavelength laser 31 is reflected a high number of times in the laser resonant cavity, and the reflected signal generated by the light energy is fully utilized, and the light energy utilization rate is high.

[0106] In some embodiments, the first reflector 21 and the second reflector 22 are coated with a reflective film with high reflectivity to the second wavelength laser 31 on the side facing the laser resonant cavity, so that the reflectivity of the first reflector 21 to the second wavelength laser 31 is not less than 95%, and the reflectivity of the second reflector 22 to the second wavelength laser 31 is not less than 95%, which helps to reduce the loss in the cavity and increase the optical power in the cavity.

[0107] In a specific embodiment, the reflectivity of the first reflector 21 to the second wavelength laser 31 is not less than 99.9%, and the reflectivity of the second reflector 22 to the second wavelength laser 31 is not less than 99.9%.

[0108] In some embodiments, the transmittance of the first wavelength laser 11 emitted by the pump source 10 through the first reflector 21 and / or the second reflector 22 to the first wavelength laser 11 is not less than 80%, so as to ensure that the first wavelength laser 11 enters the laser resonant cavity as much as possible.

[0109] When the pump source 10 is located on a side of the first reflector 21 away from the laser resonant cavity, the transmittance of the first reflector 21 to the first wavelength laser 11 is not less than 80%.

[0110] When the pump source 10 is located on the side of the second reflector 22 away from the laser resonant cavity, the transmittance of the second reflector 22 to the first wavelength laser 11 is not less than 80%.

[0111] When one pump source 10 is located on the side of the first reflector 21 away from the laser resonant cavity and the other pump source 10 is located on the side of the second reflector 22 away from the laser resonant cavity, the transmittance of the first reflector 21 and the second reflector 22 to the first wavelength laser 11 is not less than 80%.

[0112] In some embodiments, the laser resonance cavity formed by the first reflecting mirror and the second reflecting mirror is a stable cavity, which is any one of a plano-concave cavity, a double-concave cavity, and a convex-concave cavity.

[0113] In practical applications, the first reflector 21 is a plane reflector or a concave reflector, etc. The second reflector 22 is a plane reflector or a concave reflector, etc. The specific structure of the first reflector 21 and the second reflector 22 is related to factors such as the optical power required for detection and the shape of the beam.

[0114] In this specific embodiment, the first reflector 21 is a plane reflector, and the second reflector 22 is a concave mirror. A steady-state cavity composed of a plane-concave mirror is formed between the first reflector 21 and the second reflector 22, so that the laser resonant cavity has a lower intracavity loss, and the second wavelength laser 31 has a very high intensity in the cavity.

[0115] For example, when using a 5W laser diode pump, the laser resonant cavity can generate an optical power of more than 200W, which can meet the detection requirements of 0.1 micron particles.

[0116] In some embodiments, reference Figure 7The particle counter includes a reflector, which is denoted as the second reflector 22. The second reflector 22 is arranged at an interval with a laser crystal 30. The laser crystal 30 is provided with an optical coating 32 on a side surface facing the pump source 10. A laser resonant cavity is formed between the optical coating 32 and the second reflector 22. The pump source 10 is located outside the laser resonant cavity. The first wavelength laser 11 emitted by the pump source 10 enters the laser resonant cavity through the optical coating 32 and / or the second reflector 22. The second wavelength laser 31 forms an optical oscillation between the optical coating 32 and the second reflector 22.

[0117] In other words, in some embodiments, a pump source 10 is provided, and the pump source 10 is located on the side of the optical coating 32 away from the laser resonant cavity, and the first wavelength laser 11 emitted by the pump source 10 is directly emitted to the laser crystal 30 through the optical coating 32 and enters the laser resonant cavity.

[0118] When this structure is adopted, the optical coating 32 has a high transmittance to the first wavelength laser 11 , so as to ensure that the first wavelength laser 11 is irradiated onto the laser crystal 30 as much as possible.

[0119] In other embodiments, one pump source 10 is provided, and the pump source 10 is located on a side of the second reflector 22 away from the laser resonant cavity, and the first wavelength laser 11 emitted by the pump source 10 enters the laser resonant cavity through the second reflector 22 .

[0120] When this structure is adopted, the second reflector 22 has a high transmittance to the first wavelength laser 11, so as to ensure that the first wavelength laser 11 enters the laser resonance cavity as much as possible.

[0121] In some other embodiments, two pump sources 10 are provided, wherein one pump source 10 is located on the side of the optical coating 32 away from the laser resonant cavity, and the first wavelength laser 11 emitted by the pump source 10 is directly irradiated to the laser crystal 30 through the optical coating 32 and enters the laser resonant cavity; and the other pump source 10 is located on the side of the second reflector 22 away from the laser resonant cavity, and the first wavelength laser 11 emitted by the pump source 10 enters the laser resonant cavity through the second reflector 22.

[0122] When this structure is adopted, the optical coating 32 and the second reflector 22 both have a high transmittance to the first wavelength laser 11, so as to ensure that the first wavelength laser 11 enters the laser resonance cavity as much as possible.

[0123] In some embodiments, the reflectivity of the optical coating 32 to the second wavelength laser 31 is not less than 95%, and the reflectivity of the second reflector 22 to the second wavelength laser 31 is not less than 95%, which helps to reduce the intracavity loss and increase the intracavity optical power.

[0124] In a specific embodiment, the reflectivity of the optical coating 32 to the second wavelength laser 31 is not less than 99.9%, and the reflectivity of the second reflector 22 to the second wavelength laser 31 is not less than 99.9%.

[0125] In some embodiments, the transmittance of the first wavelength laser 11 emitted by the pump source 10 through the optical coating 32 and / or the second reflector 22 to the first wavelength laser 11 is not less than 80%, so as to ensure that the first wavelength laser 11 enters the laser resonant cavity as much as possible.

[0126] When the pump source 10 is located on a side of the optical coating 32 away from the laser resonant cavity, the transmittance of the optical coating 32 to the first wavelength laser 11 is not less than 80%.

[0127] When the pump source 10 is located on the side of the second reflector 22 away from the laser resonant cavity, the transmittance of the second reflector 22 to the first wavelength laser 11 is not less than 80%.

[0128] When one pump source 10 is located on the side of the optical coating 32 away from the laser resonant cavity and the other pump source 10 is located on the side of the second reflector 22 away from the laser resonant cavity, the transmittance of the optical coating 32 and the second reflector 22 to the first wavelength laser 11 is not less than 80%.

[0129] In some embodiments, the photoelectric detection device includes a first photoelectric detection module 50, which is configured to detect scattered light signals of particles with a particle size of 0.1-0.3 microns.

[0130] The first photoelectric detection module 50 includes a first photoelectric detector 51 and a first scattered light collection system 52. The first scattered light collection system 52 uses a lens to collect scattered light signals, and the first photoelectric detector 51 uses a photodiode array.

[0131] The principle of the first photoelectric detection module 50 adopting the above design is: the characteristic of the lens is that the collection angle is small, and because it collects the central light beam, it has a large depth of field; while the Mankin mirror has a large collection angle and collects the edge light beam, so the depth of field is obviously smaller than that of the lens. Since the aerosol nozzle 41 has a certain width (about 1mm), only aerosol particles at a certain distance can be clearly imaged on the imaging surface where the photoelectric detector is located. When measuring 0.1 micron particles, in order to improve the signal-to-noise ratio, a photodiode array is used, with a pixel width of 0.7mm and a height of 2mm. If the image point diffuse spot exceeds 0.7mm, the signal of a particle will be received by two or more pixels, thereby causing a large error in the measured light signal. At the same time, since the light scattering signal generated by 0.1 micron particles is relatively weak, a large collection angle is required to collect more scattered light on the detector unit, so these two aspects need to be taken into account.

[0132] In this solution, since an intracavity laser power greater than 200 W can be generated, normal detection of light scattering signals can be achieved even when a smaller collection angle is used, so that the aerosol particles ejected from the aerosol nozzle 41 can be well imaged on the photodetector.

[0133] If a Mankin mirror is used, its collection angle is about 120°, then the diffuse spot produced by the particle imaging at the edge of the aerosol nozzle 41 is 1.7 mm, which greatly exceeds the pixel width of the photodetector, and the detection effect is very poor. Therefore, this design uses a lens to collect scattered light at a small collection angle, which can make full use of the array detector to improve the signal-to-noise ratio, thereby realizing the detection of 0.1 micron particle size.

[0134] In some embodiments, reference Figure 5 and Figure 6 The lens used by the first scattered light collection system 52 is a lens group 53, which is composed of two convex lenses 54.

[0135] Adding an elliptical aperture 55 to the lens group 53 can reduce the vignetting effect of the convex lens 54 on the one hand, and ensure that the dispersion in the width direction of the photodiode array pixel is as small as possible on the other hand, while increasing the collected light energy.

[0136] Of course, the lens group 53 can also be composed of more convex lenses 54 to obtain better imaging quality. In other embodiments, since the concave reflector has a similar convergent imaging effect as the convex lens, the concave reflector can also be used to perform small-angle convergent imaging to achieve the same effect.

[0137] In some embodiments, the photoelectric detection device includes a second photoelectric detection module 60, which is configured to detect scattered light signals of particles with a particle size greater than 0.3 microns. For example, the second photoelectric detection module 60 detects particles with a particle size of 0.3-10 microns.

[0138] The second photoelectric detection module 60 includes a second photoelectric detector 61 and a second scattered light collection system 62. The second scattered light collection system 62 uses a Mankin mirror to collect scattered light signals, and the second photoelectric detector 61 uses a single pixel detector.

[0139] As mentioned above, although a small collection angle can be used to detect particles with a diameter of 0.1 microns, theoretically, the scattered light energy of particles larger than 0.1 microns will be greater than 0.1 microns, so the system should also be able to meet the detection of other particle sizes larger than 0.1 microns. However, the trend of the scattered light intensity of particles changing with the increase of particle size is not monotonically increasing. At a particle size close to the laser wavelength, the scattered light will weaken with the increase of particle size, and the changes in different scattering directions are different. Therefore, if a small solid angle is used to collect scattered light, it cannot be guaranteed that the collected light signal will increase monotonically with the increase of particle size.

[0140] In order to solve this non-monotonic problem, this case uses a Mankin mirror with a large collection angle to detect particles with a particle size of more than 0.3 microns. The collected scattered light signal increases monotonically with the increase of particle size, thus meeting the needs of particle size detection. At the same time, since the scattered light signal of particles larger than 0.3 microns is very strong and the signal-to-noise ratio is very high, a single-pixel photodetector can fully meet the detection needs.

[0141] The particle counter in this embodiment uses two optical systems and two photodetectors for detection. Particles of 0.1-0.3 microns are detected by a lens and a photodiode array. An elliptical aperture is used to obtain high imaging quality and significantly reduce stray light. Particles larger than 0.3 microns are detected by a Mankin mirror and a single-pixel photodetector, which reduces or eliminates the non-monotonicity caused by the fluctuation of the particle size and the scattered light curve, thereby meeting the detection requirements of all particles larger than 0.1 microns.

[0142] In other embodiments, the second scattered light collection system 62 may also use a double concave mirror to collect scattered light signals.

[0143] In some embodiments, the particle counter includes a third photodetector 70, which is disposed outside the laser resonant cavity and is configured to detect the attenuation of optical power in the laser resonant cavity, so as to timely compensate for the change in the intensity of particle scattered light, improve the detection performance of the equipment, and play a role in detecting the working status of the laser resonant cavity.

[0144] The third photodetector 70 can detect the light power drift change in real time, thereby compensating for the received particle scattered light signal and ensuring the accuracy of the detection result.

[0145] In some embodiments, the first reflector 21 , the second reflector 22 , and the laser crystal 30 are designed to be adjustable for ease of debugging.

[0146] by Figure 1Taking the particle counter shown in the figure as an example, its working principle is as follows: the pump source 10 emits a first wavelength laser 11 which enters the laser resonant cavity through the first reflector 21. The first reflector 21 has a high transmittance to the first wavelength laser 11. The first wavelength laser 11 is converged onto the laser crystal 30.

[0147] The laser crystal 30 is stimulated to generate a second wavelength laser 31. The first reflector 21 and the second reflector 22 have a high reflectivity for the second wavelength laser 31. The second wavelength laser 31 resonates between the first reflector 21 and the second reflector 22 to form an optical power exceeding 200W.

[0148] The aerosol generating device inputs aerosol into the laser resonant cavity, and the aerosol flows out from the aerosol nozzle 41 and passes through the beam of the second wavelength laser 31 at a certain speed. When the aerosol particles pass through the beam of the second wavelength laser 31, they scatter the laser.

[0149] Since the second wavelength laser 31 beam has a higher power, it can generate stronger scattered light. Although the scattering of 0.1 micron particles is relatively weak due to their small particle size, the particle signal can also be detected due to the high power of the laser beam, thereby realizing the detection of 0.1 micron particle size.

[0150] In some embodiments, the laser crystal 30 is a ruby ​​crystal. The wavelength range of the first wavelength laser 11 emitted by the pump source 10 is [390, 450] nm. The wavelength range of the second wavelength laser 31 generated by the ruby ​​crystal is [600, 750] nm.

[0151] Ruby crystals have the advantages of high hardness, good wear resistance, and good thermal conductivity. Therefore, a larger pump light power can be used to obtain a higher intracavity power, which can detect smaller particles.

[0152] In the description of the above embodiments, specific features, structures, materials or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0153] The above is only a specific implementation of the utility model, but the protection scope of the utility model is not limited to this. Any changes or substitutions that can be easily thought of by technicians familiar with the technical field within the technical scope disclosed by the utility model should be included in the protection scope of the utility model. Therefore, the protection scope of the utility model should be based on the protection scope of the claims.

Claims

1. A particle counter, characterized in that: include: a pump source configured to emit laser light of a first wavelength; A laser resonant cavity, wherein the laser light of the first wavelength emitted by the pump source enters the laser resonant cavity; A laser crystal, which is disposed in the laser resonant cavity, and the laser crystal is configured to be irradiated by the first wavelength laser to form a second wavelength laser, and the second wavelength laser forms an optical oscillation in the laser resonant cavity; an aerosol generating device, configured to provide an aerosol gas flow into the laser resonant cavity, wherein the aerosol gas flow passes through the light beam of the laser of the second wavelength; A photoelectric detection device is configured to detect scattered light signals of aerosol particles.

2. The particle counter according to claim 1, characterized in that: The laser crystal is a Pr:YLF crystal; The wavelength range of the first wavelength laser emitted by the pump source is [400, 700] nm; The wavelength range of the second wavelength laser generated by the Pr:YLF crystal is [500, 700] nm.

3. The particle counter according to claim 2, characterized in that: The wavelength range of the first wavelength laser emitted by the pump source is [430, 490] nm.

4. The particle counter according to claim 3, characterized in that: The wavelength interval of the first wavelength laser emitted by the pump source is [439, 449] nm or [464, 474] nm or [474, 484] nm.

5. The particle counter according to claim 2, characterized in that: The wavelength range of the second wavelength laser generated by the Pr:YLF crystal is [638, 642] nm or [521, 525] nm.

6. The particle counter according to claim 1, characterized in that: The laser crystal is a ruby ​​crystal; The wavelength range of the first wavelength laser emitted by the pump source is [390, 450] nm; The wavelength range of the second wavelength laser generated by the ruby ​​crystal is [600,750] nm.

7. The particle counter according to any one of claims 1 to 6, characterized in that: The laser resonant cavity is formed between the first reflector and the second reflector, the pump source is located outside the laser resonant cavity, the first wavelength laser emitted by the pump source enters the laser resonant cavity through the first reflector and / or the second reflector, and the second wavelength laser forms an optical oscillation between the first reflector and the second reflector.

8. The particle counter according to claim 7, characterized in that: The reflectivity of the first reflector to the laser of the second wavelength is not less than 95%; The reflectivity of the second reflector to the second wavelength laser is not less than 95%.

9. The particle counter according to claim 7, characterized in that: The transmittance of the first wavelength laser emitted by the pump source to the first wavelength laser through the first reflector and / or the second reflector is not less than 80%.

10. The particle counter according to any one of claims 1 to 6, characterized in that: Includes reflector; The laser crystal is provided with an optical coating on a side surface facing the pump source, the laser resonant cavity is formed between the optical coating and the reflector, the pump source is located outside the laser resonant cavity, the first wavelength laser emitted by the pump source enters the laser resonant cavity through the optical coating and / or the reflector, and the second wavelength laser forms an optical oscillation between the optical coating and the reflector.

11. The particle counter according to any one of claims 1 to 6, characterized in that: The pump source is a laser diode.

12. The particle counter according to any one of claims 1 to 6, characterized in that: The photoelectric detection device includes a first photoelectric detection module, which is configured to detect scattered light signals of particles with a particle size of 0.1-0.3 microns.

13. The particle counter according to claim 12, characterized in that: The first photoelectric detection module includes a first photoelectric detector and a first scattered light collection system. The first scattered light collection system uses a lens to collect scattered light signals, and the first photoelectric detector uses a photodiode array.

14. The particle counter according to any one of claims 1 to 6, characterized in that: The photoelectric detection device includes a second photoelectric detection module, which is configured to detect scattered light signals of particles with a particle size greater than 0.3 microns.

15. The particle counter according to claim 14, characterized in that: The second photoelectric detection module includes a second photoelectric detector and a second scattered light collection system. The second scattered light collection system uses a Mankin mirror or a double concave mirror to collect scattered light signals. The second photoelectric detector uses a single pixel detector.

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