Control method of seed injection single-frequency pulse laser

Abstract

This invention provides a control method for a seed-injected single-frequency pulsed laser. By identifying the peak time and peak height of the resonant signal at the rising edge of the piezoelectric ceramic scanning voltage, predicting the peak value at the falling edge, and identifying the resonant signal voltage within the predicted peak time range, a trigger signal is issued when the resonant signal voltage exceeds a threshold voltage, thus achieving stable single-frequency pulsed laser output. This injection-locking method has a lower scanning voltage, resulting in higher lifespan and reliability for the piezoelectric ceramic. In other words, this invention solves the problems of high hardware cost, high scanning voltage, and low frequency stability in single-frequency pulsed lasers, enabling the output of high-energy single-frequency pulsed lasers with strong anti-interference capabilities and good frequency stability.

Description

Technical Field

[0001] This invention belongs to the field of single-frequency laser technology, and particularly relates to a control method for a seed-injection type single-frequency pulsed laser. Background Technology

[0002] A single-frequency pulsed laser is a laser that outputs a single frequency and a pulsed laser. This type of laser has wide applications in differential absorption lidar, wind measurement lidar, and coherent imaging lidar.

[0003] High-energy single-frequency pulsed laser output can be achieved through seed injection and injection-locking technology. The basic principle is as follows: a single-frequency continuous laser output from a single-frequency seed laser is injected into a passively Q-switched laser. By controlling the cavity length to resonate with the seed laser and triggering Q-switching, single-frequency laser output from the pulsed laser is achieved. Currently, injection-locking control methods still suffer from problems such as high scanning voltage, high hardware cost, and the need to improve frequency stability. Patent CN112636145A discloses an injection-locking method that uses piezoelectric ceramics to change the cavity length. When two resonant signal peaks are detected during the rising edge, the occurrence time of the third peak is determined, and a trigger signal is given 150-200μs in advance to achieve single-frequency pulsed laser output. This method requires scanning at least three resonant peaks, and the resonant cavity corresponding to the scanning voltage needs to cover at least three free spectral regions, increasing the complexity of the amplification circuit and reducing the lifespan of the piezoelectric ceramics. Patent CN104393477A discloses an injection-locking method that controls the cavity length using two piezoelectric ceramics. By using a first piezoelectric ceramic to scan the cavity length with a high-frequency sinusoidal wave, and detecting the phase of the resonant signal in the sinusoidal wave in each cycle, a bias voltage is applied to a second piezoelectric ceramic to correct the phase of the resonant signal in the next cycle. This process ultimately achieves peak value at an ideal point, providing a trigger signal and realizing single-frequency pulsed laser output. Although this method only requires scanning at least one resonant peak, the overall structure is complex, increasing hardware costs. Summary of the Invention

[0004] To address the problems of high hardware cost, high scanning voltage, and low frequency stability of single-frequency pulsed lasers in existing technologies, this invention provides a control method for a seed-injection type single-frequency pulsed laser, which can achieve stable single-frequency pulsed laser output and enable piezoelectric ceramics to have a longer lifespan and higher reliability.

[0005] A method for controlling a seed-injected single-frequency pulsed laser includes the following steps:

[0006] S1: The continuous single-frequency seed laser 1 outputs a seed laser to the passive Q-switched laser 2, causing interference within the resonant cavity of the passive Q-switched laser 2 to generate a resonant signal; wherein, the length of the resonant cavity is related to the piezoelectric ceramic 2-3 in the passive Q-switched laser 2, and different voltages applied to the piezoelectric ceramic 2-3 result in different expansion and contraction of the piezoelectric ceramic 2-3, thus corresponding to different resonant cavity lengths;

[0007] S2: The injection lock controller 4 outputs a triangular wave to the piezoelectric ceramic 2-3. At the same time, the photodetector 2-2 in the slave Q-switched laser 2 receives the resonant signal formed in the resonant cavity of the slave Q-switched laser 2 under the current triangular wave.

[0008] S3: Determine the reference time t based on the highest voltage value of the resonant signal at the rising edges of three consecutive triangular waves and the time when the highest voltage value is located. x And based on the reference time t x Determine the trigger period;

[0009] S4: During the triggering period, determine whether the output voltage of photodetector 2-2 is greater than the set threshold voltage V. t If so, the injection locking controller 4 sends a trigger signal to the Q driver 3 to control the Q switch 2-1 to open or close, so that the slave Q-switched laser 2 outputs a single-frequency pulse laser.

[0010] Furthermore, the reference time t x The method for determining it is as follows:

[0011] Let V1 be the voltage at the highest peak value of the resonant signal located at the rising edge of the current triangular wave, and let t1 be the time when V1 is located.

[0012] Read the voltage V2 of the highest peak value of the resonant signal at the rising edge of the previous triangular wave, and the time t2 at which voltage V2 is located;

[0013] Read the voltage V3, which is the highest peak value of the resonant signal at the rising edge of the previous triangular wave, and the time t3 at which the voltage V3 is located;

[0014] Take the differences between each pair of times t1, t2, and t3. If |t2-t3|<Δt, |t1-t2|>Δt, and |t1-t3|>Δt simultaneously, then t x =t2, if any one of them is not satisfied, then t x = t1, where Δt is the set difference threshold.

[0015] Furthermore, at the rising edge of the triangular wave, the stretching of the piezoelectric ceramic within the time interval Δt is less than one-quarter of the output laser wavelength of the Q-switched laser.

[0016] Furthermore, based on the reference time t x The method for determining the trigger period is as follows:

[0017] Obtain the center point of the trigger period 2×t0-t x Where t0 is the peak voltage moment of the current triangular wave;

[0018] Meanwhile, the width of the triggering period is more than twice the full width at half maximum (FWHM) of the resonant signal.

[0019] Furthermore, the cavity length of the piezoelectric ceramic scanning within a triangular wave is greater than the wavelength of the driven Q-switched laser.

[0020] Furthermore, the starting point of the rising edge of each triangular wave cycle is the zero point of the time record.

[0021] Beneficial effects:

[0022] This invention provides a control method for a seed-injected single-frequency pulsed laser. By identifying the peak time and peak height of the resonant signal at the rising edge of the piezoelectric ceramic scanning voltage, predicting the peak value at the falling edge, and identifying the resonant signal voltage within the predicted peak time range, a trigger signal is issued when the resonant signal voltage exceeds a threshold voltage, thus achieving stable single-frequency pulsed laser output. This injection-locking method has a lower scanning voltage, resulting in a longer lifespan and higher reliability for the piezoelectric ceramic. In other words, this invention solves the problems of high hardware cost, high scanning voltage, and frequency stability in single-frequency pulsed lasers, enabling the output of high-energy single-frequency pulsed lasers with strong anti-interference capabilities and good frequency stability. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a laser structure based on a control method for a seed-injection single-frequency pulse laser proposed in this invention.

[0024] Figure 2 It is the timing relationship between the triangular wave voltage applied to the piezoelectric ceramic, the resonant signal, the trigger signal, and the output laser pulse. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.

[0026] Please refer to the following first. Figure 1 , Figure 1This is a schematic diagram of the laser structure of the injection locking method of the control method of the seed injection single-frequency pulse laser proposed in this invention. It can be seen that the laser structure based on the method provided by this invention includes a continuous single-frequency seed laser 1, a passively Q-switched laser 2, a Q driver 3, and an injection locking controller 4.

[0027] A continuous-frequency seed laser 1 is used to output a single-frequency continuous laser and serves as the frequency reference source for the passively Q-switched laser 2. The passively Q-switched laser 2 includes a Q-switch 2-1, a photodetector 2-2, and a piezoelectric ceramic 2-3. The passively Q-switched laser 2 is the core controlled device in the injection-locked system, used to output a single-frequency Q-switched laser. The Q-driver 3 is the driver for the Q-switch 2-1. The injection-locked controller 4 is the core control device in the injection-locked system.

[0028] The specific implementation parameters of the device used in this invention are as follows:

[0029] The continuous-wave single-frequency seed laser is a monolithic non-planar ring-cavity Er:YAG laser with an average output power >50mW and a linewidth <10kHz. The driven Q-switched laser is also an Er:YAG laser. The pump source is a fiber laser with a continuous power of 30W and a center wavelength of 1532nm. The gain medium is an Er:YAG laser crystal with a doping concentration of 0.25 at.%, and a crystal size of φ4×60mm. The Q-switch is an acousto-optic modulator. A piezoelectric ceramic with parameters of 0.127μm / V was selected. At a scanning voltage amplitude of 30V and a corresponding cavity length scanning length of 3.8μm, a single-frequency pulse with a pulse energy ≥6mJ, a repetition rate ≥500Hz, and a linewidth ≤5MHz was obtained.

[0030] Please see Figure 2 The injection locking control process includes the following steps:

[0031] S1. Injection: The continuous single-frequency seed laser 1 outputs a seed laser into the passive Q-switched laser 2, causing interference within the resonant cavity of the passive Q-switched laser 2 to generate a resonant signal; wherein, the length of the resonant cavity is related to the piezoelectric ceramic 2-3 in the passive Q-switched laser 2, and different voltages applied to the piezoelectric ceramic 2-3 result in different amounts of expansion and contraction of the piezoelectric ceramic 2-3, thus corresponding to different lengths of the resonant cavity;

[0032] S2, Scanning: The injection lock controller 4 outputs a triangular wave to the piezoelectric ceramic 2-3. At the same time, the photodetector 2-2 in the driven Q-switched laser 2 receives the resonant signal formed in the resonant cavity of the driven Q-switched laser 2 under the current triangular wave.

[0033] S3. Prediction: Determine the reference time t based on the highest voltage value of the resonant signal at the rising edges of three consecutive triangular waves and the time when the highest voltage value is located.x And based on the reference time t x Determine the trigger period;

[0034] Specifically, at the rising edge of the triangular wave, the peak value of the resonant signal is identified, and the starting point of each rising edge is set as time zero. Then, the reference time t... x The method for determining it is as follows:

[0035] Let V1 be the voltage at the highest peak value of the resonant signal located at the rising edge of the current triangular wave, and let t1 be the time when V1 is located.

[0036] Read the voltage V2 of the highest peak value of the resonant signal at the rising edge of the previous triangular wave, and the time t2 at which voltage V2 is located;

[0037] Read the voltage V3, which is the highest peak value of the resonant signal at the rising edge of the previous triangular wave, and the time t3 at which the voltage V3 is located;

[0038] Take the differences between each pair of times t1, t2, and t3. If |t2-t3|<Δt, |t1-t2|>Δt, and |t1-t3|>Δt simultaneously, then t x =t2, if any one of them is not satisfied, then t x = t1, where Δt is the set difference threshold.

[0039] It should be noted that the main purpose of the above logical judgment is to avoid the predicted peak time from changing due to the accidental increase in amplitude of the resonant signal peak in different triangular wave periods.

[0040] Based on the reference time t x The method for determining the trigger period is as follows:

[0041] Obtain the center point of the trigger period 2×t0-t x Where t0 is the peak voltage moment of the current triangular wave; at the same time, the width of the triggering period is greater than twice the full width at half maximum of the resonant signal.

[0042] S4. Trigger: During the triggering period, determine whether the output voltage of photodetector 2-2 is greater than the set threshold voltage V. t If so, the injection locking controller 4 sends a trigger signal to the Q driver 3 to control the Q switch 2-1 to open or close, so that the slave Q-switched laser 2 outputs a single-frequency pulse laser.

[0043] In other words, within the predicted time period of the falling edge of the triangular wave, when the output voltage of photodetector 2-2 is greater than the set threshold voltage V... tWhen the injection lock controller 4 sends a trigger signal to the Q switch 2-1, the Q value of the slave Q-switched laser 2 changes, and the slave Q-switched laser outputs a single-frequency pulse laser.

[0044] In summary, this invention discloses a control method for a seed-injected single-frequency pulsed laser. By identifying the peak time and peak height of the resonant signal at the rising edge of the piezoelectric ceramic scanning voltage, predicting the peak value at the falling edge, and identifying the resonant signal voltage within the predicted peak time range, a trigger signal is emitted when the resonant signal voltage exceeds a threshold voltage, thus achieving stable single-frequency pulsed laser output. This invention solves the problems of high hardware cost, high scanning voltage, and frequency stability in single-frequency pulsed lasers, enabling the output of high-energy single-frequency pulsed lasers with strong anti-interference capabilities and good frequency stability.

[0045] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A control method for a seed-injection type single-frequency pulse laser, characterized in that, Includes the following steps: S1: The continuous single-frequency seed laser (1) outputs seed laser to the passive Q-switched laser (2), causing interference to occur in the resonant cavity of the passive Q-switched laser (2) to obtain a resonant signal; wherein, the length of the resonant cavity is related to the piezoelectric ceramic (2-3) in the passive Q-switched laser (2), and the voltage applied to the piezoelectric ceramic (2-3) is different, the amount of expansion and contraction of the piezoelectric ceramic (2-3) is different, and the corresponding length of the resonant cavity is different; S2: The injection lock controller (4) outputs a triangular wave to the piezoelectric ceramic (2-3), and at the same time, the photodetector (2-2) in the driven Q-switched laser (2) receives the resonant signal formed in the resonant cavity of the driven Q-switched laser (2) under the current triangular wave; S3: Determine the reference time t based on the highest voltage value of the resonant signal at the rising edges of three consecutive triangular waves and the time when the highest voltage value is located. x And based on the reference time t x Determine the trigger period; S4: During the triggering period, determine whether the output voltage of the photodetector (2-2) is greater than the set threshold voltage V. t If so, the injection lock controller (4) sends a trigger signal to the Q driver (3) to control the Q switch (2-1) to open or close, so that the slave Q-switched laser (2) outputs a single-frequency pulse laser.

2. The control method for a seed-injection type single-frequency pulse laser as described in claim 1, characterized in that, Reference time t x The method for determining it is as follows: Let V1 be the voltage at the highest peak value of the resonant signal located at the rising edge of the current triangular wave, and let t1 be the time when V1 is located. Read the voltage V2 of the highest peak value of the resonant signal at the rising edge of the previous triangular wave, and the time t2 at which voltage V2 is located; Read the voltage V3, which is the highest peak value of the resonant signal at the rising edge of the previous triangular wave, and the time t3 at which the voltage V3 is located; Take the differences between each pair of times t1, t2, and t3. If |t2-t3|<Δt, |t1-t2|>Δt, and |t1-t3|>Δt simultaneously, then t x =t2, if any one of them is not satisfied, then t x = t1, where Δt is the set difference threshold.

3. The control method for a seed-injection type single-frequency pulse laser as described in claim 2, characterized in that, At the rising edge of the triangular wave, the expansion and contraction of the piezoelectric ceramic within the time interval Δt is less than one-quarter of the output laser wavelength of the Q-switched laser.

4. The control method for a seed-injection type single-frequency pulse laser as described in claim 1, characterized in that, Based on the reference time t x The method for determining the trigger period is as follows: Obtain the center point of the trigger period 2×t0-t x Where t0 is the peak voltage moment of the current triangular wave; Meanwhile, the width of the triggering period is more than twice the full width at half maximum (FWHM) of the resonant signal.

5. The control method for a seed-injection type single-frequency pulse laser as described in claim 1, characterized in that, The cavity length of the piezoelectric ceramic scanning within a triangular wave is greater than the wavelength of the driven Q-switched laser.

6. The control method for a seed-injection type single-frequency pulse laser as described in claim 2, characterized in that, The rising edge of each triangular wave cycle begins at time zero in the time record.

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