A dual-path controlled injection locking method for spaceborne high-energy single-frequency lasers

Abstract

The present invention provides a dual-path controlled injection locking method for a satellite-borne high-energy, single-frequency laser. The dual-path controlled injection system includes an injection locking controller, a seed laser, an oscillator, an oscillator power supply, an RTP phase modulator, a piezoelectric ceramic (PZT), a photodetector, a Q-switch driver, an amplifier, an amplifier power supply, and a Q-switch. This novel dual-path controlled injection locking technology utilizes an RTP phase modulator for rapid cavity length scanning, supplemented by a PZT for slow cavity length scanning. This solves the problem of poor energy stability in satellite-borne, high-energy, compact, single-frequency lasers, improving energy stability by an order of magnitude and achieving high-energy, single-frequency pulsed laser output on the order of 100 millijoules with an output better than 0.5%. The high-stability, high-energy, single-frequency laser output achieved by this invention can be used in satellite-borne wind measurement lidars and satellite-borne hyperspectral lidars.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and in particular to a dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser. Background Art

[0002] Spaceborne direct wind lidar and hyperspectral lidar can detect global three-dimensional wind fields and cloud-aerosol patterns, which are crucial for accurate weather forecasting and battlefield environmental assurance. The stability of the laser energy emitted by the lidar affects the accuracy of atmospheric data inversion. Both these technologies require single-frequency pulsed lasers with high energy stability in the hundreds of millijoules.

[0003] There are two main technical methods for achieving single-frequency pulsed lasers: seed injection locking technology and seed chopping amplification technology. Seed injection locking technology involves injecting a single-frequency continuous seed light signal into a laser oscillator. The oscillator's resonant cavity length is controlled through a piezoelectric ceramic (PZT) or RTP phase modulator, so that the laser longitudinal mode adjacent to the seed light frequency in the oscillator oscillates first, extracts inversion particles, and suppresses the oscillation of other longitudinal modes, thereby obtaining a single-frequency pulsed laser output. Seed chopping amplification technology involves directly modulating the continuous seed laser into pulsed light through an acousto-optic modulator (AOM), and then obtaining a single-frequency pulsed laser through pulse shaping and amplification. Compared with seed chopping amplification technology, seed injection locking technology has the advantages of simple devices, no need for pulse shaping, high electro-optical efficiency, and high pulse energy, and is widely used in single-frequency pulsed lasers.

[0004] Spaceborne direct wind lidars and hyperspectral lidars often use Nd:YAG lasers at 1064nm, 532nm, or 355nm. They employ injection locking combined with amplification to achieve high-energy, single-frequency laser output. Injection locking schemes generally employ two types of oscillator cavities: end-pumped rod-shaped crystal structures and side-pumped slab-shaped crystal structures. In end-pumped rod-shaped crystal structures, continuous pumping or long pulses of 1.5ms or greater are typically used, significantly exceeding the 230μs upper energy level lifetime of Nd:YAG. The rod-shaped crystal inversion population remains essentially stable when the PZT triangular voltage is swept, and the Q-switch onset does not significantly affect the output energy. Consequently, energy stability can be better than 0.5%. However, the output energy is only in the millijoules, increasing the pressure on subsequent amplification and increasing the overall size of the laser. In side-pumped slab-shaped crystal structures, the oscillator output energy can reach tens of millijoules, reducing the pressure on subsequent amplification and resulting in a more compact structure. However, long-pulse pumping of slab crystals at hundreds of hertz repetition rates generates significant heat accumulation, causing significant thermal distortion of the beam spot, impacting laser output energy and beam quality, and reducing LD lifetime and laser reliability. Therefore, a short-pulse pumping method is generally employed, with a pump pulse width of 250μs. A high-frequency, fast-response RTP phase modulator is used to scan the cavity length in the last 40μs of LD pumping to achieve injection locking. Because the short pump pulse duration approaches the upper energy level lifetime, the number of upper energy level inversions in the crystal increases with increasing pump duration. The later the Q switch is turned on, the greater the output energy. Due to the external environment causing slow drift in the cavity length, the timing of the resonance peak during high-voltage scanning is uncertain, leading to uncertainty in the Q switch turn-on timing and output energy jitter, which can reach 5% to 10%. The maximum Q switch turn-on time fluctuation, i.e., the time interval between two resonance signal peaks, is inversely proportional to the quotient of the RTP phase modulator sweep voltage and the RTP phase modulator sweep time. Therefore, shortening the time for the RTP phase modulator to linearly scan the high voltage can improve the stability of the output energy. However, the linear scanning high voltage of the RTP phase modulator is generally 2kV to 3kV. Completing the linear scanning of the kilovolt-level high voltage in microseconds poses a great challenge to the injection-locked controller.

[0005] Therefore, under existing technical conditions, compact side-pumped slab crystal single-frequency lasers have the problem of poor energy stability. Summary of the Invention

[0006] The present invention aims to solve the problem of poor laser stability caused by the uncertainty of the time when the resonance peak appears during high-voltage scanning due to slow drift of the cavity length. A dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser is provided. The method adopts an RTP phase modulator to quickly adjust the scanning cavity length, supplemented by a PZT to slowly scan the cavity length. This solves the problem of poor energy stability of the satellite-borne high-energy compact single-frequency laser and can improve the energy stability by an order of magnitude to obtain a high-energy single-frequency pulse laser output of hundreds of millijoules with a value better than 0.5%. The high-stability, high-energy single-frequency laser output achieved by the present invention can be used in satellite-borne wind measurement lidars and satellite-borne hyperspectral lidars.

[0007] The present invention provides a dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser. The dual-path controlled injection locking system is used to perform dual-path controlled injection locking of the satellite-borne high-energy single-frequency laser. The dual-path controlled injection locking system includes an injection locking controller, an oscillator power supply connected to the injection locking controller, an RTP phase modulator, a piezoelectric ceramic, a photodetector, a Q-switch driver, an amplifier power supply, an oscillator connected to the oscillator power supply, a seed laser optically connected to the oscillator, an amplifier connected to the amplifier power supply and a Q-switch connected to the oscillator, the amplifier is optically connected to the oscillator, and the photodetector is located on one side of the oscillator.

[0008] The injection-locked controller outputs voltage or current signals to control the oscillator power supply, RTP phase modulator, piezoelectric ceramic, Q-switch driver and amplifier power supply respectively;

[0009] The RTP phase modulator rapidly scans the oscillator cavity length under the control of the injection-locked controller output voltage. The piezoelectric ceramic is bonded to the oscillator's cavity mirror and performs slow cavity length scanning compensation under the control of the injection-locked controller output voltage. The oscillator is a slab crystal side-pumped oscillator. The seed laser outputs a continuous seed laser that is injected into the oscillator. The oscillator, driven by a Q switch, outputs pulsed laser light that is amplified to the hundreds of millijoules by an amplifier.

[0010] The method of dual-path controlled injection locking comprises the following steps:

[0011] S1, the seed laser outputs continuous seed laser and injects it into the oscillator;

[0012] S2, the injection-locked controller outputs a synchronization signal to the oscillator power supply, and the injection-locked controller outputs a triangular wave voltage to control the RTP phase modulator. The refractive index of the RTP phase modulator changes linearly with the triangular wave voltage, thereby changing the oscillator cavity length. The oscillator outputs a pulsed laser under the control of the injection-locked controller;

[0013] S3, the photodetector detects the resonance signal with changing intensity during the change of the oscillator cavity length, and feeds the resonance signal back to the injection locking controller;

[0014] The injection locking controller determines whether the absolute value of the difference between time T0 and time T1 is less than 1μs, where time T0 is the tth time after the pump pulse rises. r +t' moment, t r is the upper energy level lifetime of the slab crystal in the oscillator, t' is ≤t r / 10 is a fixed value; T1 is the moment when the injection-locked controller reads the peak of the resonant signal and turns on the Q switch;

[0015] If not, the injection locking controller applies voltage to the piezoelectric ceramic so that the time T1 at which the peak of the resonance signal of the next cycle appears gradually approaches the time T0, and returns to step S2 to enter the next cycle of injection locking; if yes, proceeds to step S4;

[0016] S4. The oscillator outputs a pulse laser of the order of tens of millijoules to the amplifier, and the amplifier amplifies the pulse laser of the order of tens of millijoules to the order of hundreds of millijoules. A dual-path controlled injection locking method for satellite-borne high-energy single-frequency lasers is completed.

[0017] The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser described in the present invention is, as a preferred embodiment, in step S3, the injection locking controller controls the voltage applied to the piezoelectric ceramic through a PID algorithm so that the time T1 when the peak of the resonance signal appears gradually approaches the time T0.

[0018] The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser according to the present invention is preferably implemented in step S3. r is 230μs, t' is 10μs, and T0 is 240μs;

[0019] The synchronization signal for the amplifier pumping start is the same as the synchronization signal for the oscillator pumping start, both at time T0.

[0020] The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser described in the present invention is, as a preferred embodiment, in step S3, the injection locking controller sets a resonance signal reading threshold, and resonance signal peaks below the threshold are automatically ignored.

[0021] The present invention discloses a dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser. As a preferred embodiment, the seed laser outputs a single-frequency continuous seed laser with a beam quality of M 2 Less than 1.1 times the diffraction limit; the oscillator outputs single-frequency pulse laser.

[0022] The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser described in the present invention is preferably such that the wavelength of the single-frequency continuous laser is 1064 nm.

[0023] The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser described in the present invention is preferably a Q-switched laser with an Nd:YAG slab crystal as a gain medium, and the oscillator is a compact oscillator.

[0024] In the dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser described in the present invention, as a preferred embodiment, the amplifier includes a Nd:YAG slab crystal.

[0025] In the dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser described in the present invention, as a preferred embodiment, both the oscillator and the amplifier use conduction cooling for thermal control.

[0026] The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser described in the present invention is a preferred embodiment, wherein the amplifier output stability is better than 0.5% of a 100-Hz 100-millijoule high-energy single-frequency laser.

[0027] The present invention has the following advantages:

[0028] The present invention solves the energy jitter problem caused by the short pumping time of a compact, high-energy, single-frequency laser by quickly adjusting the scanning cavity length through an RTP phase modulator, supplemented by slow scanning of the cavity length through a PZT. This improves the laser energy stability by one order of magnitude without increasing the requirements for the response speed of the high-voltage circuit or the volume of the laser optical cavity, thus making the output laser energy stability of the compact, high-energy, single-frequency laser better than 0.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a flow chart of a dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser.

[0030] Figure 2 The figure is a schematic diagram of the structure of a dual-path controlled injection locking system for a dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser.

[0031] Reference numerals:

[0032] 1. Injection-locked controller; 2. Oscillator power supply; 3. RTP phase modulator; 4. Piezoelectric ceramics; 5. Photodetector; 6. Q-switch driver; 7. Amplifier power supply; 8. Oscillator; 9. Seed laser; 10. Amplifier; 11. Q-switch. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0034] Example 1

[0035] like Figures 1-2 As shown, a dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser is described. The system comprises an injection locking controller 1, an oscillator power supply 2, an RTP phase modulator 3, a piezoelectric ceramic (PZT) 4, a photodetector 5, a Q-switch driver 6, an amplifier power supply 7, an oscillator 8, a seed laser 9, an amplifier 10, and a Q-switch 11.

[0036] The injection-locked controller 1 outputs a voltage or current signal to respectively control the RTP phase modulator 3, PZT 4, oscillator power supply 2, Q-switch driver 6, and amplifier power supply 7; the seed laser 9 outputs continuous fundamental transverse mode and single longitudinal mode seed laser, which are injected into the oscillator 8; the injection-locked controller 1 outputs a synchronization signal to the oscillator power supply 2, and the injection-locked controller 1 outputs a triangular wave voltage to control the RTP phase modulator 3. The refractive index of the RTP phase modulator 3 changes linearly with the triangular wave voltage, thereby changing the cavity length of the oscillator 8. The photodetector 5 detects the intensity change resonance signal during the change of the cavity length of the oscillator 8 and feeds the detected resonance signal back to the injection-locked controller 1; the oscillator 8 realizes single-frequency pulse laser output under the control of the injection-locked controller 1; the oscillator 8 outputs a single-frequency pulse laser of the order of tens of millijoules to the amplifier 10; the amplifier 10 amplifies the single-frequency pulse laser to a 1064nm single-frequency pulse laser of the order of hundreds of millijoules with energy jitter better than 0.5%.

[0037] The injection locking controller 1 implements rapid scanning of the cavity length by applying a linear high voltage of the order of kilovolts to the RTP phase modulator 3 at the order of ten microseconds.

[0038] PZT4 is bonded to the oscillator 8 cavity mirror to perform slow scanning compensation for the cavity length;

[0039] Oscillator 8 adopts a compact design of Nd:YAG slab crystal side pumping, which can achieve single-frequency 1064nm pulse laser output of tens of millijoules.

[0040] Both the oscillator 8 and the amplifier 10 are thermally controlled using conduction cooling.

[0041] The seed laser 9 outputs a 1064nm single-frequency continuous laser with a beam quality of M 2 Less than 1.1 times the diffraction limit.

[0042] The amplifier 10 uses Nd:YAG slabs.

[0043] The pumping time of the amplifier 10 is 240 μs, which ensures the amplification efficiency of the amplifier 10 and the energy stability of the output laser in the order of hundreds of millijoules.

[0044] This embodiment can achieve satellite-borne high-energy single-frequency pulse laser output of hundreds of millijoules with strong anti-interference capability, strong environmental adaptability, and good energy stability.

[0045] The specific dual-path control injection locking method is:

[0046] S1, seed laser 9 outputs continuous 1064nm single-frequency laser and injects it into oscillator 8;

[0047] S2, injection locking controller 1 outputs a synchronization signal to oscillator power supply 2; oscillator power supply 2 supplies power to the LD of oscillator 8, providing a stable pump source for the Nd:YAG crystal in oscillator 8; injection locking controller 1 outputs a triangular wave voltage to control RTP phase modulator 3, and the refractive index of RTP phase modulator 3 changes linearly with the triangular wave voltage; oscillator 8 changes the optical cavity length during the linear change of the refractive index of RTP phase modulator 3;

[0048] S3. Detector 5 detects resonant signals of varying intensities during the change in the optical cavity length of oscillator 8 and feeds this information back to injection-locked controller 1. The injection-locked controller 1 reads the peak of the resonant signal. The controller sets an optimized signal reading threshold, automatically ignoring resonant signal peaks below the threshold, thereby improving injection-locked stability. The controller then determines the peak of the resonant signal, starting with the rising edge of the pump pulse from oscillator 8 and setting the 240 μs mark of pumping time as T0. The controller reads the time of the resonant signal peak and turns on Q-switch 11 at this time, setting this time as T1. If the difference between T1 and T0 is not zero, the controller applies a voltage to PZT 4 and uses a PID algorithm to adjust and control PZT 4, gradually aligning the peak of the resonant signal with T0. Ultimately, the absolute value of the difference between T1 and T0 is less than 1 μs, reducing output energy jitter. The PID algorithm is a closed-loop control algorithm. PID stands for Proportional, Integral, and Differential coefficient, representing three control algorithms, respectively. The combination of these three algorithms can effectively control PZT4 and thus adjust the cavity length deviation. The precise positioning process of PZT4 makes the peak moment of the resonance signal approach T0 and tend to be stable. The synchronization signal for the start of pumping of amplifier 10 is the same as the synchronization signal for the start of pumping of oscillator 8. The pumping time of amplifier 8 is 240μs.

[0049] S4, oscillator 8 transmits the output high-stability ten-millijoule laser to the amplifier; amplifier power supply 7 provides pumping to the Nd:YAG slab of amplifier 10 under the synchronization signal; amplifier 10 amplifies the single-frequency pulse laser and outputs a 1064nm single-frequency pulse laser of the hundred-millijoule level with energy stability better than 0.5%.

[0050] This invention's dual-path controlled injection locking technology is applied to a satellite-borne, high-energy, 355nm, single-frequency pulsed laser. This technology employs a three-stage RTP phase modulator for rapid cavity length scanning, supplemented by a PZT4 for slow cavity length scanning. This technology achieves high-energy, single-frequency laser output at 100Hz and 100mJ with energy stability exceeding 0.5%. While the energy stability of single-frequency pulsed lasers is 8% when injection-locking using only the three-stage RTP phase modulator for rapid cavity length scanning, the dual-path controlled injection locking technology improves this to 0.5%, an order of magnitude improvement.

[0051] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser, characterized by: A dual-path controlled injection locking system is used to perform dual-path controlled injection locking of a satellite-borne high-energy single-frequency laser. The dual-path controlled injection locking system comprises an injection locking controller (1), an oscillator power supply (2) connected to the injection locking controller (1), an RTP phase modulator (3), a piezoelectric ceramic (4), a photodetector (5), a Q-switch driver (6), an amplifier power supply (7), an oscillator (8) connected to the oscillator power supply (2), a seed laser (9) optically connected to the oscillator (8), an amplifier (10) connected to the amplifier power supply (7) and a Q-switch (11) connected to the oscillator (8), wherein the amplifier (10) is optically connected to the oscillator (8), and the photodetector (5) is located on one side of the oscillator (8); The injection locking controller (1) outputs a voltage or current signal to respectively control the oscillator power supply (2), the RTP phase modulator (3), the piezoelectric ceramic (4), the Q switch driver (6) and the amplifier power supply (7); The RTP phase modulator (3) performs a rapid scan of the cavity length of the oscillator (8) under the control of the output voltage of the injection locking controller (1); the piezoelectric ceramic (4) is bonded to the cavity mirror of the oscillator (8) and performs a slow scan compensation of the cavity length under the control of the output voltage of the injection locking controller (1); the oscillator (8) is a slab crystal side-pumped oscillator; the seed laser (9) outputs a continuous seed laser and injects it into the oscillator (8); the oscillator (8) outputs a pulsed laser under the drive of the Q switch (11) and is amplified to a hundred millijoules level by the amplifier (10); The method of dual-path controlled injection locking comprises the following steps: S1, the seed laser (9) outputs a continuous seed laser and injects it into the oscillator (8); S2, the injection locking controller (1) outputs a synchronization signal to the oscillator power supply (2), the injection locking controller (1) outputs a triangular wave voltage to control the RTP phase modulator (3), the refractive index of the RTP phase modulator (3) changes linearly with the triangular wave voltage, thereby changing the oscillator cavity length, and the oscillator (8) outputs a pulsed laser under the control of the injection locking controller (1); S3, the photodetector (8) detects a resonance signal with a changing intensity during the process of the oscillator cavity length changing, and feeds the resonance signal back to the injection locking controller (1); The injection locking controller (1) determines whether the absolute value of the difference between time T0 and time T1 is less than 1 μs, wherein time T0 is the tth time after the pump pulse rises. r +t' moment, t r is the upper energy level lifetime of the slab crystal in the oscillator (8), t'≤t r / 10; time T1 is the time when the injection locking controller (1) reads the peak value of the resonance signal and turns on the Q switch (11); If not, the injection locking controller (1) applies voltage to the piezoelectric ceramic (4) so ​​that the time T1 at which the peak of the resonance signal of the next cycle appears gradually approaches the time T0, and returns to step S2 to enter the injection locking of the next cycle; if yes, enters step S4; S4. The oscillator (8) outputs a pulse laser of the order of ten millijoules to the amplifier (10), and the amplifier (10) amplifies the pulse laser of the order of ten millijoules to the order of one hundred millijoules, thereby completing a dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser.

2. The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser according to claim 1, characterized in that: In step S3, the injection locking controller (1) controls the voltage applied to the piezoelectric ceramic (4) through a PID algorithm so that the time T1 at which the peak of the resonance signal appears gradually approaches the time T0.

3. The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser according to claim 1, characterized in that: In step S3, t r is 230μs, t' is 10μs, and T0 is 240μs; The synchronization signal for the amplifier (10) to start pumping is the same as the synchronization signal for the oscillator (8) to start pumping, both at time T0.

4. The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser according to claim 1, characterized in that: In step S3, the injection locking controller (1) sets a resonance signal reading threshold, and resonance signal peaks below the threshold are automatically ignored.

5. The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser according to claim 1, characterized in that: The seed laser (9) outputs a single-frequency continuous seed laser with a beam quality of M 2 Less than 1.1 times the diffraction limit; the oscillator (8) outputs single-frequency pulse laser.

6. The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser according to claim 5, characterized in that: The wavelength of the single-frequency continuous laser is 1064 nm.

7. The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser according to claim 1, characterized in that: The oscillator (8) is a Q-switched laser using Nd:YAG slab crystal as a gain medium, and the oscillator (8) is a compact oscillator.

8. The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser according to claim 1, characterized in that: The amplifier (10) includes a Nd:YAG slab crystal.

9. The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser according to claim 1, characterized in that: The oscillator (8) and the amplifier (10) are both thermally controlled using conduction cooling.

10. The dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser according to claim 1, characterized in that: The amplifier (10) has an output stability of better than 0.5% of a 100-Hz, 100-millijoule, high-energy single-frequency laser.

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