Open Access
Add to BibSonomy
Abstract
Non-collinear stimulated Brillouin scattering (SBS) amplification can obtain high peak power Stokes output while ensuring the stability, but the frequency mismatch reduces the energy conversion efficiency of the system. In this paper, a dual-frequency pulse laser based on acousto-optic crystal modulation is designed. The output pulse pair can be used as pump and Stokes light, respectively, which realizes the active frequency matching of the gain medium Brillouin frequency shift during the SBS amplification process and helps to maintain ideal energy conversion efficiency. The dual-frequency laser finally produced a laser pulse pair with a pulse width adjustment range of 100 ps-50 ns, a frequency shift range of 0 GHz-2 GHz, and the polarization extinction ratio (PER) reaches 20.82dB.
© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
The huge energy supply brought by nuclear fusion has received more and more attention. The proposal of the inertial confinement nuclear fusion (ICF) has brought dawn to solve the problem of energy shortage. As the key technology of ICF, shock ignition [1–3] requires a narrow pulse with high peak power and high energy to bombard the target pellet. In order to obtain this kind of high-energy pulse, researchers have provided a variety of solutions [4–11]. Stimulated Brillouin scattering (SBS) has the characteristics of both pulse compression and Brillouin amplification, so it is considered to be an ideal solution for generating short width and high peak power pulse [12–25].
The Stokes seed light of the common Brillouin amplification system is generated by the self-excited SBS noise that occurs after the laser is focused through the lens. However, the SBS process caused by the noise is not stable, and this collinear amplification system cannot carry high pump energy, the high energy generated by the focalization of the pump light will cause threshold breakdown of the gain medium and other nonlinear optical effects, resulting in the time-domain jitter of the output Stokes seed light. To solve this problem, the non-collinear SBS amplification structure in which the pump and Stokes light intersect at a certain angle can not only carry more energy, but also reduce the system loss caused by the complex optical structure. However, the problem of frequency mismatch caused by the increase of angle between pump and Stokes light is the insufficiency of the non-collinear SBS amplification structure. In recent years, the non-collinear SBS amplification with active frequency matching has obtained high Brillouin gain under the conditions of different gain media and a large angle of 35° and a conversion efficiency equivalent to the collinear structure [26,27]. The key technology is to realize the active control of the frequency difference between the pump and Stokes light, so as to complete the Brillouin frequency matching of different gain media.
The dual-frequency pulse laser designed in this paper performs two Bragg diffractions through reverse cascade of LiNbO3 crystals. The system combines arbitrary waveform generator (AWG) and fine time delay control to realize the frequency shift of seed pulse. Finally, the output with adjustable pulse width and controllable frequency shift in a certain range is obtained. The experimental results show that the central wavelength of the pump and Stokes pulse is 1064 nm, the pulse width adjustment range is 100 ps-50 ns, and the frequency shift range of the two pulses is 0 GHz-2 GHz, which provides a Stokes seed light source that can meet different Brillouin frequency shifts for active frequency matching of non-collinear SBS amplification.
2. Experimental device
2.1 Overall structure of the system
The dual-frequency laser consists of single longitudinal mode fiber laser (DFB), AWG, amplitude modulator (AM), multichannel synchronizer, clock signal generator, acousto-optic modulator (AOM), fiber amplifier (AMP) and power amplifier (μ-AMP). The composition of the system is shown in Fig. 1.
DFB is used to provide a single longitudinal mode linearly polarized continuous light with a central wavelength of 1064 nm as the basic light source of the system. AWG is used to write the timing and width information of pulse pair, and input it into AM in the form of electrical signal. AM is actually an intensity modulator, which uses the principle of Mach-Zehnder phase interference and is driven by the electric signal provided by AWG to shape the continuous light of DFB, and finally provides the system with arbitrarily shaped and high contrast laser pulse. AOM(X) uses Bragg diffraction to shift the frequency of the incident pulse. In addition, the synchronous signal can control the generation time of diffraction in the acousto-optic crystal, so that AOM can achieve the effect of optical switch. In addition, AOM can suppress time domain noise and improve the signal-to-noise ratio of output pulse. 1 MHz-20 MHz-AOM frequency shifter can achieve selective frequency shift from 1 MHz to 20 MHz (increment step is 1 MHz), 200 MHz-AOM frequency shifter can achieve single 200 MHz fixed positive frequency shift. Setting 1 MHz-20 MHz frequency shift loop can meet the precise fine tuning under the condition of small frequency shift, while 200 MHz frequency shift loop can meet the rapid coarse tuning of large frequency shift. The absorption of fiber link and the diffraction of acousto-optic crystal result in large energy loss. Therefore, AMP and μ-AMP are embedded in the system to compensate the energy loss of each part with low noise, and improve the peak power of pulse. Since the laser structure contains multiple AOM optical switching devices, their start-up delay and light-on time need to be strictly controlled. Therefore, the system adds a high-precision clock source and a multichannel time synchronizer to independently control the AOM, so as to ensure that the laser can work orderly and the seed light can be properly processed in the time domain in the fixed optical path. The designs of multichannel synchronization and frequency shift loop are described in detail.
2.2 Multichannel time synchronization
The main function of multichannel synchronizer is to provide low jitter and high-quality synchronous trigger signal for dual-frequency laser system, so as to ensure the normal and orderly operation of complex system. The rear panel and connection information of multichannel synchronizer are shown in Fig. 2.
During the running of system, the synchronizer provides a square pulse as the synchronization signal (CHX) for each AOM. The delay of the synchronization signal arriving at the AOM determines the start time of the internal AOM frequency shift process, and the width of the synchronization signal determines the duration of the internal AOM frequency shift process. When the pulse does not enter the frequency shift loop and only passes through the main optical path once, the initial delay and width parameters of each synchronization signal are shown in Table 1.
Table 1. Initial setting values of synchronous signal parameters
CH1 and CH4 channels provide synchronous signals for AOM1 and AOM4. The purpose is to use its optical switching function to divide the pulse pair into two pulses in time domain and enter two frequency shift loops respectively. CH2 and CH5 provide synchronous signals for the two acousto-optic modulators (1MHz-20MHz-AOM and 200MHz-AOM) embedded in the frequency shift loop. The purpose is to control the frequency shift times and make the frequency shift of the output pulse meet the application requirements. Every time the optical pulse passes through the frequency shift loop, 50% of the light will be transmitted to points A and B. A pulse sequence shown in Fig. 3 can be observed at these two points. The delay and frequency difference between any two adjacent-pulses of the pulse sequence are equal. In order to obtain only the ideal frequency shift seed pulse, CH3 and CH6 control the start delay of AOM3 and AOM6, so as to filter the frequency shift components in the first few of the pulse sequence.
The time of the seed pulse arriving at C after frequency shift is delayed, the synchronization signal delay of AOM7 should be increased accordingly. The calculation formula of AOM7 delay t is as follows:
where t0 is the initial delay of AOM7 synchronization signal, TC is the time required for the pulse to pass through a frequency shift loop, and k = 1, 2, 3… 9 is the number of optical pulse circles. On the whole, the AOMs involved in the system all have the functions of frequency shift and optical switch. The time synchronization signal is mainly used to control them to start at the appropriate time node and work in a reasonable time range. It should be emphasized that the AWG can write a pulse square wave of any width within its maximum time domain width. However, considering the limitation of the synchronous electrical signal width on the optical duration of AOM, part of the light will be stuck if the square wave written by AWG is too wide to pass through AOM. Therefore, the maximum pulse width is set as 50ns in this paper.2.3 Theoretical basis and design of the frequency shift loop
The presence of an internal acoustic field deforms the crystal and causes periodic density modulation. The final result is a periodic change in the refractive index of the crystal, which functions like an “optical phase gate”. When the light incident into the crystal, it is affected by the “grating” and produces diffraction effect. Figure 4 shows the acousto-optic Bragg diffraction principle.
The driving RF signal is loaded on the piezoelectric transducer, and the ultrasonic wave with the same frequency is excited to couple into the acousto-optic crystal. The incident photon and phonon exchange energy in the crystal to generate polarization wave, which excite light radiation to form diffracted light. The wave vector and frequency between light field and sound field satisfy the following relationship:
where k is the light wave vector; K is the sound wave vector; υ is the light field frequency; f is the sound field frequency. Subscripts i and d denote incident light and diffracted light respectively. “±” depends on the positive and negative diffraction order, and the selection rule is “ + “ is the up-frequency shift; “ - “ is the down-frequency shift. In order to ensure that the acousto-optic device works in the Bragg diffraction region, the acousto-optic interaction length L should meet the following conditions: L0 is the characteristic length of acousto-optic medium; n is the refractive index of acousto-optic medium; V is the sound velocity of the medium; λ is the working wavelength. Equation (5) shows that the crystal length is inversely proportional to the square of the single minimum frequency shift. In order to achieve small single frequency shift, it is necessary to increase the size of acousto-optic crystal, which is obviously not suitable for practical engineering applications. The dual-frequency laser adopts double crystal reverse cascade technology, which breaks through the limitation of Bragg diffraction characteristic length on the size of single acousto-optic crystal under low frequency conditions. The working principle of the double crystal acousto-optic frequency shifter is shown in Fig. 5.The incident light enters the LiNbO3 crystal and interacts with the ultrasonic wave with frequency f1 to produce the first diffraction. The second diffraction occurs when the diffraction output acts as the incident light of the second acousto-optic crystal and interacts with the ultrasonic wave of frequency f2. The second diffraction output acts as the output light of the device. Therefore, the single minimum frequency shift is no longer limited by the crystal size, It is only related to the difference between f1 and f2. At this time, the wave vector and frequency between the output light field and the sound field meet the following requirements:
At present, the gain media commonly used for SBS amplification are perfluorocarbon liquid (PFCS) and perfluoropolyether liquid (PFPE), whose Brillouin frequency shift are generally less than 2 GHz [8]. The maximum frequency shift of this system is 2 GHz. On the one hand, the setting of this upper limit takes into account that the practical application does not require excessive frequency shift. On the other hand, repeated acousto-optic frequency shift will seriously lose pulse energy and interfere with the stability of the system. The frequency shift loops are shown in Fig. 6.
The specific frequency shift process is as follows: the pulse pair is divided into two pulses by AOM1 and AOM4 in time domain and enters the frequency shifter through a 2×1 coupler. Each time the incident pulse passes through the frequency shifter, the corresponding positive frequency shift will appear. The output diffractive light of the frequency shifter is divided into two paths with equal energy by a 1×2 beam splitter with a spectral ratio of 50:50, one of which enters AOM3 and AOM6, and the other one enters the compensation loop where AMP is located, so that the energy of pulse transmission back to the 2×1 coupler is consistent with the initial energy and the next frequency shift is carried out. Through the control of synchronous signal, the two pulses are regularly shifted several times within the frequency shift loop to reach the ideal frequency shift requirements, and selectively output the pulse that meets the frequency shift requirements. The frequency changes of the pulse after passing through the frequency shifting loop are:
3. Experimental results and analysis
3.1 Pulse width adjustability
In this paper, AWG70000 series software is used to edit AWG waveform file. The waveform type, duration, timing position and amplitude value are set respectively. As the input RF signal voltage of AM must be between 150 mV and 200 mV, the pulse amplitude setting should meet the requirements of AM. The software unit is pts, 1 pts = 100 ps. In the experiment, four square wave waveforms of 100 ps, 500 ps, 10 ns and 50 ns were prepared, and the pulse amplitude was 0.4 V, as shown in Fig. 7.
Fig. 7. Schematic diagram of monopulse waveform compilation. (a) 100 ps. (b) 500 ps. (c) 10 ns. (d) 50 ns.
Due to the verification of the pulse width adjustable characteristics of the dual-frequency optical fiber system, it is only necessary to write a single square wave pulse of different widths in the experiment and make them pass through one of the two frequency shift loops. The final waveforms output by the oscilloscope are shown in Fig. 8. Compared with the pulse width of the programmed waveform, the error of the output seed light width is 22.0%, 3.1%, 2.1% and 0.94% respectively. It can be seen that both 100 ps and 500 ps output have different degrees of broadening. We believe that the broadening of the pulse is related to the response time (<1ns) of the photodetector (THORLABS-DET08CFC/M), oscilloscope (Tektronix DSA71254C) and environmental noise. The width of the actual output pulse can basically be matched with the programmed pulse waveform, and there is no light loss or jamming. This not only verifies the adjustable pulse width of the system, but also reflects that the multichannel synchronous control device works normally.
The previous experiment verifies a single frequency shift path and does not check the stability of the system when two frequency shift loops work together. We also analyzes the performance of the whole system under the condition of input pulse pair. The pulse pair waveforms prepared are shown in Fig. 9.
Fig. 9. Schematic diagram of pulse pair waveform compilation. (a) 500ps-1ns. (b) 1ns-2ns. (c) 2ns-5ns. (d) 5ns-10ns.
The selection of the time interval between the two pulses in the pulse pair is related to the response sensitivity of AOM. In order to ensure that AOM will not affect the passage of seed light, we measured the optical path in the design and set the time interval as 200ns. After time domain separation, the two pulses entered the 1MHz-20MHz and 200MHz frequency shifting loops, respectively. In the experiment, the two pulses were only shifted once without continuous frequency shifting. The pulse pair finally obtained at AOM7 after beam combination is shown in Fig. 10.
After two pulses pass through two frequency shift paths, the time interval after combining is shortened from 200 ns to 188 ns, which is related to the design of the internal structure of the frequency shift ring. In addition, in the beat frequency test, the waveform writing should also consider compensating the time interval of 188 ns. Because the former pulse needs to be diffracted twice when it passes through the 1MHz-20MHz frequency shift loop, the energy consumption of the former pulse is higher than that of the later pulse from the output of the oscilloscope. In order to solve this problem, small energy pulse can be used as Stokes light, and large energy pulse can be used as pump light.
3.2 Frequency shift controllability
It is the most important function of dual-frequency laser to shift the frequency independently after the time-domain separation of pulses, and it is also the key to realize non-collinear SBS amplification. In this paper, beat frequency is used to measure the frequency difference of two pulses. Limited by the response accuracy of oscilloscope, the minimum frequency difference of two pulses is set to 200 MHz. In addition, the frequency shift differences of 800 MHz, 1.4 GHz and 2 GHz are tested respectively, and the results are shown in Fig. 11.
The single increment of the above four frequency shifts is 600MHz, and the errors with the ideal frequency shift are 0.2%, 0.26%, 0.14% and 0.05% respectively. Finally, the dual-frequency laser realizes the maximum 2GHz frequency difference between the two pulses. In practical application, the system can actively control the frequency difference of the output pulse pair according to the different Brillouin frequency shift of the gain medium, so as to maintain the Brillouin gain of the amplification system. We test the frequency difference matching degree of the output pulse pair to the Brillouin frequency shift of HT-110 (550MHz) and FC-40 (1050MHz). The beat frequency results are shown in Fig. 12.
Finally, the pulse frequency difference of the dual-frequency system corresponding to the two media is 550.77 MHz and 1050.63 MHz respectively, and the error with the ideal Brillouin frequency shift is 0.14% and 0.06% respectively. Because the energy conversion efficiency of SBS amplification process is also affected by the purity of gain medium, the length of reaction cell and the external environment, the small error caused by frequency difference can be ignored compared with other interference factors.
3.3 Energy stability
SBS amplification is completed by energy conversion. In the process of energy transfer from pump light to Stokes light, a stable pump energy supply is required. Therefore, the energy stability of μ-AMP output light are tested in this paper. The pumping current of the amplifier were set as 700mA, 800mA, 900mA and 1A successively, and the detection time was 10min. The output energy curve was shown in Fig. 13.
The output of dual-frequency laser is maintained at the nJ level. With the increase of pump current, the energy of single pulse increases by two times. It can be seen from the figure that the output energy basically presents a horizontal trend, and its fluctuation error is 10−2 nJ. The variance of energy variation driven by four kinds of pump currents remains in the order of 10−3. With the increase of pump current, the energy stability decreases. In order to keep the energy of the system in a stable condition, the system should be operated for 10 min -20 min before the experiment.
4. Conclusion
In this paper, an active broad-band and high-precision Brillouin Stokes seed light generation technology is proposed by using acousto-optic crystal modulation. Through the AWG waveform writing function, the output pulse width can be adjusted in the range of 100 ps-50 ns. The reverse cascade of double crystal overcomes the problem of too large size of acousto-optic crystal in the case of small frequency shift, achieves the maximum dynamic range of 2 GHz frequency shift. In order to solve the synchronization problem caused by time jitter in the process of Stokes seed light generation, a cascaded synchronization system is constructed. Combined with fine delay control technology, multichannel photoelectric precise synchronization signal regeneration is realized. The active generation of wide-band high-precision Stokes seed light is expected to obtain important applications in high energy and high frequency lasers, laser beam combination, pulse compression and so on.
Funding
National Natural Science Foundation of China (61905062, 61927815, 61905061, 62075056); China Postdoctoral Science Foundation (2020M670613); Hebei Postdoctoral Scholarship Project (B2020003026); Hebei Science and Technology Innovation Strategy Project (20180601).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. S. Payun and B. Malekynia, “Thermal resonance effect by a strong shock wave in D–T fuel side-on ignition by laser-driven block acceleration,” Laser Part. Beams 37(4), 332–340 (2019). [CrossRef]
2. S. Weber and C. Riconda, “Temperature dependence of parametric instabilities in the context of the shock-ignition approach to inertial confinement fusion,” High Pow Laser Sci Eng 3(1), 51–63 (2015). [CrossRef]
3. L. J. Perkins, R. Betti, J. H. Nuckolls, and K. N. LaFortune, “Shock Ignition: A New Approach to High Gain Inertial Confinement Fusion on the National Ignition Facility,” Phys. Rev. Lett 103(4), 045004 (2009). [CrossRef]
4. R. Betti, C. D. Zhou, K. S. Anderson, L. J. Perkins, W. Theobald, and A. A. Solodov, “Shock ignition of thermonuclear fuel with high areal density,” Phys. Rev. Lett. 98(15), 155001 (2007). [CrossRef]
5. F. Quinlan, S. Gee, S. Ozharar, and P. J. Delfyett, “Ultralow-jitter and amplitude-noise semiconductor-based actively mode-locked laser,” Opt. Lett. 31(19), 2870–2872 (2006). [CrossRef]
6. S. Q. Yang, E. A. Ponomarev, and X. Y. Bao, “40-GHz Transform-Limited Pulse Generation From FM Oscillation Fiber Laser With External Cavity Chirp Compensation,” IEEE Photon. Technol. Lett. 16(7), 1631–1633 (2004). [CrossRef]
7. W. H. Cao, S. H. Liu, C. J. Liao, Q. Guo, and H. C. Jin, “Picosecond Chirped Pulse Compression in Single-Mode Fibers,” Acta Opt. Sin. 15(02), 180–185 (1995).
8. W. H. Cao, S. H. Liu, C. J. Liao, and Q. Guo, “Compression of Bright Optical Pulse Pair in the Normal-dispersion Regime of Single-mode Fibers,” Acta Phys. Sin. 46(5), 919–928 (1997). [CrossRef]
9. W. H. Cao, Y. W. Zhang, S. H. Liu, Q. Guo, and W.C. Xu, “Compression of Bright Optical Pulse by Dark Solitons in the Normal Dispersion Region of Single-Mode Fibers,” Acta Opt. Sin. 15(03), 281–286 (1995).
10. B. Kibler, R. Fischer, P. A. Lacourt, F. Courvoisier, R. Ferriere, L. Larger, D.N. Neshev, and J.M. Dudley, “Optimized one-step compression of femtosecond fibre laser soliton pulses around 1550 nm to below 30fs in highly nonlinear fibre,” Electron. Lett. 43(17), 915–916 (2007). [CrossRef]
11. B Kibler, C Billet, A Lacourt P, R. Ferriere, and J. M. Dudley, “All-fiber source of 20-fs pulses at 1550 nm using two-stage linear-nonlinear compression of parabolic similaritons,” IEEE Photon. Technol. Lett. 18(17), 1831–1833 (2006). [CrossRef]
12. H. X. Liu, Y. L. Li, C. Yang, X. K. Gu, W. W. Hu, Y. P. Zhang, and Y. M. Zhang, “1.35 ns SBS laser pulse,” Optik 184, 394–398 (2019). [CrossRef]
13. Z. X. Bai, Y. L. Wang, Z. W. Lu, H. Yuan, Z. X. Zheng, S. S. Li, Y. Chen, Z. H. Liu, C. Cui, H. L. Wang, and R. Liu, “High Compact, High Quality Single Longitudinal Mode Hundred Picoseconds Laser Based on Stimulated Brillouin Scattering Pulse Compression,” Appl. Sci. 6(1), 29 (2016). [CrossRef]
14. Z. H. Liu, Y. L. Wang, Y. R. Wang, H. Yuan, Z. X. Bai, H. L. Wang, R. Liu, S. S. Li, H.K. Zhang, L. X. Zhou, T. Tan, W. M. He, and Z. W. Lu, “Generation of high-energy 284 ps laser pulse without tail modulation by stimulated Brillouin scattering,” Chin. Opt. Lett. 14(9), 091901 (2016). [CrossRef]
15. C. Y. Feng, X. Z. Xu, and J. C. Diels, “High-energy sub-phonon lifetime pulse compression by stimulated Brillouin scattering in liquids,” Opt. Express 25(11), 12421–12434 (2017). [CrossRef]
16. Z. H. Liu, Y. L. Wang, H. L. Wang, Z. X. Bai, S. S. Li, H. K. Zhang, Y. R. Wang, W. M. He, D. Y. Lin, and Z. W. Lu, “Pulse temporal compression by two-stage stimulated Brillouin scattering and laser-induced breakdown,” Appl. Phys. Lett. 110(24), 88 (2017). [CrossRef]
17. Z. X. Bai, Y. L. Wang, Z. W. Lu, L. Jiang, H. Yuan, and Z. H. Liu, “Demonstration of an ultraviolet stimulated Brillouin scattering pulse compressed hundred picosecond laser in LiB3O5 crystals,” J. Opt. 19(8), 085502 (2017). [CrossRef]
18. Z. H. Liu, Y. L. Wang, Z. X. Bai, Y. R. Wang, D. Jin, H. L. Wang, H. Yuan, D. Y. Lin, and Z. W. Lu, “Pulse compression to one-tenth of phonon lifetime using quasi-steady-state stimulated Brillouin scattering,” Opt. Express 26(18), 23051–23060 (2018). [CrossRef]
19. H. L. Wang, S. Cha, Y. L. Wang, H. J. Kong, and Z. W. Lu, “SBS pulse compression using bulk fused silica by diode-pumped solid-state lasers at 1 kHz repetition rate,” Opt. Laser Technol. 128, 106258 (2020). [CrossRef]
20. H. X. Liu, “Research on medium for ultrashort pulse laser by SBS,” Laser & Infrared 049(004), 387–394 (2019).
21. A. A. Kuz’min, O. V. Kulagin, and V. I. Rodchenkov, “Formation of nanosecond SBS-compressed pulses for pumping an ultra-high power parametric amplifier,” Quantum Electron. 48(4), 344–350 (2018). [CrossRef]
22. H. Yuan, Z. W. Lu, Y. L. Wang, Z.X. Zheng, and Y. Chen, “Hundred picoseconds laser pulse amplification based on scalable two-cells Brillouin amplifier,” Laser Part. Beams 32(3), 369–374 (2014). [CrossRef]
23. H. L. Wang, S. Cha, H. J. Kong, Y. L. Wang, and Z. W. Lu, “Sub-nanosecond stimulated Brillouin scattering pulse compression using HT270 for kHz repetition rate operation,” Opt. Express 27(21), 29789–29802 (2019). [CrossRef]
24. Z. J. Kang, Z. W. Fan, Y. T. Huang, H. B. Zhang, W. Q. Ge, M. S. Li, X. C. Yan, and G. X. Zhang, “High-repetition-rate, high-pulse-energy, and high-beam-quality laser system using an ultraclean closed-type SBS-PCM,” Opt. Express 26(6), 6560–6571 (2018). [CrossRef]
25. Y. D. Lian, Y. H. Wang, Y. Q. Zhang, S.W. Han, Y. Yu, X. Qi, N. N. Luan, Z. X. Bai, Y. L. Wang, and Z. W. Lv, “Research progress of stimulated Brillouin scattering pulse compression technique,” High Power Laser and Particle Beams 33(5), 051001 (2021). [CrossRef]
26. H. Yuan, Y. L. Wang, Z. W. Lu, and Z. X. Zheng, “Active frequency matching in stimulated Brillouin amplification for production of a 2.4 J, 200 ps laser pulse,” Opt. Lett. 43(3), 511–514 (2018). [CrossRef]
27. H. Yuan, Y. L. Wang, C. Y. Zhu, Z. X. Zheng, and Z. W. Lu, “Investigation of sub-phonon lifetime pulse amplification in active frequency matching stimulated Brillouin scattering,” Opt. Express 27(12), 16661–16670 (2019). [CrossRef]
