Simulation method of laser Doppler spectrum

Abstract

The invention relates to the technical field of laser, in particular to a laser Doppler spectrum simulation method. The laser Doppler spectrum simulation method comprises the following steps: representing incident laser as a virtual photon group; obtaining state parameters of the virtual photons at the initial moment; calculating state parameters after the virtual photons and the discrete particle swarms act; counting the frequency shift of the virtual photons emitted from the discrete particle swarms to generate a frequency spectrum; according to the simulation method of the laser Doppler spectrum, in the simulation process, virtual photons are propelled in the space in the area where a particle swarm is located in the movement direction of the virtual photons so as to simulate the transportation process of a laser light field, and photon state parameter changes after interaction of the photons and particles are calculated; and counting photons which leave the regional space where the particle swarm is located and return to be received by the probe, thereby obtaining the distribution condition of power spectrum intensity along with frequency shift, and realizing accurate simulation and simulation of the laser Doppler spectrum in the particle swarm.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, in particular to a method for simulating laser Doppler spectrum. Background Art

[0002] Laser Doppler interferometry is an experimental diagnostic technique that uses the optical Doppler effect to measure an object's velocity in real time and without contact. Existing laser Doppler interferometry uses a monochromatic laser incident on the surface of a moving object. Upon reflection, the laser's frequency changes due to the Doppler effect. The frequency-shifted reflected light is then mixed with an unshifted reference beam, and the mixed signal is recorded on an oscilloscope. The oscillation period of the mixed signal is proportional to the object's radial velocity along the diagnostic direction. By analyzing the temporal changes in the mixing signal's frequency, the object's velocity history can be determined.

[0003] Laser Doppler interferometry velocimetry can be used to diagnose a single interface or a large number of discrete particles. When the diagnostic target is a discrete particle group, the laser interacts with the numerous particles, and the frequency shift of the reflected light is correlated with the velocity of each particle. The spectrum image obtained by laser velocimetry appears as a diffuse band of a certain width. Laser Doppler spectrum analysis of a single interface is relatively simple, as the spectrum lines intuitively reflect the velocity of the interface. However, the spectrum signal for a discrete particle group is a comprehensive reflection of the information from numerous particles, and existing technologies do not allow for optical simulation of the laser Doppler spectrum for discrete particle groups. Summary of the Invention

[0004] The purpose of the present invention is to provide a feasible technical approach for optically simulating the laser Doppler spectrum of discrete particle groups, which is not possible in the prior art.

[0005] The present invention provides a laser Doppler spectrum simulation method for performing Doppler spectrum simulation on a discrete particle group. The simulation method includes:

[0006] Characterize the incident laser light as a group of virtual photons;

[0007] Get the state parameters of the virtual photon at the initial moment;

[0008] Calculate the state parameters after the virtual photons interact with the discrete particle group;

[0009] Count the frequency shifts of virtual photons emitted from a discrete particle group to generate a spectrum;

[0010] The state parameters include at least one of spatial position, propagation direction, polarization state and frequency.

[0011] Optionally, the position vector H of the spatial position is: H=[x, y, z], where z is the height position value, x is the lateral position value, and y is the longitudinal position value;

[0012] The cosine vector u of the propagation direction is:

[0013] u=[u x ,u y ,u z ]

[0014]

[0015] Among them, θ is the angle between the virtual photon trajectory and the z-axis, is the angle between the virtual photon trajectory and the x-axis;

[0016] The Stokes vector S of the polarization state is:

[0017] S=[I,U,V,Q]

[0018] The frequency ω is:

[0019] ω i,0 =2πc / λ

[0020] Wherein, c is the speed of light, and λ is the wavelength of the incident laser.

[0021] Optionally, obtaining the initial state parameters of the virtual photon includes:

[0022] Determine the height position value at the initial moment: z = 0;

[0023] Performing random sampling based on the light intensity distribution of the incident laser at the initial moment to determine the lateral position value x and the longitudinal position value y at the initial moment;

[0024] If the incident laser is a uniform beam and the light intensity distribution is such that the light intensity remains constant within the range of the light spot, then:

[0025] x i =r i cosε i ;y i =r i sinε i ;

[0026] If the incident laser is a Gaussian beam and the light intensity distribution is Gaussian from the center of the spot outward, then:

[0027] x i =r i cosε i ;y i =r i sinε i ;

[0028] Among them, Ф j is the spot diameter of the uniform light beam; Ф g is the waist diameter of the Gaussian beam; RND is a random number generated by a computer random function; r i represents the distance between the i-th virtual photon and the center of the light spot; ε i represents the position angle of the i-th virtual photon; x i is the lateral position value of the i-th virtual photon, y i is the longitudinal position value of the i-th virtual photon;

[0029] If the incident laser is a collimated beam, the cosine vector of the virtual photon at the initial moment is:

[0030]

[0031] If the incident laser is unpolarized light, the Stokes vector of the virtual photon at the initial moment is:

[0032] S=[1,0,0,0]

[0033] If the incident laser is linearly polarized light, the Stokes vector of the virtual photon at the initial moment is:

[0034] S=[1,1,0,0], or S=[1,-1,0,0], or S=[1,0,1,0], or S=[1,0,-1,0];

[0035] If the incident laser is right-handed circularly polarized light, the Stokes vector of the virtual photon at the initial moment is:

[0036] S=[1,0,0,1]

[0037] If the incident laser is left-handed circularly polarized light, the Stokes vector of the virtual photon at the initial moment is:

[0038] S=[1,0,0,-1]

[0039] The frequency of the virtual photon at the initial moment is:

[0040] ω i,0 =2πc / λ

[0041] Where c is the speed of light and λ is the wavelength of the incident laser.

[0042] Optionally, the calculating of state parameters after the virtual photons interact with the discrete particle group includes:

[0043] The position vector of the updated virtual photon after movement is:

[0044]

[0045] Among them, H i,new =[x i,new ,y i,new ,z i,new ] is the updated space vector of virtual photon i, H i =[x i ,y i ,z i ] is the space vector of virtual photon i before the movement is updated, Δl is the movement distance of the virtual photon each time, u i =[u x,i ,u y,i ,u z,i ] is the cosine vector of virtual photon i before motion update.

[0046] Optionally, the calculating of state parameters after the virtual photons interact with the discrete particle group includes:

[0047] determining whether the virtual photon interacts with the discrete particle;

[0048] If the virtual photon is scattered after interacting with the discrete particle, determining the deflection angle and rotation angle of the virtual photon after scattering;

[0049] If the third component u of the cosine vector of the virtual photon before scattering z Satisfy: |u z |≥0.9999, then the updated cosine vector of the virtual photon after movement is:

[0050]

[0051] If the third component u of the cosine vector of the virtual photon before scattering z Satisfy: |u z |<0.9999, then the updated cosine vector of the virtual photon after movement is:

[0052]

[0053] Among them, α is the deflection angle before and after the virtual photon scattering, and the value range of α is 0~π; β is the rotation angle before and after the virtual photon scattering, and the value range of β is 0~2π; u i =[u x,i ,u y,i ,u z,i ] is the cosine vector of virtual photon i before motion update, u i,new =[u x,i,new ,u y,i,new ,u z,i,new ] is the updated cosine vector of the virtual photon i’s motion.

[0054] Optionally, determining whether the virtual photon interacts with the discrete particle includes:

[0055] Get the free path length l of the virtual photon free-path for:

[0056]

[0057] Where ΔV is the volume of the space unit before and after the virtual photon motion update; K ext is the extinction coefficient of the particle, d is the diameter of a single particle, ∑K ext πd 2 / 4 is the sum of the scattering cross sections of particles in a spatial unit;

[0058] According to the free path length, the extinction probability p of the virtual photon before and after movement is calculated. ext for:

[0059] p ext =exp(Δl / l free-path )

[0060] Among them, Δl is the distance before and after the virtual photon motion update;

[0061] Sampling virtual photons to generate random probability of extinction;

[0062] If the extinction random probability is less than the extinction probability, it is determined that the virtual photon does not interact with the scattering particle;

[0063] If the extinction random probability is not less than the extinction probability, it is determined that the virtual photon interacts with the scattering particle, and the absorption probability is calculated to be p a =K abs / K ext , the scattering probability is p s =K sca / K ext , and p a +p s =1;

[0064] If the extinction random probability is less than the absorption probability, the virtual photon is considered to be absorbed by the scattering particles and no subsequent calculation is performed on the virtual photon; otherwise, the virtual photon is considered to be scattered and the deflection angle and rotation angle of the virtual photon after scattering are determined.

[0065] Optionally, determining the deflection angle and rotation angle of the virtual photon after scattering includes:

[0066] The phase space probability p(α,β) of determining the scattering deflection direction of the virtual photon is:

[0067] p(α,β)=s 11(α)I+s 12 (α)[Qcos(2β)+Usin(2β)]

[0068]

[0069]

[0070] Among them, α is the deflection angle before and after the virtual photon is scattered, β is the rotation angle before and after the virtual photon is scattered; S1(α) is the polarization component of the scattered light intensity of the virtual photon along the horizontal direction, S2(α) is the polarization component of the scattered light intensity along the vertical direction, λ is the laser wavelength, K sca is the scattering coefficient of the virtual photon, a n and b n is the Michaelis coefficient, P n is the Legendre function, is the first-order Legendre function coupling function; I, Q, and U are the first, fourth, and second components of the Stokes vector S of the virtual photon, respectively;

[0071] The cosine random number of the deflection angle, the rotation angle random number and the phase space probability random number p are generated by sampling by the rejection method. rand If p rand >p(α,β), then continue sampling to generate cosine random numbers, rotation angle random numbers and phase space probability random numbers p rand If p rand ≤p(α,β), then stop sampling and determine that the deflection angle and rotation angle random numbers corresponding to the cosine random number are the deflection angle and rotation angle after the virtual photon is scattered.

[0072] Optionally, the calculating of state parameters after the virtual photons interact with the discrete particle group includes:

[0073] If the virtual photon is scattered after interacting with the discrete particles, the Stokes vector of the updated virtual photon after movement is:

[0074] S i,new =R(-γ)M(α)R(β)S i

[0075] Among them, α is the deflection angle of the virtual photon before and after scattering, and the value range of α is 0~π; β is the rotation angle of the virtual photon before and after scattering, and the value range of β is 0~2π; γ is the offset angle of the polarization direction before and after scattering; R is the polarization rotation matrix; M is the scattering matrix; S i is the Stokes vector before scattering;

[0076] The calculation formula for γ is:

[0077]

[0078] The calculation formula for R is:

[0079]

[0080] The calculation formula for M is:

[0081]

[0082] in,

[0083] δ=β / γ

[0084]

[0085] Among them, α is the deflection angle of the virtual photon before and after scattering, β is the rotation angle of the virtual photon before and after scattering, S1(α) is the polarization component of the scattered light intensity of the virtual photon along the horizontal direction, S2(α) is the polarization component of the scattered light intensity along the vertical direction, is the complex conjugate of S1(α), is the conjugate complex number of S2(α), λ is the laser wavelength, K sca is the scattering coefficient of the virtual photon, a n and b n is the Michaelis coefficient, P n is the Legendre function, is the first-order Legendre function coupling function.

[0086] Optionally, the calculating of state parameters after the virtual photons interact with the discrete particle group includes:

[0087] If the virtual photon is scattered after interacting with the discrete particles, the frequency of the updated virtual photon after movement is:

[0088]

[0089] Among them, ω i is the frequency of virtual photon i before scattering, ω i,new is the frequency of virtual photon i after scattering, v i,old is the velocity vector of the particle corresponding to the last scattering of virtual photon i, v i is the velocity vector of the particle corresponding to the current scattering of virtual photon i, u i is the cosine vector of virtual photon i before motion update, and c is the speed of light.

[0090] Optionally, the statistical frequency shift of virtual photons emitted from the discrete particle group to generate a spectrum I(Δω) comprises:

[0091]

[0092] Among them, ωi,f is the emission frequency of virtual photon i after movement, ω i,0 is the incident frequency of virtual photon i, x i,f 、y i,f 、z i,f are the position vector components of virtual photon i after movement, u x,i,f 、u y,i,f 、u z,i,f are the cosine vector components of the virtual photon i after movement, Ф is the diameter of the spot, θ c is the acceptance angle of the optical fiber at the laser output end.

[0093] The laser Doppler spectrum simulation method provided by the present invention has the following beneficial effects:

[0094] Virtual photons are propagated along their direction of motion in the space within the region where the particle group is located to simulate the transport process of the laser light field. During this process, the changes in the photon state parameters after the photons interact with the particles are calculated; the photons that leave the space within the region where the particle group is located and return to be received by the probe are statistically analyzed, and the distribution of power spectrum intensity with frequency shift is obtained, thereby achieving accurate simulation and simulation of the laser Doppler spectrum in the particle group. BRIEF DESCRIPTION OF THE DRAWINGS

[0095] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0096] Figure 1 A schematic diagram of a process flow in a method for simulating a laser Doppler spectrum provided in an embodiment of the present invention;

[0097] Figure 2 A schematic diagram of the relationship between the cosine vector u of a virtual photon and the virtual photon trajectory in the laser Doppler spectrum simulation method provided by an embodiment of the present invention;

[0098] Figure 3 A schematic diagram of the principle of laser Doppler velocimetry diagnosis of discrete particle groups in the laser Doppler spectrum simulation method provided by an embodiment of the present invention;

[0099] Figure 4 A schematic diagram of a flow chart for calculating state parameters after virtual photons interact with a discrete particle group in a laser Doppler spectrum simulation method provided by an embodiment of the present invention;

[0100] Figure 5A schematic diagram of a process for updating the cosine vector of the propagation direction of a virtual photon after movement in the laser Doppler spectrum simulation method provided by an embodiment of the present invention;

[0101] Figure 6 A schematic diagram of a spatial unit before and after a virtual photon motion update in the laser Doppler spectrum simulation method provided by an embodiment of the present invention;

[0102] Figure 7 A schematic diagram of a device for simulating laser Doppler spectrum provided in an embodiment of the present invention;

[0103] Figure 8 A schematic diagram of the working principle of the laser Doppler spectrum simulation device provided by an embodiment of the present invention.

[0104] Description of reference numerals:

[0105] 100-probe; 200-incident laser; 300-particle group; 400-reflected laser;

[0106] 500-incident laser information simulation unit;

[0107] 600-Particle Information Simulation Unit;

[0108] 700-Doppler generation unit. DETAILED DESCRIPTION

[0109] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0110] The present invention will be further described in detail below through specific implementation examples in conjunction with the accompanying drawings.

[0111] The embodiment of the present invention provides a method for simulating laser Doppler spectrum, which is used to simulate the Doppler spectrum of discrete particle groups. Figure 1 As shown, the simulation method includes the following steps:

[0112] S102, characterizing the incident laser light as a virtual photon group;

[0113] In this step, the incident laser is equivalent to a virtual photon group composed of multiple virtual photons. By analyzing the movement of each virtual photon in the discrete particle group, the propagation of the incident laser in the discrete particle group is further analyzed.

[0114] S104, obtaining the state parameters of the virtual photon at the initial moment; the initial state parameters include: at least one of: spatial position, propagation direction, polarization state and frequency. In the embodiment of the present invention, these four state parameters are taken as an example.

[0115] S106, calculate the state parameters after the virtual photon interacts with the discrete particle group; wherein, the state parameters in this step include: at least one of: spatial position, propagation direction, polarization state and frequency. In the embodiment of the present invention, these four state parameters are still taken as an example, and their state parameters correspond to the state parameters at the initial moment mentioned above, and the changes of the virtual photon i in the discrete particle group are calculated, as follows.

[0116] The spatial position is represented by a position vector H, which is: H = [x, y, z], where z is the height position value, x is the horizontal position value, and y is the vertical position value;

[0117] The propagation direction is represented by the cosine vector u of the propagation direction, which is:

[0118] u=[u x ,u y ,u z ]

[0119]

[0120] Among them, the relationship between the cosine vector u of the virtual photon propagation direction and the virtual photon trajectory is as follows: Figure 2 As shown, θ is the angle between the virtual photon trajectory and the z-axis, is the angle between the projection line of the virtual photon trajectory in the xy plane and the x-axis, and the angle between the projection line of the virtual photon trajectory in the xy plane and the x-axis is

[0121] The polarization state is represented by the Stokes vector S of the polarization state, which is: S = [I, U, V, Q];

[0122] For frequency ω: i,0 =2πc / λ; where c is the speed of light and λ is the wavelength of the incident laser.

[0123] S108, counting the frequency shifts of virtual photons emitted from the discrete particle group to generate a spectrum.

[0124] like Figure 3As shown, the principle of laser Doppler velocimetry diagnosis of particle groups is presented. Monochromatic laser light starts from the probe 100, forms the incident laser light 200, and is incident on the particle group 300. The laser light interacts with different particles in succession. After each interaction, the propagation direction of the laser light will change, that is, the scattering effect. At the same time, under the Doppler effect, the frequency of the laser light will also change. After multiple scattering and frequency shifts, the laser light leaves the area where the particle group is located and forms a reflected laser light 400. At least part of the reflected laser light 400 is received by the probe 200 to form a Doppler spectrum. For ease of understanding, the incident laser 200 is characterized as a photon group composed of multiple photons, each photon has its state parameters, including: spatial position, propagation direction, polarization state and frequency; the virtual photons are advanced along their motion direction in the space within the region where the particle group is located to simulate the transport process of the laser light field. In this process, the changes in the photon state parameters after the interaction between the photons and the particles are calculated; the photons that leave the space within the region where the particle group is located and return to be received by the probe are statistically analyzed, and then the distribution of the power spectrum intensity with frequency shift is obtained, thereby realizing accurate simulation and simulation of the laser Doppler spectrum in the particle group (taking a discrete particle group as an example).

[0125] The above steps S102, S104, S106, and S108 will be further described in detail below.

[0126] For step S102 above, a virtual simulation method for the state characteristics of the incident laser is provided. Specifically, the Monte Carlo method is used to describe the laser state characteristics. The particle nature of light is used to equate the incident laser to a large number of virtual photon groups. Each virtual photon represents a possible laser propagation. The virtual photon contains state information in four dimensions: spatial position, propagation direction, polarization state, and frequency. For example, the state parameters in steps S104 and S106 can achieve a numerical description of the incident laser under different initial light intensity distributions, collimation characteristics, polarization states, and wavelengths.

[0127] In the above step S104, the virtual photon i is taken as the research object, and its initial state parameters refer to the state parameters of the virtual photon at the initial moment, which can be determined as follows.

[0128] For the position vector H = [x, y, z] of the spatial position at the initial moment, including the lateral position value x, the longitudinal position value y, and the height position value z, the laser is emitted from the probe 100, and the height position at the initial moment is determined to be zero, that is, z = 0; random sampling is performed based on the light intensity distribution of the incident laser at the initial moment, and then the lateral position value x and the longitudinal position value y at the initial moment are determined as follows:

[0129] If the incident laser is a uniform beam and the light intensity distribution is such that the light intensity remains constant within the range of the light spot, then:

[0130] x i =r i cosε i ;y i =r i sinε i ;

[0131] If the incident laser is a Gaussian beam and the light intensity distribution is Gaussian from the center of the spot to the outside, then:

[0132] x i =r i cosε i ;y i =r i sinε i ;

[0133] Among them, Ф j is the spot diameter of the uniform beam; Ф g is the waist diameter of the Gaussian beam; RND is a random number generated by a computer random function, which is a statistical sample generated according to the probability density of the laser intensity distribution. The existing random number generation method can be used and will not be described here; r i represents the distance between the i-th virtual photon and the center of the light spot; ε i represents the position angle of the i-th virtual photon; x i is the lateral position value of the i-th virtual photon, y i is the longitudinal position value of the i-th virtual photon;

[0134] For the propagation direction at the initial moment, taking the incident laser as a collimated beam as an example, at this time, the cosine vector u of the virtual photon at the initial moment is [u x ,u y ,u z ] are as follows:

[0135]

[0136] For the initial polarization state, the Stokes vector is determined according to the polarization state characteristics of the incident laser, as follows:

[0137] If the incident laser is unpolarized light, the Stokes vector of the virtual photon at the initial moment is:

[0138] S=[1,0,0,0]

[0139] If the incident laser is linearly polarized light, the Stokes vector of the virtual photon at the initial moment is:

[0140] S=[1,1,0,0], or S=[1,-1,0,0], or S=[1,0,1,0], or S=[1,0,-1,0];

[0141] If the incident laser is right-handed circularly polarized light, the Stokes vector of the virtual photon at the initial moment is:

[0142] S=[1,0,0,1]

[0143] If the incident laser is left-handed circularly polarized light, the Stokes vector of the virtual photon at the initial moment is:

[0144] S=[1,0,0,-1]

[0145] For the frequency state parameters of the virtual photons at the initial moment, taking the incident laser as a monochromatic laser as an example, the frequencies of all virtual photons at the initial moment are the same, and the relationship between the virtual photon frequency and wavelength is:

[0146] ω i,0 =2πc / λ

[0147] Where c is the speed of light and λ is the wavelength of the incident laser.

[0148] In the above step S106, the virtual photon i is still taken as the research object. It is located in the area where the discrete particle group is located. The state parameters after the interaction with the discrete particles correspond to the state parameters at the initial moment. The state parameters after the interaction between the virtual photon i and the discrete particles will change. Specifically, the changes in the discrete particle group are as follows: Figure 4 As shown, the following steps are included:

[0149] S1062, updating the position vector of the virtual photon after movement;

[0150] S1064, updating the cosine vector of the propagation direction of the virtual photon after movement;

[0151] S1066, updating the polarization state of the virtual photon after movement;

[0152] S1068, updating the frequency of the virtual photon after movement.

[0153] In step S1062, for ease of understanding, after the virtual photon starts from the probe 100 and enters the discrete particle, the distance the virtual photon moves each time is set to Δl, and the position vector H after the virtual photon moves is updated in combination with the cosine vector of the virtual photon. i,new for:

[0154]

[0155] Among them, H i,new =[x i,new ,y i,new ,z i,new ] is the updated space vector of virtual photon i, H i=[x i ,y i ,z i ] is the space vector of virtual photon i before the movement is updated, Δl is the distance of each movement of virtual photon, u i =[u x,i ,u y,i ,u z,i ] is the cosine vector of virtual photon i before motion update.

[0156] In step S1064, the cosine vector of the propagation direction of the virtual photon after movement is updated, such as Figure 5 As shown, it specifically includes the following sub-steps: S10642, S10644, S10646, S10648, specifically:

[0157] Step S10642: determining whether the virtual photon interacts with the discrete particle; this step specifically includes:

[0158] (1) Collect statistics on the particle information of each virtual photon along its propagation path and calculate the free path length l of the virtual photon free-path for:

[0159]

[0160] Where ΔV is the volume of the space unit before and after the virtual photon motion update; K ext is the extinction coefficient of the particle, d is the diameter of a single particle, ∑K ext πd 2 / 4 is the sum of the particle scattering cross sections within the spatial unit; as shown in the figure, specifically, Figure 6 shown.

[0161] (2) Based on the above free path length and the Lambert-Beer law, the extinction probability p of the virtual photon before and after movement is calculated. ext for:

[0162] p ext =exp(Δl / l free-path )

[0163] Among them, Δl is the distance before and after the virtual photon movement update, such as Figure 6 As shown, the calculation formula can be: Δl=|H i,new -H i |;

[0164] (3) Determine whether the virtual photon interacts with the discrete particle based on random sampling of the extinction probability. Specifically, a random number can be generated for each virtual photon, that is, sampling the virtual photons to generate the random probability of extinction;

[0165] (4) If the extinction random probability is less than the extinction probability, it is determined that the virtual photon has not interacted with the scattering particles, that is, the virtual photon has not encountered the discrete particles, but has directly penetrated. At this time, the virtual photon only changes its position before and after movement, and its propagation direction, polarization state, and frequency remain unchanged;

[0166] (5) If the extinction random probability is not less than the extinction probability, it is determined that the virtual photon interacts with the scattering particle. At this time, the extinction calculation process will be further performed. The extinction process of the virtual photon and the discrete particle can be subdivided into two types of effects, namely, the absorption effect and the scattering effect. The further calculation results show that the occurrence probabilities of these two types of effects are: the absorption probability is p a =K abs / K ext , the scattering probability is p s =K sca / K ext , and p a +p s =1;K sca , K ext , respectively the scattering coefficient and the absorption coefficient. Both coefficients are related to the particle size, material and wavelength of discrete particles. They are obtained through the existing classical scattering theory and will not be elaborated here.

[0167] (6) Based on the above step (5), random sampling can be further used to determine whether the photon absorbs or scatters. Specifically, a random probability of extinction (random number) is generated for each virtual photon. If the random probability of extinction is less than the probability of absorption, it is considered that the virtual photon is absorbed by the scattering particles, and the light energy of the virtual photon is converted into the thermal energy of the discrete particles, completely disappearing in the light field transport system, and no subsequent calculation is performed on the virtual photon; if the random probability of extinction is not less than the probability of absorption, it is considered that the virtual photon is scattered, and the propagation direction, polarization state, and frequency of the virtual photon will change accordingly. It is necessary to further determine the deflection angle and rotation angle of the virtual photon after scattering (for details, see the following step S10644).

[0168] Step S10644: If the virtual photon is scattered after interacting with the discrete particle, its propagation direction will change, and the deflection angle and rotation angle of the virtual photon after scattering are determined. Specifically, this step includes:

[0169] (a) The phase space probability p(α, β) of the direction of scattering and deflection of a virtual photon is determined as:

[0170] p(α,β)=s 11 (α)I+s 12 (α)[Qcos(2β)+U sin(2β)]

[0171]

[0172]

[0173] Among them, α is the deflection angle of the virtual photon before and after scattering, and its variation range is 0~π; β is the rotation angle of the virtual photon before and after scattering, and its variation range is 0~2π; S1(α) is the polarization component of the scattered light intensity of the virtual photon along the horizontal direction, which is a complex number; S2(α) is the polarization component of the scattered light intensity along the vertical direction, which is a complex number; λ is the laser wavelength, K sca is the scattering coefficient of the virtual photon, a n and b n is the Michaelis coefficient, P n is the Legendre function, is the first-order Legendre function coupling function; I, Q, and U are the first, fourth, and second components of the Stokes vector S of the virtual photon, respectively; It is an infinite series, which will converge as n gradually increases. For the convenience of calculation, n can be taken as a specific value, for example, n=15. Of course, other values ​​can also be selected, which is not limited here.

[0174] (b) After the phase space probability function of the virtual photon scattering deflection direction is determined, three random numbers are generated by sampling through the rejection method: the cosine random number of the deflection angle, the rotation angle random number, and the phase space probability random number p rand (represents the randomness of the scattering deflection direction p rand ), where the cosine random number cos(α) is uniformly sampled from 0 to 1, the rotation angle random number β is uniformly sampled from 0 to 2π, and the phase space probability random number p is uniformly sampled from 0 to 2π. rand In uniform sampling; if p rand >p(α,β), then repeat the generation of the above three random numbers, that is, continue to sample and generate cosine random numbers, rotation angle random numbers and phase space probability random numbers p rand If p rand ≤p(α,β), then stop sampling, and determine that the deflection angle and rotation angle random numbers corresponding to the cosine random number are the deflection angle and rotation angle after the virtual photon is scattered.

[0175] Step S10646: After obtaining the scattering deflection direction of the virtual photon, the direction cosine vector of the virtual photon is updated. Specifically, if the third component u of the cosine vector of the virtual photon before scattering is z Satisfaction|u z |≈1, for example, take |u z When |≥0.9999, after scattering, the cosine vector of the updated virtual photon movement is:

[0176]

[0177] Step S10648: If the third component u of the cosine vector of the virtual photon before scattering z Not satisfied |u z |≈1, for example, take |u z |<0.9999, then after scattering, the updated cosine vector of the virtual photon movement is:

[0178]

[0179] Among them, α is the deflection angle before and after the virtual photon scattering, and the value range of α is 0~π; β is the rotation angle before and after the virtual photon scattering, and the value range of β is 0~2π; u i =[u x,i ,u y,i ,u z,i ] is the cosine vector of virtual photon i before motion update, u i,new =[u x,i,new ,u y,i,new ,u z,i,new ] is the updated cosine vector of the virtual photon i’s motion.

[0180] In step S1066, after the virtual photon is scattered, its polarization state will also change. Specifically, updating the polarization state of the virtual photon after movement includes the following sub-steps:

[0181] If a virtual photon is scattered after interacting with a discrete particle, the Stokes vector of the updated virtual photon is:

[0182] S i,new =R(-γ)M(α)R(β)S i

[0183] Among them, α is the deflection angle of the virtual photon before and after scattering, and the value range of α is 0~π; β is the rotation angle of the virtual photon before and after scattering, and the value range of β is 0~2π; γ is the offset angle of the polarization direction before and after scattering; R is the polarization rotation matrix; M is the scattering matrix; S i is the Stokes vector before scattering;

[0184] The calculation formula for γ is:

[0185]

[0186] R is a 4×4 deflection rotation matrix, and its calculation formula is:

[0187]

[0188] M is a 4×4 scattering matrix, and the calculation formula is:

[0189]

[0190] in,

[0191] δ=β / γ

[0192]

[0193] Among them, α is the deflection angle of the virtual photon before and after scattering, β is the rotation angle of the virtual photon before and after scattering, S1(α) is the polarization component of the scattered light intensity of the virtual photon along the horizontal direction, S2(α) is the polarization component of the scattered light intensity along the vertical direction, is the complex conjugate of S1(α), is the conjugate complex number of S2(α), λ is the laser wavelength, K sca is the scattering coefficient of the virtual photon, a n and b n is the Michaelis coefficient, P n is the Legendre function, is the first-order Legendre function coupling function.

[0194] In step S1068, under the Doppler effect, the frequency of the virtual photons will change after they are scattered by the scattering particles. The frequency of the virtual photons after movement is updated, which specifically includes the following sub-steps:

[0195] If the virtual photon is scattered after interacting with the discrete particles, the frequency of the updated virtual photon after movement is:

[0196]

[0197] Among them, ω i is the frequency of virtual photon i before scattering, ω i,new is the frequency of virtual photon i after scattering, v i,old is the velocity vector of the particle corresponding to the last scattering of virtual photon i, v i is the velocity vector of the particle corresponding to the current scattering of virtual photon i, u i is the cosine vector of virtual photon i before motion update, and c is the speed of light.

[0198] It should be noted that the frequency shift process of virtual photons after interacting with discrete particles is similar to a Markov chain. After being scattered from a particle, it continues to be transported in a new direction until it interacts with the next particle and scatters, and then continues to be transported after updating the direction. This transport process will continue until the virtual photons leave the particle field, such as Figure 1 As shown, the virtual photon is emitted from the particle field in the form of reflected laser. Assuming that the velocity of the particle when the virtual photon is scattered for the first time is v1 and the velocity of the particle when it is scattered for the second time is v2, in the process of transport of the virtual photon in the particle field, when the virtual photon is scattered for the first time, the frequency calculation is v i,oldEqual to the velocity of the probe, that is, v i,old =0,v i is equal to the velocity of the particle at the time of first scattering, that is, v1; when the photon is scattered for the second time, v i,old Equal to the velocity of the particle at the time of first scattering, that is, v1, v i =v2 is equal to the particle's velocity at the second scattering. Furthermore, the particle's velocity vector is input information for the calculation and is associated with the particle's position. In transport calculations, when a virtual photon propagates to a certain spatial location in the particle field, the particles within that spatial location have a certain average velocity, which is considered the particle's velocity at the time of scattering. The particle's velocity vector does not change with the photon transport process.

[0199] As can be seen from the sub-steps of step S106 above, this step provides a simulation and calculation method for the optical field transport process in a high-speed particle swarm. Specifically, during the virtual photon propulsion process, random sampling is used to determine whether the virtual photons interact with the particles, and the various state parameters of the virtual photons in the discrete particle swarm can be obtained. The absorption, scattering, and frequency shift processes under the interaction between photons and particles are simulated. During this propulsion process, the virtual photons in the particle field, after completing transmission or scattering, will continue to propagate in space with the updated motion direction, polarization state, and frequency. When all virtual photons leave the particle field or are absorbed by the particles, the simulation calculation of the laser transport process ends. The spectrum of the virtual photons after being emitted from the discrete particle swarm will be further explained in step S108 below.

[0200] In the above step S108, the frequency shift of virtual photons emitted from the discrete particle group is counted to generate a spectrum i(Δω), which specifically includes:

[0201]

[0202] Among them, ω i,f is the emission frequency of virtual photon i after movement, ω i,0 is the incident frequency of virtual photon i, x i,f 、y i,f 、z i,f are the position vector components of virtual photon i after movement, u x,i,f 、u y,i,f 、u z,i,f are the cosine vector components of the virtual photon i after its movement, Ф is the diameter of the light spot (the diameter of the light spot in the case of a uniform beam or the waist diameter of a Gaussian beam), θ c is the acceptance angle of the optical fiber at the laser output end.

[0203] In step S108, a theoretical method for generating a laser Doppler spectrum based on the transport simulation results of the above-mentioned light field is provided. Specifically, virtual photons are screened in combination with information such as the physical size and light receiving angle of the speed measuring probe, and statistical analysis is performed on the virtual photons that meet the conditions in the frequency domain. Virtual photons within the probe diameter range and with a direction angle smaller than the optical fiber receiving angle are selected, and the frequency shift information of the relevant virtual photons is statistically analyzed to generate an instantaneous spectrum. A distribution curve of light intensity versus frequency shift is obtained, and a laser Doppler spectrum image is generated based on the time-series simulation and statistical results.

[0204] The embodiment of the present invention also provides a device for simulating laser Doppler spectrum, which uses the above method to simulate the laser transport process in a discrete particle group, such as Figure 7 As shown, the device includes an incident laser information simulation unit 500, a particle information simulation unit 600 and a Doppler spectrum generation unit 700, wherein the incident laser information simulation unit 500 is used to simulate the incident laser state information, the particle information simulation unit 600 is used to simulate and calculate the state information during the interaction between virtual photons and particles, and the Doppler spectrum generation unit 700 generates a Doppler spectrum based on the outgoing laser state information.

[0205] Specifically, such as Figure 8 As shown, first, in the incident laser information simulation unit, a large number of virtual photons that meet its characteristics are generated according to the incident laser information, and the virtual photons are initialized and simulated, that is, the initial position, direction, polarization vector and frequency of the photons are determined according to the laser intensity distribution, collimation, polarization characteristics and wavelength; then, in the particle information simulation unit, the propagation and transport process of the virtual photons is simulated in combination with the particle information, and the position vector information of the virtual photons is updated during the propagation and transport process in the space where the particle group is located. The extinction probability is obtained according to the laser free path length, and the scattering probability is obtained according to the particle size. By sampling the virtual photons, it is judged whether the photons are directly penetrated, absorbed or scattered. When a photon passes through directly, its movement direction, polarization state and frequency remain unchanged, otherwise extinction processing is performed, that is, when a virtual photon is absorbed by a particle, the photon transport ends and is removed in the simulation. When a virtual photon is scattered, the propagation / movement direction and polarization state of the virtual photon are updated according to the scattering theory, and the frequency of the virtual photon is updated according to the Doppler effect. When all photons are absorbed or leave the scattering field, the simulation of the light field transport process ends; finally, in the Doppler spectrum generation module, the frequency shift of the virtual photons that return to the probe and whose reflection angle is within the collection angle is statistically analyzed to obtain the Doppler power spectrum distribution, thereby realizing the output of the Doppler simulation spectrum under discrete particle groups.

[0206] In summary, the laser Doppler spectrum simulation method and simulation device provided by the embodiments of the present invention, based on optical transport theory and combined with the Doppler effect, theoretically simulate the laser's direct penetration, scattering, and absorption processes in discrete media. This meticulously characterizes the changes in laser motion direction, polarization state, and frequency caused by particle optical scattering, and is capable of performing sequential optical field transport simulations of particle fields at different moments, thereby achieving accurate and continuous simulation and simulation of laser Doppler spectra for discrete particle groups. This simulation device and simulation method can provide simulation and simulation of laser Doppler spectra for powders and micro-nanoparticles over a wide speed range and particle size range. It can be applied to the analysis and simulation of material interface destruction under strong impact, aerospace engine spray combustion, blood cell flow, and particle Doppler spectra in hot and cold spraying. It has important implications for scientific and engineering fields such as impact damage, aerospace, biological detection, atmospheric environmental monitoring, and chemical process improvement.

[0207] In the description of the present invention, it should be noted that the terms "upper", "lower", "front", "horizontal", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention 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. Therefore, they cannot be understood as limitations on the present invention.

[0208] In the description of the present invention, it should be noted that, unless otherwise specified or limited, the term "mounted" should be understood in a broad sense. For example, it can mean a fixed connection, a detachable connection, or an integral connection; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0209] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for simulating a laser Doppler spectrum, characterized in that: Used for performing Doppler spectrum simulation on discrete particle groups, the simulation method includes: Characterize the incident laser light as a group of virtual photons; Get the state parameters of the virtual photon at the initial moment; Calculate the state parameters after the virtual photons interact with the discrete particle group; Count the frequency shifts of virtual photons emitted from a discrete particle group to generate a spectrum; The state parameters include at least one of spatial position, propagation direction, polarization state and frequency.

2. The simulation method according to claim 1, characterized in that The position vector H of the spatial position is: H = [x, y, z], where z is the height position value, x is the horizontal position value, and y is the vertical position value; The cosine vector u of the propagation direction is: in=[in x ,in y ,in z ] Among them, θ is the angle between the virtual photon trajectory and the z-axis, is the angle between the virtual photon trajectory and the x-axis; The Stokes vector S of the polarization state is: S=[I,U,V,Q] The frequency ω is: oh i,0 =2πc / λ Wherein, c is the speed of light, and λ is the wavelength of the incident laser.

3. The simulation method according to claim 2, characterized in that The obtaining of the initial state parameters of the virtual photon includes: Determine the height position value at the initial moment: z = 0; Performing random sampling based on the light intensity distribution of the incident laser at the initial moment to determine the lateral position value x and the longitudinal position value y at the initial moment; If the incident laser is a uniform beam and the light intensity distribution is such that the light intensity remains constant within the range of the light spot, then: x i =r i cosε i ;y i =r i sinε i ; If the incident laser is a Gaussian beam and the light intensity distribution is Gaussian from the center of the spot outward, then: x i =r i cosε i ;y i =r i sinε i ; Among them, Ф j is the spot diameter of the uniform light beam; Ф g is the waist diameter of the Gaussian beam; RND is a random number generated by a computer random function; r i represents the distance between the i-th virtual photon and the center of the light spot; ε i represents the position angle of the i-th virtual photon; x i is the lateral position value of the i-th virtual photon, y i is the longitudinal position value of the i-th virtual photon; If the incident laser is a collimated beam, the cosine vector of the virtual photon at the initial moment is: If the incident laser is unpolarized light, the Stokes vector of the virtual photon at the initial moment is: S＝[1,0,0,0] If the incident laser is linearly polarized light, the Stokes vector of the virtual photon at the initial moment is: S=[1,1,0,0], or S=[1,-1,0,0], or S=[1,0,1,0], or S=[1,0,-1,0]; If the incident laser is right-handed circularly polarized light, the Stokes vector of the virtual photon at the initial moment is: S＝[1,0,0,1] If the incident laser is left-handed circularly polarized light, the Stokes vector of the virtual photon at the initial moment is: S＝[1,0,0,-1] The frequency of the virtual photon at the initial moment is: oh i,0 =2πc / λ Where c is the speed of light and λ is the wavelength of the incident laser.

4. The simulation method according to claim 2, characterized in that The calculation of the state parameters after the virtual photons interact with the discrete particle group includes: The position vector of the updated virtual photon after movement is: Among them, H i,new =[x i,new ,y i,new ,z i,new ] is the updated space vector of virtual photon i, H i =[x i ,y i ,z i ] is the space vector of virtual photon i before the movement is updated, Δl is the movement distance of the virtual photon each time, u i =[u x,i ,u y,i ,u z,i ] is the cosine vector of virtual photon i before motion update.

5. The simulation method according to claim 2, wherein: The calculation of the state parameters after the virtual photons interact with the discrete particle group includes: determining whether the virtual photon interacts with the discrete particle; If the virtual photon is scattered after interacting with the discrete particle, determining the deflection angle and rotation angle of the virtual photon after scattering; If the third component u of the cosine vector of the virtual photon before scattering z Satisfy: |u z |≥0.9999, then the updated cosine vector of the virtual photon after movement is: If the third component u of the cosine vector of the virtual photon before scattering z Satisfy: |u z |<0.9999, then the updated cosine vector of the virtual photon after movement is: Among them, α is the deflection angle before and after the virtual photon scattering, and the value range of α is 0~π; β is the rotation angle before and after the virtual photon scattering, and the value range of β is 0~2π; u i =[u x,i ,u y,i ,u z,i ] is the cosine vector of virtual photon i before motion update, u i,new =[u x,i,new ,u y,i,new ,u z,i,new ] is the updated cosine vector of the virtual photon i’s motion.

6. The simulation method according to claim 5, characterized in that The determining that the virtual photons interact with the discrete particles includes: Get the free path length l of the virtual photon free-path for: Where ΔV is the volume of the space unit before and after the virtual photon motion update; K ext is the extinction coefficient of the scattering particles, d is the diameter of a single scattering particle, ∑K ext πd 2 / 4 is the sum of the scattering cross sections of particles in a spatial unit; According to the free path length, the extinction probability p of the virtual photon before and after movement is calculated. ext for: p ext =exp(Δl / l free-path ) Among them, Δl is the distance before and after the virtual photon motion update; Sampling virtual photons to generate random probability of extinction; If the extinction random probability is less than the extinction probability, it is determined that the virtual photon does not interact with the scattering particle; If the extinction random probability is not less than the extinction probability, it is determined that the virtual photon interacts with the scattering particle, and the absorption probability is calculated to be p a =K abs / K ext , the scattering probability is p s =K sca / K ext , and p a +p s =1; If the extinction random probability is less than the absorption probability, the virtual photon is considered to be absorbed by the scattering particles and no subsequent calculation is performed on the virtual photon; otherwise, the virtual photon is considered to be scattered and the deflection angle and rotation angle of the virtual photon after scattering are determined.

7. The simulation method according to claim 5 or 6, characterized in that: Determining the deflection angle and rotation angle of the virtual photon after scattering includes: The phase space probability p(α,β) of determining the scattering deflection direction of the virtual photon is: p(a,b)=s 11 (a)I+s 12 (a)[Qcos(2β)+U sin(2β)] Among them, α is the deflection angle before and after the virtual photon is scattered, β is the rotation angle before and after the virtual photon is scattered; S1(α) is the polarization component of the scattered light intensity of the virtual photon along the horizontal direction, S2(α) is the polarization component of the scattered light intensity along the vertical direction, λ is the laser wavelength, K sca is the scattering coefficient of the virtual photon, a n and b n is the Michaelis coefficient, P n is the Legendre function, is the first-order Legendre function coupling function; I, Q, and U are the first, fourth, and second components of the Stokes vector S of the virtual photon, respectively; The cosine random number of the deflection angle, the rotation angle random number and the phase space probability random number p are generated by sampling by the rejection method. rand If p rand >p(α,β), then continue sampling to generate cosine random numbers, rotation angle random numbers and phase space probability random numbers p rand If p rand ≤p(α,β), then stop sampling and determine that the deflection angle and rotation angle random numbers corresponding to the cosine random number are the deflection angle and rotation angle after the virtual photon is scattered.

8. The simulation method according to claim 2, characterized in that The calculation of the state parameters after the virtual photons interact with the discrete particle group includes: If the virtual photon is scattered after interacting with the discrete particles, the Stokes vector of the updated virtual photon after movement is: S i,new =R(-γ)M(α)R(β)S i Among them, α is the deflection angle of the virtual photon before and after scattering, and the value range of α is 0~π; β is the rotation angle of the virtual photon before and after scattering, and the value range of β is 0~2π; γ is the offset angle of the polarization direction before and after scattering; R is the polarization rotation matrix; M is the scattering matrix; S i is the Stokes vector before scattering; The calculation formula for γ is: The calculation formula for R is: The calculation formula for M is: in, δ=β / γ Among them, α is the deflection angle of the virtual photon before and after scattering, β is the rotation angle of the virtual photon before and after scattering, S1(α) is the polarization component of the scattered light intensity of the virtual photon along the horizontal direction, S2(α) is the polarization component of the scattered light intensity along the vertical direction, is the complex conjugate of S1(α), is the conjugate complex number of S2(α), λ is the laser wavelength, K sca is the scattering coefficient of the virtual photon, a n and b n is the Michaelis coefficient, P n is the Legendre function, is the first-order Legendre function coupling function.

9. The simulation method according to claim 2, characterized in that: The calculation of the state parameters after the virtual photons interact with the discrete particle group includes: If the virtual photon is scattered after interacting with the discrete particles, the frequency of the updated virtual photon after movement is: Among them, ω i is the frequency of virtual photon i before scattering, ω i,new is the frequency of virtual photon i after scattering, v i,old is the velocity vector of the particle corresponding to the last scattering of virtual photon i, v i is the velocity vector of the particle corresponding to the current scattering of virtual photon i, u i is the cosine vector of virtual photon i before motion update, and c is the speed of light.

10. The simulation method according to claim 2, characterized in that: The frequency shift of virtual photons emitted from the discrete particle group is statistically generated to generate a spectrum I(Δω), including: Among them, ω i,f is the emission frequency of virtual photon i after movement, ω i,0 is the incident frequency of virtual photon i, x i,f 、y i,f 、z i,f are the position vector components of virtual photon i after movement, u x,i,f 、u y,i,f 、u z,i,f are the cosine vector components of the virtual photon i after movement, Ф is the diameter of the spot, θ c is the acceptance angle of the optical fiber at the laser output end.

Images