Iron resonance fluorescence doppler lidar and laser generation device and method

Abstract

The application belongs to the technical field of laser radar, and discloses a laser generation device and method of iron resonance fluorescence Doppler laser radar. A first seed source and a second seed source respectively output continuous light; a first laser processor realizes real-time adjustment of the central wavelength of the continuous light after power amplification, frequency doubling, frequency stabilization and beat frequency of the continuous light; a second laser processor performs beam combination and beat frequency on the continuous light adjusted by the first seed source and the continuous light emitted by the second seed source, and locks the difference frequency signal on an applied radio frequency signal, and controls the radio frequency signal to cyclically jump within a certain interval; a pulse laser amplifier amplifies and nonlinearly frequency converts the continuous light emitted by the second seed source after locking, and outputs single-frequency stabilized narrowband pulse laser, while realizing time-sharing frequency hopping output of pulse light among three frequencies. The laser generation device provides a reliable light source for high-precision detection of atmospheric temperature, wind field and iron atom number density in the region from the top of the middle layer to the bottom of the thermal layer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser radar, and particularly relates to an iron resonance fluorescence Doppler laser radar and a laser generation device and method. BACKGROUND

[0002] Temperature and wind field are important environmental parameters for representing atmospheric state. In the region from the top of the mesosphere to the bottom of the thermosphere, about 75km to 115km height interval, due to lack of effective observation means, the observation data of temperature and wind field vertical distribution in the height range are relatively scarce. The resonance fluorescence laser radar uses the metal atoms, ions and the like specific to the region from the top of the mesosphere to the bottom of the thermosphere as tracers, and through exciting the resonance fluorescence signals of the tracers, the temperature and wind field can be detected. Compared with sounding rockets, passive remote sensing and microwave active remote sensing and the like, the resonance fluorescence laser radar has the advantages of continuous observation, high space-time resolution, high precision and the like, and becomes a powerful tool for detecting the region from the top of the mesosphere to the bottom of the thermosphere. At present, the international mainly uses sodium resonance fluorescence laser radar to measure temperature and wind field, and the iron resonance fluorescence Doppler laser radar has the advantages of all-day detection and the like, and is another effective means for detecting temperature and wind field profiles in the region from the top of the mesosphere to the bottom of the thermosphere. In the iron resonance fluorescence Doppler laser radar system, the laser light source is the most important component, and is required to output single-frequency, narrow-line-width, pulsed laser with frequency stabilization, and also to realize time-sharing frequency hopping output of three frequencies. Due to the difficulty in laser technology, the development of the iron resonance fluorescence Doppler laser radar is limited. At present, only the University of Illinois at Urbana-Champaign, the University of Colorado at Boulder and the German Aerospace Center have successfully developed this type of laser radar. SUMMARY

[0003] In order to provide stable narrow-line-width, single-frequency, frequency-stabilized pulsed laser, and realize time-sharing frequency hopping output of three frequencies, the application provides an iron resonance fluorescence Doppler laser radar and a laser generation device and method, and the specific scheme is as follows:

[0004] The laser generation device comprises a first seed source, a first laser processor, a second seed source and a second laser processor.

[0005] The first seed source is used for outputting continuous seed laser.

[0006] The first laser processor is used for power amplification, frequency doubling and frequency stabilization processing on the continuous seed laser, and mixing the laser after power amplification and frequency doubling and frequency stabilization processing to obtain a difference frequency signal, and adjusting the center wavelength of the continuous seed laser according to the difference frequency signal.

[0007] The second seed source is used for outputting continuous seed laser.

[0008] The second laser processor is used for mixing and frequency beating the continuous seed laser after the first seed source adjustment and the continuous seed laser emitted by the second seed source, and locking the difference frequency signal on an externally provided radio frequency signal, wherein the radio frequency signal has a fixed carrier frequency difference w, a center frequency required for temperature and wind measurement, and a frequency hopping amount Δf between two wing frequencies; the radio frequency signal is controlled to cyclically hop between w-Δf, w and w+Δf, and after locking, the continuous light emitted by the second seed source is amplified and output.

[0009] Further, the first laser processor comprises a first fiber amplifier, an active frequency stabilization unit, and a first servo feedback unit.

[0010] The first fiber amplifier is used for power amplifying the continuous seed laser.

[0011] The active frequency stabilization unit is used for frequency doubling and frequency stabilizing the continuous seed laser after power amplification.

[0012] The first servo feedback unit is used for mixing the laser after frequency stabilization with the laser after power amplification to obtain a difference frequency signal as an input of negative feedback adjustment to adjust the center wavelength of the first seed source.

[0013] Further, the second laser processor comprises a signal generation unit, a signal frequency beating and locking unit, a second servo feedback unit, a second fiber amplifier, and a pulse laser.

[0014] The signal generation unit is used for adding a frequency difference w between an output frequency and a center frequency of iron fluorescence spectrum lines, a center frequency required for temperature and wind measurement, and a frequency hopping amount Δf to a radio frequency modulation signal.

[0015] The signal frequency beating and locking unit is used for mixing and frequency beating the continuous seed laser output after the first seed source adjustment and the continuous light of the second seed source, and locking the detected difference frequency signal on the radio frequency signal through an optical phase-locked loop.

[0016] The second servo feedback unit is used for making the radio frequency signal cyclically hop between w+Δf, w and w+Δf through a PID control circuit.

[0017] The second fiber amplifier is used for power amplifying the second seed source and injecting the pulse laser.

[0018] Further, the active frequency stabilization unit comprises a frequency doubling crystal and a frequency stabilization unit.

[0019] The frequency doubling crystal is used for frequency doubling the continuous seed laser.

[0020] The frequency stabilization unit is used to stabilize the continuous seed laser frequency by using iodine molecular absorption spectral lines in a saturated absorption spectroscopy technique.

[0021] In another embodiment of the present application, a laser radar is also disclosed, which comprises any of the above iron resonance fluorescence Doppler laser radar laser generating devices, and the laser generating device further comprises a transmitting unit, the transmitting unit comprising a first beam splitter, a second beam splitter, a beam expander, an adjusting frame and a laser mirror;

[0022] The laser mirror is mounted on the adjusting frame;

[0023] The first beam splitter is coated with a λ / 3 wavelength reflection film, a λ / 2 wavelength and a λ wavelength anti-reflection film;

[0024] The second beam splitter is coated with a λ / 2 wavelength reflection film and a λ wavelength anti-reflection film, wherein λ is the center wavelength of the second seed source output;

[0025] The beam expander adopts an adjustable magnification of 2-5 times.

[0026] Further, the laser radar further comprises a receiving unit, the receiving unit comprising a receiving telescope and a pinhole diaphragm, and the receiving telescope adopts a coaxial cassette system;

[0027] The receiving telescope comprises a concave parabolic primary mirror, a hyperboloid secondary mirror and a corner reflector arranged in sequence;

[0028] The pinhole diaphragm is arranged at the rear side of the receiving telescope and is used to control the field of view angle of the receiving telescope.

[0029] Further, the receiving unit further comprises a movable lens group, a daytime detection unit and a night detection unit;

[0030] The receiving unit is used to control the transmission of the echo signal received by the receiving telescope to the daytime detection unit or the night detection unit;

[0031] The night detection unit comprises a first narrowband interferometer filter, a first collimating lens, a first narrowband filter, a first converging lens and a first photodetector arranged in sequence;

[0032] The daytime detection unit comprises a second narrowband interferometer filter, a second collimating lens, a second narrowband filter, a second converging lens and a second photodetector arranged in sequence.

[0033] Further, the laser radar further comprises a data processing unit, the data processing unit comprising a data acquisition card and a computing unit;

[0034] The data acquisition card is connected with the first photoelectric detector and the second photoelectric detector, and is used for converting an electric signal into a digital signal.

[0035] The calculation unit is connected with the data acquisition card, and is used for obtaining temperature, wind field and iron atom number density detection results through the digital signal.

[0036] Further, the laser radar further comprises an energy monitoring unit and a frequency monitoring unit,

[0037] The energy monitoring unit is used for monitoring the λ / 3 wavelength laser, and eliminating the laser radar original data in the time period corresponding to the energy fluctuation abnormality.

[0038] The frequency monitoring unit is used for frequency mixing the remaining λ wavelength, frequency hopping pulse light and the continuous light of the laser radar, obtaining the frequency stability of the pulse light, and eliminating the laser radar original data in the abnormal time period, wherein the abnormal time is the time period corresponding to the frequency stability greater than a set value.

[0039] In another embodiment, the application further discloses a laser generation method of the iron resonance fluorescence Doppler laser radar, and the laser generation method comprises the following steps:

[0040] The first laser beam with a center wavelength of λ is power amplified and then frequency doubled, then the saturated absorption spectrum technology is used to realize the frequency stabilization output of the first laser beam by using the λ / 2 wavelength iodine molecular transition spectrum, and the frequency difference w between the locking point of the iodine molecular frequency stabilization and the center frequency of the first laser beam after frequency doubling is calculated.

[0041] The frequency mixed signal is obtained by mixing the frequency stabilized output first light beam and the power amplified first light beam, and the PID control circuit is used to adjust the center wavelength λ of the first laser beam by taking the frequency mixed signal as the negative feedback input.

[0042] The frequency difference w to be corrected, the center frequency and the frequency hopping amount between the two wing frequencies required for temperature measurement and wind measurement are added to the radio frequency modulation signal.

[0043] The frequency mixed signal is obtained by mixing the frequency stabilized output first light beam and the power amplified first light beam, and the PID control circuit is used to adjust the center wavelength λ of the first laser beam by taking the frequency mixed signal as the negative feedback input.

[0044] The modulation signal is phase-locked and power-amplified, and then injected into a pulse laser to obtain a λ / 3 wavelength pulse laser.

[0045] The application has the following beneficial effects:

[0046] (1) The application proposes that the output light of the first seed source and the second seed source is divided into two beams, one continuous light beam of the first seed source enters the iodine absorption cell after power amplification by the first optical fiber amplifier and first nonlinear frequency conversion by the frequency doubling crystal to realize frequency stabilization, the other stable frequency light beam is combined with the output light of the second seed source to perform beat frequency, and the difference frequency signal is locked on the radio frequency signal through the optical phase-locked loop technology, the radio frequency signal is controlled to cyclically jump within a certain interval and the frequency is stabilized; the other continuous light beam of the second seed source also has the characteristics of frequency stabilization and frequency hopping, and is power amplified through the second optical fiber amplifier and used as the seed injection source of the pulse laser; the processes of seed injection locking, power amplification and nonlinear frequency conversion in the power laser are completed to realize the output of the required pulse laser, and the pulse laser has the corresponding characteristics of narrow linewidth, frequency stabilization and frequency hopping.

[0047] (2) The application proposes that the optical phase-locked loop technology is used to replace the commonly used acousto-optic modulator in the sodium resonance fluorescence Doppler laser radar to realize the jump of different frequencies, and compared with the frequency hopping by using the acousto-optic modulator, the method has higher optical efficiency and can obtain higher seed light output power. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 A structure diagram of a laser generation device of an iron resonance fluorescence Doppler laser radar proposed by the application;

[0049] Figure 2 A working principle diagram of a laser generation device of an iron resonance fluorescence Doppler laser radar proposed by the application;

[0050] Figure 3 A schematic diagram of the relationship between the relative positions of absorption peaks and signal strengths in the embodiment of the application. DETAILED DESCRIPTION

[0051] As Figure 1 shown, the application discloses a Doppler laser radar laser generation device, the laser generation device comprises a first seed source, a first laser processor, a second seed source and a second laser processor;

[0052] The first seed source is used for outputting continuous seed laser;

[0053] The first laser processor is used for power amplifying, frequency doubling and frequency stabilizing the continuous seed laser, and mixing the laser after power amplification and frequency doubling and frequency stabilization to obtain a difference frequency signal, and adjusting the center wavelength of the continuous seed laser according to the difference frequency signal;

[0054] The second seed source is used for outputting continuous seed laser;

[0055] The second laser processor performs frequency mixing of the continuous seed laser after adjustment of the first seed source and the continuous seed laser emitted by the second seed source, and phase-locks the difference frequency signal on an externally provided radio frequency signal, wherein the radio frequency signal has a fixed carrier frequency difference w, a center frequency required for temperature and wind measurement, and a frequency hopping amount Δf between two wing frequencies. The radio frequency signal is controlled to cyclically hop between w-Δf, w, and w+Δf, and after locking, the continuous light emitted by the second seed source is amplified and output.

[0056] For example, the first seed source outputs 20 mW of kHz order narrow linewidth 1116 nm continuous seed laser, and the center wavelength can be adjusted within a certain range. The continuous seed laser output by the first seed source is processed by the first laser processor. First, the first laser processor amplifies the power of the continuous seed laser, and outputs the amplified 1116 nm continuous light. The amplified 1116 nm continuous light is frequency doubled to obtain continuous light of 558 nm wavelength. The frequency of the continuous light after frequency doubling is stabilized. Finally, the power amplified and frequency stabilized continuous light is mixed. The difference frequency signal obtained after mixing is used as the input of negative feedback adjustment. Finally, the center wavelength of the first seed source is adjusted by the PID control circuit, so that the first seed source outputs continuous light of stable frequency and 1116 nm wavelength. The main operation steps of the PID control circuit are proportional-differential-integral. The second seed source also outputs about 20 mW of kHz order narrow linewidth 1116 nm continuous seed laser, and the center wavelength can be adjusted within a certain range. The second laser processor performs frequency mixing of the continuous seed laser after adjustment of the first seed source and the continuous seed laser emitted by the second seed source, and phase-locks the difference frequency signal on an externally provided radio frequency signal, wherein the radio frequency signal has a fixed carrier frequency difference w, a center frequency required for temperature and wind measurement, and a frequency hopping amount Δf between two wing frequencies. The radio frequency signal is controlled to cyclically hop between w-Δf, w, and w+Δf; after locking, the radio frequency signal adds the frequency difference and the frequency modulation amount to the continuous light emitted by the second seed source, that is, the continuous light emitted by the second seed source also has the characteristics of frequency stabilization and frequency hopping. The second seed source can output 1116 nm wavelength frequency stabilized continuous light, and the laser frequency will hop between 1116 nm-Δf, 1116 nm, and 1116 nm+Δf. After power amplification, stable narrow linewidth, single frequency, and frequency stabilized pulsed laser can be output.

[0057] Further, the first laser processor includes a first fiber amplifier, an active frequency stabilization unit, and a first servo feedback unit.

[0058] The first fiber amplifier is configured to amplify the power of the continuous seed laser.

[0059] The active frequency stabilization unit is configured to perform frequency stabilization processing on the continuous seed laser after power amplification and frequency doubling.

[0060] The first servo feedback unit is configured to mix the laser after frequency stabilization processing with the laser after power amplification to obtain a beat frequency signal as an input of negative feedback adjustment to adjust the center wavelength of the first seed source.

[0061] For example, the first seed source emits 20 mW of kHz narrow linewidth 1116 nm continuous seed laser, which is preliminarily amplified in the first fiber amplifier, and the amplified 1116 nm laser is output. For example, the first fiber amplifier is a ytterbium-doped fiber amplifier. The active frequency stabilization unit performs frequency stabilization processing on the laser after power amplification by the first seed source after frequency doubling operation, and obtains laser with more stable frequency. The first servo feedback unit mixes the laser after frequency stabilization processing with the laser after power amplification to obtain a beat frequency signal, and uses the beat frequency signal as an input of negative feedback to adjust the center wavelength of the laser emitted by the first seed source in the opposite direction, so that the first seed source outputs 1116 nm wavelength continuous light with stable frequency.

[0062] Further, the active frequency stabilization unit includes a frequency doubling crystal and a frequency stabilization unit.

[0063] The frequency doubling crystal is configured to perform frequency doubling on the continuous seed laser.

[0064] The frequency stabilization unit is configured to use a saturated absorption spectroscopy technique to realize frequency stabilization of the continuous seed laser by using an iodine molecular absorption spectrum.

[0065] Specifically, the 1116 nm wavelength continuous light output by the first fiber amplifier obtains 558 nm wavelength laser after passing through the frequency doubling crystal. The saturated absorption spectroscopy technique is used to realize frequency stabilization of the 1116 nm wavelength laser by using an iodine molecular absorption spectrum near 558 nm, but there is a frequency difference w between the locking point of the iodine molecular frequency stabilization and the center frequency after frequency doubling of the 1116 nm wavelength.

[0066] Further, the second laser processor includes a signal generation unit, a signal beat frequency locking unit, a second servo feedback unit, a second fiber amplifier, and a pulsed laser.

[0067] The signal generation unit is configured to add the frequency difference w between the output frequency and the center frequency of the iron fluorescence spectrum, the center frequency and the frequency hopping amount Δf between the two wing frequencies required for temperature and wind measurement, and an additional radio frequency modulation signal.

[0068] The signal beat frequency locking unit is configured to perform beam combination beat frequency on the continuous seed laser output after adjustment of the first seed source and the continuous light of the second seed source, and lock the detected beat frequency signal on the radio frequency signal through an optical phase-locked loop.

[0069] The second servo feedback unit is configured to make the radio frequency signal cyclically jump among w-Δf, w and w+Δf through a PID control circuit.

[0070] The second optical fiber amplifier is configured to inject the pulse laser of 372 nm wavelength into the pulse laser of 372 nm wavelength after power amplification.

[0071] Specifically, the signal generation unit is configured to input the frequency difference correction and the frequency hopping amount, and superimpose the required frequency difference w to be corrected, the center frequency required for temperature measurement and wind measurement, and the frequency modulation amount Δf between the two wing frequencies on the radio frequency modulation signal. Meanwhile, the signal beat frequency locking unit is configured to perform beam combination and beat frequency on the continuous seed laser output after adjustment of the first seed source and the continuous light of the second seed source, lock the detected difference frequency signal on the radio frequency signal through an optical phase-locked loop, and make the radio frequency signal cyclically jump among w-Δf, w and w+Δf through a PID control circuit. After locking, the second seed source can output the continuous light of 1116 nm wavelength with stable frequency, and the laser frequency jumps among 1116 nm-Δf, 1116 nm and 1116 nm+Δf. After power amplification through the second optical fiber amplifier, the pulse laser of 372 nm wavelength is injected into the pulse laser of 372 nm wavelength, and finally the pulse light of 372 nm wavelength with stable frequency is output, which is consistent with the center wavelength of the iron resonance fluorescence spectrum line, and the frequency cyclically jumps among the center wavelength of the iron resonance fluorescence spectrum line-3Δf, 0 and +3Δf.

[0072] For example, the first seed source outputs the continuous seed laser of 1116 nm wavelength, the laser power is 23 mW, the laser line width is 3.3 kHz, and the center wavelength tuning range is 1115.90 nm to 1116.70 nm. The first optical fiber amplifier amplifies the laser power. After amplification, the 1116 nm wavelength laser passes through the frequency doubling crystal to obtain the laser of 558 nm wavelength. The stable frequency unit uses the modulation saturated absorption spectrum technology to lock the frequency of the laser after frequency doubling at the half waist position of the absorption peak near 558 nm wavelength. The vacuum center wavelength of the iron atom fluorescence spectrum line is 372.0993 nm, and the accurate laser wavelength of the required seed light is 1116.2979 nm. There is a frequency difference of about 1.163 GHz between the locking point of the iodine molecule stable frequency near 558 nm and the center frequency of the laser after frequency doubling of 1116.2979 nm wavelength. The first servo feedback unit mixes the continuous light of 1116 nm wavelength output from the stable frequency unit and the continuous light of 1116 nm wavelength directly output from the first optical fiber amplifier. The frequency difference obtained by mixing is used as the input of negative feedback adjustment, and then the PID system control is performed to adjust the center wavelength of the first seed source, so that the first seed source outputs the continuous light of 1116 nm wavelength with stable frequency.

[0073] The second seed source is used to output 1116 nm continuous seed laser, laser power is 23 mW, laser linewidth is 4.2 kHz, and center wavelength tuning range is 1115.95 nm to 1116.65 nm; the signal generation unit adds the required 1.163 GHz-250 MHz, 1.163 GHz and 1.163 GHz+250 MHz frequencies to the radio frequency modulator signal; the signal beat frequency locking unit performs beam combination and beat frequency on the 1116 nm wavelength continuous light emitted by the first seed source after adjustment and the 1116 nm wavelength continuous light emitted by the second seed source, and the detected beat frequency signal is locked on a high-precision radio frequency signal through an optical phase-locked loop. The second servo feedback unit realizes the cyclic hopping of the radio frequency signal between 1.163 GHz-250 MHz, 1.163 GHz and 1.163 GHz+250 MHz by using a PID control circuit, and the relocking time of the hopping is in the order of milliseconds. After locking, the second seed source can output 1116 nm wavelength stable continuous light, and the laser frequency will hop between 1116.2979 nm-250 MHz, 1116.2979 nm and 1116.2979 nm+250 MHz; after the laser output by the second seed source after locking is amplified in power by the second fiber amplifier, it is injected into a 372 nm wavelength pulsed laser, and finally 372.0993 nm wavelength stable pulsed light consistent with the center wavelength of the iron resonance fluorescence spectrum is output, and cyclic hopping between the center wavelengths of the iron resonance fluorescence spectrum-750 MHz, 0 MHz and +750 MHz is realized.

[0074] Exemplarily, due to laser frequency jitter, the deviation of the center frequency and the effective scattering cross sections of the two wing frequencies is caused, thereby causing systematic errors of temperature and radial wind speed obtained by three-frequency ratio Doppler technology. 1 MHz laser frequency jitter causes the systematic errors of temperature and wind speed to be 0.25 K and 0.32 m / s respectively, and therefore the absolute frequency locking of the frequency of the outgoing laser is needed.

[0075] Due to the influence of factors such as frequency chirp, the frequency stability of the seed source should be controlled to be hundreds of kHz. Since there is no suitable atomic or molecular spectrum line at 1116 nm wavelength as a frequency reference point, and there is a relatively strong iodine molecular transition spectrum near 558 nm wavelength, the saturated absorption spectrum of iodine molecules near 558 nm after frequency doubling is selected as the reference. The full width at half maximum of the 558 nm iodine molecular spectrum is about hundreds of kHz, and if the frequency locking can be locked at the position of the zero point of the saturated absorption spectrum error signal by the frequency stabilization system and the subsequent feedback circuit, the frequency stability of the continuous light output by the seed source is also hundreds of kHz.

[0076] Since the locking point of the iodine molecular frequency stabilization is different from the 1116.2979 nm wavelength, the center frequency after frequency tripling is 372.0993 nm, and there is a frequency difference between the center frequencies after frequency doubling, when the frequency is locked at the zero point of the saturated absorption spectrum error signal, the frequency of the 372 nm pulsed laser is different from the center frequency of the iron resonance fluorescence spectrum, and the frequency difference is 0.0003 nm.Figure 3 The position of the absorption peak 4 is 1.163 GHz, so that the wavelength of the output seed light after frequency stabilization cannot be accurately corresponding to the wavelength of 1116.2979 nm, and another second seed source with similar performance needs to be introduced to correct the frequency difference w by using optical beat frequency locking technology, so that the output laser frequency of the second seed source is the required frequency. In addition, the optical beat frequency locking technology can replace the acousto-optic modulator commonly used in sodium resonance fluorescence Doppler laser radar to realize the jump switching among the three frequencies.

[0077] The optical beat frequency locking technology is a method of locking the frequency and phase of an optical signal by using electrical feedback control, and the purpose is to realize the synchronization of the frequency and phase between two or more different optical carriers. The frequency difference between the two lasers is locked on the externally provided radio frequency signal w0, so that the frequency difference between the two lasers is transformed into a quantity set according to the size of w.

[0078] Suppose that the laser frequency of the first seed source output after frequency stabilization is f1, and the frequency difference between the center frequency f0 corresponding to 1116.2979 nm and f1 is w, that is, f0=f1+w. The laser frequency of the second seed source is f2, and the two lasers are combined to beat. According to the principle of laser beat frequency, the combined light signal will contain the frequency difference component f2-f1 and the frequency sum component f2+f1 of the two lasers. Due to the limitation of the bandwidth of the photodetector, the sum frequency component is filtered out, and the detector can only detect the signal of the difference frequency part. The detected difference frequency signal is locked on the high-precision radio frequency signal w0, that is, after locking, f2-f1=w0. By using a circuit to realize the change of the radio frequency signal w0 between w-250 MHz, w and w+250 MHz, then the second seed source main output, that is, the laser frequency f2 output by the second seed source will jump between f0-250 MHz, f0 and f0+250 MHz.

[0079] In another embodiment of the present application, a laser generation method for an iron resonance fluorescence Doppler laser radar is also disclosed, and the laser generation method comprises the following steps:

[0080] The first laser beam with a center wavelength of λ is power amplified and then frequency doubled, and then a saturated absorption spectrum technology is used to realize the frequency stabilization output of the first laser beam by using an iodine molecular transition spectrum with a wavelength of λ / 2, and a frequency difference w between the locking point of the iodine molecule frequency stabilization and the center frequency of the first laser beam after frequency doubling is calculated.

[0081] The first light beam output after frequency stabilization and the first light beam after power amplification are mixed to obtain a difference frequency signal, and a PID control circuit is used to adjust the center wavelength λ of the first laser beam by taking the difference frequency signal as a negative feedback input.

[0082] The frequency difference w of the required correction, the center frequency required by the temperature and wind measurement, and the frequency hopping amount between the two wings are added to the radio frequency modulation signal;

[0083] The adjusted first laser beam and the second laser beam are combined to generate a beat frequency, the difference frequency signal is locked to the modulation signal through an optical phase-locked loop, and the modulation signal is cyclically changed between w-Δf, w and w+Δf through a PID control circuit.

[0084] The modulation signal is injected into a pulsed laser based on a Nd:YAG solid laser crystal after frequency locking and power amplification, and after seed injection locking, power amplification and twice nonlinear frequency conversion, laser pulses of the required wavelength are obtained, and the specific value is 372.0993 nm.

[0085] In another embodiment of the application, a laser radar is also disclosed, which comprises the laser generating device of the iron resonance fluorescence Doppler laser radar of any one of the above embodiments, and the laser radar comprises a transmitting unit, the transmitting unit comprising a first beam splitter, a second beam splitter, a beam expander, an adjusting frame and a laser reflector.

[0086] The laser reflector is mounted on the adjusting frame.

[0087] The first beam splitter is coated with a λ / 3 wavelength reflection film, a λ / 2 wavelength and a λ wavelength anti-reflection film.

[0088] The second beam splitter is coated with a λ / 2 wavelength reflection film and a λ wavelength anti-reflection film, wherein λ is the center wavelength of the second seed source output.

[0089] The beam expander adopts an adjustable magnification of 2-5 times.

[0090] For example, the first beam splitter is coated with a 372 nm wavelength reflection film, a 558 nm wavelength and a 1116 nm wavelength anti-reflection film; the second beam splitter is coated with a 558 nm wavelength reflection film and a 1116 nm wavelength anti-reflection film. The beam expander adopts an adjustable magnification of 2-5 times, and the laser divergence angle is controlled between 0.1 mrad and 0.2 mrad. The emitted 372 nm wavelength pulsed laser is reflected by a high reflection mirror and enters a Galilean beam expander, which is used 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. At the same time, the laser reflector posture is adjusted by the adjusting frame to control the pointing of the laser beam emitted into the atmosphere, so that the transmitting and receiving optical axes of the laser radar are parallel, thereby ensuring the receiving efficiency.

[0091] Further, the laser radar further comprises a receiving unit, the receiving unit comprising a receiving telescope and a pinhole diaphragm, and the receiving telescope adopts a coaxial cassette system.

[0092] The receiving telescope comprises a concave parabolic primary mirror, a hyperboloid secondary mirror and a corner reflector arranged in sequence.

[0093] The pinhole diaphragm is arranged at the rear side of the receiving telescope and is used for controlling the field of view and the divergence angle of the receiving telescope.

[0094] Exemplarily, the receiving telescope adopts a coaxial cassette system and is composed of a concave parabolic primary mirror with a diameter of 1000 mm, a hyperboloid secondary mirror with a diameter of 190 mm and a corner reflector with a diameter of 25.4 mm, and is used for receiving three frequency echo signals; the zenith angle is 30 degrees, and if the direction is east, the receiving telescope can be used for measuring the zonal wind; if the direction of the laser beam and the telescope is changed to north, the receiving telescope can be used for measuring the meridional wind.

[0095] The pinhole diaphragm is used for controlling the field of view of the receiving telescope; the field of view of the receiving telescope is controlled to be within 0.4 mrad in consideration of the daytime detection; meanwhile, the divergence angle of the laser beam cannot be less than 0.1 mrad due to the influence of the iron atom saturation effect, and the field of view of the receiving telescope needs to be greater than the divergence angle of the laser beam to ensure the receiving efficiency of the system.

[0096] Further, the receiving unit further comprises a movable lens group, a daytime detection unit and a night detection unit;

[0097] The receiving unit is used for controlling the echo signals received by the receiving telescope to be transmitted to the daytime detection unit or the night detection unit;

[0098] The night detection unit comprises a first narrowband interferometer filter, a first collimating lens, a first narrowband filter, a first converging lens and a first photodetector arranged in sequence.

[0099] The daytime detection unit comprises a second narrowband interferometer filter, a second collimating lens, a second narrowband filter, a second converging lens and a second photodetector arranged in sequence.

[0100] Specifically, since the sunlight background noise is extremely strong during daytime detection, in order to more effectively obtain the effective echo signals, different optical structures are adopted in the daytime and the night in the embodiment to obtain the echo signals. During the daytime, the echo signals are transmitted to the daytime detection unit by the movable lens group, and the daytime detection unit collects and processes the echo signals; during the night, the position of the movable lens group is adjusted, the echo signals are transmitted to the night detection unit, and the night detection unit collects and processes the echo signals. Exemplarily, the bandwidth of the first narrowband filter is 0.15 nm, and the second narrowband interferometer filter is composed of two different FP etalons connected in sequence, and the comprehensive bandwidth is less than 5 pm.

[0101] Further, the laser radar further comprises a data processing unit, the data processing unit comprising a data acquisition card and a computing unit;

[0102] The data acquisition card is connected with the first photodetector and the second photodetector, and is used to convert the electrical signal into a digital signal;

[0103] The computing unit is connected with the data acquisition card, and is used to obtain the temperature, wind field and iron atom density detection result through the digital signal.

[0104] Specifically, after the first photodetector or the second photodetector converts the optical signal of the echo signal into an electrical signal, the data acquisition card quantizes the electrical signal into a digital signal, and the computing unit obtains the detection result of the temperature, wind field and iron density through the digital signal.

[0105] Further, the laser radar further comprises a high-speed chopper, the high-speed chopper is used to suppress the low-altitude strong backscattering echo signal, and prevent the saturation of the photodetector and the photon counting card; the drive motor speed of the high-speed chopper is set to 7200 revolutions per minute, the frequency of the electrical pulse signal generated by the conversion circuit is 480 Hz, and the 60 Hz pulse signal output is realized through 8 frequency division of the digital delay pulse generator DG645.

[0106] Further, the laser radar further comprises a timing control unit, taking the 60 Hz pulse sequence from the high-speed chopper as the main pulse signal of the timing control of the entire iron resonance fluorescence Doppler laser radar, and realizing the synchronous triggering of the 372 nm wavelength pulsed laser, the frequency monitoring unit and the acquisition unit.

[0107] Further, the laser radar further comprises an energy monitoring unit and a frequency monitoring unit;

[0108] The energy monitoring unit is used to monitor the λ / 3 wavelength laser, and eliminate the laser radar original data in the time period corresponding to the energy fluctuation anomaly;

[0109] The frequency monitoring unit is used to perform beam frequency mixing on the remaining λ wavelength laser, frequency hopping pulse light and continuous light of the laser radar, obtain the frequency stability of the pulse light, and eliminate the laser radar original data in the abnormal time period, wherein the abnormal time is the time period corresponding to the frequency stability greater than a set value.

[0110] Specifically, the energy monitoring unit, the pulsed laser from the 372nm wavelength Nd:YAG solid-state laser passes through the first beam splitter, 95% of the pulsed light is reflected to the beam expander, 5% of the pulsed light transmits through the beam splitter and then enters the energy monitoring unit and the frequency monitoring unit through the second beam splitter. The 372nm wavelength pulsed light is measured by a laser energy meter for a long time, the measured laser pulse energy data is displayed and stored in real time, and the subsequent laser radar raw data in the time period corresponding to the abnormal fluctuation of energy is removed;

[0111] The frequency monitoring unit, the remaining 1116nm wavelength frequency stabilized and frequency hopping pulsed light from the 372nm wavelength Nd:YAG solid-state laser is coupled into an optical fiber through a five-dimensional adjusting frame, and is combined with 1116nm wavelength continuous light from the 1116nm wavelength three-frequency stabilized seed laser to perform beat frequency, and the obtained frequency difference can indirectly reflect the frequency stability of the pulsed light; if the frequency stability is greater than a set value of 1MHz, the laser radar raw data in the corresponding time period needs to be removed.

[0112] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1.A laser generation device of an iron resonance fluorescence Doppler lidar, characterized in that, the laser generation device comprises a first seed source, a first laser processor, a second seed source and a second laser processor; the first seed source is configured to output continuous seed laser; the first laser processor is configured to perform power amplification and frequency-doubled frequency stabilization on the continuous seed laser, and perform frequency mixing on the laser after power amplification and frequency-doubled frequency stabilization to obtain a difference frequency signal, and adjust the center wavelength of the continuous seed laser according to the difference frequency signal; the second seed source is configured to output continuous seed laser; the second laser processor is configured to perform beam combination and frequency mixing on the continuous seed laser after adjustment by the first seed source and the continuous seed laser emitted by the second seed source, and phase-lock the difference frequency signal on an externally provided radio frequency signal, wherein the radio frequency signal is loaded with a signal having a fixed carrier frequency difference w, a center frequency required for temperature and wind measurement, and a frequency hopping amount Δf between two wing frequencies; the radio frequency signal is controlled to cyclically hop between w-Δf, w and w+Δf, and after locking, the continuous light emitted by the second seed source is amplified and output. 2.The laser generation device of the iron resonance fluorescence Doppler lidar according to claim 1, characterized in that, the first laser processor comprises a first fiber amplifier, an active frequency stabilization unit and a first servo feedback unit; the first fiber amplifier is configured to perform power amplification on the continuous seed laser; the active frequency stabilization unit is configured to perform frequency stabilization on the continuous seed laser after frequency doubling after power amplification; the first servo feedback unit is configured to perform frequency mixing on the laser after frequency stabilization and the laser after power amplification to obtain a difference frequency signal as an input of negative feedback adjustment to adjust the center wavelength of the first seed source. 3.The laser generation device of the iron resonance fluorescence Doppler lidar according to claim 2, characterized in that, the second laser processor comprises a signal generation unit, a signal frequency mixing and locking unit, a second servo feedback unit, a second fiber amplifier and a pulse laser; the signal generation unit is configured to add the frequency difference w between the output frequency and the center frequency of the iron fluorescence spectrum line, the center frequency required for temperature and wind measurement, and the frequency hopping amount Δf between two wing frequencies to the radio frequency modulation signal; the signal frequency mixing and locking unit is configured to perform beam combination and frequency mixing on the continuous seed laser after adjustment by the first seed source and the continuous light of the second seed source, and lock the detected difference frequency signal on the radio frequency signal through an optical phase-locked loop; the second servo feedback unit is configured to make the radio frequency signal cyclically hop between w-Δf, w and w+Δf through a PID control circuit; the second fiber amplifier is configured to perform power amplification on the continuous light of the second seed source and inject the pulse laser. 4.The laser generation device of the iron resonance fluorescence Doppler lidar according to claim 2, characterized in that: the active frequency stabilization unit comprises a frequency-doubling crystal and a frequency stabilization unit; the frequency-doubling crystal is configured to perform frequency doubling on the continuous seed laser; the frequency stabilization unit is configured to use the saturated absorption spectroscopy technology to realize the stabilization of the frequency of the continuous seed laser by using the iodine molecular absorption spectrum. 5.The lidar according to any one of claims 1-4, wherein the lidar further comprises a transmitting unit, the transmitting unit comprising a first beam splitter, a second beam splitter, a beam expander, an adjusting frame and a laser mirror. The laser mirror is mounted on the adjusting frame. The first beam splitter is coated with a λ / 3 wavelength reflective film, a λ / 2 wavelength and a λ wavelength anti-reflection film. The second beam splitter is coated with a λ / 2 wavelength reflective film and a λ wavelength anti-reflection film, wherein λ is the center wavelength of the second seed source output. The beam expander has an adjustable magnification of 2-5 times. 6.The lidar according to claim 5, wherein the lidar further comprises a receiving unit, the receiving unit comprising a receiving telescope and a pinhole diaphragm. The receiving telescope adopts a coaxial cassette system. The receiving telescope comprises a concave parabolic primary mirror, a hyperboloid secondary mirror and a corner reflector arranged in sequence. The pinhole diaphragm is arranged at the rear side of the receiving telescope and is used to control the field of view of the receiving telescope. 7.The lidar according to claim 6, wherein the receiving unit further comprises a movable lens group, a daytime detection unit and a night detection unit. The receiving unit is used to control the transmission of the received echo signal to the daytime detection unit or the night detection unit. The night detection unit comprises a first narrowband interferometer filter, a first collimating lens, a first narrowband filter, a first converging lens and a first photodetector arranged in sequence. The daytime detection unit comprises a second narrowband interferometer filter, a second collimating lens, a second narrowband filter, a second converging lens and a second photodetector arranged in sequence. 8.The lidar according to claim 7, wherein the lidar further comprises a data processing unit, the data processing unit comprising a data acquisition card and a computing unit. The data acquisition card is connected to the first photodetector and the second photodetector and is used to convert the electrical signal into a digital signal. The computing unit is connected to the data acquisition card and is used to obtain the temperature, wind field and iron atom number density detection results through the digital signal. 9.The lidar according to claim 5, wherein the lidar further comprises an energy monitoring unit and a frequency monitoring unit. The energy monitoring unit is used to monitor the λ / 3 wavelength laser and eliminate the original data of the lidar in the time period with abnormal energy fluctuation. The frequency monitoring unit is used to combine the λ wavelength, frequency hopping pulsed light and the continuous light of the remaining laser of the lidar to obtain the frequency stability of the pulsed light and eliminate the original data of the lidar in the abnormal time period, wherein the abnormal time is the time period corresponding to the frequency stability greater than a set value. 10.A laser generation method of an iron resonance fluorescence Doppler lidar, comprising the following steps: ​ ​ ​ ​ ​ The first laser beam with a center wavelength of λ is power amplified and then frequency doubled, and then a saturated absorption spectrum technology is used to realize frequency stabilization of the first laser beam by using an iodine molecular transition spectrum with a wavelength of λ / 2, and a frequency difference w between a locking point of the iodine molecular frequency stabilization and a center frequency of the first laser beam after frequency doubling is calculated; The first laser beam after frequency stabilization is mixed with the first laser beam after power amplification to obtain a difference frequency signal, and a PID control circuit is used to adjust the center wavelength λ of the first laser beam by taking the difference frequency signal as a negative feedback input; A frequency difference w to be corrected, a center frequency and a frequency hopping amount between two wing frequencies required for temperature and wind measurement are added to a radio frequency modulation signal; The adjusted first laser beam is combined with a second laser beam to obtain a beat frequency, the difference frequency signal is locked on the modulation signal by an optical phase-locked loop, and the modulation signal is cyclically hopped between w-Δf, w and w+Δf by using a PID control circuit; The modulation signal is phase-locked and power-amplified to inject a pulse laser to obtain a λ / 3 wavelength pulse laser.

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