CN110797741B - Q-switched laser output control method and laser output device for eliminating seed laser light leakage in coherent wind detection radar - Google Patents
Q-switched laser output control method and laser output device for eliminating seed laser light leakage in coherent wind detection radar Download PDFInfo
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Abstract
The invention relates to a Q-switched laser output control method and a laser output device for eliminating seed laser light leakage in a coherent wind measurement radar, which are used for eliminating interference of the seed laser light leakage on echo signals of the coherent wind measurement laser radar. According to the invention, on the basis of adopting the seed injection resonant cavity, the flow of the injection locking control system method is optimized, and the door opening time of the acousto-optic Q switch is controlled, so that the seed laser can not enter the driven annular oscillation cavity in the time interval before the pulse echo signal returns, thereby eliminating the interference of the seed laser light leakage on the coherent wind lidar echo signal.
Description
Technical Field
The invention belongs to the technical field of coherent laser wind measuring radar equipment, and particularly relates to a control method for eliminating echo signal interference caused by seed laser light leakage in a coherent wind measuring radar and a laser output device.
Background
The coherent laser wind measuring radar can monitor the atmospheric three-dimensional wind field in real time and has wide application in the fields of aviation, aerospace, wind power generation, weather forecast and the like. The adoption of an injection locking Q-switched pulse laser as a coherent laser wind-measuring radar laser light source is one of the mainstream modes in the field of the current coherent laser wind-measuring radar.
The working mode of the injection locking Q-switched pulse laser is that seed light with single frequency, narrow line width and good beam quality is injected into the driven Q-switched laser resonant cavity for amplification, and the output Q-switched pulse is established on the basis of the seed laser, so that the injection locking Q-switched pulse laser has the characteristics of high output pulse energy, single frequency, stable central frequency and the like, and is very suitable for coherent laser radar application.
At present, for a ring-shaped driven Q-switched laser resonant cavity, two injection locking modes are mainly adopted, wherein one mode is to inject seed laser from an output mirror, and the other mode is to inject seed laser from a diffraction order of an acousto-optic Q-switched crystal. Because the seed laser injected from the diffraction order of the acousto-optic Q-switched crystal does not need a frequency shifter additionally for heterodyne detection of radar echo signals, and the feedback of the bidirectional light emitting of the driven laser to the seed laser does not need to be worried, the method is more suitable for coherent laser wind measuring radars.
Research shows that for a coherent laser wind radar light source injecting seed laser into a diffraction order of an acousto-optic Q-switched crystal, after a Q-switched pulse is emitted, a Q switch is powered on to close the pulse output, at the moment, seed light enters a driven laser, leaks out from an output mirror and is emitted into the atmosphere (called seed laser light leakage), the seed laser and the Q-pulse laser participate in extraction of a heterodyne beat frequency interference wind measurement signal through backscattering of atmospheric molecules, and therefore the signal-to-noise ratio of an echo signal is reduced. And with the increase of the detection distance, the echo signal of the Q pulse laser is gradually weakened, and the reflection signal of the seed laser leaked in the near field is larger than the echo signal of the Q pulse laser, so that the improvement of the wind measuring distance of the coherent laser wind measuring radar is seriously restricted.
At present, no relevant report about the interference problem of seed laser light leakage on coherent laser wind finding radar echo signals is found in the field; the research and research on the problem and the proposed solution are more fresh.
Disclosure of Invention
In order to solve the above problems, the present invention aims to provide a method and an apparatus for eliminating interference of seed laser light leakage on coherent wind lidar echo signals, so as to achieve the purposes of improving radar echo signal-to-noise ratio, increasing coherent wind lidar detection distance, and the like.
Therefore, in a first aspect of the present invention, a method for controlling Q-switched laser output to eliminate seed laser light leakage in coherent wind radar is provided, the method comprising:
a. generating seed laser and injecting the seed laser into a driven laser;
b. controlling a driven laser to carry out frequency shift and amplification on the seed laser;
c. monitoring the peak value of the resonance signal of the amplified laser to control the turn-on of a Q-switching switch in the driven laser so as to generate Q-switching pulse laser output;
d. receiving a detection echo signal after Q-switched pulse laser output irradiates a target object for scattering;
the Q-switched switch is characterized in that the Q-switched switch is provided with a Q-switched crystal, the first-order diffraction order of the Q-switched crystal is used as at least one part of an injection channel of the seed laser injection slave laser, so that the Q-switched crystal is controlled to cut off the injection of the seed laser while Q-switched pulse laser output is generated, and the Q-switched crystal is kept cut off before a detection echo signal is received.
Further, the Q-switched crystal is kept cut off in time tau, and tau satisfies: tau is more than or equal to tau0Wherein, wherein τ is0The time required by the output Q-switched pulse laser to come and go the detection range of the coherent wind measuring radar is obtained.
Further, tau is less than laser upper energy level life tau of the output Q-switched pulse laserr。
Further, the Q-switch is controlled by a voltage rf signal, so that the on/off of the Q-switched pulse laser output and the cut-off/on of the injection of the seed laser are triggered simultaneously, that is: when the Q-switch is turned on to generate Q-switched pulse laser output, the Q-switched crystal cuts off the injection of the seed laser; when the Q-switch is closed to output, the Q-switch crystal conducts injection of the seed laser.
Further, the seed laser is frequency shifted by modulating the first order diffraction order of the Q crystal.
In a second aspect of the present invention, a Q-switched laser output control method for eliminating seed laser light leakage in coherent wind radar is provided, the method comprising:
a. generating seed laser and injecting the seed laser into a driven laser;
b. controlling a driven laser to carry out frequency shift and amplification on the seed laser;
c. monitoring the peak value of the resonance signal of the amplified laser to control the turn-on of a Q-switching switch in the driven laser so as to generate Q-switching pulse laser output;
d. receiving a detection echo signal after Q-switched pulse laser output irradiates a target object for scattering;
the method is characterized in that a first cut-off switch is arranged on a channel of a seed laser injection slave laser to generate Q-switched pulse laser output, the cut-off switch is controlled to cut off injection of the seed laser, and the cut-off switch is kept cut off before a detection echo signal is received.
Further, the cut-off switch is kept cut off within the time tau, and the tau satisfies the following conditions: tau is more than or equal to tau0In which τ is0The time required by the output Q-switched pulse laser to come and go the detection range of the coherent wind measuring radar is obtained.
Further, tau is less than laser upper energy level life tau of the output Q-switched pulse laserr。
In a third aspect of the present invention, a Q-switched laser output device for coherent wind radar is provided, wherein the laser output device applies the Q-switched laser output control method; the laser output device includes: the system comprises a seed laser, a driven laser and an injection locking control system, wherein the seed laser is used for generating seed laser;
the slave laser includes:
the pumping source is used for providing energy for the seed laser amplified by the driven laser;
a gain medium for providing sufficient population inversion to amplify the seed laser in the stimulated emission state;
the resonant cavity is used for injecting the seed laser and oscillating and amplifying the seed laser therein;
the piezoelectric ceramic actuator PZT is used for changing the cavity length of the resonant cavity;
a resonance signal detector for detecting a resonance signal of the amplified laser;
the Q-switching switch is used for Q-switching in the inner cavity of the resonant cavity to generate Q-switched pulse laser output; the Q-switching switch is provided with a Q-switching crystal, the first diffraction order of the Q-switching crystal is used as at least one part of an injection channel of the seed laser to be injected into the driven laser, and the seed laser is subjected to frequency shift;
the injection locking control system includes:
the Q-switching switch driver is used for generating a voltage radio frequency signal supplied to the Q-switching switch so as to drive the Q-switching switch to be switched on and off;
the CPLD is used for generating a periodic scanning signal to control the piezoelectric ceramic actuator PZT to periodically scan the cavity length of the resonant cavity to generate a resonant signal; and the CPLD is also used for receiving the resonance signal detected by the resonance signal detector and judging the peak value of the resonance signal so as to generate a Q-switching signal to control the Q-switching switch to drive the Q-switching switch to generate a voltage radio frequency signal to drive the Q-switching switch to be switched on and off.
Further, the resonant cavity is a ring resonant cavity.
The invention has the advantages that:
(1) according to the method for eliminating interference of seed laser light leakage on coherent wind lidar echo signals, the Q-switched crystal is used as a seed laser injection channel, the control time sequence of injection locking is optimized, so that the turn-on time of the acousto-optic Q switch is longer than or equal to the propagation time of the radar wind lidar echo signals, the seed laser cannot be emitted into the atmosphere during the period, and the interference of the seed laser light leakage on the wind lidar echo signals is eliminated. And because the acousto-optic Q switch integrates the on-off of the Q switch and the on-off of the injection channel at the same time, the synchronous trigger control of the Q switch and the injection channel can be realized only based on one voltage radio-frequency signal of the Q switch, so that the intensification and the reliability of the system are fully improved.
(2) According to the method for eliminating the interference of the seed laser light leakage on the coherent wind lidar echo signal, the seed laser cannot be emitted into the atmosphere before the detection echo signal is received by controlling the cut-off time of the cut-off switch, so that the interference of the seed laser light leakage on the wind lidar echo signal is eliminated.
(3) The invention can keep the seed laser cut off in the preset time tau, thereby being capable of setting the following steps without extra setting: judging whether to receive the wind measuring echo signal under the condition of a monitor and other devices (under the condition of configuring the monitor and other devices, the fact that the seed laser injection channel can be conducted by the side receiving the wind measuring echo signal is monitored at first) and determining when the seed laser injection channel can be conducted based on the preset time tau; therefore, the effect of eliminating the interference of seed laser light leakage on a wind measurement echo signal is ensured, the whole system is more intensive under the condition of reducing the cost, a small-volume laser device is convenient to form, and the power consumption is reduced and the reliability of the whole system is improved due to the reduction of related devices.
(4) The invention makes the preset time tau less than the laser upper energy level life tau of the output Q-switched pulse laserrAnd spontaneous transition fluorescence which is enough to influence a coherent wind lidar echo signal is prevented from being generated by the upper-level particles within the time tau and emitted to the atmosphere, so that the interference of the spontaneous fluorescence on the wind lidar echo signal is eliminated, and the improvement of the measurement distance of the coherent wind lidar is facilitated.
(5) The invention utilizes the diffraction order of the Q-switched crystal to shift the frequency of the injected seed laser, thereby avoiding the extra need of a frequency shifter for heterodyne detection of radar echo signals, avoiding the worry of feedback of bidirectional light emission of the driven laser to the seed laser, leading the whole system to be more intensive under the condition of reducing the cost, being convenient for forming a small-volume laser device, and reducing the power consumption and increasing the reliability of the whole system due to the reduction of related devices.
(6) The invention preferably adopts the annular oscillation cavity, thereby eliminating the spatial hole burning effect, fully utilizing the number of particles of the upper energy level of the gain medium and having no pulse tailing and multi-pulse phenomenon effect.
Drawings
FIG. 1 is a schematic structural diagram of a Q-switched laser output device according to the present invention;
FIG. 2 is a timing diagram illustrating the operation of the injection locking control system;
FIGS. 3(b) and (a) are schematic diagrams illustrating comparison of interference detection effects corresponding to echo signals, respectively, if the Q-switched laser output control method of the present invention is applied;
fig. 4(a) and (b) are schematic flow diagrams of Q-switched laser output control methods corresponding to two embodiments of the present invention, respectively.
Description of reference numerals:
1-a pump source; 2-a gain medium; 3-piezoceramic actuators PZT; 4. 5, 6, 7-chamber mirror; 8-a resonant signal detector; 9-a Q-switch; 10-seed laser; 11-Q-switched switch drive; 12-an upper computer; 13-a microcontroller; 14-CPLD; 15-high voltage amplification module.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
Referring to fig. 1, a schematic structural diagram of a Q-switched laser output device according to the present invention is shown. The laser output device includes: seed laser 10, slave laser (module) and injection locking control system:
(1) seed laser
The seed laser is used for generating seed laser with single frequency, narrow line width and good beam quality.
(2) Driven laser
The slave laser includes: the device comprises a pumping source 1, a gain medium 2, a piezoelectric ceramic actuator PZT, a resonant cavity (enclosed by cavity mirrors 4, 5, 6 and 7), a resonant signal detector 8 and a Q-switch 9. Wherein,
and the pumping source 1 is used for providing energy for the driven laser to amplify the seed laser.
And the gain medium 2 is used for providing enough population inversion to amplify the seed laser in the stimulated radiation state.
And the resonant cavity (oscillation cavity) is used for injecting the seed laser and carrying out oscillation amplification in the seed laser. Preferably, the resonant cavity is a ring resonant cavity, and the ring resonant cavity has the advantages that the spatial hole burning effect can be eliminated, the number of particles on the upper energy level of the gain medium is fully utilized, and the pulse trailing and multi-pulse phenomenon effects do not exist. As a preferred way of a ring cavity, the cavity mirrors 4, 5, 6, 7 are used to form a closed ring resonator, providing laser amplification positive feedback and mode selection.
A piezoceramic actuator PZT3 for varying the cavity length of the resonant cavity. As a preferable mode, the PZT can be pasted on a certain cavity mirror of the driven laser and used for changing the cavity length of the driven laser and searching the resonance point of the seed laser in the driven laser.
A Q-switch 9 for Q-switching in the cavity of the resonant cavity to generate Q-switched pulse laser output; the Q-switched switch has a Q-switched crystal. Preferably, the seed laser is injected into the ring slave laser from the first order diffraction order of the Q-switch 9, so that the first order diffraction order is injected into at least a part of the injection channel of the slave laser as seed laser, and the seed laser can be shifted in frequency for coherent wind radar signal heterodyne beat frequency detection. The Q-switch can be selected from active Q-switches such as electro-optical Q-switch or acousto-optical Q-switch. In a preferred embodiment, the Q-switch of the present invention is an acousto-optic Q-switch.
And the resonance signal detector 8 is used for detecting a resonance signal of the seed light in the driven ring laser cavity, and the resonance signal is converted into a digital signal through the analog-to-digital conversion module and then is input into the CPLD14 of the injection locking control system.
The injection locking control system receives an output signal of the resonance detector, and adopts a scanning-maintaining-triggering technology or a scanning-triggering technology to adjust the intracavity loss of the driven resonant cavity so as to generate injection locking Q-switched pulse laser.
(3) Injection locking control system
The injection locking control system includes: the system comprises a Q-switch driver 11, an upper computer 12, a microcontroller 13, a CPLD14 and a high-voltage amplification module 15. Wherein,
the CPLD14 is used for generating a periodic sawtooth wave scanning signal (see the attached figure 2), and controls the PZT3 to periodically scan the cavity length of the driven laser after being amplified by the high-voltage amplification module 15 so as to generate a resonance signal; and the CPLD is also used for receiving the resonance signal detected by the resonance signal detector, judging the peak value of the resonance signal after the CPLD module receives the externally input resonance signal, and generating a TTL signal (namely, as a Q-switching signal) to control the Q-switching switch drive 11 to generate a voltage radio-frequency signal to drive the on-off state of the Q-switching switch 9, thereby generating a Q-switching pulse. Furthermore, the CPLD14 may also generate a TTL signal (called a Q-switched synchronization signal) that is the same as the Q-switched signal, as a synchronization signal of the radar echo signal acquisition and processing system.
And the Q-switch driver 11 is used for generating a voltage radio-frequency signal supplied to the Q-switch to drive the Q-switch to be turned on and off. Here, the Q-switched signal is coupled to a signal input of the Q-switched switch driver 11. The signal input end of the Q-switch driver 11 means that when an external signal is input into the Q-switch driver 11 from this port, the on-time of the Q-switch 9 will be determined by the external signal and will not be determined by the internal signal of the Q-switch driver 11.
And the high-voltage amplification module 15 is used for amplifying the sawtooth wave scanning signal generated by the CPLD14, applying the sawtooth wave scanning signal to the piezoceramic actuator PZT3 and changing the cavity length of the resonant cavity of the driven laser.
The upper computer 12 and the microcontroller 13 can be connected with the CPLD14 through serial ports to control the working state of the CPLD14 and realize human-computer interaction.
Fig. 4(a) and (b) are schematic flow diagrams of Q-switched laser output control methods corresponding to two embodiments of the present invention, respectively. The method for controlling the output of the Q-switched laser according to the present invention will be described in detail with reference to specific embodiments 1 and 2 of the present invention.
Specific example 1: seed laser light leak elimination based on cut-off switch
Referring to fig. 4(a), the Q-switched laser output control method for eliminating seed laser light leakage in coherent wind radar provided by the invention mainly comprises the following steps:
first, a seed laser is generated and injected into the slave laser.
And secondly, controlling the driven laser to shift the frequency of the seed laser and amplify the seed laser.
Then, monitoring the peak value of the resonance signal of the amplified laser to control the turn-on of a Q-switching switch in the driven laser, thereby generating the output of Q-switching pulse laser; in this embodiment, a first cut-off switch (not shown) may be provided on the channel of the seed laser injection slave laser to generate the Q-switched pulsed laser output while controlling the cut-off switch to cut off the injection of the seed laser and to keep the cut-off switch off until the detection echo signal is received.
And then, receiving a detection echo signal after the Q-switched pulse laser outputs and irradiates the target object for scattering.
In this embodiment, it is preferable that the cut-off switch is kept off for a time τ that satisfies: tau is more than or equal to tau0Wherein, wherein τ is0The time required by the output Q-switched pulse laser to come and go the detection range of the coherent wind measuring radar is obtained. For example, the range of coherent wind radar is judged in advance or the expected range is set as s, and the time tau required for the laser to come and go to the range is calculated0The calculation formula is tau02s/c, where c is the speed of light. Therefore, the time for which the cut-off switch is kept off (i.e. the tissue seed laser injection continues) tau is made to be greater than or equal to tau0And the seed laser cannot enter the driven resonant cavity within the time tau, so that the seed laser cannot emit and influence the receiving of the coherent wind lidar echo signal.
Therefore, the invention can ensure the effect of eliminating the interference of seed laser light leakage to the wind measuring echo signal under the condition of not additionally arranging devices such as a monitor for monitoring whether the wind measuring echo signal is received or not by keeping the seed laser cut off within the preset time tau, ensures that the whole system is more intensive under the condition of reducing the cost, is convenient for forming a small-volume laser device, and reduces the power consumption and increases the reliability of the whole system due to the reduction of related devices.
It is further preferred in this embodiment that τ is less than (and more preferably much less than) the laser upper-level lifetime τ of the output Q-switched pulsed laserr. Therefore, spontaneous transition fluorescence which is enough to influence echo signals of the coherent wind lidar and is emitted to the atmosphere is prevented from being generated by the upper-level particles within the time tau, interference of the spontaneous fluorescence on the wind echo signals is eliminated, and the measurement distance of the coherent wind lidar is promoted.
Therefore, embodiment 1, as an aspect of the present invention, provides a method for eliminating interference of seed laser light leakage on an echo signal of a coherent wind lidar, which ensures that seed laser cannot be emitted into the atmosphere before receiving the sounding echo signal by controlling a cut-off hold time of a cut-off switch, so as to eliminate interference of seed laser light leakage on the echo signal of the wind lidar.
Specific example 2: seed laser light leakage elimination based on Q-switched crystal
Referring to fig. 4(b), another Q-switched laser output control method for eliminating seed laser light leakage in a coherent wind radar provided by the present invention mainly includes the following steps:
first, a seed laser is generated and injected into the slave laser.
And secondly, controlling the driven laser to shift the frequency of the seed laser and amplify the seed laser.
Then, monitoring the peak value of the resonance signal of the amplified laser to control the turn-on of a Q-switch (in the embodiment, the Q-switch is an acousto-optic Q-switch) in the driven laser, so as to generate the output of Q-switched pulse laser; in the present embodiment, the Q-switch has a Q-switching crystal, the first order diffraction order of which is injected as seed laser light into at least a part of the injection channel of the slave laser, to control the Q-switching crystal to cut off the injection of the seed laser light while generating the Q-switching pulse laser output, and to keep the Q-switching crystal cut off until the detection echo signal is received.
The seed laser is injected from the first diffraction order of the Q-switched crystal, so that the device of additionally arranging a cut-off switch outside the Q-switched switch in the embodiment 1 is avoided. In the second aspect, the injected seed laser can be shifted in frequency by utilizing the diffraction order of the Q-switched crystal, so that a frequency shifter is not additionally needed for heterodyne detection of radar echo signals, the feedback of the two-way light emitting of the driven laser to the seed laser is not needed, the whole system is more intensive under the condition of reducing the cost, a small-volume laser device is convenient to form, and the power consumption is reduced and the reliability of the whole system is improved due to the reduction of related devices. In the third aspect, the Q-switch can be synchronously triggered by integrating the on-off of the Q-switch and the on-off of the injection channel, so that the Q-switch and the injection channel can be controlled only based on one voltage radio-frequency signal of the Q-switch, and the intensification and the reliability of the system are fully improved.
As an example in this embodiment, a specific working process of the Q-switched crystal may be: when the output port of the Q-switched signal of the injection locking control system outputs a low level, a voltage (or a high voltage) is applied to the Q-switched crystal, at the moment, seed laser can enter a resonant cavity of a driven laser and oscillate in the resonant cavity of the driven laser, the driven laser is in a low Q state, and pulse laser cannot be emitted; the method comprises the steps that a sawtooth wave scanning signal is used for periodically scanning the cavity length of a driven resonant cavity, when seed laser resonates with the driven resonant cavity, a resonant signal reaches a peak value, a high level is output by a Q-switching signal output port of an injection locking control system at the moment, no voltage (or low voltage) is added to a Q-switching crystal, a driven laser is in a high Q state, pulse laser is emitted, meanwhile, the seed laser cannot enter the driven resonant cavity and cannot be emitted to the atmosphere along with the pulse laser, the Q-switching signal output continues to keep the high level (if the keeping time is more than or equal to the round-trip time of the pulse signal), therefore, the seed laser cannot interfere the receiving of pulse echoes, and the interference of seed laser light leakage on coherent wind lidar.
And then, receiving a detection echo signal after the Q-switched pulse laser outputs and irradiates the target object for scattering.
In the embodiment, the Q-switched crystal is preferably kept to cut off the injection of the seed laser within the time tau, and the tau satisfies the following conditions: tau is more than or equal to tau0In which τ is0The time required by the output Q-switched pulse laser to come and go the detection range of the coherent wind measuring radar is obtained. For example, the range of coherent wind radar is judged in advance or the expected range is set as s, and the time tau required for the laser to come and go to the range is calculated0The calculation formula is tau02s/c, where c is the speed of light. Therefore, the time for which the cut-off switch is kept off (i.e. the tissue seed laser injection continues) tau is made to be greater than or equal to tau0And the seed laser cannot enter the driven resonant cavity within the time tau, so that the seed laser cannot be emitted to influence the receiving of the coherent wind lidar echo signal.
It is further preferred in this embodiment that τ is less than (and more preferably much less than) the laser upper-level lifetime τ of the output Q-switched pulsed laserr. Thereby avoiding the self-generation of enough self-influence signals of coherent wind lidar echo signals by the particles at the upper energy level in the time tauThe transition fluoresces and emits into the atmosphere.
In this embodiment, the Q-switch is preferably controlled by a voltage signal (high/low level as described above) such that turning on/off the output of the Q-switched pulsed laser and turning off/on the injection of the seed laser are triggered simultaneously, that is: when the Q-switch is turned on to generate Q-switched pulse laser output, the Q-switched crystal cuts off the injection of the seed laser; when the Q-switch is closed to output, the Q-switch crystal conducts injection of the seed laser. Therefore, the Q switch is simultaneously integrated with the on-off of the Q switch and the on-off of the injection channel, and is synchronously triggered through the Q switch, so that the Q switch and the injection channel can be controlled only based on one voltage radio-frequency signal of the Q switch, and the intensification and the reliability of the system are fully improved.
In the embodiment, preferably, the seed laser is frequency-shifted by adjusting the first-order diffraction order of the Q crystal, and is used for coherent wind radar signal heterodyne beat frequency detection. Therefore, a frequency shifter is not additionally needed for heterodyne detection of radar echo signals, the feedback of the bidirectional light emitting of the driven laser to the seed laser is not needed, the whole system is more intensive under the condition of reducing the cost, a small-size laser device is convenient to form, and the power consumption is reduced and the reliability of the whole system is improved due to the reduction of related devices.
Therefore, as another aspect of the present invention, embodiment 2 provides another method for eliminating interference of seed laser light leakage on a coherent wind lidar echo signal, in which a Q-switched crystal is used as a seed laser injection channel, and a control timing sequence of injection locking is optimized, so that an on time of an acousto-optic Q switch is greater than or equal to a propagation time of the radar wind lidar echo signal, and it is ensured that seed laser cannot be emitted into the atmosphere during this period, thereby eliminating interference of seed laser light leakage on the wind lidar echo signal. And because the acousto-optic Q switch integrates the on-off of the Q switch and the on-off of the injection channel at the same time and is synchronously triggered by the Q switch, the acousto-optic Q switch and the injection channel can be controlled only based on one voltage radio-frequency signal of the Q switch, so that the intensification and the reliability of the system are fully improved.
Further, as shown in fig. 2, as an operating state timing diagram of the injection locking control system corresponding to embodiment 2, a periodic sawtooth wave scanning signal generated by the CPLD, a resonance signal detected by the resonance signal detector, a Q-switched signal for eliminating seed laser light leakage from detecting a coherent wind lidar echo signal, an acousto-optic Q-driven radio frequency output signal (i.e., a voltage signal applied to a Q-switched switch by a Q-switched switch drive), a Q-switched operating mode (a blank part indicates that the Q-switched is on, and a filled part indicates that the Q-switched is off), and a timing sequence of whether seed laser enters the driven resonant cavity are sequentially performed from top to bottom. Where f is the frequency of the sawtooth scanning signal, i.e., the pulse repetition frequency of the Q-switched laser. The cavity length of the driven laser is periodically scanned by sawtooth waves generated by the CPLD at the frequency f, when the seed laser and the resonant cavity of the driven laser resonate, a resonant signal reaches a peak value, and at the moment, a Q-switching signal port of the CPLD outputs a high level for a duration of tau.
As an example of embodiment 2, let τ be the round trip time of laser light corresponding to the expected radar wind finding distance, and τ be set to be equal to or greater than τ0For example, if the expected radar wind finding distance (usually the expected maximum distance, i.e. range) is 30km and the time required for the laser to traverse 30km is about 200 μ s, then τ should be set to a parameter equal to or greater than 200 μ s. Preferably, the parameter of tau setting is slightly larger than 200 mus and far smaller than the laser upper energy level life tau of the output Q-switched pulse laserr. As shown in fig. 2, in the duration τ of the high level of the Q-switched signal, the radio frequency output signal driven by the acousto-optic Q is at a low level, the Q-switched is in an on state, and Q-switched pulse emission is performed, however, in this period, the seed laser cannot be injected into the driven resonant cavity from the diffraction order of the acousto-optic Q, and cannot be emitted into the atmosphere, and in the limited time of pulse echo signal acquisition, the interference of the seed laser light leakage on the coherent laser wind finding radar echo signal is eliminated.
Referring to fig. 3(b) and (a), there are schematic diagrams illustrating comparison of the interference detection effect of echo signals when the Q-switched laser output control method of the present invention is applied. The vertical axis represents the echo signals of the atmospheric wind field at different distances obtained by coherent heterodyne detection, and the horizontal axis represents the frequency. Fig. 3(a) shows the interference of the seed laser light leakage to the echo signal, and fig. 3(b) shows the echo signal of the wind-measuring radar obtained by the method of the present invention after the seed laser light leakage is eliminated.
In summary, the invention provides a method and a laser output device for eliminating interference of seed laser on echo signals of coherent laser wind-measuring radar, by matching with an annular driven resonant cavity and optimized injection locking control, under the condition of ensuring output of single-frequency pulses, by properly prolonging the opening time of an acousto-optic Q switch, the seed laser is prevented from entering the driven resonant cavity within the detection time of the echo signals of the wind-measuring radar, so that the interference of the seed laser on the wind-measuring echo signals is eliminated, and the measurement distance of the coherent laser wind-measuring radar is favorably improved.
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. A Q-switched laser output control method for eliminating seed laser light leakage in coherent wind detection radar comprises the following steps:
a. generating seed laser and injecting the seed laser into a driven laser;
b. controlling the driven laser to carry out frequency shift and amplification on the seed laser;
c. monitoring the peak value of the resonance signal of the amplified laser to control a Q-switching switch in the driven laser to be switched on so as to generate Q-switching pulse laser output;
d. receiving a detection echo signal after the Q-switched pulse laser outputs and irradiates a target object for scattering;
wherein the Q-switch has a Q-switching crystal, the first order diffraction order of the Q-switching crystal is used as at least one part of the injection channel of the slave laser for injecting the seed laser into the slave laser, so as to control the Q-switching crystal to cut off the injection of the seed laser while generating Q-switching pulse laser output, and to keep the Q-switching crystal cut off before receiving the detection echo signal.
2. The method of claim 1, wherein: keeping the Q-switched crystal switched off for a time τ that satisfies:
τ≥τ0wherein, wherein τ is0The time required for the output Q-switched pulse laser to come and go to the detection range of the coherent wind measuring radar is obtained.
3. The method of claim 2, wherein: the tau is less than the laser upper energy level life tau of the output Q-switched pulse laserr。
4. The method of controlling Q-switched laser output according to any of claims 1-3, wherein: the Q-switching switch is controlled by a voltage radio frequency signal, and when the Q-switching switch is turned on to generate the output of the Q-switching pulse laser, the Q-switching crystal cuts off the injection of the seed laser; when the Q-switching switch is turned off to output, the Q-switching crystal conducts injection of the seed laser.
5. The method of controlling Q-switched laser output according to any of claims 1-3, wherein: the seed laser carries out the frequency shift through the first-order diffraction order of the Q-switched crystal.
6. A Q-switched laser output control method for eliminating seed laser light leakage in coherent wind detection radar comprises the following steps:
a. generating seed laser and injecting the seed laser into a driven laser;
b. controlling the driven laser to carry out frequency shift and amplification on the seed laser;
c. monitoring the peak value of the resonance signal of the amplified laser to control a Q-switching switch in the driven laser to be switched on so as to generate Q-switching pulse laser output;
d. receiving a detection echo signal after the Q-switched pulse laser outputs and irradiates a target object for scattering;
the method is characterized in that a first cut-off switch is arranged on a channel for injecting the seed laser into the driven laser to generate Q-switched pulse laser output, the cut-off switch is controlled to cut off the injection of the seed laser, and the cut-off switch is kept cut off before the detection echo signal is received.
7. The method of claim 6, wherein: keeping the cut-off switch switched off for a time τ, which satisfies:
τ≥τ0in which τ is0The time required for the output Q-switched pulse laser to come and go to the detection range of the coherent wind measuring radar is obtained.
8. The method of claim 7, wherein: the tau is less than the laser upper energy level life tau of the output Q-switched pulse laserr。
9. A Q-switched laser output device for coherent wind radar, which applies the Q-switched laser output control method according to any one of claims 1 to 5; the laser output device includes:
a seed laser for generating the seed laser, the slave laser, and an injection locking control system;
the slave laser includes:
the pumping source is used for providing energy for the driven laser to amplify the seed laser;
a gain medium for providing sufficient population inversion to amplify the seed laser in a stimulated emission state;
the resonant cavity is used for injecting the seed laser and oscillating and amplifying the seed laser therein;
the piezoelectric ceramic actuator PZT is used for changing the cavity length of the resonant cavity;
a resonance signal detector for detecting the resonance signal of the amplified laser light;
the Q-switching switch is used for Q-switching in an inner cavity of the resonant cavity to generate the Q-switched pulse laser output; the Q-switching switch is provided with the Q-switching crystal, an order of diffraction of the Q-switching crystal is used as at least one part of an injection channel of the slave laser, and the seed laser is subjected to frequency shift;
the injection lockout control system comprises:
the Q-switching switch driver is used for generating a voltage radio frequency signal supplied to the Q-switching switch so as to drive the Q-switching switch to be switched on and off;
a CPLD for generating a periodic scanning signal to control the piezoceramic actuator PZT to periodically scan the cavity length of the resonant cavity to generate the resonant signal; and the CPLD is also used for receiving the resonance signal detected by the resonance signal detector and judging the peak value of the resonance signal so as to generate a Q-switching signal to control the Q-switching switch to drive the voltage radio-frequency signal to drive the Q-switching switch to be switched on and off.
10. The Q-switched laser output device according to claim 9, characterized in that: the resonant cavity is an annular resonant cavity.
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