Optical device for detecting tiny particles

Abstract

The invention discloses an optical device for detecting tiny particles, which belongs to the field of optical detection and comprises a laser illumination system and a scattered light collection system. The laser illumination system comprises an optical fiber laser, a cylindrical lens, a first diaphragm, a light sensitive area and a light trap which are sequentially arranged in the first direction, the optical fiber laser is used for emitting a laser beam, and the laser beam sequentially passes through the cylindrical lens, the first diaphragm and the light sensitive area to enter the light trap; the scattered light collecting system comprises a spherical reflector, a second diaphragm and a photodiode which are sequentially arranged in the second direction, the spherical reflector and the second diaphragm are arranged on the two sides of the photosensitive area, and the first direction is perpendicular to the second direction; the spherical reflector is provided with a reflecting spherical surface, the laser beam is scattered after irradiating the particles in the photosensitive area to form scattered light, and the scattered light is reflected to the second diaphragm through the reflecting spherical surface and enters the photodiode through the second diaphragm.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical detection, and in particular relates to an optical device for detecting extremely small particles. Background Art

[0002] Currently, the principle of laser scattering is widely used in particle detection, such as laser dust particle counters. Laser scattering refers to the phenomenon in which the direction of photons of light changes after the interaction between a laser beam and matter. Laser dust particle counters use this principle to detect suspended particles in the air in real time.

[0003] Typically, a laser dust particle counter consists of an illumination system and a scattered light collection system, such as the Chinese invention patent publication number CN1570604A, titled Micro Optical Sensor for Laser Dust Particle Counter. Figure 1 As shown, the optical sensor includes an illumination system, a scattered light collection system, an air path system, and a preamplifier circuit. The illumination system consists of a laser light source assembly 101, a cylindrical mirror 102, and a light trap. The laser light source assembly 101 emits a collimated laser beam, which is focused one-dimensionally by the cylindrical mirror 102 onto a photosensitive area 104. The scattered light collection system primarily comprises a spherical reflector 103, a field stop 105, a photodetector 106, and a preamplifier circuit 107. The photodetector 106 collects scattered light generated by dust particles in the measured airflow and converts it into an electrical signal. The preamplifier circuit 107 removes noise from the electrical pulse signal output by the photodetector 106 and amplifies the signal to a sufficient amplitude before feeding it into subsequent processing circuits.

[0004] The above structure can realize particle detection based on the principle of laser scattering. However, the laser beam quality of the above device is poor, the divergence angle is large, and the focusing accuracy is low, which affects the resolution and sensitivity of particle detection. At the same time, the laser beam emitted by the cylindrical lens has a certain divergence angle, which easily affects the detection accuracy. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides an optical device for detecting extremely small particles. The technical problem to be solved by the present invention is achieved through the following technical solutions: In a first aspect, the present invention provides an optical device for detecting extremely small particles, comprising a laser illumination system and a scattered light collection system; The laser illumination system includes a fiber laser, a cylindrical lens, a first aperture, a light-sensitive area, and a light trap arranged in sequence along a first direction. The fiber laser is used to emit a laser beam, which passes through the cylindrical lens, the first aperture, and the light-sensitive area in sequence and is incident on the light trap. The scattered light collection system includes a spherical reflector, a second aperture, and a photodiode arranged in sequence along a second direction, the spherical reflector and the second aperture being arranged on both sides of the light sensitive area, and the first direction and the second direction being perpendicular to each other; The spherical reflector has a reflecting spherical surface. When the laser beam is irradiated on the particles in the light sensitive area, it is scattered and forms scattered light. The scattered light is reflected by the reflecting spherical surface to the second aperture and is incident on the photodiode through the second aperture.

[0006] In one embodiment of the present invention, the distance between the light sensitive area and the cylindrical lens is 17.99 mm to 19.99 mm.

[0007] In one embodiment of the present invention, the curvature radius of the reflective spherical surface is 22 mm to 24 mm, and the focal length is 11 mm to 12 mm.

[0008] In one embodiment of the present invention, the reflecting spherical surface is located on the lower surface of the spherical reflector, the aperture of the spherical reflector is 28mm-32mm, the edge thickness of the spherical reflector is 7mm-9mm, and the center thickness is 1mm-3mm.

[0009] In one embodiment of the present invention, the distance between the spherical vertex of the reflecting sphere and the light sensitive area is 18 mm to 20 mm, the forward full angle of the reflecting sphere is 96.1° to 96.5°, the backward full angle is 34.5° to 34.9°, the reflection efficiency is 0.93 to 0.97, and the surface accuracy is less than 1 / 2 of the wavelength of the laser beam.

[0010] In one embodiment of the present invention, the focal length of the cylindrical lens is 22.74 mm to 23.14 mm, the radius of curvature is 11.27 mm to 11.67 mm, and the center thickness is 3.66 mm to 4.05 mm.

[0011] In one embodiment of the present invention, the light trap includes three black glass plates spliced ​​together in sequence, and the surface of the black glass plates is coated with an anti-reflection film layer. The transmittance of the anti-reflection film layer to the laser beam is greater than or equal to 99.5%, and the reflectivity of the anti-reflection film layer to the laser beam is less than or equal to 0.5%.

[0012] In one embodiment of the present invention, the first aperture includes a first rectangular hole, the laser beam passes through the first rectangular hole and enters the light sensitive area, and the size of the first rectangular hole is 3 mm*2 mm.

[0013] In one embodiment of the present invention, the second aperture includes a second rectangular hole, the light beam reflected by the reflecting spherical surface passes through the second rectangular hole and is incident on the photodiode, and the size of the second rectangular hole is 6 mm*6 mm.

[0014] In one embodiment of the present invention, the fiber laser, cylindrical lens, first aperture, light trap, spherical reflector, second aperture, and photodiode are all mounted in a housing; The fiber laser is detachably connected to a collimating lens.

[0015] Compared with the prior art, the present invention has the following beneficial effects: In the above-mentioned scheme of the present application, the optical device includes a laser illumination system and a scattered light collection system; the laser illumination system includes a fiber laser, a cylindrical lens, a first aperture, a photosensitive area, and a light trap arranged in sequence along a first direction, the fiber laser is used to emit a laser beam, and the laser beam passes through the cylindrical lens, the first aperture, and the photosensitive area in sequence and is incident on the light trap; the scattered light collection system includes a spherical reflector, a second aperture, and a photodiode arranged in sequence along a second direction, the spherical reflector and the second aperture are arranged on both sides of the photosensitive area, and the first direction and the second direction are perpendicular to each other; the spherical reflector has a reflective spherical surface, and the laser beam is scattered after being irradiated on the particles in the photosensitive area to form scattered light, which is reflected by the reflective spherical surface to the second aperture and then incident on the photodiode through the second aperture. With this structure, firstly, because the fiber laser has excellent beam quality, high directivity, and good power stability, it can improve the resolution and sensitivity of particle detection compared to the commonly used traditional laser diodes or semiconductor lasers. Secondly, the present application provides a first aperture between the cylindrical lens and the photosensitive area. When the laser beam passes through the first aperture, the first aperture can limit the passage of divergent light, thereby suppressing the background noise caused by the divergent beam and improving detection accuracy. In addition, the present application provides a second aperture. The light beam reflected by the reflecting sphere first enters the second aperture and then enters the photodiode through the second aperture. By providing the second aperture, the amount of stray light outside the field of view that enters the photodiode can be reduced, thereby improving the system's measurement sensitivity and repeatability.

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of a particle counter in the prior art; Figure 2 is a schematic diagram of an optical device provided by an embodiment of the present invention; Figure 3 Schematic diagram of a light trap in an embodiment of the present invention.

[0018] Reference numerals: 1 - fiber laser, 2 - cylindrical lens, 3 - first aperture, 4 - light sensitive area, 5 - light trap, 6 - spherical mirror, 7 - second aperture, 8 - photodiode. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0020] Currently, the principle of laser scattering is widely used in particle detection, such as laser dust particle counters. Laser scattering refers to the phenomenon in which the direction of photons of light changes after the interaction between a laser beam and matter. Laser dust particle counters use this principle to detect suspended particles in the air in real time.

[0021] Typically, a laser dust particle counter consists of an illumination system and a scattered light collection system, such as the Chinese invention patent publication number CN1570604A, titled Micro Optical Sensor for Laser Dust Particle Counter. Figure 1 As shown, the optical sensor includes an illumination system, a scattered light collection system, an air path system, and a preamplifier circuit. The illumination system is composed of a laser light source assembly 101, a cylindrical mirror 102, and a light trap. The laser light source assembly 101 emits a collimated laser beam, which is focused in one dimension by the cylindrical mirror 102 on a light-sensitive area 104. The scattered light collection system is mainly composed of a spherical reflector 103, a field aperture 105, a photodetector 106, and a preamplifier circuit 107. The photodetector 106 is used to collect the scattered light generated by dust particles in the measured airflow and convert it into an electrical signal. The preamplifier circuit 107 is used to remove noise from the electrical pulse signal output by the photodetector 106 and amplify the signal to a considerable amplitude before sending it to a subsequent processing circuit. With the above structure, particle detection can be achieved based on the principle of laser scattering. However, the above device has the following disadvantages: First, in the above-mentioned device, the semiconductor laser has poor beam quality, a large divergence angle, and low focusing accuracy, which affects the resolution and sensitivity of particle detection. When the power is high, the performance is easily degraded due to heat dissipation problems. In addition, it is sensitive to environmental changes and has poor stability, which will lead to reduced reliability of the detection system and measurement accuracy.

[0022] Secondly, since no aperture is added behind the cylindrical lens in the above device, the laser beam in the illumination system has a certain divergence angle. The divergent beam generates strong scattered light with the sampling nozzle in the cavity, affecting the accurate reading of the particle signal.

[0023] In addition, the optical sensors in the existing technology rely on specific laser light source components, requiring that the beam cross-section output by the light source be elliptical and form a certain angle with the generatrix of the cylindrical mirror. Such strict requirements on the light source characteristics may limit their use in certain application scenarios. If the beam shape or angle of the light source does not meet the requirements, it may cause uneven illumination intensity in the photosensitive area, thereby affecting the accuracy of particle counting and particle size resolution.

[0024] Furthermore, existing technologies have the advantage of using spherical mirrors as scattered light collection elements, which offer the advantage of lower costs. However, parameters such as the curvature radius, reflectivity, and surface finish of the spherical mirrors still require high precision. Failure to meet these requirements will directly affect the efficiency of scattered light collection and image quality, thereby reducing the performance of the entire system.

[0025] Furthermore, the size and position of the field stop used in the prior art need to be precisely calculated and adjusted based on the imaging position and image size of the light-sensitive area of ​​the spherical reflector. This precise adjustment may be difficult in actual assembly and use.

[0026] Furthermore, existing technologies lack effective measures to eliminate background noise and external electromagnetic interference. Because the noise generated by the diffraction of the illumination laser beam is DC, and external electromagnetic interference is typically low-frequency, these noise and interference signals can be mixed into the measurement signal, resulting in a low signal-to-noise ratio. This low signal-to-noise ratio directly impacts measurement accuracy and counting efficiency, limiting the device's application in high-precision detection scenarios.

[0027] To address these challenges, the present invention provides a compact, highly sensitive, and robust optical device for detecting extremely small particles. This device optimizes the laser illumination system and scattered light collection system to achieve higher particle detection resolution and signal-to-noise ratio. The optical device in this embodiment is suitable for high-precision counting and particle size analysis of particles such as aerosols, dust, and particulate matter.

[0028] See Figure 2 and Figure 3 An embodiment of the present invention provides an optical device for detecting extremely small particles, including a laser illumination system and a scattered light collection system; the laser illumination system includes a fiber laser 1, a cylindrical lens 2, a first aperture 3, a light-sensitive area 4, and a light trap 5 arranged in sequence along a first direction, the fiber laser 1 is used to emit a laser beam, and the laser beam passes through the cylindrical lens 2, the first aperture 3, and the light-sensitive area 4 in sequence and is incident on the light trap 5; the scattered light collection system includes a spherical reflector 6, a second aperture 7, and a photodiode 8 arranged in sequence along a second direction, the spherical reflector 6 and the second aperture 7 are arranged on both sides of the light-sensitive area 4, and the first direction and the second direction are perpendicular to each other; the spherical reflector 6 has a reflective spherical surface, and the laser beam is scattered after being irradiated on the particles in the light-sensitive area 4 to form scattered light, and the scattered light is reflected by the reflective spherical surface to the second aperture 7, and is incident on the photodiode 8 through the second aperture 7.

[0029] In some embodiments of the present application, a fiber laser 1 is a device that uses a rare-earth-doped optical fiber as a gain medium and generates laser light using pump light excitation. Its core feature is that the laser light is generated and transmitted within a thin optical fiber, combining high beam quality, high efficiency, high stability, and a compact structure.

[0030] In some embodiments of the present application, a cylindrical lens 2 is an optical element having cylindrical curvature, one or both of which are cylindrical surfaces. Unlike a spherical lens, a cylindrical lens 2 only converges or diverges light in one dimension and has no optical power in the other dimension.

[0031] In some embodiments of the present application, the optical trap 5 is a technology that uses the momentum transfer of laser to capture and manipulate microscopic particles in a non-contact manner. It forms a three-dimensional potential well through a highly focused laser beam, which can stably confine dielectric particles near the focus of the beam and achieve precise movement, rotation or mechanical measurement.

[0032] In some embodiments of the present application, the distance between the light-sensitive area 4 and the cylindrical lens 2 is 17.99 mm to 19.99 mm, and the light-sensitive area 4 has a rectangular cross-sectional light distribution.

[0033] In some embodiments of the present application, a fiber laser 1 emits a laser beam, which becomes a parallel beam after passing through a collimating lens. The laser beam is then focused in one dimension by a cylindrical lens 2 to form a light-sensitive area 4 of a certain size and light intensity. After passing through the light-sensitive area 4, the laser beam is incident on a light trap 5 and is completely absorbed by the light trap 5. The scattered light collection system includes a spherical reflector 6, a second aperture 7, and a photodiode 8. The photodiode 8 is used to collect and convert particle scattered light signals. The spherical reflector 6 is used to collect scattered light from tiny particles within a certain solid angle, and the second aperture 7 is used to filter out stray light other than the scattered light. When tiny particles pass through the light-sensitive area 4, the generated scattered light of a certain intensity positively correlated with the particle size is reflected by the spherical reflector 6 to the photodiode 8, which receives it and converts it into a pulse signal proportional to the particle size.

[0034] In some embodiments of the present application, the illumination system utilizes a fiber laser 1 to emit a laser beam, which is then converted to a parallel beam by a collimating lens. To meet sampling flow and concentration requirements, the photosensitive region 4 is a region of a certain size with uniform illumination. The focal length of the cylindrical lens 2 is relatively long relative to the selected length of the photosensitive region 4, resulting in a large focal depth for the focused laser beam. Therefore, the illumination intensity of the photosensitive region 4 can be considered uniform along the optical axis of the illumination system.

[0035] In some embodiments of the present application, the scattered light collection system adopts a spherical reflector 6 with a reflection efficiency of 0.95. It can efficiently collect and focus scattered light, enhance the intensity of the light signal, improve the detection accuracy and resolution, and also improve the illumination uniformity of the light-sensitive area 4 and improve the detection stability. The spherical reflector 6 has a simple structure and low cost, can expand the particle size detection range, and significantly improve the system performance and cost performance.

[0036] In some embodiments of the present application, in the scattered light collection system, stray light in the scattered light collection module will directly enter the photodiode 8, so it is necessary to place the second aperture 7 close to the photodiode 8 to prevent stray light outside the light-sensitive area 4 from entering the photodiode 8. The light-transmitting parts of the first aperture 3 and the second aperture 7 are both rectangular holes.

[0037] In the above-mentioned solution of the present application, the optical device includes a laser illumination system and a scattered light collection system. The laser illumination system includes a fiber laser 1, a cylindrical lens 2, a first aperture 3, a photosensitive area 4, and a light trap 5, which are arranged in sequence along a first direction. The fiber laser 1 is used to emit a laser beam, which passes through the cylindrical lens 2, the first aperture 3, and the photosensitive area 4 and is incident on the light trap 5. The scattered light collection system includes a spherical reflector 6, a second aperture 7, and a photodiode 8, which are arranged in sequence along a second direction. The spherical reflector 6 and the second aperture 7 are arranged on both sides of the photosensitive area 4, with the first direction and the second direction being perpendicular to each other. The spherical reflector 6 has a reflective spherical surface. After the laser beam is irradiated on the particles in the photosensitive area 4, it is scattered and forms scattered light. The scattered light is reflected by the reflective spherical surface to the second aperture 7, and then incident on the photodiode 8 through the second aperture 7. With this structure, firstly, because the fiber laser 1 has excellent beam quality, high directivity, and good power stability, it can improve the resolution and sensitivity of particle detection compared to conventional laser diodes or semiconductor lasers commonly used. Secondly, the present application provides a first aperture 3 between the cylindrical lens 2 and the photosensitive area 4. When the laser beam passes through the first aperture 3, the first aperture 3 can limit the passage of divergent light, thereby suppressing the background noise caused by the divergent beam and improving the detection accuracy. In addition, the present application provides a second aperture 7. The light beam reflected by the reflecting sphere first enters the second aperture 7 and then enters the photodiode 8 through the second aperture 7. By providing the second aperture 7, the stray light outside the field of view can be reduced from entering the photodiode 8, thereby improving the measurement sensitivity and repeatability of the system.

[0038] Specifically, the illumination system uses a high-quality fiber laser 1 as the excitation light source. This type of laser has excellent beam quality, high directivity, and good power stability. Compared with traditional laser diodes or semiconductor lasers, the beam output by the fiber laser 1 is easier to collimate and focus, significantly improving the overall optical path stability and focus consistency of the system, thereby enhancing the accuracy and repeatability of particle detection.

[0039] Secondly, due to the divergence of the laser beam in the illumination system module, it is prone to unintended scattering within the sample chamber and from structures such as the sampling nozzle, interfering with accurate particle signal detection. This embodiment avoids this by placing a first aperture 3 after the cylindrical lens 2. The aperture has a rectangular aperture that allows only parallel beams along the principal optical axis to pass through, significantly suppressing background noise caused by the diverging beam and improving the detection signal-to-noise ratio.

[0040] Furthermore, this embodiment uses a fiber laser 1 as the light source. The laser beam emitted by it is converted into a parallel beam by a collimating lens. Combined with an adjustable beam shaping structure, the beam size, shape, and divergence angle can be flexibly adjusted according to different measurement requirements. Compared to the uneven illumination caused by the fixed optical path design in the existing technology, this solution can achieve matching optimization based on the receiving area of ​​the photosensor, effectively improving the uniformity of the illumination intensity distribution, thereby enhancing the accuracy of particle counting and particle size resolution.

[0041] Furthermore, to improve light signal collection efficiency and focusing accuracy, this embodiment uses a reflector material with high reflectivity and low surface roughness. The spherical reflector 6 is manufactured using a high-precision mold and polishing process, ensuring that its curvature radius, reflection efficiency, and surface finish meet design requirements. These optimizations significantly enhance the system's responsiveness to weak scattered signals.

[0042] Furthermore, this embodiment uses optical simulation software to globally simulate the system's optical path to determine the optimal position and opening size of second aperture 7. The aperture is mounted using an adjustable mechanical bracket and assisted by an automated alignment system or a high-precision micro-displacement platform for adjustment. This ensures a close match between the aperture's field of view and the detector's photosensitive area, minimizing the entry of stray light outside the field of view and improving the system's measurement sensitivity and repeatability.

[0043] This embodiment also incorporates a light trap 5 at the end of the optical path to absorb residual light beams, effectively suppressing stray light interference with the measurement signal. Furthermore, an electromagnetic shielding coating or metal casing is added to the photodetector housing, combined with a grounding design, effectively suppressing external electromagnetic interference with the signal link, thereby improving the system's measurement accuracy and anti-interference capabilities in complex electromagnetic environments.

[0044] In some embodiments of the present application, the fiber laser 1, cylindrical lens 2, first aperture 3, light trap 5, spherical reflector 6, second aperture 7, and photodiode 8 are all mounted within a housing, with a collimator optic detachably attached to the fiber laser 1. This structure improves the stability of the mounting of the fiber laser 1, cylindrical lens 2, first aperture 3, light trap 5, spherical reflector 6, second aperture 7, and photodiode 8. The collimator optic optic can be used to collimate the laser light emitted by the fiber laser 1.

[0045] In some embodiments of the present application, a fiber laser 1 is used as a light source. The size of the fiber laser 1 is 105mm*69mm*43mm, the wavelength of the output laser is 976nm, and the beam is collimated by a fiber collimating lens with an outer diameter of 13mm.

[0046] In some embodiments of the present application, the cylindrical lens 2 is made of N-BK7, and the effective focal length of the cylindrical lens 2 is 22.74mm~23.14mm, preferably 22.94mm; the radius of curvature is 11.27mm~11.67mm, preferably 11.47mm; and the center thickness is 3.66mm~4.05mm, preferably 3.85mm. The size of the cylindrical lens 2 is 15mm*12.5mm*3.85mm. The installation distance between the cylindrical lens 2 and the fiber laser 1 should be as short as possible, and the distance between the cylindrical lens 2 and the photosensitive area should be controlled between 17.99mm and 19.99mm to optimize the beam transmission and detection effect.

[0047] In some embodiments of the present application, the first aperture 3 includes a first rectangular hole, and the laser beam passes through the first rectangular hole and is incident on the light sensitive area 4. The size of the first rectangular hole is 3mm*2mm, and the distance between the first aperture 3 and the cylindrical lens 2 is 8mm.

[0048] In some embodiments of the present application, Figure 3 As shown, the light trap 5 includes three black glass plates spliced ​​in sequence, and the surface of the black glass plate is coated with an anti-reflection film layer. The transmittance of the anti-reflection film layer to the laser beam is greater than or equal to 99.5%, and the reflectivity of the anti-reflection film layer to the laser beam is less than or equal to 0.5%.

[0049] In some embodiments of the present application, the light trap 5 has an applicable wavelength of 976 nm, a maximum average power of 800 mW, and a maximum average power density of 2.25 W / mm². The reflector material of the light trap 5 is three pieces of black glass, and the surface is coated with an anti-reflection film with a transmittance of 99.5% to reduce stray light interference. The distance between the light trap 5 and the light-sensitive area 4 is 17 mm.

[0050] In some embodiments of the present application, the curvature radius of the reflective sphere is 22mm-24mm, preferably 23mm; the focal length is 11mm-12mm, preferably 11.5mm. By optimizing the curvature radius and focal length of the reflective sphere, this structure can optimize the reflected light path, thereby improving the accuracy and sensitivity of signal detection.

[0051] In some embodiments of the present application, the reflecting spherical surface is located on the lower surface of the spherical reflector 6, and the light-clearing aperture of the spherical reflector 6 is 28mm~32mm, preferably 30mm; the edge thickness of the spherical reflector 6 is 7mm~9mm, preferably 8mm; the center thickness is 1mm~3mm, preferably 2mm.

[0052] In some embodiments of the present application, the distance between the vertex of the reflective sphere and the light-sensitive area 4 is 18 mm to 20 mm, preferably 19 mm; the forward full angle of the reflective sphere is 96.1° to 96.5°, preferably 96.3°; the backward full angle is 34.5° to 34.9°, preferably 34.7°; the reflection efficiency is 0.93° to 0.97, preferably 0.95, and the surface accuracy is less than 1 / 2 the wavelength of the laser beam. The base material of the spherical reflector 6 is quartz glass, and the surface finish of the reflective sphere is 20 to 40.

[0053] In some embodiments of the present application, the second aperture 7 includes a second rectangular hole. The light beam reflected by the reflecting spherical surface passes through the second rectangular hole and is incident on the photodiode 8. The size of the second rectangular hole is 6 mm*6 mm. The distance between the second aperture 7 and the photodiode 8 is 2 mm.

[0054] In some embodiments of the present application, the photodiode 8 is located at the conjugate point of the spherical total reflection mirror to achieve the collection of scattered light and the measurement of the scattered intensity within a larger solid angle. The light-receiving surface size of the photodiode 8 is 5mm*5mm, and the distance between the photodiode 8 and the light-sensitive area 4 is 8mm.

[0055] In some embodiments of the present application, the minimum detection particle size of the above-mentioned optical device for detecting extremely small particles is 0.1 μm, and the detectable particle size range is 0.1~20 μm, that is, the particle size detection range is 1:200, and the signal-to-noise ratio of the minimum detection particle size is greater than 4:1, which can significantly improve the precision and accuracy of particle measurement.

[0056] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying 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 limiting the present invention.

[0057] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0058] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0059] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. An optical device for detecting extremely small particles, characterized in that: Including laser illumination system and scattered light collection system; The laser illumination system includes a fiber laser, a cylindrical lens, a first aperture, a light-sensitive area, and a light trap arranged in sequence along a first direction, wherein the fiber laser is used to emit a laser beam, and the laser beam passes through the cylindrical lens, the first aperture, and the light-sensitive area in sequence and is incident on the light trap; The scattered light collection system includes a spherical reflector, a second aperture, and a photodiode arranged in sequence along a second direction, the spherical reflector and the second aperture are arranged on both sides of the light sensitive area, and the first direction and the second direction are perpendicular to each other; The spherical reflector has a reflecting spherical surface. After the laser beam is irradiated on the particles in the light-sensitive area, it is scattered and forms scattered light. The scattered light is reflected by the reflecting spherical surface to the second aperture and is incident on the photodiode through the second aperture.

2. The optical device for detecting extremely small particles according to claim 1, characterized in that: The distance between the light sensitive area and the cylindrical lens is 17.99 mm to 19.99 mm.

3. The optical device for detecting extremely small particles according to claim 1, characterized in that: The curvature radius of the reflecting spherical surface is 22 mm to 24 mm, and the focal length is 11 mm to 12 mm.

4. The optical device for detecting extremely small particles according to claim 3, characterized in that: The reflecting spherical surface is located on the lower surface of the spherical reflector. The light aperture of the spherical reflector is 28mm~32mm. The edge thickness of the spherical reflector is 7mm~9mm, and the center thickness is 1mm~3mm.

5. The optical device for detecting extremely small particles according to claim 4, characterized in that: The distance between the spherical vertex of the reflecting sphere and the light sensitive area is 18 mm to 20 mm, the forward full angle of the reflecting sphere is 96.1° to 96.5°, the backward full angle is 34.5° to 34.9°, the reflection efficiency is 0.93 to 0.97, and the surface accuracy is less than 1 / 2 of the wavelength of the laser beam.

6. The optical device for detecting extremely small particles according to claim 1, characterized in that: The focal length of the cylindrical lens is 22.74 mm to 23.14 mm, the radius of curvature is 11.27 mm to 11.67 mm, and the center thickness is 3.66 mm to 4.05 mm.

7. The optical device for detecting extremely small particles according to claim 1, wherein: The light trap includes three black glass plates spliced ​​together in sequence. The surfaces of the black glass plates are coated with an antireflection film layer. The transmittance of the antireflection film layer to the laser beam is greater than or equal to 99.5%, and the reflectivity of the antireflection film layer to the laser beam is less than or equal to 0.5%.

8. The optical device for detecting extremely small particles according to claim 1, wherein: The first aperture includes a first rectangular hole, the laser beam passes through the first rectangular hole and enters the light sensitive area, and the size of the first rectangular hole is 3 mm*2 mm.

9. The optical device for detecting extremely small particles according to claim 1, characterized in that: The second aperture includes a second rectangular hole. The light beam reflected by the reflecting spherical surface passes through the second rectangular hole and is incident on the photodiode. The size of the second rectangular hole is 6 mm*6 mm.

10. The optical device for detecting extremely small particles according to claim 1, characterized in that: It also includes a housing, wherein the fiber laser, cylindrical lens, first aperture, light trap, spherical reflector, second aperture and photodiode are all installed in the housing; The optical fiber laser is detachably connected with a collimating mirror.

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