CN115267818A - Mie scattering Doppler lidar system based on dual F-P interferometer and multi-longitudinal mode laser - Google Patents

Abstract

The invention discloses a direct detection Mie scattering Doppler laser radar system based on a double F-P interferometer and multi-longitudinal mode laser. A1064 nm solid multi-longitudinal-mode pulse laser is adopted, the longitudinal mode interval is 2GHz, and the longitudinal mode interval is integral multiple of the free spectrum interval of an F-P interferometer. The double-F-P interferometer is designed into a whole, the free spectrum spacing is 2GHz, the spectrum width is 180MHz, and the interval of the peak and the peak of the frequency spectrum is 200MHz. The center frequency of each longitudinal mode of the emitted laser is locked at the position of the cross point of the frequency spectrums of the two F-P interferometers. The receiving light path consists of a double F-P interferometer, a beam splitter and a reflector. The invention adopts the multi-longitudinal-mode laser, so that the transmitting system is low in cost and miniaturized, the laser energy utilization rate, the stability and the environmental adaptability of the Doppler laser radar system are obviously improved, the multi-longitudinal-mode Doppler laser radar can detect the atmospheric wind field of the troposphere at high precision, and the optical characteristic of aerosol can be detected at higher precision.

Description

Mi-scattering Doppler lidar based on dual F-P interferometers and multi-longitudinal mode lasers system

technical field

The invention relates to a laser radar system capable of detecting the tropospheric atmospheric wind field with high precision and the optical characteristics of aerosols with high precision, in particular to a direct detection meter scattering Doppler laser based on a double F-P interferometer and a multi-longitudinal mode laser radar system.

Background technique

Wind is the main driving force of water vapor, aerosol, carbon cycle and sea-air exchange, and is an important factor affecting human production and life. Real-time high-precision and high-spatial-resolution wind field data are used to improve climate models, study global climate change, promote atmospheric thermodynamics and dynamics research, improve the accuracy of weather forecasts, ensure the safety of take-off and landing of aerospace vehicles, and improve the utilization of wind energy. There are important applications in terms of rate and so on. Doppler lidar is a new type of atmospheric wind field remote sensing detection equipment developed in the past 30 years. Compared with traditional sodar and microwave radar, it has greatly improved in terms of temporal and spatial resolution, angular orientation and maneuverability. Moreover, it can also detect the three-dimensional wind field under sunny conditions, and is currently one of the most effective tools for high-precision, high-temporal-resolution remote sensing detection of the three-dimensional wind field. Therefore, the research on Doppler lidar technology is of great significance. Due to the importance of wind field measurement, many universities and research institutions at home and abroad have carried out research on Doppler lidar technology, which can be divided into two categories according to different detection systems: coherent detection and direct detection. However, the current Doppler lidar, whether it adopts a coherent detection system or a direct detection system, uses a narrow-linewidth, frequency-stabilized single longitudinal mode laser as its emission source. The limitation of only using a single longitudinal mode laser has caused the existing Doppler lidar system to have relatively strict requirements on the working environment. Once the environmental conditions are not met, the detection performance of the system may be affected, and it may even fail to work normally. This is a serious problem. This restricts the industrial application and airborne and spaceborne applications of Doppler lidar.

Attempts to use multi-longitudinal mode lasers as emission sources for high spectral resolution aerosol lidar, temperature measurement lidar, and Doppler lidar are one of the frontier hotspots of current research. This is because if the multi-longitudinal mode laser can be used as the emission light source of these lidar systems, it can not only reduce the system cost, reduce the system volume, improve the stability and environmental adaptability of the system, but also improve the measurement accuracy of the parameters to be measured in the system . In 2008, Gong Mali and others did a preliminary analysis and research on the feasibility of using multi-longitudinal-mode lasers as the emission source of F-P interferometer double-edge Doppler lidar, which did not involve frequency matching errors, actual system design and performance analysis, etc. question. In 2013, Bruneau et al. built a multi-longitudinal-mode wind lidar system based on M-Z interferometer, and realized the detection of boundary layer wind field. In 2015, Jin et al. and Ristori et al. proposed the concept of multi-longitudinal-mode high-spectral resolution lidar technology, and further conducted in-depth research on tunable M-Z interferometer multi-longitudinal-mode high-spectral resolution lidar technology. In 2018, the Huadengxin research group conducted further research, and the designed ultraviolet domain multi-longitudinal mode high-spectral resolution lidar can realize fine detection of aerosol optical parameters within a height of 10km. In 2017, Liu Dong's research group at Zhejiang University used the designed wide-field Michelson interferometer to carry out multi-longitudinal-mode high-spectral resolution lidar aerosol detection technology and theoretical research. It can be seen that the current research on multi-longitudinal-mode lidar at home and abroad is mainly focused on high-spectral resolution aerosol lidar, and the design and research of multi-longitudinal-mode Doppler lidar system based on dual F-P interferometers has not been reported yet.

Contents of the invention

The technical problem to be solved by the present invention is to provide a direct detection meter scattering Doppler lidar system based on double F-P interferometer and multi-longitudinal mode laser, which can use multi-longitudinal mode meter scattering Doppler laser radar system based on double F-P interferometer Lidar detects the tropospheric atmospheric wind field with high precision and detects the optical characteristics of aerosols with high precision.

The technical solution adopted by the present invention to solve the technical problem is: the wind field measurement principle of the present invention is shown in Fig. 1, Fig. 2 and Fig. 3, and Fig. 2 is a partially enlarged view of Fig. 1 . Adopt integrated double FP interferometer, the free spectral spacing (FSR) of FP interferometer 1 and FP interferometer 2 is the same, is 2GHz, and the peak-to-peak interval of the spectrum of both is 200MHz; Multi-longitudinal mode laser emission wavelength is λ= 1064nm, the longitudinal mode spacing FP matches the FSR of the interferometer, and the center frequency of each longitudinal mode is locked at the intersection of the spectrum of FP interferometer 1 and FP interferometer 2. Multi-longitudinal mode pulsed laser light is emitted into the atmosphere, and when it encounters moving aerosols and molecules in the atmosphere, the total backscattering spectrum is the superposition of all single longitudinal mode Mie and Rayleigh scattering spectra, while the scattering spectrum will be broadened and multiple The Puler frequency shift, as shown in Figure 1 and Figure 2. Due to the large mass of aerosol particles, the broadening of the Rayleigh scattering spectrum caused by Brownian motion can be ignored, and the spectral width of the aerosol meter scattering is approximately the spectral width of the emitted laser; while the mass of atmospheric molecules is small, the Rayleigh scattering spectrum caused by their thermal motion is significantly broadened, In the process of wind field measurement using meter scattering signal, Rayleigh scattering signal can be regarded as white noise. The Doppler frequency shift v _d is related to the macroscopic motion velocity (vector wind speed) V of the aerosol and molecules, that is, v _d = 2V _r /λ, V _r = V cos φ is the radial wind speed, φ is the direction of the vector wind speed and the light beam The included angle of the emission direction. In order to measure the Doppler frequency shift (radial wind speed), a small part of the atmospheric backscattered light is used for energy monitoring, and most of it is divided into two beams to enter the FP interferometer 1 and FP interferometer 2 respectively. . In the case of different radial wind speeds, the ratio of the transmitted signal of the equally divided meter scattered light after passing through FP interferometer 1 and FP interferometer 2 will be obviously different. The functional relationship of the frequency shift can be inverted to obtain the radial wind speed, as shown in Figure 3. The signal of the energy monitoring channel can be retrieved to obtain the backscatter ratio, and further used to correct the wind speed retrieval results.

The transmittance function of the parallel light of monochromatic light with frequency v incident on the i-th F-P interferometer is

Where: i=1,2; η _i =[1-A/(1-R _i )] ² (1-R _i )/(1+R _i ) is the average transmittance of the i-th FP interferometer, R _{e, i} , R _i and A are the effective reflectance, actual reflectance and plate absorption loss coefficient of the i-th FP interferometer, respectively; v _i and v _FSR are the center frequency and free spectral spacing.

After the multi-longitudinal mode laser is incident into the atmosphere, the echo function of each single longitudinal mode spectral line in the multi-longitudinal mode can still be approximated by a Gaussian line shape, but the intensity of each longitudinal mode is modulated by the laser medium gain curve. Therefore, the total normalized echo spectrum function of the aerosol-meter scattering and molecular Rayleigh scattering of the multi-longitudinal-mode laser is:

Among them: Δv _a = δv/(4ln2) ^1/2 is the spectral width of a single longitudinal mode meter scattering spectrum 1/e height, δv is the half-maximum spectral width of a single longitudinal mode of the emitted laser; Δv _m = (Δv _a ² +Δv _r ² ) ^1/2 is the spectral width at 1/e height of the Rayleigh scattering spectrum of a single longitudinal mode, Δv _r =(8kT/Mλ ² ) ^1/2 is the Rayleigh scattering spectral width increment, k is the Boltzmann constant , T is the atmospheric temperature, M is the average mass of atmospheric molecules, λ is the wavelength of the emitted laser light; v ₀ is the center frequency of the emitted laser light; q is the longitudinal mode number referenced to the selected center frequency v ₀ (the q of the center frequency is 0) ; v _d is the Doppler frequency shift; Λ is the longitudinal mode interval; C _q is the relative intensity of each spectral line (it is stipulated that the relative intensity at v ₀ is 1).

After being collimated by the collimating mirror, the transmittances of the meter and Rayleigh scattered light with a full divergence angle of 2θ ₀ incident on the double FP interferometer are respectively

Bring (1)～(3) into (4)～(5) and integrate:

T _ia (v ₀ +v _d )=η _i (1+2σ _ia ) (6)

T _im (v ₀ +v _d )=η _i (1+2σ _im ) (7)

In the formula

where v' _FSR = 2v _FSR /(1+cosθ ₀ ). When the condition Λ=pv' _FSR is satisfied, p=1, 2, ..., the above formula can be simplified as

This formula is completely consistent with the results obtained by using a single longitudinal mode light source.

Therefore, the number of atmospheric backscattered photoelectrons at height _z received by two edge channels and one energy monitoring channel detector is

N ₁ (z, v _d , T)=a ₁ [N _a (z)T _1a (V ₀ +v _d -v ₁ )+N _m (z)T _1m (v ₀ +v _d -v ₁ ,T )] (9)

N ₂ (z, v _d , T)=a ₂ [N _a (z)T _2a (v ₀ +v _d -v ₂ )+N _m (z)T _2m (v ₀ +v _d -v ₂ ,T )] (10)

N _e (z) = a ₃ [N _a (z) + N _m (z)] (11)

In the formula: a ₁ , a ₂ , a ₃ are calibration constants; T is the atmospheric temperature at z height; N _a (z) and N _m (z) are the vertical height z~z+Δz received by the lidar receiver respectively The number of meters and Rayleigh backscattered photoelectrons, Δz is the vertical range resolution, and Na( _z ) and _Nm (z) can be obtained from the lidar equation. From (9) ~ (11) formula:

In the formula: R _β =(N _a +N _m )/N _m is the backscattering ratio. Simultaneously (12) (13) two equations, get

Where: T _i is the effective transmittance of the i-th FP interferometer. The wind speed and backscatter ratio can be retrieved simultaneously by using the nonlinear iterative method for equation (14). According to the error transfer formula, the wind speed measurement error V _V and the backscatter ratio measurement error ε _R are respectively:

分别为T_i的后向散射比灵敏度和速度灵敏度，i＝1，2；SNR_i为T_i的探测信噪比。in:

are the backscattering ratio sensitivity and velocity sensitivity of T _i respectively, i=1, 2; SNR _i is the detection signal-to-noise ratio of T _i .

The overall structure of the laser radar system of the present invention is shown in FIG. 4 . A Nd:YAG multi-longitudinal mode pulse laser is used as the emission source to emit a 1064nm laser beam. The emitted laser is divided into two beams by the first beam splitter, and the transmitted light, which occupies most of the energy, is expanded by the beam expander, the first 45-degree reflector and the two-dimensional scanner light guide, and finally passes through vertically at a preset angle The glass plate enters the atmosphere to be measured. The atmospheric backscattered light is received by the Cassegrain telescope, coupled into a section of 200m long multimode bare fiber jumper delay by the first convex lens, and then enters an input branch of the first 1×2 fiber coupler. The light reflected by the first beam splitter with little energy enters one end of the second 1×2 fiber coupler as a reference light, and after passing through a section of 100m long multimode bare fiber, the backscattered light is transmitted by the other end of the same side The branch end is output and enters the other input branch end of the first 1×2 fiber coupler. The optical signal output from the first 1×2 fiber coupler is collimated by the collimator, filtered by the narrow-band interference filter, and then divided into two beams by the second beam splitter, and the reflected beam is converged by the second convex lens into the first An avalanche photodiode; the transmitted beam is divided into two beams equally by the third beam splitter. The transmitted beam of the third beam splitter is incident on the F-P interferometer 1 of the double F-P interferometer, and the transmitted optical signal is converged by the third convex lens into the second avalanche photodiode; the reflected beam of the third beam splitter is sent by the second After the light is guided by the 45-degree mirror, it is incident on the F-P interferometer 2, and the transmitted light signal is converged by the fourth convex lens and enters the third avalanche photodiode. The role of the reference light is system calibration and the measurement and locking of the emitted light frequency. A 200m long multimode bare fiber jumper is used to delay the backscattered light, so that the reference light and the backscattered light are staggered in timing. The output signals of the three avalanche photodiodes are collected by a multi-channel acquisition card, and then the industrial computer performs data processing, storage, data inversion and result display. The 1064nm Nd:YAG multi-longitudinal mode pulse laser, double F-P interferometer, two-dimensional scanner, multi-channel acquisition card, etc. of the whole system are all controlled by the industrial computer through the RS232 interface.

The laser radar system described in the present invention consists of a 1064nm Nd:YAG multi-longitudinal mode pulse laser, a first beam splitter, a beam expander, a first 45-degree reflector, a two-dimensional scanner, a glass plate, a Cassegrain telescope, and a first beam splitter. A convex lens, 200m long multimode bare fiber jumper, the first 1×2 fiber coupler, the second 1×2 fiber coupler, 100m long multimode bare fiber, collimator, narrow-band interference filter, the second branch Beam mirror, second convex lens, first avalanche photodiode, third beam splitter, double F-P interferometer, third convex lens, second avalanche photodiode, second 45-degree mirror, fourth convex lens, third avalanche photodiode , multi-channel acquisition card, trigger circuit, F-P interferometer controller, two-dimensional scanner controller, laser drive power supply and industrial computer, characterized by: 1064nm Nd: YAG multi-longitudinal mode pulse laser and laser drive power supply, trigger The circuit is connected, the laser emits 1064nm multi-longitudinal mode pulsed light, and the longitudinal mode interval is 2GHz, which is an integer multiple of the free spectrum interval of the double F-P interferometer. The double F-P interferometer is designed as a whole to ensure the relative stability between each frequency spectrum. The free spectral spacing of F-P interferometer 1 and F-P interferometer 2 is both 2GHz, the spectral width is 180MHz, and the effective light aperture is the same. The peak-to-peak interval of the spectrum of F-P interferometer 1 and F-P interferometer 2 is 200MHz. The center frequency of each longitudinal mode of the emitted laser is locked at the intersection of the spectrum of F-P interferometer 1 and F-P interferometer 2. Under this design parameter, it is most favorable for wind speed measurement, and the effect of a single measurement with a multi-longitudinal-mode laser is the same as that of multiple measurements with a single-longitudinal-mode laser. After the emitted laser beam is split by the first beam splitter (transmission and reflection ratio 99/1), most of the laser light is transmitted and a small part of the laser light is reflected. After the transmitted beam is expanded by the beam expander, the first 45-degree mirror and the light guide of the two-dimensional scanner, it finally vertically passes through the glass plate at a preset angle and enters the measured area of the atmosphere. The atmospheric backscattered light is received by the Cassegrain telescope, and then coupled into a 200m long multimode bare fiber jumper by the first convex lens. The focus of the first convex lens is on the end face of the coupling fiber. The 200m-long multimode bare fiber jumper is connected to an input branch end of the first 1×2 fiber coupler. The beam-combining end of the second 1×2 fiber coupler communicates with a section of 100m long multimode bare optical fiber. The reflected light beam of the first beam splitter is used as reference light, and a small amount of it is freely coupled into a branch end of the second 1×2 fiber coupler through space. After passing through a section of 100m long multimode bare optical fiber, the backscattered light is output from the other branch end on the same side, and the branch end communicates with the other input branch end of the first 1×2 fiber coupler. Both the reference light and the backscattered light are output from the beam combining end of the first 1×2 fiber coupler, and the subsequent optical paths are exactly the same. The role of the reference light is system calibration and the measurement and locking of the emitted light frequency. The backscattered light is delayed by using a 200m long multimode bare fiber jumper, so that the reference light and the backscattered light are just staggered in timing. The optical signal output from the beam-combining end of the first 1×2 fiber coupler is collimated by a collimator, and the collimated beam aperture is slightly smaller than the effective aperture of the F-P interferometer 1, and then filtered by a 1064nm narrow-band interference filter The light is divided into two beams by the second beam splitter, and the reflected beam is converged to the photosensitive surface of the first avalanche photodiode by the second convex lens; the transmitted beam is divided into two beams by the third beam splitter. The transmitted light beam of the third beam splitter is incident on the F-P interferometer 1 of the double F-P interferometer, and the light signal transmitted from it is converged to the photosensitive surface of the second avalanche photodiode by the third convex lens; the reflected light beam of the third beam splitter is obtained by After the light is guided by the second 45-degree mirror, it is incident on the F-P interferometer 2, and the transmitted light signal is converged by the fourth convex lens to the photosensitive surface of the third avalanche photodiode. The first avalanche photodiode, the second avalanche photodiode, and the third avalanche photodiode are connected to the multi-channel acquisition card, the multi-channel acquisition card is connected to the trigger circuit, the F-P interferometer controller is connected to the double F-P interferometer, and the two-dimensional scanner is controlled connected to the 2D scanner. The laser drive power supply, trigger circuit, F-P interferometer controller, and two-dimensional scanner controller are connected to the industrial computer and are uniformly controlled by the industrial computer.

Owing to adopting above-mentioned technical scheme, the advantage that the present invention has and positive effect are: compared with existing Doppler lidar system, 1, adopt multi-longitudinal-mode laser to construct Doppler lidar as emission light source, both realized The laser emission system is low cost and miniaturized, and does not require precise control of the resonant cavity, which can significantly improve the stability and environmental adaptability of the Doppler lidar system; 2. The optimized system parameters not only meet the requirements of the longitudinal mode laser The mode spacing matches the free spectral spacing of the double F-P interferometer, and it is more suitable for multi-longitudinal-mode laser wind field measurement, so that all longitudinal modes can be used for measurement efficiently. The longitudinal mode laser source has the same measurement effect for multiple times, which greatly improves the utilization rate of laser energy; 3. The multi-longitudinal mode Doppler lidar can not only detect the tropospheric atmospheric wind field with high precision, but also detect the optical characteristics of aerosol with high precision at the same time .

Description of drawings

Fig. 1 is a schematic diagram of wind speed measurement in the present invention.

Fig. 2 is a partially enlarged view of Fig. 1 of the present invention.

Fig. 3 is a schematic diagram of wind speed measurement in the present invention.

Fig. 4 is a structural block diagram of the present invention.

In the figure 1. 1064nm Nd: YAG multi-longitudinal mode pulsed laser, 2. First beam splitter, 3. Beam expander, 4. First 45-degree mirror, 5. Two-dimensional scanner, 6. Glass plate, 7 .Cassegrain telescope, 8. The first convex lens, 9.200m long multimode bare fiber jumper, 10. The first 1×2 fiber coupler, 11. The second 1×2 fiber coupler, 12.100m long multimode bare fiber Optical fiber, 13. Collimator, 14. Narrowband interference filter, 15. Second beam splitter, 16. Second convex lens, 17. First avalanche photodiode, 18. Third beam splitter, 19. Double F-P Interferometer, 20. The third convex lens, 21. The second avalanche photodiode, 22. The second 45-degree mirror, 23. The fourth convex lens, 24. The third avalanche photodiode, 25. Multi-channel acquisition card, 26. Trigger Circuit, 27. F-P interferometer controller, 28. Two-dimensional scanner controller, 29. Laser drive power supply, 30. Industrial computer.

Detailed ways

Structural framework of the present invention is shown in Figure 4.

In Fig. 4, the 1064nm Nd:YAG multi-longitudinal mode pulse laser (1) is respectively connected to the laser driving power supply (29) and the trigger circuit (26). The laser light emitted by the 1064nm Nd:YAG multi-longitudinal mode pulse laser (1) is divided into two beams by the first beam splitter (2). The transmitted light beam, which accounts for most of the energy, is expanded by the beam expander (3), guided by the first 45-degree mirror (4) and the two-dimensional scanner (5), and finally vertically passes through the glass plate at a preset angle ( 6) Enter the atmospheric area to be measured. Its atmospheric backscattered light is received by the Cassegrain telescope (7), and then coupled into a 200m long multimode bare fiber jumper (9) by the first convex lens (8). The focus of the first convex lens (8) is on the coupling fiber (9) End face. The 200m long multi-mode bare fiber jumper (9) communicates with an input branch end of the first 1×2 fiber coupler (10). The bundle end of the second 1×2 fiber coupler (11) communicates with a section of 100m long multimode bare optical fiber (12). The reflected beam of the first beam splitter (2) is used as reference light, and a small amount of it is freely coupled into a branch end of the second 1×2 fiber coupler (11) through space. After passing through a section of 100m long multimode bare optical fiber (12), its backscattered light is output by the other branch end on the same side, and this branch end communicates with the other input branch end of the first 1×2 fiber coupler (10) . Both the reference light and the backscattered light are output from the beam-combining end of the first 1×2 fiber coupler (10), and the subsequent optical paths are exactly the same. The backscattered light is delayed by using a 200m long multimode bare fiber jumper (9), so that the reference light and the backscattered light are just staggered in timing. The optical signal output from the beam combining end of the first 1×2 fiber coupler (10) is collimated by the collimating mirror (13), and the aperture of the collimated beam is slightly smaller than the F-P interferometer 1 in the double F-P interferometer (19) The effective light aperture, which is filtered by the 1064nm narrow-band interference filter (14), is divided into two beams by the second beam splitter (15), and the reflected beam is converged by the second convex lens (16) to the first avalanche photoelectric The photosensitive surface of the diode (17); the transmitted light beam is divided into two equally by the third beam splitter (18). The transmitted light beam of the third beam splitter (18) is just incident on the F-P interferometer 1 of the double F-P interferometer (19), and the optical signal transmitted therefrom is converged to the second avalanche photodiode (21) by the third convex lens (20) Photosensitive surface; the reflected light beam of the third beam splitter (18) is incident on the F-P interferometer 2 of the double F-P interferometer (19) after being guided by the second 45-degree reflector (22), and the light signal transmitted therefrom The fourth convex lens (23) converges to the photosensitive surface of the third avalanche photodiode (24). The first avalanche photodiode (17), the second avalanche photodiode (21), the third avalanche photodiode (24) are connected to the multi-channel acquisition card (25), and the multi-channel acquisition card (25) is connected to the trigger circuit (26) , the F-P interferometer controller (27) is connected to the double F-P interferometer (19), and the two-dimensional scanner controller (28) is connected to the two-dimensional scanner (5). The laser drive power supply (29), the trigger circuit (26), the F-P interferometer controller (27), and the two-dimensional scanner controller (28) are connected to the industrial computer (30), and are uniformly controlled by the industrial computer (30).

Claims (1)

1. A direct detection meter scattering Doppler lidar system based on dual F-P interferometers and multi-longitudinal mode lasers, consisting of a 1064nm Nd:YAG multi-longitudinal mode pulse laser, a first beam splitter, a beam expander, and a first 45 Degree reflector, two-dimensional scanner, glass plate, Cassegrain telescope, first convex lens, 200m long multimode bare fiber jumper, first 1×2 fiber coupler, second 1×2 fiber coupler, 100m long Multimode bare fiber, collimator, narrow-band interference filter, second beam splitter, second convex lens, first avalanche photodiode, third beam splitter, double F-P interferometer, third convex lens, second avalanche photoelectric Composed of diode, second 45-degree mirror, fourth convex lens, third avalanche photodiode, multi-channel acquisition card, trigger circuit, F-P interferometer controller, two-dimensional scanner controller, laser drive power supply and industrial computer, its features Yes: 1064nm Nd:YAG multi-longitudinal-mode pulsed lasers are respectively connected to the laser drive power supply and trigger circuit. The laser emits 1064nm multi-longitudinal-mode pulsed light, and the longitudinal mode interval is 2GHz, which is an integer multiple of the free spectrum interval of the double F-P interferometer. The double F-P interferometer is designed as a whole to ensure the relative stability between each frequency spectrum. The free spectral spacing of F-P interferometer 1 and F-P interferometer 2 is both 2GHz, the spectral width is 180MHz, and the effective light aperture is the same. The peak-to-peak interval of the spectrum of F-P interferometer 1 and F-P interferometer 2 is 200MHz. The center frequency of each longitudinal mode of the emitted laser is locked at the intersection of the spectrum of F-P interferometer 1 and F-P interferometer 2. Under this design parameter, it is most favorable for wind speed measurement, and the effect of a single measurement with a multi-longitudinal-mode laser is the same as that of multiple measurements with a single-longitudinal-mode laser. After the emitted laser beam is split by the first beam splitter (transmission and reflection ratio 99/1), most of the laser light is transmitted and a small part of the laser light is reflected. After the transmitted beam is expanded by the beam expander, the first 45-degree mirror and the light guide of the two-dimensional scanner, it finally vertically passes through the glass plate at a preset angle and enters the measured area of the atmosphere. The atmospheric backscattered light is received by the Cassegrain telescope, and then coupled into a 200m long multimode bare fiber jumper by the first convex lens. The focus of the first convex lens is on the end face of the coupling fiber. The 200m-long multimode bare fiber jumper is connected to an input branch end of the first 1×2 fiber coupler. The beam-combining end of the second 1×2 fiber coupler communicates with a section of 100m long multimode bare optical fiber. The reflected light beam of the first beam splitter is used as reference light, and a small amount of it is freely coupled into a branch end of the second 1×2 fiber coupler through space. After passing through a section of 100m long multimode bare optical fiber, the backscattered light is output from the other branch end on the same side, and the branch end communicates with the other input branch end of the first 1×2 fiber coupler. Both the reference light and the backscattered light are output from the beam combining end of the first 1×2 fiber coupler, and the subsequent optical paths are exactly the same. The role of the reference light is system calibration and the measurement and locking of the emitted light frequency. The backscattered light is delayed by using a 200m long multimode bare fiber jumper, so that the reference light and the backscattered light are just staggered in timing. The optical signal output from the beam-combining end of the first 1×2 fiber coupler is collimated by a collimator, and the collimated beam aperture is slightly smaller than the effective aperture of the F-P interferometer 1, and then filtered by a 1064nm narrow-band interference filter The light is divided into two beams by the second beam splitter, and the reflected beam is converged to the photosensitive surface of the first avalanche photodiode by the second convex lens; the transmitted beam is divided into two beams by the third beam splitter. The transmitted beam of the third beam splitter is incident on the F-P interferometer 1, and the transmitted optical signal is converged by the third convex lens to the photosensitive surface of the second avalanche photodiode; the reflected beam of the third beam splitter is reflected by the second 45° After the light is guided by the mirror, it is incident on the F-P interferometer 2, and the transmitted light signal is converged by the fourth convex lens to the photosensitive surface of the third avalanche photodiode. The first avalanche photodiode, the second avalanche photodiode, and the third avalanche photodiode are connected to the multi-channel acquisition card, the multi-channel acquisition card is connected to the trigger circuit, the F-P interferometer controller is connected to the double F-P interferometer, and the two-dimensional scanner is controlled connected to the 2D scanner. The laser drive power supply, trigger circuit, F-P interferometer controller, and two-dimensional scanner controller are connected to the industrial computer and are uniformly controlled by the industrial computer.

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