Double-path control injection locking method for satellite-borne large-energy single-frequency laser

Abstract

The invention provides a two-way control injection locking method for a satellite-borne large-energy single-frequency laser. A two-way control injection system comprises an injection locking controller, a seed laser, an oscillator, an oscillator power supply, an RTP phase modulator, piezoelectric ceramics (PZT), a photoelectric detector, a Q switch driver, an amplifier, an amplifier power supply and a Q switch. The invention relates to a novel double-path control injection locking technology, adopts an RTP phase modulator to quickly adjust the scanning cavity length, and is assisted by a PZT to slowly scan the cavity length, so that the problem of poor energy stability of a satellite-borne large-energy compact single-frequency laser is solved, and the energy stability of the satellite-borne large-energy compact single-frequency laser is improved. The energy stability can be improved by one order of magnitude, and large-energy single-frequency pulse laser output superior to 0.5% of hundred millijoule magnitude can be obtained; the high-stability large-energy single-frequency laser output realized by the invention can be used for satellite-borne wind measurement laser radars and satellite-borne hyperspectral laser radars.

Description

Technical Field

[0001] The 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 laser radar and spaceborne hyperspectral laser radar can detect global three-dimensional wind fields and cloud-aerosols, which is of great significance for accurate weather forecasting and battlefield environmental protection. The stability of laser energy emitted by the laser radar affects the accuracy of atmospheric detection data inversion. Both spaceborne direct wind laser radar and spaceborne hyperspectral laser radar require that the laser they use is a single-frequency pulse laser, and at the same time, the laser output is required to have high energy stability and a laser of the order of hundreds of millijoules.

[0003] There are two main technical methods to achieve single-frequency pulsed lasers: seed injection locking technology and seed chopping amplification technology. Seed injection locking technology is to inject a single-frequency continuous seed light signal into a laser oscillator. The length of the oscillator resonant cavity is controlled by 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 other longitudinal mode oscillations, thereby obtaining a single-frequency pulse laser output. Seed chopping amplification technology is to directly modulate the continuous seed laser into pulse light through an acousto-optic modulator (AOM), and then obtain a single-frequency pulse 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 large pulse energy, and is widely used in single-frequency pulse lasers.

[0004] Satellite-borne direct wind laser radar and satellite-borne hyperspectral laser radar often use 1064nm, 532nm or 355nm lasers of the Nd:YAG series, and use injection locking combined with amplification technology to obtain high-energy single-frequency laser output. In the injection locking scheme, the oscillator cavity is generally divided into two types: end-pumped rod crystal structure and side-pumped slab crystal structure. In the end-pumped rod crystal structure, continuous pumping or long pulse pumping greater than or equal to 1.5ms is usually used, which is much longer than the upper energy level lifetime of Nd:YAG 230μs. When the PZT triangle wave voltage is scanned, the number of inverted particles in the rod crystal is basically stable, and the Q switch opening time will not significantly affect the output energy. Therefore, the energy stability can be better than 0.5%, but the output energy is only in the millijoule level, which increases the pressure of subsequent amplification and increases the overall structure of the laser. In the side-pumped slab crystal structure, the oscillator output energy can reach ten millijoules, which reduces the pressure of subsequent amplification and the structure tends to be compact. However, if the slab crystal is pumped with a long pulse width at a repetition rate of 100 Hz, a large amount of heat will accumulate, which will not only cause serious thermal distortion of the light spot, affect the laser output energy and beam quality, but also reduce the LD life and laser reliability. Therefore, a short pulse width pumping method is generally used, with a pump pulse width of 250μs. The RTP phase modulator that can respond quickly at high frequency is used to scan the cavity length in the last 40μs of the LD pumping to complete the injection locking. Since the short pulse pumping duration is close to the upper energy level lifetime, the number of upper energy level inversion particles in the crystal increases with the increase of the pumping duration, and the later the Q switch is turned on, the greater the output energy. Since the external environment can cause the cavity length to drift slowly, the time when the resonance peak appears during high-voltage scanning is uncertain, resulting in uncertainty in the Q switch opening time, causing the output energy to jitter, and the energy jitter amplitude can reach 5% to 10%. The maximum value of the Q switch opening time fluctuation, that is, the time interval between the two resonance signal peaks, is inversely proportional to the quotient of the RTP phase modulator scanning voltage and the RTP phase modulator scanning 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 locking 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 of occurrence of the resonance peak during high-voltage scanning due to the slow drift of the cavity length. A dual-path controlled injection locking method for a satellite-borne large-energy single-frequency laser is provided. The RTP phase modulator is used to quickly adjust the scanning cavity length, assisted by the PZT slow scanning cavity length, to solve the problem of poor energy stability of the satellite-borne large-energy compact single-frequency laser, and the energy stability can be improved by one order of magnitude to obtain a large-energy single-frequency pulse laser output of the order of 100 millijoules better than 0.5%; the high-stability large-energy single-frequency laser output achieved by the present invention can be used for satellite-borne wind measurement laser radars and satellite-borne hyperspectral laser radars.

[0007] The present invention provides a dual-path control injection locking method for a satellite-borne large-energy single-frequency laser. A dual-path control injection locking system is used to perform dual-path control injection locking of the satellite-borne large-energy single-frequency laser. The dual-path control injection locking system comprises 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 ceramics, Q-switch driver and amplifier power supply respectively;

[0009] The RTP phase modulator performs a fast scan of the oscillator cavity length under the control of the injection locking controller output voltage. The piezoelectric ceramic is bonded to the cavity mirror of the oscillator and performs a slow scan compensation of the cavity length under the control of the injection locking 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 outputs a pulsed laser driven by a Q switch and is amplified to the order of hundreds of millijoules by an amplifier.

[0010] The method of dual-path control 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 locking controller outputs a synchronization signal to the oscillator power supply, the injection locking 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, and the oscillator outputs a pulsed laser under the control of the injection locking controller;

[0013] S3, the photodetector detects the resonance signal with intensity change during the change of the oscillator cavity length, and feeds back the resonance signal 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 1 μs, where time T0 is the tth time after the pump pulse rises. r +t' time, t r is the upper energy level lifetime of the slab crystal in the oscillator, t' is ≤t r / 10; T1 is the moment when the injection locking controller reads the peak value of the resonance 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 when 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, enter 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 a satellite-borne high-energy single-frequency laser 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 mode, 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 described in the present invention is, as a preferred embodiment, in step S3, t 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 control 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 dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser described in the present invention is, as a preferred method, a seed laser outputs a single-frequency continuous seed laser with a beam quality M 2 Less than 1.1 times the diffraction limit; the oscillator outputs single-frequency pulsed laser.

[0022] 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, a wavelength of the single-frequency continuous laser is 1064nm.

[0023] 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, the oscillator is a Q-switched laser using a Nd:YAG slab crystal as a gain medium, and the oscillator is a compact oscillator.

[0024] 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 amplifier includes a Nd:YAG slab crystal.

[0025] 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, thermal control of both the oscillator and the amplifier is performed using conduction cooling.

[0026] 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 mode, an amplifier output stability better than 0.5% of a 100 Hz 100 mJ high-energy single-frequency laser.

[0027] The present invention has the following advantages:

[0028] The present invention uses an RTP phase modulator to quickly adjust the scanning cavity length, supplemented by a PZT to slowly scan the cavity length, to solve the energy jitter problem caused by the short pumping time of a compact large-energy single-frequency laser, and to improve the laser energy stability by one order of magnitude without increasing the requirements for the response speed of the high-voltage circuit and the volume of the laser optical cavity, so that the compact large-energy single-frequency laser output laser energy stability is better than 0.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It 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 schematic diagram of the structure of a dual-path controlled injection locking system is 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 described clearly and completely 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 control injection locking method for a satellite-borne high-energy single-frequency laser, 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 locking controller 1 outputs voltage or current signals to control the RTP phase modulator 3, PZT 4, oscillator power supply 2, Q switch driver 6, and amplifier power supply 7 respectively; the seed laser 9 outputs continuous fundamental transverse mode and single longitudinal mode seed laser, which are injected into the oscillator 8; the injection locking controller 1 outputs a synchronization signal to the oscillator power supply 2, and 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, and thus changes 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 locking controller 1; the oscillator 8 realizes single-frequency pulse laser output under the control of the injection locking controller 1; the oscillator 8 outputs a single-frequency pulse laser of the order of ten 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 and with energy jitter better than 0.5%.

[0037] The injection locking controller 1 implements a fast scan 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, the seed laser 9 outputs a continuous 1064nm single-frequency laser and injects it into the oscillator 8;

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

[0048] S3, the detector 5 detects the resonance signal of different intensities during the change of the optical cavity length of the oscillator 8 and feeds it back to the injection locking controller 1; the injection locking controller 1 reads the peak value of the resonance signal; the injection locking controller sets an optimized signal reading threshold, and the resonance signal peak value below the threshold is automatically ignored, which can improve the stability of injection locking; the injection locking controller 1 judges the peak value of the resonance signal, taking the rising edge of the pump pulse of the oscillator 8 as the starting point, and setting the 240μs moment of the pump as T0; the injection locking controller 1 reads the moment of the peak value of the resonance signal and turns on the Q switch 11 at this moment, and sets this moment as T1. If the difference between T1 and T0 is not zero, the injection locking controller 1 applies a voltage to PZT4, and uses the PID algorithm to adjust and control PZT4, so that the moment when the peak value of the resonance signal appears gradually approaches T0. Finally, the absolute value of the difference between T1 and T0 is less than 1μs, which reduces the jitter of the output energy. Among them, the PID algorithm is a closed-loop control algorithm, and PID is the abbreviation of proportion, integral, and differential coefficient, which represent three control algorithms respectively. The combination of these three algorithms can effectively control PZT4, and then adjust the cavity length deviation. The precise positioning process of PZT4 makes the time when the peak of the resonance signal appears approach T0 and tend to be stable. The synchronization signal at the beginning of the pumping of amplifier 10 is the same as the synchronization signal at the beginning of the 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 slabs of amplifier 10 under the synchronization signal; amplifier 10 amplifies the single-frequency pulse laser and outputs 1064nm single-frequency pulse laser of the order of one hundred millijoules with an energy stability better than 0.5%.

[0050] The satellite-borne high-energy 355nm single-frequency pulse laser uses the dual-path control injection locking technology of this invention, uses RTP phase modulator 3 to quickly adjust the scanning cavity length, and uses PZT4 to slowly scan the cavity length, to obtain a high-energy single-frequency laser output of 100 Hz and 100 mJ with energy stability better than 0.5%. When only RTP phase modulator 3 is used to quickly adjust the scanning cavity length for injection locking, the energy stability of the single-frequency pulse laser is 8%. After using the dual-path control injection locking technology, the energy stability is increased to 0.5%, achieving an order of magnitude improvement.

[0051] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A dual-path controlled injection locking method for a satellite-borne high-energy single-frequency laser, characterized in that: 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 driven by the Q switch (11) and is amplified to a hundred millijoules level by the amplifier (10); The method of dual-path control 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 back the resonance signal 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' time, 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 when 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 when 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. A 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) comprises 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: Both the oscillator (8) and the amplifier (10) are thermally controlled using conduction cooling.

10. A 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 100Hz, 100mJ high-energy single-frequency laser.

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