CN110187362B - Ultraviolet and infrared synchronous working dual-frequency wind lidar - Google Patents
Ultraviolet and infrared synchronous working dual-frequency wind lidar Download PDFInfo
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- CN110187362B CN110187362B CN201910444225.9A CN201910444225A CN110187362B CN 110187362 B CN110187362 B CN 110187362B CN 201910444225 A CN201910444225 A CN 201910444225A CN 110187362 B CN110187362 B CN 110187362B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
- G01P5/26—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the direct influence of the streaming fluid on the properties of a detecting optical wave
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/88—Lidar systems specially adapted for specific applications
- G01S17/95—Lidar systems specially adapted for specific applications for meteorological use
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/481—Constructional features, e.g. arrangements of optical elements
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/481—Constructional features, e.g. arrangements of optical elements
- G01S7/4814—Constructional features, e.g. arrangements of optical elements of transmitters alone
- G01S7/4815—Constructional features, e.g. arrangements of optical elements of transmitters alone using multiple transmitters
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- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
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Abstract
The invention provides a dual-frequency wind measuring laser radar with ultraviolet and infrared synchronous working, which respectively locks the frequency of emergent laser at the rising edge and the falling edge of a transmittance curve of an F-P interferometer by combining time division multiplexing and wavelength division multiplexing technologies to form double edges for frequency discrimination. The ultraviolet laser and the near-infrared laser are emitted by the same laser, and the periodic structure of the F-P interferometer is utilized, so that the lasers with the two wavelengths can be used for atmospheric wind field detection, wherein the ultraviolet laser is used for detecting Rayleigh scattering signals of atmospheric molecules, and the infrared laser is used for detecting the meter scattering signals of atmospheric aerosol. The system scheme provided by the invention simplifies the receiving light path and improves the wind field detection capability of the wind lidar.
Description
Technical Field
The invention relates to a laser radar, in particular to a double-frequency wind measuring laser radar capable of synchronously working by ultraviolet and infrared.
Background
The wind measurement laser radar has great significance for improving the accuracy of long-term weather forecast, improving a climate research model, improving military environment forecast and the like. Therefore, the measurement of the atmospheric wind field is receiving more and more attention, and the research and development of the wind field detection system are actively carried out by the international civil aviation organization, the world meteorological organization, the research organizations of aerospace of all countries in the world, and other organizations.
The doppler wind lidar can be classified into coherent detection and direct detection according to different detection principles. Coherent detection detects the wind speed in a mode that laser atmosphere echo signals are coherent with local oscillator laser. Direct detection utilizes a frequency discriminator to convert Doppler shift information into relative change of energy so as to detect the atmospheric wind speed. In the direct detection wind-measuring laser radar based on the edge technology, the F-P interferometer has the advantages of steep edge, high speed and sensitivity, optimized setting aiming at different detection targets and working wavelengths and the like, and is the most widely applied frequency discriminator in the direct detection wind-measuring laser radar.
At present, two independent wind lidar units are used for detecting the wind speeds of different heights of the atmosphere based on different measuring wavelengths, and the wind lidar units comprise a laser light source, a laser transmitting system, a laser receiving system, a frequency discriminator, a detector and the like, so that the wind lidar units are expensive in manufacturing cost and large in size. How to simultaneously measure wind speeds at different heights by using a single laser radar to reduce the cost is an urgent problem to be solved.
Disclosure of Invention
Technical problem to be solved
In view of the above problems, the present invention provides a wind lidar based on a dual-frequency laser and a dual-channel F-P interferometer cavity, which can simultaneously realize detection of wind speeds at different heights, so as to solve the cost problem of using multiple wind lidar.
(II) technical scheme
The invention provides a double-frequency wind lidar with ultraviolet and infrared synchronous working, which comprises:
the seed laser module is used for outputting seed laser with a first wavelength; the first wavelength is a near-infrared band;
the first acousto-optic frequency shifter is used for shifting the frequency of the seed laser and outputting the 1 st laser; the center frequency of the 1 st laser is less than that of the seed laser;
the first frequency doubling module is used for carrying out frequency doubling and frequency tripling on the input 1 st laser and outputting first frequency doubled laser, wherein the first frequency doubled laser comprises the 1 st laser, the 1 st frequency doubled laser and the 1 st frequency tripled laser;
the second acousto-optic frequency shifter is used for shifting the frequency of the seed laser and outputting 2 nd laser; the center frequency of the 2 nd laser is greater than that of the seed laser;
the second frequency doubling module is used for carrying out frequency doubling and frequency tripling on the input 2 nd laser and outputting second frequency doubled laser, wherein the second frequency doubled laser comprises the 2 nd laser, the 2 nd frequency doubled laser and the 2 nd frequency tripled laser;
the 1 st frequency-third laser and the 2 nd frequency-third laser are ultraviolet bands;
the laser output by the first frequency doubling module is divided into two beams, one beam is used as signal light, and the other beam is used as reference light; the laser output by the second frequency doubling module is also divided into two beams, one beam is used as signal light, and the other beam is used as reference light;
the beam expanding system is used for expanding signal light in the first frequency doubling laser and the second frequency doubling laser and outputting the expanded signal light to the atmosphere;
the receiving telescope is used for receiving the atmosphere echo signal;
the color separation mirror is used for receiving the atmosphere echo signal and the reference light and separating the received signal into a first wavelength laser and a second wavelength laser to be output respectively;
the first wavelength laser is input to a first F-P interferometer, and the second wavelength laser is input to a second F-P interferometer;
the detection module is used for detecting signals output by the first F-P interferometer and the second F-P interferometer;
the data acquisition and processing module is used for acquiring and analyzing the signals output by the detection module;
the center frequencies of the 1 st laser and the 2 nd laser are respectively positioned on the rising edge and the falling edge of the transmittance curve of the adjacent interference level in the transmittance curve of the first F-P interferometer; the transmittance curve of the first F-P interferometer is the corresponding relation between the transmittance of the first F-P interferometer and the incident light frequency;
the center frequencies of the 1 st frequency-tripling laser and the 2 nd frequency-tripling laser are respectively positioned on the rising edge and the falling edge of the transmittance curve of the adjacent interference level in the transmittance curve of the second F-P interferometer; and the transmittance curve of the second F-P interferometer is the corresponding relation between the transmittance of the second F-P interferometer and the incident light frequency.
The optical fiber switch further comprises a time division reflection transmission switch, wherein the time division reflection transmission switch comprises a rotating mirror and a rotation control assembly, the rotating mirror is provided with a transmission area and a reflection area, the transmission area is used for transmitting incident optical signals, and the reflection area is used for reflecting the incident optical signals;
the first frequency doubling laser and the second frequency doubling laser are respectively incident to the transmission area and the reflection area of the rotating mirror;
the beam expanding system comprises a first beam expanding lens;
the rotation control assembly is used for controlling the rotation of the rotating mirror so that the laser emitted by the first frequency doubling module and the laser output by the second frequency doubling module are alternately output to the first beam expanding mirror.
Alternatively, the beam expanding system includes a second beam expanding lens and a third beam expanding lens, where the second beam expanding lens is configured to output the first frequency-doubled laser light to the atmosphere, and the third beam expanding lens is configured to output the second frequency-doubled laser light to the atmosphere.
Further, the center frequencies of the 1 st laser and the 2 nd laser are respectively positioned at the half waist of the transmittance curve of the adjacent interference level in the transmittance curve of the first F-P interferometer; and the center frequencies of the 1 st frequency-tripling laser and the 2 nd frequency-tripling laser are respectively positioned on the rising edge and the falling edge of the transmittance curve of the adjacent interference level in the transmittance curve of the second F-P interferometer.
Furthermore, the second F-P interferometer includes a temperature adjusting unit or an air pressure adjusting unit, and the 1 st frequency-tripled laser and the 2 nd frequency-tripled laser are respectively located on the rising edge and the falling edge of the transmittance curve of the adjacent interference level in the transmittance curve of the second F-P interferometer by adjusting the temperature adjusting unit or the air pressure adjusting unit.
Further, the first F-P interferometer comprises a temperature adjusting unit or an air pressure adjusting unit, and the 1 st laser and the 2 nd laser are respectively positioned on the rising edge and the falling edge of the transmittance curve of the adjacent interference level in the transmittance curve of the first F-P interferometer by adjusting the temperature adjusting unit or the air pressure adjusting unit.
Further, the center frequency of the 1 st laser is larger than that of the seed laser by a first frequency interval; the center frequency of the 2 nd laser is smaller than the center frequency of the seed laser by a second frequency interval.
(III) advantageous effects
According to the technical scheme, the invention has the following beneficial effects:
the invention discloses a double-frequency wind measuring laser radar with ultraviolet and infrared synchronous working, which adopts a push-pull acousto-optic modulation mode to generate two pulse signals which are symmetrically distributed relative to an F-P interferometer; adjusting the absolute frequency of the seed light to enable the 1 st laser and the 2 nd laser to be respectively positioned at the half waist of the adjacent interference level transmittance of the first F-P interferometer; and by adjusting the air pressure adjusting unit/the temperature adjusting unit of the second F-P interferometer, the frequency tripling laser corresponding to the 1 st laser and the 2 nd laser is also positioned at the rising edge and the falling edge of the adjacent transmittance of the second F-P interferometer. By adopting the system, the laser outputs laser with two wavelengths simultaneously, and the wind speed of the atmosphere at the lower layer and the atmosphere at the upper layer is measured simultaneously by using a single laser radar at low cost.
The invention combines time division multiplexing and wavelength division multiplexing technologies, respectively locks the frequency of the emitted laser at the rising edge and the falling edge of the F-P interferometer, and forms double edges for frequency discrimination. The ultraviolet laser and the near-infrared laser are emitted by the same laser, and the periodic structure of the F-P interferometer is utilized, so that the lasers with the two wavelengths can be used for atmospheric wind field detection, wherein the ultraviolet laser (355nm) is used for detecting Rayleigh scattering signals of atmospheric molecules, and the infrared laser (1064nm) is used for detecting the meter scattering signals of atmospheric aerosol. The system scheme provided by the invention simplifies the receiving light path and improves the wind field detection capability of the wind lidar.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions and advantages of the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a block diagram of a dual-frequency wind lidar capable of synchronously operating ultraviolet and infrared according to an embodiment of the present invention;
fig. 2 is a block diagram of another structure of a dual-frequency wind lidar capable of synchronously operating in ultraviolet and infrared according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a rotating mirror of a dual-frequency wind lidar for ultraviolet and infrared synchronous operation according to an embodiment of the present invention;
FIG. 4a is a graph of the transmittance of 1064 nmFPI;
FIG. 4b is a graph showing the light intensity of the 1064nm signal, i.e., the 1 st laser;
FIG. 4c is a schematic diagram of the emitted 1 st and 2 nd laser beams;
FIG. 4d is a schematic spectrum of a 355nm laser-excited Rayleigh scattering signal;
FIG. 4e is a graph of 355nmFPI transmittance.
[ notation ] to show
31-a reflective region; 32-transmissive region.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings. It should be noted that in the drawings or description, the same drawing reference numerals are used for similar or identical parts. Implementations not depicted or described in the drawings are of a form known to those of ordinary skill in the art. Additionally, while exemplifications of parameters including particular values may be provided herein, it is to be understood that the parameters need not be exactly equal to the respective values, but may be approximated to the respective values within acceptable error margins or design constraints. Directional phrases used in the embodiments, such as "upper," "lower," "front," "rear," "left," "right," and the like, refer only to the orientation of the figure. Accordingly, the directional terminology used is intended to be in the nature of words of description rather than of limitation.
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
As shown in fig. 1, an embodiment of the present invention provides a dual-frequency wind lidar capable of synchronously operating in ultraviolet and infrared, including:
and the seed laser module is used for outputting seed laser with a first wavelength.
And the beam splitter divides the seed laser into two beams.
The first acousto-optic frequency shifter is used for shifting the frequency of the first beam of seed laser to output the 1 st laser; the center frequency of the 1 st laser is smaller than that of the seed laser.
An Acousto-optic frequency shifter, AOFS (acoustto-optical frequency shifts), is capable of shifting the frequency of an input laser optical signal.
The first frequency doubling module is used for carrying out frequency doubling and frequency tripling on the input 1 st laser and outputting first frequency doubled laser, wherein the first frequency doubled laser comprises the 1 st laser, the 1 st frequency doubled laser and the 1 st frequency tripled laser.
The second acousto-optic frequency shifter is used for shifting the frequency of the second beam of seed laser and outputting 2 nd laser; the center frequency of the 2 nd laser is greater than that of the seed laser.
And the second frequency doubling module is used for performing frequency doubling and frequency tripling on the input 2 nd laser and outputting second frequency doubled laser, wherein the second frequency doubled laser comprises the 2 nd laser, the 2 nd frequency doubled laser and the 2 nd frequency tripled laser.
The first wavelength is a near-infrared band, and the 1 st frequency-tripled laser and the 2 nd frequency-tripled laser are ultraviolet bands.
The laser output by the first frequency doubling module is divided into two beams, one beam is used as signal light, and the other beam is used as reference light; the laser output by the second frequency doubling module is divided into two beams, one beam is used as signal light, and the other beam is used as reference light.
And the beam expanding system is used for outputting the signal light of the first frequency doubling laser and the second frequency doubling laser to the atmosphere after being alternately expanded.
And the receiving telescope is used for receiving the atmosphere echo signal.
And the color separation mirror is used for receiving the atmospheric echo signal and the reference light of the first frequency doubling laser and the second frequency doubling laser, and separating the received signal into the first wavelength laser and the second wavelength laser to be output respectively.
The first wavelength laser light is input to a first F-P interferometer and the second wavelength laser light is input to a second F-P interferometer.
The detection module is used for detecting signals output by the first F-P interferometer and the second F-P interferometer;
and the data acquisition and processing module is used for acquiring and analyzing the signals output by the detection module.
The center frequencies of the 1 st laser and the 2 nd laser are respectively positioned on the rising edge and the falling edge of the transmittance curve of the adjacent interference level in the transmittance curve of the first F-P interferometer; and the transmittance curve of the first F-P interferometer is the corresponding relation between the transmittance of the first F-P interferometer and the incident light frequency.
The center frequencies of the 1 st frequency-tripling laser and the 2 nd frequency-tripling laser are respectively positioned on the rising edge and the falling edge of the transmittance curve of the adjacent interference level in the transmittance curve of the second F-P interferometer; and the transmittance curve of the second F-P interferometer is the corresponding relation between the transmittance of the second F-P interferometer and the incident light frequency.
The transmittance of an ideal F-P interferometer (Fabry-Perot interferometer, also known as FPI) is an Airy function:
in the formula, 1 is the length of the etalon cavity; r is the reflectivity of the corresponding wavelength; l is the optical loss; c is high speed; v is the frequency of the incident light; theta is the angle between the incident light and the normal of the etalon reflecting surface; f is the effective fineness. When the cavity length of the etalon is fixed, the transmittance is only related to the incident light frequency and changes periodically. The etalon transmittance curves mentioned in the invention are all the corresponding relations of the etalon cavity length, transmittance (transmission light intensity) and incident light frequency. Each transmittance profile includes a plurality of interference levels, each interference level including a rising edge and a falling edge.
Furthermore, the invention also comprises two laser amplification modules which are respectively positioned between the first acousto-optic frequency shifter and the first frequency doubling module and between the second acousto-optic frequency shifter and the second frequency doubling module and are used for amplifying the laser output by the first acousto-optic frequency shifter and the second acousto-optic frequency shifter. The laser amplification module comprises a laser oscillation stage and an amplification stage. In some examples, the laser may have only an oscillating stage. The function of the laser pulse amplification device is to amplify the laser pulse so as to generate a high-power laser pulse with a certain repetition frequency.
As shown in fig. 2, the beam expanding system of the dual-frequency wind lidar with ultraviolet and infrared synchronous operation comprises: a time division reflective transmission switch and a beam expander. The time division reflection transmission switch comprises a rotating mirror and a rotation control component, wherein the rotating mirror is provided with a transmission area 32 and a reflection area 31, the transmission area 32 is used for transmitting incident optical signals, and the reflection area 31 is used for reflecting the incident optical signals; specifically, the transmission region 32 is a hollow region, and the reflection region 31 is provided with a reflector.
The first frequency doubling laser and the second frequency doubling laser are respectively incident to the transmission area 32 and the reflection area 31 of the rotating mirror.
The beam expanding system includes a first beam expander lens.
The rotation control assembly is used for controlling the rotation of the rotating mirror so that the laser emitted by the first frequency doubling module and the laser output by the second frequency doubling module are alternately output to the first beam expanding mirror.
The rotation control assembly may continuously rotate at a predetermined speed so that the first frequency-doubled laser and the second frequency-doubled laser are alternately output at a predetermined frequency.
Specifically, the rotating mirror can be as shown in fig. 3, wherein the shaded portion is the reflective area 31 and the blank portion is the transmissive area 32. With the rotating mirror shown in fig. 3, the reflective areas 31 and the transmissive areas 32 alternate twice per rotation. In order to ensure the emitting efficiency of the first frequency doubling laser and the second frequency doubling laser, the areas of the reflecting region 31 and the transmitting region 32 are larger than the spot areas of the first frequency doubling laser and the second frequency doubling laser. In order to ensure that the first frequency doubling laser and the second frequency doubling laser are uniformly emitted, the areas of the reflection region 31 and the transmission region 32 are equal.
And the two high-energy lasers work cooperatively by setting a time division reflection transmission switch. Meanwhile, due to the arrangement of the time division reflection switch, two paths of pulse signals can share one beam expander. In an optical system, in order to measure high-rise atmosphere, the laser power is required to be large, and aiming at the problems of large beam expanding lens with large power signal, complex system, high cost and high installation and adjustment difficulty, the beam expanding lens is reduced by one, so that the hardware cost and the maintenance cost of the system can be obviously reduced. Meanwhile, the beam expander is large in size, one beam expander is reduced, the size of the whole device can be reduced, miniaturization and integration of the device are facilitated, and transportation is facilitated.
In an optional embodiment, the beam expanding system includes a second beam expander for outputting the first frequency doubled laser light to the atmosphere, and a third beam expander for outputting the second frequency doubled laser light to the atmosphere.
The center frequencies of the 1 st laser and the 2 nd laser are respectively positioned at the half waist of the transmittance curve of the adjacent interference level in the transmittance curve of the first F-P interferometer, namely a rising edge and a falling edge; and the center frequencies of the 1 st frequency-tripling laser and the 2 nd frequency-tripling laser are respectively positioned on the rising edge and the falling edge of the transmittance curve of the adjacent interference level in the transmittance curve of the second F-P interferometer. The half waist of the transmittance curve is the middle position from the lowest valley to the highest peak of the rising edge and the falling edge in the transmittance curve of one period.
The invention adopts a push-pull acousto-optic modulation mode to generate two pulse signals which are symmetrically distributed relative to a 1064 etalon.
The first F-P interferometer comprises a temperature adjusting unit or an air pressure adjusting unit, and the 1 st laser and the 2 nd laser are respectively positioned on the rising edge and the falling edge of the transmittance curve of the adjacent interference level in the transmittance curve of the first F-P interferometer by adjusting the temperature adjusting unit or the air pressure adjusting unit.
The second F-P interferometer comprises a temperature adjusting unit or an air pressure adjusting unit, and the 1 st frequency-tripled laser and the 2 nd frequency-tripled laser are respectively positioned on the rising edge and the falling edge of the adjacent interference level transmittance curve in the transmittance curve of the second F-P interferometer by adjusting the temperature adjusting unit or the air pressure adjusting unit.
And adjusting the absolute frequency of the seed light to enable the emitted 1 st laser light and the emitted 2 nd laser light to be positioned at the half waist of the adjacent interference level transmittance of the first F-P interferometer, namely the rising edge and the falling edge.
And the emitted 1 st frequency-tripled laser and the 2 nd frequency-tripled laser are positioned on the rising edge and the falling edge of the adjacent interference level transmittance of the second F-P interferometer by adjusting the air pressure adjusting unit/the temperature adjusting unit of the second F-P interferometer.
The seed laser is Nd: YAG laser, the first wavelength is 1064nm, and the wavelengths of the 1 st frequency-tripled laser and the 2 nd frequency-tripled laser are 355 nm.
The direct detection wind lidar can be divided into a Rayleigh wind lidar based on wide-spectrum molecular scattering and a Mie scattering lidar based on narrow-spectrum aerosol scattering according to different atmospheric particle carriers.
Because the rayleigh wind lidar and the mie scattering lidar have different sensitivities to the wavelength, the rayleigh wind lidar mostly adopts ultraviolet laser for detection (such as 355nm laser), and the mie scattering lidar mostly adopts visible light or near infrared laser for detection (such as 1064nm laser). The aerosol particle density in the lower atmosphere (such as the troposphere) is high, and the wind speed of the lower atmosphere can be measured by using the Mie scattering laser radar. The aerosol particles in the high-rise atmosphere (such as stratosphere) are few, the atmospheric molecular signals are more, and the high-rise atmosphere wind speed can be measured by adopting a Rayleigh wind lidar.
By the system, the laser outputs laser with infrared and ultraviolet wavelengths simultaneously, and the wind speed of the lower and upper atmospheric layers is measured simultaneously at low cost by using a single laser radar.
The central frequency of the 1 st laser is larger than that of the seed laser by a first frequency interval; the center frequency of the 2 nd laser is smaller than the center frequency of the seed laser by a second frequency interval.
Preferably, the first frequency interval is equal to the second frequency interval, and the 1 st laser and the 2 nd laser are symmetrically distributed relative to the center frequency of the seed laser.
The first frequency interval corresponds to an amount of frequency shift of the first AOFS. The second frequency interval corresponds to an amount of frequency shift of the second AOFS.
Optionally, the sum of the first frequency interval and the second frequency interval is between 1GHz and 4 GHz.
The rising edge and the falling edge of the transmittance curve of adjacent interference levels, of which the center frequencies of the 1 st laser and the 2 nd laser are respectively positioned in the transmittance curve of the first F-P interferometer, comprise:
the center frequencies of the 1 st laser and the 2 nd laser are respectively locked at two edges close to the transmittance curves of adjacent interference levels.
The center frequencies of the 1 st frequency-tripling laser and the 2 nd frequency-tripling laser are respectively positioned on the rising edge and the falling edge of the transmittance curve of the adjacent interference level in the transmittance curve of the second F-P interferometer; and the transmittance curve of the second F-P interferometer is the corresponding relation between the transmittance of the second F-P interferometer and the incident light frequency.
The operation of the lidar according to the present invention is described in a specific application scenario. In this scenario, the seed laser is a 1064nm wavelength laser.
As shown in fig. 2, as shown in the figure, the laser output by the 1064nm seed laser is divided into two parts by the beam splitter, and one part is frequency-shifted by the first AOM, then passes through the oscillation stage and the amplification stage, and then passes through the frequency doubling module and the frequency tripling module, and the 1064nm, 532nm and 355nm laser is output collinearly. And after the other seed light is subjected to frequency shift by the second AOM and passes through the other oscillation stage and the amplification stage, the other seed light passes through the frequency doubling module and the frequency tripling module and is output with lasers of 1064nm, 532nm and 355nm in a collinear manner.
The dual-frequency wind lidar of the present embodiment further comprises: set up in proper order between receiving telescope and the color separation mirror: EOM, beam combiner, mode scrambler, collimator, and reflector between color splitter and second FPI.
Two beams of laser are emitted to the atmosphere in a time-sharing manner through the reflective beam expanding system by controlling the time-division reflection transmission switch. After being received by the receiving telescope, the atmospheric echo signal is modulated by EOM, so that strong near-field signals are reduced to prevent the detector from being saturated. And then, after being combined by the beam combiner, the echo signals are input into the mode scrambler to enable light spots to be uniform, the light spots are converted into space light through the collimator, the space light is firstly separated into 1064nm laser and 355nm laser through the color splitter, and the two laser beams are detected by the detection module after passing through the first F-P interferometer and the second F-P interferometer respectively.
The detection module may be two separate detectors, i.e. a first detector and a second detector in fig. 2, respectively located between the first FPI and the data acquisition and processing module and between the second FPI and the data acquisition and processing module; or two channels of one detector, i.e. the detection module in fig. 1.
The dual-frequency wind lidar of the present embodiment further comprises: an integrating sphere. In order to realize the locking of the relative positions of the laser and the F-P interferometer, two reference lights are separated from two beams of emitted laser, the reference lights are simultaneously coupled into an optical fiber, the pulse width is widened through an integrating sphere, and the reference lights are coupled into a beam combiner and combined with an echo signal.
The working principle of the ultraviolet and infrared synchronous working dual-frequency wind lidar is shown in figure 4:
FIG. 4a shows a graph of the transmittance of 1064 nmFPI.
FIG. 4b is a graph showing the light intensity of 1064nm signal, i.e., the 1 st laser; and after the 1064nm seed light is subjected to frequency shift by the first AOM and the second AOM, the difference between the two 1064nm laser frequencies is 3.5 GHz.
By designing a 1064nm FPI, two 1064nm lasers are respectively locked at the rising edge and the falling edge of the 1064nm FPI transmittance curve.
Fig. 4c shows schematic diagrams of the emitted 1 st laser beam and 2 nd laser beam.
FIG. 4d is a graph showing the spectrum of the 355nm laser-excited Rayleigh scattering signal.
FIG. 4e shows a 355nmFPI transmittance curve.
As shown in fig. 4, after the 1064nm seed light is frequency-shifted by the first AOM and the second AOM, the frequency difference between the two 1064nm lasers is 3.5GHz, and the frequency difference between the two 355nm laser beams is 10.5 GHz. The FSR of 1064nm channel FPI was 3.7GHz, and the FSR of 355nm channel FPI was 15.6 GHz.
By utilizing the periodic structure of the FPI, two beams of laser light with the wavelength of 1064nm and two beams of laser light with the wavelength of 355nm are respectively locked on the rising edge and the falling edge of the corresponding FPI by designing the FPI with the wavelength of 1064nm and the FPI with the wavelength of 355 nm.
The invention discloses a double-frequency wind measuring laser radar with ultraviolet and infrared synchronous working, which adopts an acousto-optic frequency shift mode to generate two pulse signals which are symmetrically distributed relative to an F-P interferometer; adjusting the absolute frequency of the seed light to enable the 1 st laser and the 2 nd laser to be respectively positioned at the half waist of the adjacent interference level transmittance of the first F-P interferometer; and by adjusting the air pressure adjusting unit/the temperature adjusting unit of the second F-P interferometer, the frequency tripling laser corresponding to the 1 st laser and the 2 nd laser is also positioned at the half waist of the adjacent transmittance of the second F-P interferometer. By adopting the system, the laser outputs laser with two wavelengths simultaneously, and the wind speed of the atmosphere at the lower layer and the high layer is measured simultaneously by using a single laser radar so as to achieve the purpose of reducing the cost.
The invention combines time division multiplexing and wavelength division multiplexing technologies, respectively locks the frequency of the emitted laser at the rising edge and the falling edge of the F-P interferometer, and forms double edges for frequency discrimination. The ultraviolet laser and the near-infrared laser are emitted by the same laser, and the periodic structure of the F-P interferometer is utilized, so that the lasers with the two wavelengths can be used for atmospheric wind field detection, wherein the ultraviolet laser (355nm) is used for detecting Rayleigh scattering signals of atmospheric molecules, and the infrared laser (1064nm) is used for detecting the meter scattering signals of atmospheric aerosol. The system scheme provided by the invention simplifies the receiving light path and improves the wind field detection capability of the wind lidar.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. The utility model provides a dual-frenquency anemometry lidar of ultraviolet infrared synchronous working which characterized in that includes:
a seed laser for outputting seed laser light of a first wavelength; the first wavelength is a near-infrared band;
the first acousto-optic frequency shifter is used for shifting the frequency of the seed laser and outputting the 1 st laser; the center frequency of the 1 st laser is less than that of the seed laser;
the first frequency doubling module is used for carrying out frequency doubling and frequency tripling on the input 1 st laser and outputting first frequency doubled laser, wherein the first frequency doubled laser comprises the 1 st laser, the 1 st frequency doubled laser and the 1 st frequency tripled laser; the first frequency doubling laser output by the first frequency doubling module is divided into two beams, one beam is used as signal light, and the other beam is used as reference light;
the second acousto-optic frequency shifter is used for shifting the frequency of the seed laser and outputting 2 nd laser; the center frequency of the 2 nd laser is greater than that of the seed laser;
the second frequency doubling module is used for carrying out frequency doubling and frequency tripling on the input 2 nd laser and outputting second frequency doubled laser, wherein the second frequency doubled laser comprises the 2 nd laser, the 2 nd frequency doubled laser and the 2 nd frequency tripled laser; the second frequency doubling laser output by the second frequency doubling module is also divided into two beams, one beam is used as signal light, and the other beam is used as reference light;
the 1 st frequency-third laser and the 2 nd frequency-third laser are ultraviolet bands;
the beam expanding system is used for expanding signal light in the first frequency doubling laser and the second frequency doubling laser and outputting the expanded signal light to the atmosphere; wherein the beam expanding system comprises a time division reflective transmission switch and a first beam expander;
the time division reflection transmission switch comprises a rotating mirror and a rotation control assembly, wherein the rotating mirror is provided with a transmission area and a reflection area, the transmission area is used for transmitting incident optical signals, and the reflection area is used for reflecting the incident optical signals; the first frequency doubling laser and the second frequency doubling laser are respectively incident to the transmission area and the reflection area of the rotating mirror;
the rotation control assembly is used for controlling the rotation of the rotating mirror to enable first frequency doubling laser emitted by the first frequency doubling module and second frequency doubling laser output by the second frequency doubling module to be alternately output to the first beam expander, so that the first frequency doubling laser and the second frequency doubling laser are alternately output at a preset frequency;
the receiving telescope is used for receiving the atmosphere echo signal;
the color separation mirror is used for receiving the atmospheric echo signal and reference light in the first frequency doubling laser and the second frequency doubling laser, and separating the received signal into first wavelength laser and second wavelength laser to be output respectively;
the first wavelength laser is input to a first F-P interferometer, and the second wavelength laser is input to a second F-P interferometer;
the detection module is used for detecting signals output by the first F-P interferometer and the second F-P interferometer;
and the data acquisition and processing module is used for acquiring and analyzing the signals output by the detection module.
2. The dual-frequency wind lidar of claim 1, wherein the beam expanding system comprises a second beam expander and a third beam expander, the second beam expander being configured to output the first frequency doubled laser to the atmosphere, and the third beam expander being configured to output the second frequency doubled laser to the atmosphere.
3. The ultraviolet-infrared synchronous working dual-frequency wind lidar according to claim 1, wherein the center frequencies of the 1 st laser and the 2 nd laser are respectively located at the half-waists of the transmittance curves of adjacent interference levels in the transmittance curve of the first F-P interferometer, and the transmittance curve of the first F-P interferometer is the corresponding relation between the transmittance of the first F-P interferometer and the incident light frequency; the center frequencies of the 1 st frequency-tripling laser and the 2 nd frequency-tripling laser are respectively positioned at the rising edge and the falling edge of the adjacent interference level transmittance curve in the transmittance curve of the second F-P interferometer, and the transmittance curve of the second F-P interferometer is the corresponding relation between the transmittance of the second F-P interferometer and the incident light frequency.
4. The ultraviolet-infrared synchronous working dual-frequency wind lidar according to claim 3, wherein the second F-P interferometer comprises a temperature adjusting unit or an air pressure adjusting unit, and the 1 st frequency doubling laser and the 2 nd frequency doubling laser are respectively positioned on the rising edge and the falling edge of the transmittance curve of the adjacent interference level in the transmittance curve of the second F-P interferometer by adjusting the temperature adjusting unit or the air pressure adjusting unit; the first F-P interferometer comprises a temperature adjusting unit or an air pressure adjusting unit, and the 1 st laser and the 2 nd laser are respectively positioned on the rising edge and the falling edge of the transmittance curve of the adjacent interference level in the transmittance curve of the first F-P interferometer by adjusting the temperature adjusting unit or the air pressure adjusting unit.
5. The ultraviolet-infrared synchronously operating dual-frequency wind lidar of claim 1, wherein the center frequency of the 1 st laser is greater than the center frequency of the seed laser by a first frequency interval; the center frequency of the 2 nd laser is smaller than the center frequency of the seed laser by a second frequency interval.
6. The dual-frequency wind lidar of claim 1, further comprising, disposed between the receiving telescope and the dichroic mirror in sequence: the EOM, the beam combiner, the mode scrambler, the collimator and the reflecting mirror between the color separation mirror and the second FPI; after being received by a receiving telescope, an atmospheric echo signal is firstly modulated by EOM, the echo signal is input into a mode scrambler after being combined by a beam combiner to enable light spots to be uniform, then the light spots are converted into space light through a collimator, 1064nm laser and 355nm laser are separated through a color separation mirror, and the space light is detected by a detection module after respectively passing through a first F-P interferometer and a second F-P interferometer.
7. The ultraviolet-infrared synchronously operating dual-frequency wind lidar of claim 1, further comprising an integrating sphere; after the width of the reference light pulse is widened by the integrating sphere, the reference light pulse is coupled into a beam combiner to be combined with the echo signal.
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