Sodium thermal wind-Rayleigh lidar system based on all-fiber acousto-optic modulation

Abstract

The present invention relates to a sodium temperature wind-Rayleigh laser radar system based on all-fiber acousto-optic modulation, comprising: a semiconductor laser, a first amplifying fiber laser, a first pump laser, a fiber beam splitter, a fiber acousto-optic modulation unit, a fiber beam combiner, a second fiber amplifying laser, a second pump laser, a first frequency doubling module, a second frequency doubling module, a frequency locking module, a hundred millijoules-level pulse pump laser, a pulse dye amplifier, a 532nm reflector driven by a precision translation stage, a beam expansion unit, a transmitting optical path unit, a receiving telescope unit, a subsequent optical path unit, a collection unit and a control unit. The present invention realizes the measurement of atmospheric temperature, wind speed, sodium atom density at an altitude of 80-105km and atmospheric temperature at 30-70km.

Description

Technical Field

[0001] The present invention relates to a laser radar, and in particular to a sodium temperature wind-Rayleigh laser radar system and method based on all-fiber acousto-optic modulation, which is used for atmospheric temperature profiles, wind speed profiles and sodium atom density profiles in the mesosphere top and lower thermosphere regions, and the Rayleigh temperature of atmospheric molecules in the stratosphere to the mesosphere top region. Background Art

[0002] Lidar is an irreplaceable active optical remote sensing method for detecting atmospheric parameter profiles. It uses laser as the system light source and has the characteristics of high temporal and spatial resolution. In recent decades, Lidar has developed rapidly, from the initial atmospheric density Lidar to the current Lidars with various functions, such as temperature Lidar, wind Lidar, atomic density Lidar, carbon dioxide Lidar, trace gas Lidar, etc.

[0003] The middle and upper atmosphere above the troposphere is an active area for various atmospheric fluctuations, such as various types of atmospheric gravity waves, atmospheric tidal waves and planetary waves. These atmospheric fluctuations will affect the energy balance and momentum balance of the atmosphere, thereby driving changes in atmospheric circulation and affecting changes in the space weather environment. To study these issues, it is necessary to extract atmospheric fluctuation information by detecting the vertical distribution profiles of atmospheric elements, so as to further study changes in the space environment and climate change. An effective means of detecting the temperature profiles of the stratosphere and mesosphere is Rayleigh lidar. At present, many Rayleigh lidars have been deployed around the world to detect atmospheric temperature and wind fields, among which Rayleigh temperature lidars are more common, while Rayleigh wind lidars are relatively rare. The detection of atmospheric temperature and wind speed in the mesosphere top and lower thermosphere mainly uses narrow-band sodium temperature wind lidar. Colorado State University and the University of Colorado in the United States have cooperated to first realize the temperature and wind speed measurement of sodium lidar based on dye seed lasers, spatial acousto-optic modulation combined with optical choppers. In China, the University of Science and Technology of China, the Space Science Application Center of the Chinese Academy of Sciences and the Wuhan Institute of Mathematics and Physics have successively developed sodium temperature wind lidars. In these narrowband sodium temperature wind lidar systems, one of the important issues is how to achieve the emission of three-frequency lasers. Acousto-optic modulation is a device that realizes frequency changes. As for the implementation method of acousto-optic modulation frequency hopping and the laser emission method after frequency conversion, there are currently three technical methods: the first is spatial light frequency hopping combined with optical gate trap to achieve three-frequency time-sharing emission, the second is spatial light frequency hopping combined with chopper disk to achieve three-frequency time-sharing emission, and the third is to use optical fiber acousto-optic modulation combined with magneto-optic switch to achieve three-frequency time-sharing emission. The first method uses spatial light coupling and is greatly affected by environmental conditions. Vibration, temperature and airflow will affect the stability of the modulation part. Due to the influence of the action time and oscillation of mechanical parts, the optical gate trap cannot work very fast. It can usually only be opened and closed once every few seconds, and the switching time interval for the three frequencies is relatively large. The third method, fiber-optic acousto-optic modulation combined with magneto-optical switching, is more stable than the first two methods, but the switching speed of the magnetic switch is generally in the millisecond range, which is not suitable for fast switching in situations where the laser pulse frequency is high. In addition, magnetic switches are often used in optical communications. The operating wavelength of conventional products is not suitable for sodium thermal wind lidars. Customization of sodium thermal wind lidars is expensive, and the optical efficiency is not high. In addition, at the lidar system level, the current sodium thermal wind lidars and Rayleigh lidar systems are independently operated, and there is no integrated sodium thermal wind-Rayleigh lidar. Summary of the invention

[0004] The technology of the present invention solves the problem: In order to overcome the shortcomings of the prior art, a sodium temperature wind-Rayleigh lidar system based on all-fiber acousto-optic modulation is provided to measure the atmospheric temperature, wind speed, sodium atom density at an altitude of 80-105km and the atmospheric temperature at 30-70km.

[0005] The system uses a semiconductor laser to output a 1178nm seed laser. The seed laser is divided into two paths through a first-stage optical fiber amplification. One path is used for laser frequency locking after frequency doubling, and the other path is subjected to all-fiber acousto-optic modulation to achieve microsecond or even nanosecond rapid switching of the three frequency lasers required for measuring the sodium layer temperature and wind speed at an altitude of 80-105km. The 532nm pump light source used for the sodium layer temperature and wind speed is used to achieve temperature detection at 30-70km through time-sharing switching, thereby ultimately realizing a sodium temperature wind-Rayleigh lidar system based on all-fiber acousto-optic modulation, which meets the needs of detecting the atmospheric temperature, wind speed and sodium atomic density at an altitude of 80-105km in the top of the mesosphere and the lower thermosphere, as well as the atmospheric temperature in the altitude range of 30-70km, and realizes a single-shot pulse switching laser frequency and a rapid switching wavelength sodium temperature wind lidar-Rayleigh lidar system.

[0006] The invention proposes a sodium warm wind-Rayleigh laser radar system based on all-fiber acousto-optic modulation, comprising: a semiconductor laser, a first amplifying fiber laser, a first pumping laser, a fiber beam splitter, a fiber acousto-optic modulation unit, a fiber combiner, a second fiber amplifying laser, a second pumping laser, a first frequency doubling module, a second frequency doubling module, a frequency locking module, a hundred millijoules-level pulse pumping laser, a pulse dye amplifier, a 532nm reflector driven by a precision translation stage, a beam expansion unit, a transmitting optical path unit, a receiving telescope unit, a subsequent optical path unit, a collection unit and a control unit;

[0007] The semiconductor laser is used to output a continuous seed laser with a narrow line width of 1178nm and a KHz level of tens of mW;

[0008] The first amplifying fiber laser, under the 1120nm laser pumping output by the first pump laser, preliminarily amplifies the power of the 1178nm continuous seed laser output by the semiconductor laser in the fiber working material, and outputs the amplified 1178nm laser;

[0009] The polarization-maintaining fiber beam splitter divides the 1178nm laser light amplified by the first amplifying fiber laser into two paths, one path is 10%-20% of the total power of the 1178nm laser light for laser frequency locking, and the other path is 90%-80% of the total power of the 1178nm laser light for input to the fiber acousto-optic modulation part for frequency conversion;

[0010] The first frequency doubling crystal doubles the 1178nm laser light, which is 10%-20% of the total power, split by the polarization-maintaining fiber beam splitter into a 589nm laser light, and the laser frequency locking unit accurately locks the laser wavelength of the semiconductor laser through the saturated fluorescence spectrum or absorption spectrum of sodium atoms;

[0011] The fiber-optic acousto-optic modulation unit modulates a strong 1178nm laser sequence into 1178nm, 1178nm+315MHz, and 1178nm-315MHz lasers through a fiber-optic acousto-optic modulation device in which light waves and sound waves interact, and the laser pulse width after the sequence is in the millisecond level; the fiber-optic acousto-optic modulation unit specifically includes: a first fiber-optic acousto-optic modulator, a second fiber-optic acousto-optic modulator, a first fiber-optic attenuator, a third fiber-optic acousto-optic modulator, and a second fiber-optic attenuator;

[0012] The first polarization-maintaining fiber acousto-optic modulator realizes the modulation of the frequency of the light wave by the sound wave by applying the radio frequency modulator signal externally; the first polarization-maintaining fiber acousto-optic modulator works in two states, one is the modulation state, and the other is the non-modulation state, with two-way port outputs, the modulation state changes the frequency of the light wave by +315MHz, and outputs at one port; the non-modulation state does not change the frequency of the light wave, and outputs at the other port, and the working state of the first polarization-maintaining fiber acousto-optic modulator is realized by an external TTL electrical frequency controlled acousto-optic driver;

[0013] The second polarization-maintaining fiber acousto-optic modulator also works in two states, one is a modulation state and the other is a non-modulation state. The modulation state changes the frequency of the light wave to -315MHz and outputs at one port; the non-modulation state does not change the frequency of the light wave and outputs at another port. The working state of the second polarization-maintaining fiber acousto-optic modulator is realized by an external TTL electrical frequency-controlled acousto-optic driver.

[0014] The third polarization-maintaining fiber acousto-optic modulator also works in two states, one is a modulation state and the other is a non-modulation state. The modulation state changes the frequency of the light wave to -315MHz and outputs at one port; the non-modulation state does not change the frequency of the light wave and outputs at the other port but is not used. The working state of the third polarization-maintaining fiber acousto-optic modulator is realized by an external TTL electrical frequency-controlled acousto-optic driver.

[0015] The first polarization-maintaining fiber attenuator is connected to the non-modulation port of the second polarization-maintaining fiber acousto-optic modulator, and changes the intensity of the optical power signal by adjustment;

[0016] The second polarization-maintaining fiber attenuator is a manual or electric attenuator connected to the modulation port of the third polarization-maintaining fiber acousto-optic modulator, and changes the optical power signal intensity by manual or voltage adjustment;

[0017] The optical fiber coupler is used to couple the output of the first polarization-maintaining optical fiber attenuator, the output of the second polarization-maintaining optical fiber attenuator and the second polarization-maintaining optical fiber acousto-optic modulator into one output;

[0018] The second amplifying fiber laser preliminarily amplifies the laser powers of 1178nm, 1178nm+315MHz, and 1178nm-315MHz output by the fiber coupler in the fiber working material under the 1120nm laser pumping output by the second pump laser;

[0019] The second frequency doubling crystal is used to frequency-double the amplified 1178nm, 1178nm+315MHz, 1178nm-315MHz lasers into 589.158nm, 589.158nm+630MHz, 589.158nm-630MHz lasers, and the frequency-doubled 589.158nm and its three flanking frequency lasers are input as seed lasers into the pulse dye amplifier;

[0020] The pulse dye amplifier amplifies the millisecond-level wide pulse 589.158nm and three-frequency seed lasers on its flanks outputted by the second frequency-doubling crystal into a 10 nanosecond-level pulse 589.158.158nm and three-frequency narrow pulse lasers on its flanks with a peak power of megawatts under the pumping of a 532nm laser outputted by a hundred-millijoule-level pulse pump laser;

[0021] The 532nm reflector driven by the precision translation stage is arranged on the optical path of the pump pulse dye amplifier. When the sodium temperature wind detection is performed, the 532nm reflector is quickly moved away so that the pulse pump laser of the hundred millijoules level pumps the pulse dye amplifier; when the Rayleigh temperature detection is performed, the 532nm reflector is quickly moved to the optical path and turned at a 45-degree angle to the 532nm emission optical path;

[0022] The laser beam expander adopts a Galilean structure to change the laser divergence angle of the laser radar so that the laser divergence angle meets the field of view angle requirement of the receiving telescope. A laser beam expander is set at 532nm and 589nm respectively.

[0023] The emission optical path unit comprises an optical path turning reflector and an emission reflector driven by a motor, and is used to emit three laser beams of frequencies around 589.158 nm and 532 nm laser beam expanded by the laser beam expander into the atmosphere;

[0024] The receiving telescope unit is used to receive backscattered echo signals after the interaction between the laser and the atmosphere, wherein the backscattered echo signals include Rayleigh scattering signals and resonant sodium fluorescence backscattering signals;

[0025] The subsequent optical path unit extracts effective echo signals from the echo signals received by the receiving telescope and converts them into electrical signals for collection by the collection device; the 532nm and 589nm echo signals are detected independently through two paths respectively; the subsequent optical path unit includes a chopper disc, a collimating lens, a 532nm filter, a 589nm filter, a converging lens and a photomultiplier tube;

[0026] The acquisition unit collects and records the electrical signals as digital echo signals and stores them on a storage hard disk of an acquisition computer, and obtains temperature, wind speed and sodium atom density by analyzing and processing the collected echo signals;

[0027] The control unit includes a working timing control part and a component action control part. The working timing control part is used to coordinate the pump laser, the acousto-optic modulation unit, the laser frequency locking unit, the pulse dye amplifier, the emission coupling unit and the acquisition device in the sodium warm wind-Rayleigh laser radar system to work in sequence; the component action control part is used to control the light beam emitting antenna in the emission coupling optical path.

[0028] Compared with the prior art, the advantages of the present invention are as follows: the present invention adopts all-fiber acousto-optic modulation combined with a fiber attenuator to realize the fiber acousto-optic modulation unit of the laser radar system, generates three-frequency seed lasers required by the system, greatly improves the switching speed of the three frequencies, and the switching time can reach nanoseconds, which can meet the needs of detecting small-scale atmospheric fluctuations in the top of the mesosphere and the lower thermosphere; in addition, the fiber coupling method can greatly improve the stability of the system, make the system more compact, reduce the system volume, and reduce the system weight; combined with the attenuator, the laser emission power of the three frequencies can be basically consistent, reducing the system detection error caused by the different powers of the three frequencies; using a precision translation stage to drive the 532nm reflector to change the optical path, a pulsed 532nm laser can be used to complete the two functions of pumping dye amplifier and Rayleigh temperature detection, greatly reducing the system cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0030] Figure 1 This is the schematic diagram of the sodium warm wind-Rayleigh lidar system based on all-fiber acousto-optic modulation;

[0031] Wherein: semiconductor laser 1, first amplifying fiber laser 2, first pump laser 3, fiber beam splitter 4, fiber acousto-optic modulation unit 5, fiber combiner 6, second fiber amplifying laser 7, second pump laser 8, first frequency doubling module 9, second frequency doubling module 10, frequency locking module 11, 100 mJ level pulsed 532 nm laser 12, pulse dye amplifier 13, 532 nm reflector driven by high stability translation stage 14, beam expansion unit 15, transmitting optical path unit 16, receiving telescope unit 17, subsequent optical path unit 18, acquisition processing unit 19, control unit 20, motor driver 21.

[0032] Figure 2 This is a diagram of the internal composition of the fiber optic acousto-optic modulation unit;

[0033] Among them: a first fiber acousto-optic modulator 101, a second fiber acousto-optic modulator 102, a first fiber attenuator 103, a third fiber acousto-optic modulator 104, and a second fiber attenuator 105.

[0034] Figure 3 It is the timing control diagram of the fiber optic acousto-optic modulation unit;

[0035] Wherein: 201 is a TTL level control signal of a controller provided to the first polarization-maintaining fiber acousto-optic modulator 101, and 202 is a radio frequency control signal outputted by the controller to the acousto-optic device of the first polarization-maintaining fiber acousto-optic modulator 101; similarly, 203 and 204 are respectively a TTL level control signal of a controller provided to the second polarization-maintaining fiber acousto-optic modulator 102 and a radio frequency signal outputted by the controller to the acousto-optic device; 205 and 206 are respectively a TTL level control signal of a controller provided to the second polarization-maintaining fiber acousto-optic modulator 104 and a radio frequency signal outputted by the controller to the acousto-optic device. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] like Figure 1As shown, a sodium warm wind-Rayleigh laser radar system based on all-fiber acousto-optic modulation of the present invention is used to detect the atmospheric temperature, wind speed and sodium atomic density at an altitude of 80-105 km in the mesosphere top-lower thermosphere region. The sodium warm wind-Rayleigh laser radar system based on all-fiber acousto-optic modulation comprises: a semiconductor laser 1, a first amplifying fiber laser 2, a first pumping laser 3, a fiber beam splitter 4, a fiber acousto-optic modulation unit 5, a fiber combiner 6, a second fiber amplifying laser 7, a second pumping laser 8, a first frequency doubling module 9, a second frequency doubling module 10, a frequency locking module 11, a 100-millijoule pulse 532nm laser 12, a pulse dye amplifier 13, a 532nm reflector 14 driven by a high-stability translation stage, a beam expansion unit 15, a transmitting optical path unit 16, a receiving telescope unit 17, a subsequent optical path unit 18, a collection and processing unit 19, a control unit 20, and a motor driver 21.

[0038] The semiconductor laser 1 is used to output a continuous seed laser with a narrow line width of 1178nm and a frequency bandwidth of the order of KHz with a power of tens of mW. The wavelength can be precisely adjusted by adjusting the internal grating and changing the diode voltage and temperature. The final operating wavelength is around 1178.316nm, and the laser output is output through fiber coupling.

[0039] The first amplifying fiber laser 2 preliminarily amplifies the power of the 1178nm seed laser output by the semiconductor laser in the fiber working material under the 1120nm continuous laser pumping output by the first pump laser 3.

[0040] The polarization-maintaining fiber beam splitter 4 divides the 1178 nm laser amplified by the first amplifying fiber laser 2 into two paths with a fraction ratio of 10 / 90, 10% for laser frequency locking and 90% for input to the fiber acousto-optic modulation part for frequency conversion.

[0041] The second frequency doubling module 10 usually adopts a periodically poled lithium niobate PPLN crystal to frequency double the 10% 1178nm laser separated by the polarization-maintaining fiber beam splitter 4 into a 589nm laser. The 589nm laser after frequency doubling is less than 1mW. The laser frequency locking module 11 obtains an error signal by multiplying the saturated fluorescence spectrum or absorption spectrum of the sodium atom with the modulated sine wave or triangle wave signal, and feeds it back to the controller matched with the semiconductor laser 1, thereby adjusting the laser wavelength output by the semiconductor laser 1, so that the laser wavelength after frequency doubling is locked at the D2a peak of the sodium atom saturation spectrum of 589.158nm, corresponding to the precise laser wavelength of the semiconductor laser 1 of 1178.316nm.

[0042] The fiber acousto-optic modulation unit 5 modulates the 1178nm laser sequence into 1178nm, 1178nm+315MHz, and 1178nm-315MHz lasers through the interaction of light waves and sound waves.

[0043] like Figure 2 As shown, the fiber optic acousto-optic modulation unit 5 specifically includes: a first fiber optic acousto-optic modulator 101, a second fiber optic acousto-optic modulator 102, a first fiber optic attenuator 103, a third fiber optic acousto-optic modulator 104, and a second fiber optic attenuator 105.

[0044] The first polarization-maintaining fiber acousto-optic modulator 101 realizes the modulation of the frequency of the light wave by the sound wave by the external RF modulator signal. It works in two states, one is the modulation state and the other is the non-modulation state, and the two states are output by two ports respectively. The modulation state changes the frequency of the light wave to +315MHz, and the first port is fiber-coupled output; the non-modulation state does not change the frequency of the light wave, and the second port is fiber-coupled output. The RF signal output state of the RF modulator is realized by external TTL level control. When the TTL level is high, the laser frequency is modulated to +315MHz, and when the TTL level is low, the laser frequency is not modulated. The first port outputs to the second polarization-maintaining fiber acousto-optic modulator 102; the second port outputs to the third polarization-maintaining fiber acousto-optic modulator 104.

[0045] The second polarization-maintaining fiber acousto-optic modulator 102 is similar to the first polarization-maintaining fiber acousto-optic modulator 101, and also works in two states, one is the modulation state and the other is the non-modulation state. Different from the first polarization-maintaining fiber acousto-optic modulator 101, the modulation state changes the frequency of the light wave to -315MHz, and the first port is fiber-coupled output; the non-modulation state does not change the frequency of the light wave, and the second port is fiber-coupled output. The RF signal output state of the RF modulator is realized by external TTL level control. When the TTL level is high, the laser frequency is modulated to -315MHz, and when the TTL level is low, the laser frequency is not modulated. The first port outputs to the fiber combiner 6; the second port outputs to the first polarization-maintaining fiber attenuator 103.

[0046] The third polarization-maintaining fiber acousto-optic modulator 104 also works in two states, one is a modulation state and the other is a non-modulation state. The modulation state changes the light wave frequency to -315MHz, and the first port is fiber-coupled for output; the non-modulation state does not change the light wave frequency, and the second port is fiber-coupled for output, which is not used in the present invention. Its working state is also realized by an external TTL level. The first port outputs to the second polarization-maintaining fiber attenuator 105.

[0047] The first polarization-maintaining fiber attenuator 103 can be a manual or electric attenuator, which is connected to the second port of the second polarization-maintaining fiber acousto-optic modulator 102, and changes the optical power signal intensity by manual or voltage adjustment, so that the signal intensity is close to the first port output of the second polarization-maintaining fiber acousto-optic modulator 102.

[0048] The second polarization-maintaining fiber attenuator 105 can be a manual or electric attenuator, which is connected to the first port of the third polarization-maintaining fiber acousto-optic modulator 104, and changes the optical power signal intensity to be close to the first port output of the second polarization-maintaining fiber acousto-optic modulator 102 through manual or voltage adjustment.

[0049] Figure 3 201 is a working timing diagram of the fiber AOM unit 5, 202 is a TTL level control signal of the controller of the first polarization-maintaining fiber AOM 101, 203 is a radio frequency control signal of the controller output to the acousto-optic device of the first polarization-maintaining fiber AOM 101; similarly, 203 and 204 are respectively a TTL level control signal of the controller of the second polarization-maintaining fiber AOM 102 and a radio frequency signal of the controller output to the acousto-optic device; 205 and 206 are respectively a TTL level control signal of the controller of the third polarization-maintaining fiber AOM 104 and a radio frequency signal of the controller output to the acousto-optic device. Table 1 shows the working status of the AOM unit 5. The first state is when the first polarization-maintaining fiber AOM 101 modulates the frequency +315MHz, the second polarization-maintaining fiber AOM 102 modulates the frequency -315MHz, and the third polarization-maintaining fiber AOM 104 does not modulate the frequency, and the final output of the fiber combiner 6 is f0 (f0 is the frequency corresponding to the 1178nm laser wavelength). The second state is when the first polarization-maintaining fiber AOM 101 modulates the frequency +315MHz, the second polarization-maintaining fiber AOM 102 does not modulate the frequency, and the third polarization-maintaining fiber AOM 104 does not modulate the frequency, and the final output of the fiber combiner 6 is f0+315MHz. The third state is when the first polarization-maintaining fiber AOM 101 does not modulate the frequency, the second polarization-maintaining fiber AOM 102 does not modulate the frequency, and the third polarization-maintaining fiber AOM 104 modulates the frequency -315MHz, and the final output of the fiber combiner 6 is f0-315MHz.

[0050] Table 1 Working status of the acousto-optic modulation unit 5

[0051]

[0052] The fiber combiner 6 is used to couple the output of the first polarization-maintaining fiber attenuator 103, the output of the second polarization-maintaining fiber attenuator 105 and the first output of the second polarization-maintaining fiber acousto-optic modulator 102 into one output and ensure that the polarization state remains unchanged.

[0053] The second amplifying fiber laser 7, under the 1120nm laser pumping output by the second pump laser 8, further amplifies the laser power of the three frequency lasers 1178nm, 1178nm+315MHz, and 1178nm-315MHz output by the fiber combiner in the fiber working material.

[0054] The first frequency doubling module 9 is used to frequency double the 1178nm, 1178nm+315MHz, 1178nm-315MHz lasers amplified by the second amplifying fiber laser 7 to 589.158nm, 589.158nm+630MHz, 589.158nm-630MHz lasers. The frequency-doubled 589.158nm and its three flanking frequency lasers are input as seed lasers to the pulse dye amplifier 13.

[0055] The pulse dye amplifier 13, through three-stage dye amplification, amplifies the millisecond-level wide pulse 589.158nm and the three-frequency seed lasers on its two sides output by the first frequency-doubling crystal, under the pumping of the high-power pulse 532nm laser 12, into a 10 nanosecond pulse 589.158.158nm with a very high peak power and the three-frequency narrow pulse lasers on its two sides.

[0056] The 532nm reflector 14 driven by the precision translation stage is set at an angle of 45 degrees on the optical path of the pulse dye amplifier 13 pumped by the pulse 532nm laser of the hundred millijoules level. When sodium temperature wind detection is performed, the 532nm reflector is quickly moved away to allow the high-power pulse 532nm laser to pump the pulse dye amplifier; when Rayleigh temperature detection is performed, the 532nm reflector is quickly moved to the optical path and turned to the 532nm beam expansion unit at a 45-degree angle.

[0057] The beam expansion unit 15 adopts a Galilean structure, composed of a negative lens and a positive lens, and is used to change the divergence angle of the 532nm and 589nm emission lasers so that their divergence angles meet the field of view requirements of the receiving telescope. It includes two laser beam expanders, 532nm and 589nm. The beam expansion ratio of the 532nm laser beam expander can be 5-8 times, and the beam expansion ratio of the 589nm laser beam expander can be 2-5 times.

[0058] The emission optical path unit 16 includes an optical path turning reflector and an emission reflector with a motor drive, which is used to emit three laser beams with frequencies around 589.158nm and 532nm laser beams after the laser beam expander is expanded into the atmosphere. The motor driver 21 controls the emission reflector with a motor drive to change the direction of the laser beam in the zenith angle and azimuth angle, and the laser beam can be scanned through program control so that the echo signal is optimally received by the telescope.

[0059] The receiving telescope unit 17 is used to receive the backscattered echo signal after the interaction between the laser and the atmosphere. The backscattered echo signal of the sodium warm wind-Rayleigh laser radar system contains the resonance of the Rayleigh scattering signal and the fluorescence backscattering signal. When performing high-altitude detection of the sodium warm wind-Rayleigh laser radar system, the receiving telescope type usually adopts a reflective telescope, which can be a Newtonian type and a Cassegrain type, and the received echo signal is transmitted by optical fiber coupling. Three telescopes are set, namely the first telescope, the second telescope and the third telescope, and the telescope pointing can be adjusted. The first telescope points to the east, with a zenith angle of 20° or 30°; the second telescope points vertically to the zenith angle; the third telescope points to the south, with a zenith angle of 20° or 30°. The first telescope is provided with an optical fiber at the center of the focal plane for transmitting a 589nm echo signal; the focal plane of the second telescope is provided with two optical fibers, one is provided at the center position for transmitting a 589nm Rayleigh scattering signal, and the other is provided next to it for transmitting a 532nm echo signal. For detection in more directions, more telescopes can be set to receive echo signals.

[0060] The subsequent optical path unit 18 is used to extract the effective echo signal from the echo signal received by the receiving telescope and convert it into an electrical signal for collection by the collection device. There are four independent detections, one for the 532nm echo signal and three for the 589nm echo signal. Each optical fiber output first passes through a chopper disc, and then is collimated by its own collimating lens. After the background noise light is filtered out by the filters set on each channel, it is converged by a converging lens to a photomultiplier tube for detection. The center wavelength of each filter is determined by the wavelength of detection, that is, the center wavelength of the 532nm channel filter is 532nm, and the center wavelength of the 589nm channel filter is 589nm.

[0061] The acquisition processing unit 19 includes a signal acquisition device, a computer and a data processing and analysis part. The acquisition device is used to collect and record the electrical signal as a digital echo signal. The sodium temperature wind-Rayleigh laser radar system uses a photon counting card, which is connected to the computer through a common interface such as a USB interface or a PCI interface; the computer is used to record the echo signal and store it on an internal hard disk medium; the data processing and analysis part analyzes and processes the collected echo signal to invert the temperature, wind speed and sodium atomic density.

[0062] The control unit 20 includes a system operation timing control part, a system component motion control part, and an environment control part. The system operation timing control part is used to coordinate the various components in the system, and coordinate the pump laser, the acousto-optic modulation unit, the laser frequency locking unit, the pulse dye amplifier, the emission optical path unit, and the acquisition device in the sodium temperature wind-Rayleigh laser radar system to work in sequence; the system component motion control part is used to control the closed-loop control of the light beam emission antenna and the laser wavelength in the emission coupling optical path; the environment control part is used to control the temperature environment, humidity environment, etc. of the laser radar system.

[0063] The above embodiments are provided only for the purpose of describing the present invention, and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. Various equivalent substitutions and modifications made without departing from the spirit and principles of the present invention should all be included within the scope of the present invention.

Claims

1. A sodium warm wind-Rayleigh lidar system based on all-fiber acousto-optic modulation, characterized in that: include: Semiconductor laser, first amplifying fiber laser, first pump laser, fiber beam splitter, fiber acousto-optic modulation unit, fiber combiner, second fiber amplifying laser, second pump laser, first frequency doubling module, second frequency doubling module, frequency locking module, hundred millijoules level pulse pump laser, pulse dye amplifier, 532nm reflector driven by precision translation stage, beam expansion unit, transmitting optical path unit, receiving telescope unit, subsequent optical path unit, acquisition unit and control unit; The semiconductor laser is used to output a continuous seed laser with a narrow line width of 1178nm and a KHz level of tens of mW; The first amplifying fiber laser, under the 1120nm laser pumping output by the first pump laser, preliminarily amplifies the power of the 1178nm continuous seed laser output by the semiconductor laser in the fiber working material, and outputs the amplified 1178nm laser; The fiber beam splitter divides the 1178nm laser light amplified by the first amplifying fiber laser into two paths, one path is 10%-20% of the total power of the 1178nm laser light for laser frequency locking, and the other path is 90%-80% of the total power of the 1178nm laser light for input to the fiber acousto-optic modulation part for frequency conversion; The first frequency doubling module doubles the 1178nm laser light split by the optical fiber beam splitter, which is 10%-20% of the total power, into a 589nm laser light, and the laser frequency locking unit accurately locks the laser wavelength of the semiconductor laser through the saturated fluorescence spectrum or absorption spectrum of sodium atoms; The fiber-optic acousto-optic modulation unit modulates a strong 1178nm laser sequence into 1178nm, 1178nm+315MHz, and 1178nm-315MHz lasers through a fiber-optic acousto-optic modulation device in which light waves and sound waves interact, and the laser pulse width after the sequence is in the millisecond level; the fiber-optic acousto-optic modulation unit specifically includes: a first fiber-optic acousto-optic modulator, a second fiber-optic acousto-optic modulator, a first fiber-optic attenuator, a third fiber-optic acousto-optic modulator, and a second fiber-optic attenuator; The first fiber optic acousto-optic modulator realizes the modulation of the frequency of the light wave by the sound wave by applying the radio frequency modulator signal externally; the first fiber optic acousto-optic modulator works in two states, one is the modulation state, and the other is the non-modulation state, with two-way port output, the modulation state changes the frequency of the light wave by +315MHz, and outputs at one port; the non-modulation state does not change the frequency of the light wave, and outputs at the other port, and the working state of the first fiber optic acousto-optic modulator is realized by controlling the acousto-optic driver through an external TTL electrical frequency; The second fiber optic acousto-optic modulator also works in two states, one is a modulation state and the other is a non-modulation state. The modulation state changes the frequency of the light wave to -315MHz and outputs at one port; the non-modulation state does not change the frequency of the light wave and outputs at another port. The working state of the second fiber optic acousto-optic modulator is realized by an external TTL electrical frequency controlled acousto-optic driver. The third fiber optic acousto-optic modulator also works in two states, one is a modulation state and the other is a non-modulation state. The modulation state changes the light wave frequency to -315MHz and outputs at one port; the non-modulation state does not change the light wave frequency and outputs at the other port but is not used. The working state of the third fiber optic acousto-optic modulator is realized by controlling the acousto-optic driver through an external TTL electrical frequency. The first optical fiber attenuator is connected to the non-modulation port of the second optical fiber acousto-optic modulator, and changes the intensity of the optical power signal by adjustment; The second optical fiber attenuator is a manual or electric attenuator connected to the modulation port of the third optical fiber acousto-optic modulator, and changes the optical power signal intensity by manual or voltage adjustment; The optical fiber combiner is used to couple the output of the first optical fiber attenuator, the output of the second optical fiber attenuator and the second optical fiber acousto-optic modulator into one output; The second fiber amplifier laser preliminarily amplifies the laser powers of 1178nm, 1178nm+315MHz, and 1178nm-315MHz output by the fiber coupler in the fiber working material under the 1120nm laser pumping output by the second pump laser; The second frequency doubling module is used to frequency-double the amplified 1178nm, 1178nm+315MHz, 1178nm-315MHz lasers into 589.158nm, 589.158nm+630MHz, 589.158nm-630MHz lasers, and the frequency-doubled 589.158nm and its three flanking frequency lasers are input as seed lasers into the pulse dye amplifier; The pulse dye amplifier amplifies the millisecond-level wide pulse 589.158nm and three-frequency seed lasers on its flanks outputted by the second frequency doubling module into a 10 nanosecond-level pulse 589.158.158nm and three-frequency narrow pulse lasers on its flanks with a peak power of megawatts under the pumping of a 532nm laser outputted by a hundred-millijoule-level pulse pump laser; The 532nm reflector driven by the precision translation stage is arranged on the optical path of the pulse dye amplifier. When performing sodium temperature wind detection, the 532nm reflector is quickly moved away to allow the pulse dye amplifier to be pumped by a pulse pump laser of the hundred millijoules level. When performing Rayleigh temperature detection, the 532nm reflector is quickly moved to the optical path and turned at a 45-degree angle to the 532nm emission optical path. The beam expansion unit adopts a Galilean structure to change the laser divergence angle of the laser radar so that the laser divergence angle meets the field of view angle requirement of the receiving telescope, and a laser beam expander is set at 532nm and 589nm respectively; The emission optical path unit comprises an optical path turning reflector and an emission reflector driven by a motor, and is used to emit three laser beams of frequencies around 589.158 nm and 532 nm laser beam expanded by the laser beam expander into the atmosphere; The receiving telescope unit is used to receive backscattered echo signals after the interaction between the laser and the atmosphere, wherein the backscattered echo signals include Rayleigh scattering signals and resonant sodium fluorescence backscattering signals; The subsequent optical path unit extracts effective echo signals from the echo signals received by the receiving telescope and converts them into electrical signals for collection by the collection device; the 532nm and 589nm echo signals are detected independently through two paths respectively; the subsequent optical path unit includes a chopper disc, a collimating lens, a 532nm filter, a 589nm filter, a converging lens and a photomultiplier tube; The acquisition unit collects and records the electrical signals as echo signals and stores them on the hard disk of the acquisition computer, and obtains the temperature, wind speed and sodium atom density by analyzing and processing the collected echo signals; The control unit includes a working timing control part and a component action control part. The working timing control part is used to coordinate the pump laser, the acousto-optic modulation unit, the laser frequency locking unit, the pulse dye amplifier, the emission coupling unit and the acquisition device in the sodium warm wind-Rayleigh laser radar system to work in sequence; the component action control part is used to control the light beam emitting antenna in the emission coupling optical path.

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