Quantum Raman LiDAR System and Inversion Method of Wind Speed ​​and Temperature

Abstract

The invention provides a quantum Raman laser radar system and a method for inverting wind speed and temperature, comprising: a first beam splitter is suitable for splitting an initial laser beam into a first laser beam and a second laser beam; a telescope is suitable for emitting the first laser beam into a target atmosphere and receiving an echo signal generated by the action of the target atmosphere and the first laser beam; a Raman optical frequency comb source is suitable for generating a Raman optical frequency comb signal under the action of the second laser beam; an attenuator is suitable for attenuating the optical power of the Raman optical frequency comb signal to a single photon level; a second beam splitter is suitable for causing the Raman optical frequency comb signal with the optical power attenuated to undergo quantum interference with the echo signal; two single-photon detectors are suitable for respectively detecting and obtaining single-photon counts outputted from two outlets of the second beam splitter; and a computer obtains an interference spectrum diagram of a beat frequency signal generated after the Raman optical frequency comb signal and the echo signal undergo quantum interference according to the single-photon counts, so as to obtain the temperature and wind speed of the target atmosphere.

Description

Technical Field

[0001] At least one embodiment of the present invention relates to the field of laser radar technology, and more specifically to a quantum Raman laser radar system and a method for inverting wind speed and temperature. Background Art

[0002] Atmospheric wind field and temperature field are important indicators of atmospheric detection. It is of great scientific significance to study their role in the transport of atmospheric components, the structure of the atmospheric boundary layer and the atmospheric dynamics process. Accurate atmospheric wind field and temperature observations have great practical value in improving the accuracy of numerical weather forecasts, improving climate models, monitoring biochemical gases and ensuring aerospace safety.

[0003] In the field of Raman lidar temperature measurement, pure rotational Raman relative temperature measurement system needs other temperature measurement instruments to perform parameter correction when inverting temperature, but the parallel correction equipment is affected by atmospheric changes, so the accuracy of correction is difficult to guarantee. As for the existing absolute temperature measurement technology, most domestic and foreign scholars use a two-stage cascade spectral splitting structure to construct a pure rotational Raman absolute temperature measurement system. The spectral resolution of the imaging spectrometer splitting and the camera (Charge-coupled Device, CCD) acquisition method is low, and the residual elastic scattering signal makes the CCD easy to saturate, resulting in a low signal-to-noise ratio, a short detection distance and unsatisfactory temperature inversion effect; and the two-stage cascade splitting method of cascading the Fabry-Perot (FP) interferometer with the diffraction grating or the diffraction grating with the fiber Bragg grating has complex filtering, low optical efficiency, and requires megahertz-level frequency stabilization, resulting in a large volume and difficulty in loading.

[0004] Wind-measuring lidars are divided into two detection modes: direct and coherent. Direct wind measurement requires a laser frequency stabilizer and a frequency discriminator, with a complex receiving optical path and is sensitive to temperature gradients and stress gradients. Traditional coherent wind measurement requires the Mie scattering signal of aerosols as a detection signal, so its application scenarios are limited. It is only suitable for near-ground wind field detection and is greatly affected by weather conditions. In addition, traditional coherence requires the use of an acquisition card with a high sampling rate and requires real-time signal processing, which poses challenges to subsequent data storage and processing.

[0005] The laser radar technology for simultaneous detection of atmospheric wind field temperature includes sodium layer atmospheric detection based on sodium fluorescence, tropospheric atmospheric detection based on Fizeau interferometer and fringe technology to analyze Rayleigh Brillouin spectrum lines, etc. However, the detection altitudes of the above laser radars are different. For example, sodium fluorescence laser radar is at the top of the mesosphere, and the temperature measurement technology is mature; Rayleigh Brillouin laser radar is at the tropospheric altitude, and currently only simulation verification has been achieved. At present, the relevant technologies for simultaneous detection of low-level atmospheric wind field temperature cannot realize the simultaneous detection of low-level atmospheric wind speed and temperature based on pure rotational Raman spectrum lines. Summary of the invention

[0006] In order to solve at least one of the above-mentioned and other technical problems in the prior art, the present invention provides a quantum Raman lidar system and a method for inverting wind speed and temperature, which can realize the simultaneous detection of wind speed and temperature in the lower atmosphere, improve the accuracy of wind speed and temperature, and improve the application efficiency of the quantum Raman lidar system.

[0007] According to one aspect of the present invention, a quantum Raman laser radar system is provided, comprising:

[0008] A laser, adapted to provide an initial laser beam;

[0009] A first beam splitter, adapted to split the initial laser beam into a first laser beam and a second laser beam;

[0010] A telescope, adapted to emit the first laser beam into a target atmosphere and receive an echo signal generated by the interaction between the target atmosphere and the first laser beam;

[0011] A Raman optical frequency comb source, adapted to generate a Raman optical frequency comb signal under the action of the second laser beam;

[0012] An attenuator, adapted to attenuate the optical power of the Raman optical frequency comb signal to a single photon level;

[0013] A second beam splitter is used to cause quantum interference between the Raman optical frequency comb signal after optical power attenuation and the echo signal;

[0014] Two single-photon detectors, adapted to respectively detect and obtain single-photon counts outputted from the two outlets of the second beam splitter; and

[0015] The computer is adapted to obtain, based on the single photon counting, an interference spectrum diagram of a beat frequency signal generated after quantum interference between the Raman optical frequency comb signal and the echo signal, so as to obtain the temperature and wind speed of the target atmosphere.

[0016] According to an embodiment of the present invention, the Raman optical frequency comb source comprises:

[0017] A nitrogen pool, adapted to generate Raman scattered light by causing the second laser beam to react with nitrogen in the nitrogen pool;

[0018] A grating, adapted to separate the Raman scattered light according to wavelength;

[0019] An electro-optic modulator, adapted to modulate the frequency of the split Raman scattered light; and

[0020] The acousto-optic modulator is suitable for controlling the switching time of the Raman scattered light modulated by the electro-optic modulator to control the output of the Raman optical frequency comb signal.

[0021] According to an embodiment of the present invention, the above-mentioned quantum Raman laser radar system further includes:

[0022] A third beam splitter is used to divide the Raman optical frequency comb signal into a first Raman optical frequency comb signal and a second Raman optical frequency comb signal in proportion, and the attenuator is used to attenuate the optical power of the second Raman optical frequency comb signal to a single photon level; and

[0023] The power monitoring component is adapted to monitor the total optical power of the first Raman optical frequency comb signal to ensure the stability of the Raman optical frequency comb signal.

[0024] According to an embodiment of the present invention, the above-mentioned quantum Raman laser radar system further includes:

[0025] The filter is suitable for allowing the nitrogen Raman scattering signal in the above echo signal to pass through and filtering out the broad spectrum solar background noise.

[0026] According to one aspect of the present invention, there is provided a method for inverting wind speed and temperature using the above-mentioned quantum Raman lidar system, comprising:

[0027] According to the interference spectrum diagram of the beat frequency signal, a Doppler frequency shift and a signal-to-noise ratio of the beat frequency signal are obtained;

[0028] According to the relationship between the Doppler frequency shift and the wind speed, the wind speed of the target atmosphere is obtained by inversion;

[0029] Inverting the signal-to-noise ratio of the echo signal generated by the interaction between the target atmosphere and the first laser beam to obtain the signal-to-noise ratio of the beat frequency signal; and

[0030] Calculating the correlation coefficient between the signal-to-noise ratio of the echo signal and the intensity of the theoretical Raman spectrum line at different temperatures, thereby obtaining the temperature of the target atmosphere;

[0031] Among them, the wind speed and the temperature under different range gates are obtained according to the inversion method, so as to obtain the temperature of the target atmosphere and the wind speed of the target atmosphere with distance resolution.

[0032] According to an embodiment of the present invention, the Doppler frequency shift and the wind speed The relationship satisfies formula (1):

[0033] (1);

[0034] in, is the Doppler shift mentioned above, is the central wavelength of the Raman line corresponding to the above Doppler shift.

[0035] According to an embodiment of the present invention, the echo signal The signal-to-noise ratio satisfies formula (2):

[0036] (2);

[0037] in, is the signal-to-noise ratio of the above beat frequency signal, is the signal-to-noise ratio of the above Raman frequency comb signal, Indicates Spectrum lines.

[0038] According to an embodiment of the present invention, the signal-to-noise ratio of the echo signal is Compared with the above theoretical Raman line intensity Pearson correlation coefficient Satisfies formula (3):

[0039] (3);

[0040] in, Representative Theoretical Raman lines, is the total number of the above theoretical Raman lines, Indicates the temperature The temperature of the target atmosphere is the correlation coefficient The temperature corresponding to the maximum , is the intensity of the above theoretical Raman line when the distance corresponding to the distance gate is z.

[0041] According to an embodiment of the present invention, when the distance corresponding to the distance gate is z, the intensity of the jth theoretical Raman line is Satisfies formula (4):

[0042] (4);

[0043] in, is a constant, is the average power of the initial laser beam mentioned above, is the width of the initial laser beam mentioned above, is the receiving area of ​​the above telescope, is the molecular number density of nitrogen in the above target atmosphere, It is the distance The atmospheric extinction coefficient at It is the backscattering cross section of the rotational quantum number J corresponding to the jth spectral line in the above theoretical Raman spectral line.

[0044] According to an embodiment of the present invention, the backscattering cross section of the rotational quantum number J corresponding to the jth spectral line in the above theoretical Raman spectral line is Satisfies formula (5):

[0045] (5);

[0046] in, is the molecular number density relative to the volume concentration; is the nuclear spin constant; is the statistical weight factor; is Planck's constant; is the speed of light; is the rotation constant of the vibration ground state; is the frequency of the above initial laser beam; is the frequency shift of the rotational Raman wave number; is the anisotropy constant of the molecular polarization tensor; is the Boltzmann constant.

[0047] According to an embodiment of the present invention, a laser is provided to provide an initial laser beam, a first beam splitter is provided to split the initial laser beam into a first laser beam and a second laser beam, a telescope is used to emit the first laser beam into a target atmosphere, and an echo signal generated by the interaction between the target atmosphere and the first laser beam is received, a Raman optical frequency comb source is used to generate a Raman optical frequency comb signal under the action of the second laser beam; an attenuator is used to attenuate the optical power of the Raman optical frequency comb signal to a single photon level; a second beam splitter is used to cause quantum interference between the Raman optical frequency comb signal after the optical power is attenuated and the echo signal; two single-photon detectors are used to respectively detect and obtain single-photon counts outputted from two outlets of the second beam splitter; and a computer is used to obtain an interference spectrum diagram of a beat frequency signal generated after quantum interference between the Raman optical frequency comb signal and the echo signal based on the single-photon counts, so as to obtain the temperature and wind speed of the target atmosphere, thereby realizing simultaneous detection of wind speed and temperature in the lower atmosphere, improving the accuracy of wind speed and temperature, and improving the application efficiency of the quantum Raman lidar system. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The above contents and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0049] Figure 1 A schematic diagram showing the working principle of a quantum Raman laser radar system according to an embodiment of the present invention is shown;

[0050] Figure 2 A flow chart of a method for inverting wind speed and temperature using a quantum Raman laser radar system according to an embodiment of the present invention is schematically shown;

[0051] Figure 3 The figure schematically shows an interference spectrum diagram of a beat frequency signal in a quantum Raman laser radar system according to an embodiment of the present invention;

[0052] Figure 4 A diagram schematically shows a spectrum diagram of a Raman optical frequency comb signal in a quantum Raman laser radar system according to an embodiment of the present invention;

[0053] Figure 5 A schematic diagram of an echo signal spectrum in a quantum Raman laser radar system according to an embodiment of the present invention is shown; and

[0054] Figure 6 A schematic diagram of a theoretical Raman scattering cross section in a quantum Raman lidar system according to an embodiment of the present invention is schematically shown.

[0055] In the above drawings, the meanings of the reference numerals are as follows:

[0056] 1-Laser;

[0057] 2- first beam splitter;

[0058] 3- Telescope;

[0059] 4-Raman frequency comb source;

[0060] 5-Filter;

[0061] 6- second beam splitter;

[0062] 7- third beam splitter;

[0063] 8-Attenuator;

[0064] 9- Power monitoring component;

[0065] 10- first detector;

[0066] 11- Second detector;

[0067] 12- Computer. DETAILED DESCRIPTION

[0068] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0069] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0070] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0071] When using expressions such as "at least one of A, B, and C, etc.", they should generally be interpreted according to the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0072] Among the related technologies for simultaneous detection of atmospheric wind field and temperature, the sodium fluorescence-based lidar can detect the atmosphere at the top of the mesosphere, while the Fizeau interferometer-based lidar has only simulated and verified that it can detect the atmosphere at the height of the troposphere. Both cannot achieve simultaneous detection of wind speed and temperature in the lower atmosphere based on pure rotational Raman spectra.

[0073] In view of this, the present invention provides a quantum Raman laser radar system, which provides an initial laser beam by arranging a laser, divides the initial laser beam into a first laser beam and a second laser beam by arranging a first beam splitter, emits the first laser beam into a target atmosphere by using a telescope, and receives an echo signal generated by the action of the target atmosphere and the first laser beam, generates a Raman optical frequency comb signal by using a Raman optical frequency comb source under the action of the second laser beam; attenuates the optical power of the Raman optical frequency comb signal to the single photon level by using an attenuator; causes the Raman optical frequency comb signal with the attenuated optical power to undergo quantum interference with the echo signal by using a second beam splitter; uses two single-photon detectors to respectively detect and obtain single-photon counts outputted from two outlets of the second beam splitter; and uses a computer to obtain an interference spectrum diagram of a beat frequency signal generated by quantum interference between the Raman optical frequency comb signal and the echo signal according to the single-photon counts, so as to obtain the temperature and wind speed of the target atmosphere, thereby realizing the simultaneous detection of the wind speed and temperature of the lower atmosphere, improving the accuracy of the wind speed and temperature, and improving the application efficiency of the quantum Raman laser radar system.

[0074] Figure 1 The working principle diagram of the quantum Raman lidar system according to an embodiment of the present invention is schematically shown.

[0075] According to some embodiments of the present invention, Figure 1 As shown, the quantum Raman lidar system includes a laser 1, a first beam splitter 2, a telescope 3, a Raman optical frequency comb source 4, an attenuator 8, a second beam splitter 6, a first detector 10, a second detector 11 and a computer 12. The laser 1 is suitable for providing an initial laser beam; the first beam splitter 2 is suitable for dividing the initial laser beam into a first laser beam and a second laser beam; the telescope 3 is suitable for emitting the first laser beam into the target atmosphere and receiving the echo signal generated by the interaction between the target atmosphere and the first laser beam; the Raman optical frequency comb source 4 is suitable for generating a Raman optical frequency comb signal under the action of the second laser beam; the attenuator 8 is suitable for attenuating the optical power of the Raman optical frequency comb signal to the single photon level; the second beam splitter 6 is suitable for causing the Raman optical frequency comb signal with the attenuated optical power to undergo quantum interference with the echo signal; two single-photon detectors (i.e., the first detector 10 and the second detector 11) are suitable for respectively detecting and obtaining single-photon counts outputted from two outlets of the second beam splitter 6; and the computer 12 obtains the interference spectrum of the beat frequency signal generated by the quantum interference between the Raman optical frequency comb signal and the echo signal according to the single-photon counts, so as to obtain the temperature and wind speed of the target atmosphere.

[0076] According to some embodiments of the present invention, a laser 1 is provided to provide an initial laser beam, a first beam splitter 2 is provided to split the initial laser beam into a first laser beam and a second laser beam, a telescope 3 is used to emit the first laser beam into a target atmosphere, and an echo signal generated by the interaction between the target atmosphere and the first laser beam is received, a Raman optical frequency comb source 4 is used to generate a Raman optical frequency comb signal under the action of the second laser beam; an attenuator 8 is used to attenuate the optical power of the Raman optical frequency comb signal to a single photon level; a second beam splitter 6 is used to cause quantum interference between the Raman optical frequency comb signal after the optical power is attenuated and the echo signal; a first detector 10 and a second detector 11 are used to respectively detect and obtain single photon counts outputted from two outlets of the second beam splitter 6; and a computer 12 is used to obtain an interference spectrum diagram of a beat frequency signal generated after quantum interference between the Raman optical frequency comb signal and the echo signal based on the single photon counts, so as to obtain the temperature and wind speed of the target atmosphere, thereby realizing simultaneous detection of wind speed and temperature in the lower atmosphere, improving the accuracy of wind speed and temperature, and improving the application efficiency of the quantum Raman lidar system.

[0077] According to some embodiments of the present invention, the telescope 3 has a high-precision aiming mechanism, a stable platform, and an optimized optical system, which can ensure that the initial laser beam can be accurately and efficiently projected into the target atmospheric region. When the first laser beam interacts with gas molecules, aerosols, clouds, raindrops, ice crystals, or other particles in the target atmosphere, part of the laser energy is scattered back to the original direction or a nearby direction, and these scattered lights are echo signals. The echo signals carry information about the target atmosphere, such as position, speed, temperature, shape, physical properties, etc. The echo signals are an important basis for the quantum Raman lidar system to perform atmospheric detection and meteorological analysis.

[0078] According to some embodiments of the present invention, the splitting ratio of the second beam splitter 6 is 50:50, and it can be seen that the distribution of the number of single photons output from the two outlets is complementary, that is, if one outlet detects a photon, then the other outlet will not detect the photon. Due to the complementarity of the distribution of the number of single photons at multiple outlets, it is necessary to use the first detector 10 and the second detector 11 to simultaneously monitor the number of single photons output from the two outlets of the second beam splitter 6, so as to more completely obtain the interference result of the quantum interference between the Raman optical frequency comb signal and the echo signal. The first detector 10 and the second detector 11 can count single photons, thereby realizing the accurate detection and quantitative analysis of extremely weak target signals.

[0079] According to some embodiments of the present invention, the first beam splitter 2 splits the initial laser beam into the first laser beam and the second laser beam in a ratio of 90:10, that is, the ratio of the first laser beam to the second laser beam is 90:10.

[0080] According to some embodiments of the present invention, the Raman optical frequency comb source 4 includes a nitrogen cell, a grating, an electro-optic modulator, and an acousto-optic modulator. The nitrogen cell is suitable for generating Raman scattered light by causing the second laser beam to generate Raman scattered light by the nitrogen in the nitrogen cell; the grating is suitable for splitting the Raman scattered light by wavelength; the electro-optic modulator is suitable for modulating the frequency of the split Raman scattered light; and the acousto-optic modulator is suitable for controlling the switching time of the Raman scattered light modulated by the electro-optic modulator to control the output of the Raman optical frequency comb signal.

[0081] According to some embodiments of the present invention, the frequency of the Raman optical frequency comb source 4 is tunable.

[0082] According to some embodiments of the present invention, the quantum Raman laser radar system further includes a third beam splitter 7 and a power monitoring component 9. The third beam splitter 7 is adapted to divide the Raman optical frequency comb signal into the first Raman optical frequency comb signal and the second Raman optical frequency comb signal in proportion, the attenuator 7 is adapted to attenuate the optical power of the second Raman optical frequency comb signal to the single photon level; and the power monitoring component 9 is adapted to monitor the total optical power of the first Raman optical frequency comb signal to ensure the stability of the Raman optical frequency comb signal.

[0083] According to some embodiments of the present invention, the third beam splitter 7 is adapted to divide the Raman optical frequency comb signal into a first Raman optical frequency comb signal and a second Raman optical frequency comb signal in proportion, and the ratio of the first Raman optical frequency comb signal to the second Raman optical frequency comb signal is 10:90.

[0084] According to some embodiments of the present invention, the attenuator 7 attenuates the optical power of the second Raman optical frequency comb signal to the single-photon level, which means that the optical power is extremely low, so that only a very small number of photons are detected on average during the measurement time, and may even approach or reach the level of only one photon detected each time. By using the attenuator 7 to attenuate the optical power of the second Raman optical frequency comb signal to the single-photon level, the photons of the Raman optical frequency comb signal can be detected by the first detector 10 and the second detector 11.

[0085] According to some embodiments of the present invention, the photons in the second Raman optical frequency comb signal and the photons in the echo signal have the same degrees of freedom except for the frequencies, so the second Raman optical frequency comb signal and the echo signal can undergo quantum interference.

[0086] According to some embodiments of the present invention, the laser 1, the power monitoring component 9 and the two single-photon detectors are time synchronized. The two single-photon detectors include a first detector 10 and a second detector 11. The first detector 10 and the second detector 11 are respectively arranged at the two outlets of the second beam splitter 6, and the number of single photons output from the two outlets of the second beam splitter 6 are detected simultaneously.

[0087] According to some embodiments of the present invention, the quantum Raman lidar system further includes a filter 8, which is adapted to allow the nitrogen Raman scattering signal in the echo signal to pass through and filter out the broad-spectrum solar background noise.

[0088] According to some embodiments of the present invention, the echo received by the telescope includes a variety of scattered signals and noises, and only the nitrogen Raman scattering signal is useful information, while the solar background noise in the noise is generated by solar radiation. Although it is not direct light, it still contains a large number of photons. When these noises enter the detector, if the intensity of the noise exceeds the maximum tolerance range of the detector, it will cause the light intensity received by the detector to be too large, thereby causing the detector to be saturated. By setting the filter 8, the nitrogen Raman scattering signal in the echo signal can pass through and the solar background noise can be filtered out, so that the first detector 10 and the second detector 11 are not saturated by the solar background radiation noise and cannot detect signal photons, thereby reducing the influence of the solar background noise on the single-photon detector.

[0089] Figure 2The flowchart of the method for inverting wind speed and temperature using a quantum Raman lidar system according to an embodiment of the present invention is schematically shown.

[0090] According to another aspect of the present invention, a method for inverting wind speed and temperature using a quantum Raman lidar system is provided, such as Figure 2 As shown, the inversion method of wind speed and temperature includes operations S101 to S104.

[0091] In operation S101 , a Doppler frequency shift and a signal-to-noise ratio of the beat signal are acquired according to an interference spectrum diagram of the beat signal.

[0092] In operation S102 , the wind speed of the target atmosphere is obtained by inversion according to the relationship between the Doppler frequency shift and the wind speed.

[0093] In operation S103, a signal-to-noise ratio of an echo signal generated by the interaction between the target atmosphere and the first laser beam is obtained by inversion according to the signal-to-noise ratio of the beat frequency signal.

[0094] In operation S104, the correlation coefficient between the signal-to-noise ratio of the echo signal and the intensity of the theoretical Raman spectrum line at different temperatures is calculated to obtain the temperature of the target atmosphere.

[0095] According to some embodiments of the present invention, the wind speed and temperature under different range gates are obtained according to an inversion method, thereby obtaining the temperature of the target atmosphere and the wind speed of the target atmosphere with range resolution.

[0096] According to some embodiments of the present invention, the range resolution refers to the minimum value of the distance between two adjacent targets or atmospheric layers that a quantum Raman lidar system can distinguish. It depends on the pulse width in the quantum Raman lidar system and the performance of the receiving system. The quantum Raman lidar system can achieve a high range resolution, thereby accurately measuring the wind speed and temperature of the atmosphere at different distances.

[0097] Figure 3 The interference spectrum diagram of the beat frequency signal in the quantum Raman lidar system according to an embodiment of the present invention is schematically shown.

[0098] According to some embodiments of the present invention, Figure 3 is the spectrum diagram of the beat frequency signal after the Raman optical frequency comb signal and the echo signal undergo quantum interference. Figure 3 As shown in the figure, the horizontal axis is the frequency, in Hz, which represents the different frequency components of the beat signal; the vertical axis is the normalized amplitude, which represents the amplitude value of the beat signal at different frequency components, that is, the intensity of the beat signal at this frequency. Figure 3The interference spectrum of the beat signal can be used to obtain the Doppler frequency shift value of the center frequency of each spectral line of the beat signal. The spectrum includes Doppler frequency shift and modulation frequency shift. Since the modulation frequency shift is known, the Doppler frequency shift can be calculated, and then the radial wind speed of the target atmosphere can be inverted according to the relationship between Doppler frequency shift and wind speed. And according to Figure 3 The signal-to-noise ratio of the interference spectrum can be used to invert the signal-to-noise ratio of the echo signal.

[0099] According to some embodiments of the present invention, Doppler frequency shift and wind speed The relationship satisfies formula (1):

[0100] (1);

[0101] in, is the Doppler shift, is the central wavelength of the Raman spectrum line corresponding to the Doppler frequency shift. According to formula (1), the multiple velocity values ​​obtained by inverting multiple spectrum lines of the beat frequency signal are averaged to obtain the radial wind speed result of the target atmosphere of the current range gate.

[0102] According to some embodiments of the present invention, in the time-resolved measurement of the laser radar by the quantum Raman laser radar system, the range gate is a time window used to selectively analyze the signals received within a specific time period. This time period usually corresponds to the round-trip time of the radar pulse and is used to determine that the signal comes from a target within a specific distance range. In a range gate, the first detector 10 and the second detector 11 respectively record the arrival time of the photons of the two channels (i.e., the number of single photons output by the two outlets of the second beam splitter 6), and then divide the time window. The time window with photons is recorded as 1, and the time window without photons is recorded as 0. The coincidence count is obtained by calculating the cross-correlation of the two channels, and then converted to the frequency domain through fast Fourier transform, thereby obtaining Figure 3 Interference spectrum diagram.

[0103] According to some embodiments of the present invention, cross-correlation is a mathematical operation, and a coincidence count is obtained through the cross-correlation operation. The coincidence count refers to the number of time windows in which photons are detected simultaneously on the first detector 10 and the second detector 11. The coincidence count is obtained by calculating the cross-correlation between the sequences generated by the two single-photon detectors due to the detection of photons, so that the result of quantum interference can be obtained. These time windows correspond to the positions that are simultaneously "1" in the sequences of the two single-photon detectors. The lower the coincidence count, the less likely the two single-photon detectors detect photons simultaneously, and the higher the visibility of quantum interference.

[0104] According to some alternative embodiments of the present invention, the time window divided within the above-mentioned range gate is selected according to the response of the single-photon detector, and the time window is on the order of hundreds of picoseconds.

[0105] According to some embodiments of the present invention, the calculation formula of the signal-to-noise ratio of the signal satisfies: .

[0106] According to some embodiments of the present invention, the Raman optical frequency comb signal has multiple spectral lines with an even number of rotational quantum numbers. When calculating the signal-to-noise ratio, the spectral lines of the Raman optical frequency comb signal, the echo signal, and the beat frequency signal need to correspond one to one, wherein: For the The peak value of the spectral amplitude of the spectral line, For the The lowest value of the spectral amplitude of a spectral line. In actual calculation, multiple adjacent points can be averaged to improve the accuracy of signal-to-noise ratio calculation.

[0107] According to some embodiments of the present invention, based on the relationship between the Raman optical frequency comb signal, the echo signal and the beat signal in the coherent detection, the signal-to-noise ratio of each spectral line in the echo signal participating in the quantum beat can be calculated. The signal-to-noise ratio satisfies formula (2):

[0108] (2);

[0109] in, is the signal-to-noise ratio of the beat frequency signal, is the signal-to-noise ratio of the Raman optical frequency comb signal, Indicates Spectrum lines.

[0110] According to some embodiments of the present invention, the signal-to-noise ratio of the echo signal The intensity of the theoretical Raman line Pearson correlation coefficient Satisfies formula (3):

[0111] (3);

[0112] in, Representative Theoretical Raman lines, is the total number of theoretical Raman lines, Indicates the temperature The temperature of the target atmosphere is the correlation coefficient The temperature corresponding to the maximum , is the intensity of the theoretical Raman line when the distance corresponding to the distance gate is z, is the average value of the intensity of the theoretical Raman line when the distance corresponding to the distance gate is z, is the average signal-to-noise ratio of the echo signal.

[0113] Figure 4 A spectrum diagram of a Raman optical frequency comb signal in a quantum Raman lidar system according to an embodiment of the present invention is schematically shown.

[0114] According to some embodiments of the present invention, Figure 4 is the spectrum diagram of the Raman optical frequency comb signal. Figure 4 As shown, the horizontal axis is the wavelength in nanometers, representing multiple spectral lines of different wavelengths; the vertical axis is the normalized amplitude, representing the normalized amplitude value of different wavelengths of the Raman optical frequency comb signal, reflecting the relative intensity of each spectral line. Figure 4 Shown are the pure rotational Raman lines with an even rotational quantum number after different frequency shifts. The frequency shift is on the order of gigahertz to match the order of magnitude of the Raman scattering line width, ensuring that interference information can ultimately be collected and the intensity information of each spectral line after the frequency shift can be recorded.

[0115] According to some embodiments of the present invention, the total number of spectral lines of the Raman optical frequency comb signal is a plurality of even-numbered rotational quantum number spectral lines that make the backscattering cross section larger and the temperature sensitivity greater, and 8 spectral lines may be selected, and j=1, 2, ..., 8 correspond to J=8, 10, 12, ..., 22, respectively. Since the quantum Raman lidar system is based on the principle of quantum interference, the selection of the pure rotational Raman spectral line of nitrogen is hardly affected by the adjacent pure rotational Raman spectral line of oxygen.

[0116] According to some optional embodiments of the present invention, the above correlation coefficient The calculation process needs to traverse a certain range of temperatures T. According to the matching effect, the step size when traversing the temperature includes any one of 0.1 K, 0.5 K and 1 K, and the temperature range includes 200 K - 320 K.

[0117] Figure 5 The figure schematically shows a spectrum diagram of an echo signal in a quantum Raman lidar system according to an embodiment of the present invention.

[0118] like Figure 5 As shown, the horizontal axis is wavelength, in nanometers, representing multiple spectral lines of different wavelengths; the vertical axis is normalized amplitude, representing the normalized amplitude value of different wavelengths of the echo signal, reflecting the relative intensity of each spectral line. By analyzing the shape, peak value and frequency component of the echo signal spectrum, the characteristics of the echo signal can be deeply analyzed. And by analyzing the spectrum, the noise frequency range that needs to be filtered out can be determined, and the corresponding filter 5 can be designed for filtering, thereby improving the quality of the echo signal received by the second beam splitter 6.

[0119] According to some embodiments of the present invention, when the distance corresponding to the distance gate is z, The intensity of the theoretical Raman line Satisfies formula (4):

[0120] (4);

[0121] in, is a constant, is the average power of the initial laser beam, is the width of the initial laser beam, is the receiving area of ​​telescope 3, is the molecular number density of nitrogen in the target atmosphere, It is the distance The atmospheric extinction coefficient at It is the first line in the theoretical Raman spectrum. The backscattering cross section of the rotational quantum number J corresponding to the spectral line. It is a system constant related to the quantum efficiency and the optical efficiency of the system.

[0122] According to some embodiments of the present invention, the first Backscattering cross section of the rotational quantum number J corresponding to the spectral line Satisfies formula (5):

[0123] (5);

[0124] in, is the molecular number density relative to the volume concentration; is the nuclear spin constant; is the statistical weight factor; is Planck's constant; is the speed of light; is the rotation constant of the vibration ground state; is the frequency of the initial laser beam; is the frequency shift of the rotational Raman wave number; is the anisotropy constant of the molecular polarization tensor; is the Boltzmann constant.

[0125] Figure 6 A schematic diagram of a theoretical Raman scattering cross section in a quantum Raman lidar system according to an embodiment of the present invention is schematically shown.

[0126] like Figure 6 As shown, the horizontal axis is the wavelength in nanometers, and the vertical axis is the area of ​​the scattering cross section in m 2 / sr -1Raman scattering cross section is a physical quantity used to describe the scattering ability of a substance in the Raman scattering process. It reflects the total intensity or probability of incident light being scattered in all directions per unit area. Figure 6 The schematic diagram of the theoretical Raman scattering cross section intuitively shows the process of Raman scattering after the incident light interacts with matter, which can help understand the inelastic collision between photons and molecules, as well as the change in the frequency of scattered light.

[0127] According to some embodiments of the present invention, the molecular number density of the relative volume concentration of nitrogen is 0.78, and the nuclear spin constant of nitrogen is , the statistical weighting factors for nitrogen include (odd number) = 6 and (even number) = 3 two, Planck constant , the speed of light The rotation constant of the vibrational ground state of nitrogen is 1.9895 cm -1 , the anisotropy constant of the molecular polarization tensor of nitrogen is cm 6 , the anisotropy constant of the molecular polarizability tensor of oxygen is cm 6 , the Boltzmann constant .

[0128] According to some embodiments of the present invention, when a temperature range including a starting temperature and an ending temperature is set and a step size when traversing the temperature is set, the spectral line intensity of the Raman optical frequency comb signal at different temperatures can be theoretically calculated according to formula (4) and formula (5).

[0129] It will be appreciated by those skilled in the art that the features described in the various embodiments and / or claims of the present invention may be combined and / or combined in various ways, even if such combinations and / or combinations are not explicitly described in the present invention. In particular, the features described in the various embodiments and / or claims of the present invention may be combined and / or combined in various ways without departing from the spirit and teachings of the present invention. All of these combinations and / or combinations fall within the scope of the present invention.

[0130] The embodiments of the present invention are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present invention. Although each embodiment is described above, it does not mean that the measures in each embodiment cannot be used in combination. The scope of the present invention is defined by the attached claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A quantum Raman laser radar system, characterized in that: include: A laser, adapted to provide an initial laser beam; a first beam splitter adapted to split the initial laser beam into a first laser beam and a second laser beam; a telescope adapted to emit the first laser beam into a target atmosphere and receive an echo signal generated by the interaction of the target atmosphere and the first laser beam; A Raman optical frequency comb source, adapted to generate a Raman optical frequency comb signal under the action of the second laser beam; An attenuator, adapted to attenuate the optical power of the Raman optical frequency comb signal to a single photon level; A second beam splitter is used to cause quantum interference between the Raman optical frequency comb signal after optical power attenuation and the echo signal; Two single-photon detectors, adapted to respectively detect and obtain single-photon counts outputted from two outlets of the second beam splitter; as well as The computer is adapted to obtain, according to the single photon counting, an interference spectrum diagram of a beat frequency signal generated after quantum interference between the Raman optical frequency comb signal and the echo signal, so as to obtain the temperature and wind speed of the target atmosphere.

2. The quantum Raman laser radar system according to claim 1, characterized in that: The Raman optical frequency comb source comprises: a nitrogen pool, adapted to generate Raman scattered light by causing the second laser beam to react with nitrogen in the nitrogen pool; A grating, adapted to split the Raman scattered light according to wavelength; an electro-optic modulator, adapted to modulate the frequency of the split Raman scattered light; and The acousto-optic modulator is adapted to control the switching time of the Raman scattered light modulated by the electro-optic modulator, so as to control the output of the Raman optical frequency comb signal.

3. The quantum Raman laser radar system according to claim 1, characterized in that: Also includes: A third beam splitter is used to divide the Raman optical frequency comb signal into a first Raman optical frequency comb signal and a second Raman optical frequency comb signal in proportion, and the attenuator is used to attenuate the optical power of the second Raman optical frequency comb signal to a single photon level; as well as The power monitoring component is adapted to monitor the total optical power of the first Raman optical frequency comb signal to ensure the stability of the Raman optical frequency comb signal.

4. The quantum Raman laser radar system according to claim 1, characterized in that: Also includes: The filter is adapted to allow the nitrogen Raman scattering signal in the echo signal to pass through and filter out the broad spectrum solar background noise.

5. A method for inverting wind speed and temperature using the quantum Raman laser radar system according to any one of claims 1 to 4, characterized in that: include: Obtaining a Doppler frequency shift and a signal-to-noise ratio of the beat frequency signal according to an interference spectrum diagram of the beat frequency signal; According to the relationship between the Doppler frequency shift and the wind speed, inverting to obtain the wind speed of the target atmosphere; Inverting the signal-to-noise ratio of the echo signal generated by the target atmosphere and the first laser beam according to the signal-to-noise ratio of the beat frequency signal; as well as Calculating the correlation coefficient between the signal-to-noise ratio of the echo signal and the intensity of the theoretical Raman spectrum line at different temperatures, thereby obtaining the temperature of the target atmosphere; The wind speed and the temperature under different range gates are obtained according to the inversion method, thereby obtaining the temperature of the target atmosphere and the wind speed of the target atmosphere with range resolution.

6. The inversion method of wind speed and temperature according to claim 5, characterized in that: The Doppler shift and the wind speed The relationship satisfies formula (1): （1）； in, is the Doppler shift, is the central wavelength of the Raman spectrum line corresponding to the Doppler shift.

7. The inversion method of wind speed and temperature according to claim 5, characterized in that: The echo signal The signal-to-noise ratio satisfies formula (2): （2）； in, is the signal-to-noise ratio of the beat frequency signal, is the signal-to-noise ratio of the Raman optical frequency comb signal, Indicates Spectrum lines.

8. The inversion method of wind speed and temperature according to claim 5, characterized in that: The signal-to-noise ratio of the echo signal The intensity of the theoretical Raman line Pearson correlation coefficient Satisfies formula (3): （3）； in, Representative Theoretical Raman lines, is the total number of theoretical Raman lines, Indicates the temperature The temperature of the target atmosphere is the correlation coefficient The temperature corresponding to the maximum , is the intensity of the theoretical Raman line when the distance corresponding to the distance gate is z.

9. The inversion method of wind speed and temperature according to claim 8, characterized in that: When the distance corresponding to the range gate is z, The intensity of the theoretical Raman line Satisfies formula (4): （4）； in, is a constant, is the average power of the initial laser beam, is the width of the initial laser beam, is the speed of light, is the receiving area of ​​the telescope, is the molecular number density of nitrogen in the target atmosphere, It is the distance The atmospheric extinction coefficient at is the theoretical Raman line The backscattering cross section of the rotational quantum number J corresponding to the spectral line.

10. The inversion method of wind speed and temperature according to claim 9, characterized in that: The theoretical Raman spectrum Backscattering cross section of the rotational quantum number J corresponding to the spectral line Satisfies formula (5): （5）； in, is the molecular number density relative to the volume concentration; is the nuclear spin constant; is the statistical weight factor; is Planck's constant; is the speed of light; is the rotation constant of the vibration ground state; is the frequency of the initial laser beam; is the frequency shift of the rotational Raman wave number; is the anisotropy constant of the molecular polarization tensor; is the Boltzmann constant.

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