Universe dust multi-parameter measuring device and method based on double-light-curtain detection

Abstract

The invention provides a cosmic dust multi-parameter measuring device and method based on double-light-curtain detection, and relates to the technical field of deep space exploration, the cosmic dust multi-parameter measuring device comprises a semiconductor laser, a laser shaping system, a scattered light collecting system, a signal processing system and a laser trap, and based on the light curtain shaping technology, an upper laser detection light curtain and a lower laser detection light curtain are generated by a single laser; the full coverage of a detection area is realized through the Wetton cone array, and low-speed and low-density cosmic dust particles can be detected under the condition that the dynamic state of the particles is not interfered; a Gaussian process regression model is utilized to analyze scattering signals obtained at multiple angles, and simultaneous measurement of multiple parameters such as particle size, refractive index, speed, quantity concentration and the like can be realized; the invention has the advantages of non-contact, non-interference, large detection area, high response speed, high function integration level and the like, and is suitable for in-situ detection of low-speed cosmic dust in a deep space vacuum environment.

Description

Technical Field

[0001] The present invention relates to the field of deep space exploration technology, and in particular to a cosmic dust multi-parameter measurement device and method based on double light curtain detection. Background Art

[0002] Cosmic dust is a type of tiny solid particle widely found in outer space, typically ranging in size from submicrometers to millimeters. The formation and evolution mechanisms of cosmic dust are complex and diverse, primarily originating from fragments ejected by meteorite impacts on the surfaces of planets and their satellites, the release of frozen dust from cometary nuclei as volatiles sublime, and primordial dust particles condensed in the interstellar medium. These dust particles, diffused throughout outer space, are crucial information carriers for recording the cosmic material cycle, the formation and evolution of celestial bodies, and precise detection and analysis of their physical and chemical properties, such as particle size distribution, composition, structure, and kinetic parameters, are of great scientific value for a deeper understanding of the origin, formation, material exchange mechanisms, and long-term evolution of planetary systems in the cosmic environment.

[0003] Particle detection technology based on the principle of light scattering is a highly sensitive, non-contact, and real-time dust detection method. The basic principle of this technology is that when particles are illuminated by a light beam, they generate scattered light signals related to their particle size, refractive index, and other properties. By analyzing the intensity and polarization of the scattered light, parameters such as particle size, shape, and structure can be inferred. Prior art patent application entitled "An Optical Sensor for In-Situ Detection of Cosmic Dust in Deep Space" (Publication No. CN119124946A) discloses a cosmic dust optical sensor based on a large-area light curtain. This sensor can measure dust particle size under vacuum, low velocity, and low concentration conditions, but its measurement of parameters such as refractive index and velocity relies on other detection equipment. Italian scholars Snodgrass and others proposed a concept of constructing an upper and lower light curtain based on dual-wavelength lasers to detect dust particles (Adv. Space Res. Volume 62, pages 1947-1976, 2018). Although the concept did not provide design details, since the scheme relies on multiple lasers to generate lasers of different wavelengths to work, it will inevitably face problems such as high power consumption, heavy weight, and complex system structure. It does not meet the current requirements of miniaturization, lightweight, low power consumption, and simple structure for space dust detection. A patent application entitled "A multi-angle optical particle counting and refractive index online measurement device and method" (publication number CN112782121A) discloses a device and method for online monitoring of atmospheric particulate matter. The design is based on the joint inversion of particle size and refractive index information from multi-wavelength, multi-angle scattered light signals. However, the detection area of ​​the device is extremely limited, and it relies on an air pump-based particle sampling and injection device to ensure that the detected particles pass through the detection area individually. This air pump-based particle sampling and injection method destroys the original motion state of the particles and is not suitable for the detection of cosmic dust in a vacuum environment.

[0004] In summary, for the detection of cosmic dust particles in a vacuum environment, the current particle detection technology based on the principle of light scattering still has the following problems and shortcomings: 1) The detection area is limited; 2) It needs to rely on a sample sampling device based on an air pump to ensure that the particles pass through the detection area individually, which destroys the original motion state of the particles; 3) It is difficult to achieve multi-parameter measurement of particle size, refractive index, velocity, etc. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a multi-parameter measurement device and method of cosmic dust based on dual light curtain detection, which is suitable for use in a vacuum environment and can realize real-time measurement of multiple parameters such as the number concentration, particle size, refractive index, and velocity of cosmic dust particles. It has the advantages of non-contact, strong real-time performance, large detection area, high measurement accuracy, and no destruction of the dynamic state.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A multi-parameter measurement device for cosmic dust based on dual-light-screen detection comprises a semiconductor laser, a laser shaping system, a scattered light collection system, a signal processing system, and a laser trap. The semiconductor laser generates a laser beam, which is divided into two collimated, uniformly intensity-distributed, and similarly energy laser detection light curtains by the laser shaping system. The particle to be measured sequentially passes through the upper and lower light curtains, generating two scattered light signals. The scattered light collection system collects the forward scattered signal generated by the upper laser detection light curtain and the side scattered signal generated by the lower laser detection light curtain, respectively, and records the moments when the particle passes through the upper and lower laser detection light curtains to obtain a time difference. The signal processing system converts the light scattered signal into an electrical signal, and outputs a reading after amplification, filtering, denoising, and analog-to-digital conversion. The refractive index and particle size of the particle to be measured are obtained by inversion by substituting the signal output reading into a pre-established Gaussian process regression model for calculation, and the particle velocity is calculated based on the light curtain spacing and the time difference. The number concentration of the dust particles is determined by recording the number of particles detected per unit time by a measuring device. The laser trap absorbs the laser light from the laser detection light curtain.

[0008] The semiconductor laser outputs a pre-collimated visible light or near-infrared light beam with stable output wavelength and modulated by square wave.

[0009] The laser shaping system includes a Powell prism, an aperture, a beam splitter, a total reflection mirror, and two spherical cylindrical lenses arranged in sequence along the laser axis. The system shapes the light beam generated by the semiconductor laser into two layers of laser detection light curtains with uniform intensity distribution, collimation, and similar energy.

[0010] The Powell prism is a cylindrical lens having a structure of a combination of an aspheric surface and a flat surface made of glass or quartz glass; wherein the aspheric surface has a surface formula:

[0011]

[0012] Where c is the curvature of the curve, C k is the cone coefficient, y P , Z are the horizontal and vertical coordinates of the cross section of the surface curve respectively; the curve obtained by the above surface formula is translated along the x-axis perpendicular to the cross section to obtain the curved surface of the Powell prism; the parameters of the Powell prism must meet the condition 0.25<|c·C k |<50, that is, the absolute value of the product of curvature and cone coefficient must be between 0.25 and 50; the aspherical surface and plane surface of the Powell prism are covered with a dielectric anti-reflection coating suitable for the laser wavelength.

[0013] The aperture is a small hole structure with a metal base and a surface coated with a matte material, and is used to limit the size of the light beam and filter out stray light.

[0014] The normal of the beam splitter forms a 45° angle with the optical axis of the laser beam, so that a portion of the laser energy, such as 50% of the laser energy, is reflected and deflected 90° to serve as the lower laser detection light curtain, and the remaining laser energy continues to be transmitted upward through the beam splitter; the base of the beam splitter is quartz glass, and the front and rear surfaces are respectively covered with a dielectric beam splitting film and a dielectric anti-reflection film suitable for the laser wavelength.

[0015] The normal of the total reflection mirror forms an angle of 45° with the optical axis of the laser beam, so that the laser beam is deflected by 90°; the substrate of the total reflection mirror is glass or quartz glass, and the surface is coated with a high reflectivity dielectric film suitable for the laser wavelength used.

[0016] The optical axes of the two spherical cylindrical lenses are respectively coaxial with the laser optical axis after reflection by the beam splitter and the total reflection mirror and are at the same height; the spherical cylindrical lens is a cylindrical optical lens made of glass or quartz glass; the spherical surface and the plane surface of the spherical cylindrical mirror are covered with a dielectric anti-reflection film suitable for the laser wavelength used.

[0017] The scattered light collection system includes multiple Winston cone arrays and bandpass filters; the upper Winston cone array receives the scattered light flux at the forward scattering angle (central scattering angle of 45°), and the lower Winston cone array receives the scattered light flux at the side scattering angle (central scattering angle of 90°).

[0018] The Winston cone array uses a non-imaging concentrator made of metal, which is used to collect scattered light within a certain angle range. Its surface is a compound rotational paraboloid structure, and the inner surface is coated with a high-reflectivity precious metal film. The Winston cone surface is a surface formed by rotating a portion of a hyperbola around a specific axis. Its parabola equation is:

[0019] y 2 =4a(sinθ max +1)x,

[0020] Where x is the hyperbolic axis, y is the hyperbolic coordinate of the Winston cone, a is the outlet diameter of the Winston cone, θ max is the maximum acceptance angle of the Winston cone; the entrance diameter b of the Winston cone is determined by the following constraint relationship:

[0021]

[0022] The length l of the Winston cone is:

[0023]

[0024] The bandpass filter is a quartz-based coated interference filter element used to suppress interference light of non-target wavelengths and improve the system signal-to-noise ratio and measurement accuracy.

[0025] The signal processing system consists of a photodiode and a signal processing terminal circuit; the photodiode is sensitive to the wavelength of the laser used and is sized to fully cover the outlet of the Winston cone; when the photodiode is installed, its photosensitive surface is tightly connected to the outlet of the Winston cone; the photodiode functions to convert the light scattering signal received by the Winston cone into an electrical signal; the signal processing terminal circuit amplifies, filters, removes noise, and performs digital-to-analog conversion on the electrical signal collected by the photodiode before outputting it.

[0026] The upper and lower laser traps are coaxially arranged with the upper and lower laser detection curtains respectively. The internal material has a high absorption rate and can effectively absorb the unscattered direct laser to avoid interfering with the detection area.

[0027] The measurement method using the cosmic dust multi-parameter measurement device based on double light curtain detection comprises the following steps:

[0028] The first step is to use light scattering theory to calculate the scattered light flux of particles of different particle sizes and refractive indices within a certain range of forward and side scattering angles under specific laser wavelengths. A particle scattering database is established, and a mapping relationship between scattered light flux, particle size, and refractive index is established based on a Gaussian process regression model.

[0029] The second step is to calibrate the measuring device using standard particles of different compositions. The forward and side scattering signals of the standard particles as they pass through the detection light curtain are measured. By comparing the measured signals with the theoretically calculated data, the proportional factor is obtained based on numerical fitting to determine the calibration coefficient of the measuring device.

[0030] The third step is to measure the particles to be tested, obtain their forward and side scattering signals, and substitute the calibration coefficients into the Gaussian process regression model to invert the particle size and refractive index.

[0031] Step 4: Given that the vertical distance h between the upper and lower laser detection screens of the measuring device is known, during the measurement process, by recording the times t1 and t2 when the particle passes through the upper and lower laser detection screens, the time difference △t = t2-t1 is obtained. The particle velocity is then:

[0032] v=h / △t;

[0033] The fifth step is to record the number of particles detected per unit time through a measuring device, which is the number concentration of dust particles.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The present measuring device utilizes light curtain shaping technology. By employing non-spherical lenses such as Powell prisms, it generates two layers of uniformly intense, collimated laser detection curtains. This significantly expands the measuring device's detection area, eliminating the need for the traditional air pump-driven particle sampling unit. This makes the device suitable for detecting dust particles in vacuum environments. By achieving full coverage of the detection area through a Winston cone array, it can detect low-speed, low-density cosmic dust particles without interfering with their motion. This device offers the advantages of being non-contact, non-interfering, with a large detection area, high measurement accuracy, and a fast response time.

[0036] 2. The measuring device of the present invention constructs two layers of laser detection light curtains, which respectively obtain the scattered light flux of the dust particles to be measured within different scattering angle ranges and the time difference between the particles passing through the upper and lower layers of laser detection light curtains, and can realize the simultaneous measurement of multiple parameters such as particle size, refractive index, velocity, and number concentration.

[0037] 3. The measurement device of the present invention uses a beam splitter to split the laser energy, enabling the two beams generated by a single laser to construct upper and lower laser detection screens, respectively. This device has a simple optical system structure. Compared with multi-laser solutions, the present invention offers advantages such as high system integration, low cost, low power consumption, high stability, and easy maintenance.

[0038] 4. The measurement method of this invention utilizes a Gaussian process regression model to inversely analyze scattering data, effectively integrating scattering signatures acquired from multiple angles using dual light curtains. This method significantly improves the accuracy of particle size and refractive index calculations. The resulting mapping model between multidimensional scattering signatures and parameters such as particle size and refractive index is suitable for in-situ measurements of low-velocity cosmic dust and possesses significant engineering applicability and potential for widespread adoption. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the three-dimensional structure of the device according to an embodiment of the present invention.

[0040] Figure 2 Schematic diagram of the upper Winston cone coverage detection light curtain range according to an embodiment of the present invention.

[0041] Figure 3 Schematic diagram of the detection light curtain range covered by the lower Winston cone in an embodiment of the present invention.

[0042] Figure 4 Schematic diagram of the Winston cone structure according to an embodiment of the present invention.

[0043] Figure 5 This is a diagram of the light intensity distribution in the detection areas of the upper and lower light curtains according to an embodiment of the present invention.

[0044] Figure 6Graph 1 shows the relationship between the theoretical luminous flux reception values ​​of the upper and lower Winston cones and the particle size in an embodiment of the present invention.

[0045] Figure 7 This is the theoretical result of particle size inversion for particles with a refractive index of m=1.50 according to an embodiment of the present invention.

[0046] Figure 8 This is the theoretical result of refractive index inversion performed on particles with a refractive index of m=1.50 according to an embodiment of the present invention. DETAILED DESCRIPTION

[0047] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments and drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0048] like Figure 1 As shown, a multi-parameter measurement device for cosmic dust based on dual-light curtain detection includes a semiconductor laser 1, a laser shaping system, a scattered light collection system, a signal processing system, and a laser trap. The semiconductor laser 1 generates a laser beam, which is divided into two collimated, uniformly intensity-distributed, and similar-energy laser detection curtains, one above and one below, by the laser shaping system. The width of the laser detection curtains is 40 mm, the thickness is 3 mm, and the vertical spacing between the upper and lower laser detection curtains is h = 50 mm. The particles to be measured pass through the upper and lower light curtains in sequence, generating two scattered light signals. The scattered light collection system collects the forward (45° center angle) scattered signal F generated by the upper laser detection curtain and the forward (45° center angle) scattered signal F generated by the upper laser detection curtain. 45 and the lateral (90° central angle) scattered signal F generated by the lower laser detection curtain 90 , respectively record the time t1 and t2 when the particle passes through the upper and lower laser detection light curtains, and obtain the time difference △t=t2-t1; the signal processing system converts the optical signal [F 45 ,F 90 ] is converted into an electrical signal, and then amplified, filtered, de-noised, and analog-to-digital converted to output the reading [S 45 ,S 90 By substituting the signal output reading into a pre-established Gaussian process regression model, the refractive index m and particle size D of the particle being measured can be inverted. The particle velocity v can be calculated from the light curtain spacing h and the time difference Δt using the formula v = h / Δt. The dust particle concentration is determined by recording the number of particles detected per unit time using a measuring device. The laser trap is used to absorb the laser light from the laser detection light curtain.

[0049] The semiconductor laser 1 is a pre-collimated laser light source. In the embodiment, a semiconductor laser with a central wavelength of 976 nm, a line width not exceeding 10 nm, a peak power not less than 3.0 W, a duty cycle of 50%, and a modulation frequency of 50 kHz is used. Its fast-axis divergence angle does not exceed 10.0 mrad, the slow-axis divergence angle does not exceed 5.0 mrad, and the laser spot has an elliptical Gaussian distribution; the fast-axis beam waist width at the laser outlet is not greater than 20.0 mm, and the slow-axis beam waist width is not greater than 3.0 mm; in the embodiment, the fast-axis divergence angle of the laser is 8.5 mrad, the slow-axis divergence angle is 3.5 mrad, the fast-axis beam waist width at the laser outlet is 18.0 mm, and the slow-axis beam waist width is 2.3 mm.

[0050] Reference Figure 1 The laser shaping system includes a Powell prism 2, an aperture 3, a beam splitter 4, a total reflection mirror 5, which are arranged in sequence along the laser axis of the semiconductor laser 1, and a first spherical cylindrical lens 6a and a second spherical cylindrical lens 6b which are at the same height as the beam splitter 4 and the total reflection mirror 5 respectively; the laser beam emitted by the semiconductor laser 1 is shaped into two upper and lower beams with a width of 40mm and a thickness of 3mm, which are uniform in intensity, collimated, and have equal energy. The light intensity distribution in the detection area of ​​the laser detection light curtain of the embodiment is as follows: Figure 5 As shown, the light curtain uniformity γ is:

[0051]

[0052] Among them E i is the light intensity value of each point in the light curtain, is the average light intensity value obtained by counting each point on the light curtain, and N is the total number of light intensity measurement points in the light curtain; the number of sampling points N = 80 is selected, and the calculation is Figure 5 The uniformity of the laser detection light curtain across its width is 90.8%, exceeding 90%. Within a 40mm width, except for a high intensity within the 1-2mm range at the edge, the light intensity distribution of both the upper and lower detection light curtains is highly uniform, ensuring that the incident light intensity is similar at any point within the detection area when a particle lands.

[0053] The Powell prism 2 is a cylindrical lens having a structure of a combination of an aspheric surface and a flat surface made of glass or quartz glass, wherein the aspheric surface has a surface formula:

[0054]

[0055] Where c is the curvature of the curve, C k is the cone coefficient, y P, Z are the horizontal and vertical coordinates of the cross section of the surface curve respectively; the curve obtained by the above surface formula is translated along the x-axis perpendicular to the cross section to obtain the curved surface of the Powell prism; the parameters of the Powell prism 2 must meet the condition 0.25<|c·C k |<50, that is, the absolute value of the product of curvature and cone coefficient must be between 0.25 and 50; the curvature of the Powell prism 2 in the embodiment is 1 / 15mm -1 The cone coefficient is -7.5, the center thickness of the lens is 20mm, and the radius of its plane is 10mm; the aspherical surface and plane surface of the Powell prism are covered with a dielectric anti-reflection film suitable for the laser wavelength, and the transmittance is greater than 99.5%.

[0056] The aperture 3 is a small hole structure with a metal base and a surface coated with a matte material. The center position of the aperture is collinear with the optical axis of the laser beam. In the embodiment, the aperture 3 has an opening diameter φ=8 mm and is 50 mm away from the plane of the Powell prism 2. The base material is aluminum and is coated with pine soot ink for matte effect.

[0057] The normal of the beam splitter 4 forms an angle of 45° with the optical axis of the laser beam, and the splitting ratio is 50:50; under ideal conditions, 50% of the laser energy is reflected and deflected 90° to serve as the lower laser detection light curtain, and the remaining 50% of the energy continues to transmit upward through the beam splitter 4; in this embodiment, the length and width of the beam splitter 4 are 60 mm and 30 mm respectively, and the substrate is H-K9L glass, the front surface of which is coated with a beam splitting film with a center wavelength of 976 nm, and the rear surface is coated with an anti-reflection film with a center wavelength of 976 nm.

[0058] The normal of the total reflection mirror 5 forms an angle of 45° with the optical axis of the laser beam, causing the laser beam to be deflected by 90°. In this embodiment, the total reflection mirror 5 has a length and a width of 60 mm and 30 mm, respectively. The substrate is H-K9L glass, and its surface is coated with a high-reflection dielectric film with a central wavelength of 976 nm. The reflectivity of the total reflection mirror 5 for lasers with a central wavelength of 976 nm is greater than 99.5%.

[0059] The optical axes of the first spherical cylindrical lens 6a and the second spherical cylindrical lens 6b are respectively coaxial with the optical axis of the laser after reflection by the total reflection mirror 5 and the beam splitter 4, and are at the same height; in the embodiment, the first spherical cylindrical lens 6a and the second spherical cylindrical lens 6b are cylindrical optical lenses made of high-transmittance glass H-K9L, with a center thickness of 20mm, a length and width of the plane of 50mm and 20mm respectively, and a spherical focal length of 80mm; the spherical surface and the plane surface of the first spherical cylindrical lens 6a and the second spherical cylindrical lens 6b are covered with a dielectric anti-reflection film, and have a transmittance greater than 99.5% for 976nm laser.

[0060] The scattered light collection system includes Winston cone arrays 7 (a to d) and their matching bandpass filters 8 (a to d) respectively for the upper and lower laser detection light curtains; wherein the upper Winston cone array receives forward scattered light flux (central scattering angle of 45°); in an embodiment, the central axes of the two cones of the upper Winston cone array are at the same height as the center of the upper laser detection light curtain, the central axes of the two cones are perpendicular to each other, and both form an angle of 45° with the propagation direction of the laser detection light curtain; the lower Winston cone array receives lateral scattered light flux (central scattering angle of 90°); in an embodiment, the central axes of the two cones of the lower Winston cone array are parallel, and both are at the same height as the center of the lower laser detection light curtain, and both maintain an angle of 90° with the propagation direction of the laser detection light curtain; the entrances of the two cones of the lower layer are opposite, the central axes are staggered, and the horizontal distance is the cone radius; in an embodiment, the upper and lower detection areas covered by the Winston cone array are respectively as follows Figure 2 (Upper detection area) and Figure 3 (Lower detection area) It can be seen that the horizontal projection of the ideal detection area of ​​each Winston cone is an isosceles triangle with the Winston cone entrance diameter as the base and a vertex angle twice its maximum acceptance angle. The vertical overlap between the detection areas of the upper Winston cones 7a and 7b and the detection areas of the lower Winston cones 7c and 7d forms a parallelogram, representing the effective particle detection area of ​​the detector. In this embodiment, the effective particle detection area is greater than 45 mm × 40 mm.

[0061] like Figure 1 、 Figure 4 As shown, the Winston cone array includes four Winston cones 7a, 7b, 7c, and 7d. In the embodiment, the Winston cone is a non-imaging concentrator made of nickel, with the inner surface coated with a high-reflectivity gold film. Its surface shape is a compound rotational paraboloid structure, which can achieve efficient collection of scattered light within a certain angle range; Figure 4 As shown in Figure 1, the Winston cone is a surface formed by rotating a portion of a hyperbola around a specific axis. The parabola equation is:

[0062] y 2 =4a(sinθ max +1)x,

[0063] Where x is the hyperbolic rotation axis, y is the hyperbolic coordinate of the Winston cone, a is the outlet diameter of the Winston cone, θ max is the maximum acceptance angle of the Winston cone; the entrance diameter b of the Winston cone is determined by the following constraint relationship:

[0064]

[0065] The length l of the Winston cone is:

[0066]

[0067] In the embodiment, the maximum acceptance angles of the upper and lower Winston cones are both θ max =11.3 ° The outlet diameter a of the upper Winston cones 7a and 7b is 10.8mm, and the inlet diameter b is 55mm; the outlet diameter a of the lower Winston cones 7c and 7d is 6.86mm, and the inlet diameter b is 35mm; all Winston cones have a wall thickness of 1mm and are processed using a nickel metal base; because the cones are too long, according to structural requirements, all cones are cut to a length of 100mm. Figure 2 、 Figure 3 As shown, the entrance center of the upper Winston cone 7a is 20.0 mm away from the center axis of the light curtain, and 198.0 mm away from the center of the reflector; the entrance center of the upper Winston cone 7b is 20.0 mm away from the center axis of the light curtain, and 204 mm away from the center of the reflector; the entrance center of the lower Winston cone 7c is 6.7 mm away from the center axis of the light curtain, and 160 mm away from the center of the beam splitter; the entrance center of the lower Winston cone 7d is 6.7 mm away from the center axis of the light curtain, and 177.5 mm away from the center of the beam splitter.

[0068] like Figure 1 As shown, the bandpass filters 8 (a-d) are quartz-substrate coated interference filter elements, which are mainly used to suppress interference light of non-target wavelengths, thereby improving the system signal-to-noise ratio and measurement accuracy. In this embodiment, an interference bandpass filter with a central wavelength of 980 nm and a bandwidth of 25 nm is used. The transmittance of the central wavelength laser is greater than 90%, and the effective diameter dimensions are required to be greater than 55 mm (bandpass filters 8a, 8b) and 35 mm (bandpass filters 8c, 8d), respectively. This can fully cover the entrance of the Winston cone, effectively reduce the impact of non-working light sources on the signal processing system 9 (a-d), reduce the optical noise of the sensor, and improve the sensor measurement signal-to-noise ratio.

[0069] like Figure 1 As shown, the signal processing system 9 (a-d) is composed of a photodiode and a signal processing terminal circuit; wherein the photodiode is a photodiode sensitive to the laser wavelength used. In the embodiment, a PIN type photodiode is used, and the photoelectric conversion efficiency at the central wavelength of 976nm is greater than 0.6A / W, and the photosensitive area is 18×18mm 2 , which can fully cover the exit of each Winston cone; when the photodiode is installed, its photosensitive surface is closely connected to the exit of the Winston cone, and the forward and side light scattering signals [F 45 ,F 90 ] is converted into an electrical signal, which is then amplified, filtered, de-noised, and converted into analog to digital by the signal processing terminal circuit before being output as a digital display [S 45 ,S 90 ], which is used to invert the parameters of dust particles such as particle size and refractive index.

[0070] like Figure 1 As shown, the first laser trap 10a and the second laser trap 10b are coaxially arranged with the upper and lower laser detection light curtains respectively; the first laser trap 10a and the second laser trap 10b are composed of light-absorbing black glass. When the laser enters the trap cavity, it will be reflected and absorbed multiple times by the inner wall of the cavity; the material used in the embodiment is absorptive optical glass, the internal absorption rate of the glass is greater than 99%, and the surface of the absorptive optical glass is coated with an anti-reflection film, so that the laser penetrates into the glass and is absorbed, and the surface reflectivity is less than 1%.

[0071] The measurement method using the cosmic dust multi-parameter measurement device based on double light curtain detection comprises the following steps:

[0072] The first step is to calculate the scattered light flux [F] of spherical particles with different particle sizes (0.1 μm-1000 μm) and different refractive indices (including but not limited to: m = 1.33, 1.45, 1.56, 1.74, 2.12) in the forward direction (central scattering angle of 45°, scattering range of 33.7°-56.3°) and the side direction (central scattering angle of 90°, scattering range of 78.7°-101.3°) based on light scattering theory. 45 ,F 90 ], establish a scattered light flux database; use the scattered light flux and its corresponding particle size and refractive index as training set and test set to train Gaussian process regression model, and establish the theoretical correspondence between multi-angle scattered light flux and particle size and refractive index; the specific method is: calculate the forward and side scattered light flux arrays of particles based on the above light scattering theory [F 45 ,F 90 ] and its corresponding refractive index and particle size array [m, D] samples are randomly divided into two parts, 80% of which are used as training sets and 20% as test sets; the training set data are input into the Gaussian process regression model for training, and the mean square error value RMSE and the coefficient of determination R-square of the regression model are selected as the judgment basis to determine the kernel function of the regression model, wherein the mean square error value RMSE takes the minimum value and the coefficient of determination R-square must be as close to 1 as possible; the kernel function of the Gaussian process regression model trained in the embodiment is selected as an exponential function, and its RMSE = 20.378, R-square = 0.99, which meets the measurement requirements; the particle size inversion accuracy test is performed on the remaining 20% ​​test set, and the results show that the particle size and refractive index inversion errors obtained by the model inversion do not exceed 10%;

[0073] In the second step, the measuring device is calibrated using standard sample particles of different compositions (including but not limited to: silicon dioxide particles, refractive index m = 1.45; aluminum oxide particles, refractive index m = 1.74; silicon carbide particles, refractive index m = 2.12) to measure the forward and side scattering signals [S 45 ,S90 ], the theoretical calculation data [F 45 ,F 90 ] and the measured signal value [S 45 ,S 90 ] are compared, the proportional factor is obtained by nonlinear numerical fitting, and the calibration coefficient of the measuring device is determined;

[0074] The third step is to measure the particles to be tested and obtain their forward and side scattering signals [S 45 ,S 90 ]; Combined with the calibration coefficient, the transformation is performed and substituted into the Gaussian process regression model to invert the particle size D and refractive index m;

[0075] Step 4: Given the vertical distance h between the upper and lower laser detection screens of the measuring device, record the times t1 and t2 when the particle passes through the upper and lower laser detection screens, and obtain the time difference △t = t2-t1 when the particle passes through the upper and lower laser detection screens. The particle velocity is then:

[0076] v=h / △t;

[0077] The fifth step is to record the number of particles detected per unit time through a measuring device, which is the number concentration of dust particles.

[0078] The measuring device of this embodiment can detect multiple parameters such as particle size, refractive index, velocity, and number concentration of low-speed, low-density cosmic dust particles without disturbing the motion state of the particles themselves; it uses a beam splitter to split the laser energy, and has the advantages of high system integration, low cost, low power consumption, high stability, and easy maintenance; at the same time, it uses a Gaussian process regression model to inversely analyze the scattering data, which can effectively integrate the scattering characteristics obtained by the dual light curtain at multiple angles, and significantly improve the calculation accuracy of the particle size and refractive index.

[0079] This embodiment takes particles with a refractive index of m = 1.50 as an example to analyze the measurement results. The incident wavelength of the laser is 0.98um and the average power is 3.0W. Considering that the output duty cycle of the semiconductor laser is 50%, the peak power of the laser is 6.0W. The laser beam is divided into two layers of detection light curtains with approximately equal light intensities, and the peak power of each laser beam is 3.0W. The cross-sectional area of ​​the laser beam is 40mm*3mm. Without considering the attenuation of optical components, the power density of the laser light curtain in the detection area is approximately 2.5W / cm 2Considering that the transmittance of the interference filter is 0.9, the collection efficiency of the Winston cone is 0.7, and the photoelectric conversion coefficient of the photodiode is 0.6, the efficiency coefficient of the signal acquisition system is 0.378. Assuming the noise level of the signal processing system is less than 20mV, and setting the judgment threshold according to the signal-to-noise ratio of 2:1, the scattered signal intensity above 40mV can be identified. The signal amplification factor is 5×10 7 By estimation, the minimum detectable laser equivalent scattering cross section can be calculated as: 8.5×10 -10 cm 2 In addition, the detection rate of an optical acquisition system is defined as the ratio of the light scattered energy within the detection field angle to the total scattered energy in the entire space. That is, the larger the detection field angle, the more energy is collected, and the greater the detection rate. The experimental measurement results of Italian scholars Epifani et al. (Adv. Space Res. Vol. 29, pp. 1165-1169, 2002) show that the laser equivalent cross-sectional area of ​​a spherical olivine particle with a particle size of 10 μm is 0.434×10 -9 cm 2 In this embodiment, the maximum acceptance angle of the upper and lower Winston cones is 11.3°, and the central azimuth angles are 45° and 90° respectively. Based on the Mie scattering theory, the laser equivalent cross-sectional area of ​​the 10 μm olivine spherical particles detected by the upper and lower Winston cones is 20.52×10 -9 cm 2 , 1.72×10 -9 cm 2 On this basis, according to the approximate proportional relationship between the scattering cross section and the square of the particle size, it can be calculated that for dust particles with a refractive index of m = 1.50, the minimum particle sizes that can be detected by the upper and lower layers of the measurement system are 2.1um and 7.0um respectively.

[0080] In order to verify the accuracy of the particle size and refractive index inversion of the Gaussian process regression model, a theoretical simulation test was carried out using particles with a refractive index of m = 1.50 as an example. Figure 6 As shown in the figure, the Mie scattering theory is used to calculate the scattering flux spectra of particles with a size range of 1μm-1mm received by the upper Winston cone (scattering angle [33.7°, 56.3°]) and the lower Winston cone (scattering angle [78.7°, 101.3°]). Ten groups of values ​​are randomly selected as test data and input into the trained Gaussian process regression model. The comparison between the inverted particle size results and the actual particle size is as follows: Figure 7 The comparison between the inverted refractive index result and the true refractive index is as follows: Figure 8 As shown. Figure 7 It can be seen that the error of the inverted particle size does not exceed 10%. Figure 8 It can be seen that the inversion error of the refractive index does not exceed 15%.

Claims

1. A cosmic dust multi-parameter measurement device based on dual light curtain detection, characterized in that: The system comprises a semiconductor laser, a laser shaping system, a scattered light collection system, a signal processing system, and a laser trap. The semiconductor laser generates a laser beam, which is then split by the laser shaping system into two collimated, uniformly distributed, and similarly energetic laser detection screens. The particles to be measured sequentially pass through the upper and lower screens, generating two scattered light signals. The scattered light collection system collects the forward scattered signal from the upper laser detection screen and the side scattered signal from the lower laser detection screen, respectively. The time difference is obtained by recording the moment a particle passes through each of the two screens. The signal processing system converts the scattered light signals into electrical signals, which are then amplified, filtered, de-noised, and converted to digital output. The signal output is then fed into a pre-established Gaussian process regression model to invert the refractive index and particle size of the particles to be measured. The particle velocity is calculated from the screen spacing and the time difference. The number concentration of dust particles is determined by measuring the number of particles detected per unit time. The laser trap absorbs the laser light from the laser detection screens.

2. The device according to claim 1, characterized in that: The laser shaping system includes a Powell prism, an aperture, a beam splitter, a total reflection mirror, and two spherical cylindrical lenses arranged in sequence along the laser axis. The system shapes the light beam generated by the semiconductor laser into two layers of laser detection light curtains with uniform intensity distribution, collimation, and similar energy.

3. The device according to claim 2, characterized in that: The Powell prism is a cylindrical lens having a structure of a combination of an aspheric surface and a flat surface made of glass or quartz glass; wherein the aspheric surface has a surface formula: Where c is the curvature of the curve, C k is the cone coefficient, y P , Z are the horizontal and vertical coordinates of the cross section of the surface curve respectively; the curve obtained by the above surface formula is translated along the x-axis perpendicular to the cross section to obtain the curved surface of the Powell prism; the parameters of the Powell prism must meet the condition 0.25<|c·C k |<50, that is, the absolute value of the product of curvature and cone coefficient must be between 0.25 and 50; the aspherical surface and plane surface of the Powell prism are covered with a dielectric anti-reflection coating suitable for the laser wavelength.

4. The device according to claim 2, characterized in that: The normal of the beam splitter forms a 45° angle with the optical axis of the laser beam, so that part of the laser energy is reflected and deflected 90° to serve as the lower laser detection light curtain, and the remaining laser energy continues to be transmitted upward through the beam splitter; the base of the beam splitter is quartz glass, and the front and rear surfaces are respectively covered with a dielectric beam splitting film and a dielectric anti-reflection film suitable for the laser wavelength.

5. The device according to claim 2, characterized in that: The normal of the total reflection mirror forms an angle of 45° with the optical axis of the laser beam, so that the laser beam is deflected by 90°; the substrate of the total reflection mirror is glass or quartz glass, and the surface is coated with a high reflectivity coating suitable for the laser wavelength used.

6. The device according to claim 2, characterized in that: The optical axes of the two spherical cylindrical lenses are coaxial with the laser optical axis after reflection by the beam splitter and the total reflection mirror and are at the same height; the spherical cylindrical lens is a cylindrical optical lens made of glass or quartz glass; the spherical surface and the plane surface of the spherical cylindrical mirror are covered with a dielectric anti-reflection film.

7. The device according to claim 1, characterized in that The scattered light collection system includes multiple Winston cone arrays and bandpass filters; the upper Winston cone array receives the forward scattered light flux with a central scattering angle of 45°, and the lower Winston cone array receives the side scattered light flux with a central scattering angle of 90°.

8. The device according to claim 7, characterized in that: The Winston cone array uses a non-imaging concentrator made of metal. Its surface is a compound paraboloid structure. The inner surface is coated with a high-reflectivity precious metal film to collect scattered light within a certain angle range. The Winston cone surface is a surface formed by rotating a portion of a hyperbola around a specific axis. The parabola equation is: y 2 =4a(sinθ max +1)x, Where x is the hyperbolic axis, y is the hyperbolic coordinate of the Winston cone, a is the outlet diameter of the Winston cone, θ max is the maximum acceptance angle of the Winston cone; the entrance diameter b of the Winston cone is determined by the following constraint relationship: The length l of the Winston cone is:

9. The device according to claim 1, characterized in that The signal processing system consists of a photodiode and a signal processing terminal circuit. The photodiode is sensitive to the wavelength of the laser used and can fully cover the outlet of the Winston cone. When the photodiode is installed, its photosensitive surface is closely connected to the outlet of the Winston cone. The photodiode is used to convert the light scattering signal received by the Winston cone into an electrical signal. The signal processing terminal circuit amplifies, filters, removes noise, and performs digital-to-analog conversion on the electrical signal collected by the photodiode before outputting it.

10. A measurement method using the cosmic dust multi-parameter measurement device based on double light curtain detection according to any one of claims 1 to 9, characterized in that: The following steps are involved: The first step is to use light scattering theory to calculate the scattered light flux of particles of different particle sizes and refractive indices within a certain range of forward and side scattering angles under specific laser wavelengths. A particle scattering database is established, and a mapping relationship between scattered light flux, particle size, and refractive index is established based on a Gaussian process regression model. The second step is to calibrate the measuring device using standard particles of different compositions. The forward and side scattering signals of the standard particles as they pass through the detection light curtain are measured. By comparing the measured signals with the theoretically calculated data, the proportional factor is obtained based on numerical fitting to determine the calibration coefficient of the measuring device. The third step is to measure the particles to be tested, obtain their forward and side scattering signals, and substitute the calibration coefficients into the Gaussian process regression model to invert the particle size and refractive index. Step 4: Given that the vertical distance h between the upper and lower laser detection screens of the measuring device is known, during the measurement process, by recording the times t1 and t2 when the particle passes through the upper and lower laser detection screens, the time difference △t = t2-t1 is obtained. The particle velocity is then: v=h / △t; The fifth step is to record the number of particles detected per unit time through a measuring device, which is the number concentration of dust particles.

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