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A compact, high-power single-frequency laser based on Nd:YAG slab amplifier
Journal Pre-proof A compact, high-power single-frequency laser based on Nd:YAG slab amplifier Jianyong Ding, Guangli Yu, Ruilin Zheng, Jun Zhou, Xiaolei Zhu, Weikuan Duan, Chunqi Fang, Wei Wei
PII: DOI: Reference:
S0030-4018(20)30160-7 https://doi.org/10.1016/j.optcom.2020.125534 OPTICS 125534
To appear in:
Optics Communications
Received date : 26 September 2019 Revised date : 1 February 2020 Accepted date : 14 February 2020 Please cite this article as: J. Ding, G. Yu, R. Zheng et al., A compact, high-power single-frequency laser based on Nd:YAG slab amplifier, Optics Communications (2020), doi: https://doi.org/10.1016/j.optcom.2020.125534. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
Journal Pre-proof
Highlights
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Highlights: ·The laser for space debris observations for the first time. ·The novel method of ramp-fire with bias feedback.
·Theoretical simulation and experiment of slab amplification
·Conductively cooled bounce-pumped slab amplifier with more reliable
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and efficient.
Journal Pre-proof
*Manuscript Click here to view linked References
A compact, high-power single-frequency laser based on Nd:YAG slab
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amplifier
Jianyong Ding1,2, Guangli Yu2, Ruilin Zheng1, Jun Zhou2,3, Xiaolei Zhu3, Weikuan Duan1, Chunqi Fang1, Wei Wei1*
(1College of Electronic and Optical Engineering, Nanjing University of Posts and Telecommunications, Nanjing, 210023, China) (2Nanjing Institute of Advanced Laser Technology, Chinese Academy of Sciences, Nanjing, 210038, China)
(3Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai, 201800, China)
Abstract: High-power all-solid-state lasers have received widespread attentions as the core component of space debris observing systems, however, the system's efficiency and thermal management constrain certain practical applications. A novel kind of master oscillator power-amplifier (MOPA) system with a high optical efficiency, compact structure and simple cooling system was proposed and demonstrated, which based on single-frequency seeder and diode bounce-pumped slab amplifier. By injecting a single frequency laser, the output pulse energy achieved is about 310 mJ (@532 nm, 200 Hz), which has excellent parameters including pulse duration of 4.8 ns, beam quality M2 of 3.0 and power stability (RMS) of 1.0% for 4 h. Most importantly, the proposed MOPA system has been successfully used for space debris observations for the first time, which strongly indicates that it is a promising solution.
Key words: Single-frequency, Nd:YAG slab amplifier, Solid-state laser, MOPA .
1. Introduction
Currently, with increasing threat to satellites and space stations from space debris, monitoring and warning of space debris has become a hot issue for the development of aerospace recently [1-2].
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High-power diode-pumped solid-state laser (DPSSL) is considered to be one of the most potential laser sources for laser ranging because of their high peak power and long life-time [3-5]. However, there are still some drawbacks of high-power DPSSL will restrict the beam quality, system efficiency and complexity of cooling system, such as thermal distortion, thermal depolarization and thermal management [6]. In order to solve these problems, a series of new laser systems including rod lasers, slab lasers, InnoSlab lasers and active-mirror lasers have been developed in recent years[7-9]. The side-pumped rod laser based on the master oscillator power-amplifiers (MOPA) are the most widely used for spot symmetry and high
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pump power. In addition, 4F image transmission, spatial filtering and wave-front correction technologies are adopted to improve the beam quality [10]. In 2017, Chaoyang Li reported on a nanosecond Nd:YAG MOPA system with pulse energy of 2.36 J at 50 Hz [11]. However, it is difficult to obtain the beam output close to the
diffraction
limit
by
the
thermal
compensation
or
spatial
filtering.
Recently,
the
stimulated-brillouin-scattering phase-conjugate mirror (SBS-PCM) is introduced to realize dynamic correction of beam wave-front distortions in high-power amplification [12-13]. Unfortunately, the fluorinert liquid (FC-770) used in SBS-PCM as medium is unreliable for its fluidity and volatility, which make SBS-PCM mainly used in experiment instead of in engineering lasers. Besides, these methods for improving 1
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beam quality will greatly increase laser size and reduce reliability, which is disadvantageous for engineering applications, especially for mobile laser ranging systems. Zigzag slab lasers have shown advantages over
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conventional rod lasers in terms of beam quality and efficiency due to rectangular structure and zigzag optical transmission. In addition, the conduction cooling technology of slab crystals is more advantageous than convection cooling in terms of mechanical stability, compact structure, and water quality requirements [14-16]. The slab amplifier have developed rapidly for its compact size and efficient thermal management, especially in space laser field. In 2018, Floyd Hovis reported a 355 nm, space-qualified laser which achieved 100 mJ/pulse of single frequency 355 nm output at 150 Hz with an M2 of 3.0 [17]. The DPSSL carried by Aeolus is realized as a MOPA system, generating 60 mJ of single-frequency pulses at 355 nm wavelength, 50 Hz repetition rate and 20 ns pulse duration [18]. To the best of our knowledge, the slab laser exhibit outstanding performance in space-based lidar, but it is not reported in the space debris observation. Considering the high reliability and efficiency of observational requirement, MOPA system based on Nd:YAG slab amplifier is more advantageous to achieve high energy while maintaining a compact structure. In this work, we design a compact, high-power MOPA system based on single-frequency seeder and slab amplifiers for space debris observation for the first time, which delivers a 310 mJ high-energy pulse of 532 nm at 200 Hz. By injecting a single frequency laser, the oscillator adopted resonant detection and ramp-fire with bias feedback to achieve a single-frequency pulse. The bounce-pumped design and pumped waveguides were adopted in slab amplifier to increase amplification efficiency and pump uniformity. Simulations for slab amplifier have been implemented to choose the appropriate media parameter and pump power. The near-field and far-field beam qualities were excellent by thermal lens compensation. The proposed MOPA system has been successfully used for space debris observations for the first time, which strongly indicates that it is a promising solution.
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2. Experimental Setup
2.1 The laser system and parameters
The laser system is consisted of three parts: seed, master oscillator and amplifier unit, as shown in Fig.1. Seeder laser was a nonplanar ring oscillator (NPRO) laser with the power of 100 mW (CW) and line width of 3 kHz. Through high-precision drive and temperature control circuits, frequency stability of NPRO was less than 2 MHz in 2 min and it will become worse when working for a long time. The ramp-fire with bias feedback was used to generate a single frequency pulses with high stability of frequency and pulse. The
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oscillator length is controlled by two PZTs, PZT1 for scanning cavity by the ramp voltage at 200 Hz, PZT2 with DC bias for dynamic compensation. It could overcome the frequency jitter caused by nonlinear displacement of piezoelectric ceramics, reduce the difficulty of control system and improve mechanical stability.
2
Fig. 1 Experimental setup of MOPA system. L: lens; I: isolator; M: mirror; AMP: amplifier; P: polarizer.
The peak power of fiber-coupled LD1-LD4 was 120 W at 808 nm and pumping beam was focused to 1.2 mm. Laser crystal size of oscillator and end-pump amplifier is Φ3 mm×20 mm with doping concentration 0.8%, which was cooled by TEC under the condition of 200 Hz repetition frequency. The cavity length was about 500 mm, which rear mirror with a transmission of 5% at 1064 nm and output mirror with a transmission of 60% at 1064 nm. The electric-optical Q-switch was composed of a KD*P electro-optic modulator, quarter wave (QW) plate, and polarizer. Two QW plates were inserted at both
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ends of the laser rod to eliminate space hole burning effect.
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Fig. 2 Modular design of the bounce-pumped slab amplifier (a) 3D illustration of the module, (b) Bounce-pumped structure, 1-LD G-stacks, 2-pump waveguide, 3-Nd: YAG slab.
After passing the end-pump double-pass amplifier and isolator, laser beam was shaped into Φ 2.5 mm by the beam expander. The bounce-pumped slab amplifier adopted a symmetric conductively cooled configuration and zigzag slab design with “pump on bounce” architecture, as shown in Fig. 2. G-stack 3
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array with 4 Bars or 6 Bars was installed at the reflection point of zigzag slab. A trapezoidal waveguide with a thickness of 5 mm was used to shape the pump spot to improve pump uniformity. In case of
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1 2 high-energy pumping, LD was cooled conductively by pure water, which improves the reliability of the 3 4 amplifier greatly. To prevent thermal deformation of the structure, a poly tetra fluoroethylene (PTFE) 5 material was used to isolate the heat of the amplifier. 6 7 The crystal size of the AMP1 was 5 mm ×5 mm×112 mm with doping concentration 1.0% pumped by 8 9 12 G-stacks(48 Bars) with total peak power 7200 W, pump pulse width 150 μs. The angle of slab AMP1 10 11 end face was cut into Brewster angle. The crystal size of the AMP2 was 6 mm×8 mm×121 mm with 12 doping concentration 0.8% pumped by 14 G-stacks (84 Bars) with total peak power 12600 W, pump pulse 13 14 width 150 μs. The crystal size of the AMP3 was 8 mm×10 mm×118 mm with doping concentration 1.0% 15 16 pumped by 12 G-stacks (72 Bars) with total peak power 10800 W, pump pulse width 150 μs. The angle of 17 slab AMP2 and AMP3 end face was cut into 45°. And, the angular deviation of crystal faces at both ends 18 19 was 3° to avoid self-oscillation. Two cylindrical mirrors were used to compensate for the thermal focal 20 21 length of slab crystal horizontally and vertically. Polarizer between amplifiers was used to increase the 22 23 degree of laser's polarization. The slab crystal was soldered to the heat sink with indium to improve 24 thermal conductivity. The optical components in the slab-amplified chain were placed at an angle to avoid 25 26 lens back-laser amplification and self-oscillation. 27 28 29 2.2 Theory and measurements 30 31 32 The laser amplification formula of bounce structure Nd:YAG amplifier could be expressed by the 33 34 Frantz-Nodvik equation, as shown in Equation 1 [12]. 35 (1) 36 37 38 Where E is the output energy, Es is the saturation fluence, Aact is the cross-sectional area of the propagating 39 40 laser beam, θ is the complementary angle to the angle of incidence at the total internal reflection surface, 41 42 Ein is the input energy, As is the cross-sectional area of the slab, f is the fill factor of slab, Estore is the total 43 stored energy of slab. 44 45 Waveforms of signal and pulse were detected by an oscilloscope (MDO3054, Tektronix, China) with a 1 46 47 GHz PIN photodiode. Laser power and power stability were recorded by using a laser power meter 48 (L500W, Ophir, Isreal). Near-field and far-field spots of laser were measured by a CCD (SP620U, Spiricon, 49 50 USA). The beam quality was detected by a beam quality analyzer (M2-200S-FW, Spiricon, USA). The 51 52 frequency stability was measured by a wavelength meter (WS7, HighFinesse, Germany). All 53 54 measurements were performed at room temperature. The wave-front distortion was measured by a laser 55 interferometer (GPIXP/D, Zygo, USA) to judging the stress distribution inside the slab Nd:YAG module. 56 57 The wave-front distortion of AMP1, AMP2 , AMP3 was 0.399 λ, 0.461 λ, 0.436 λ at 633 nm. 58 59 3. Results and discussions 60 61 The signal diagram of seed injection based on ramp-fire with bias feedback is showed in Fig.3 (a). 62 63 4 64 65
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When PZT is loaded with periodic scanning voltage, the interference waveform (sine wave) of seeder laser can be detected by PD. A TTL trigger signal (channel 2) is generated to the Q switch while the peak point
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is detected by circuit system. The position of peak point is stabilized in a 10 μs time window by PZT to improve stability. The PIN photodiode can obtain the waveform shown in Fig.3 when the PZT scans the cavity. The single-frequency pulse had a narrow linewidth (60 MHz) without intensity modulation after seeder injection, which can reduce the risk of component damage and improve system safety in energy amplification.
Fig.3.The signal diagram of ramp-fire (a) the channel 1 is used to test the pulse signal. Channel 2 is the trigger signal of the Q switch. Channel 3 is the interference signal of the seed laser. Signal amplitude increases rapidly at the peak where the Q switch is triggered. Channel 4 is the signal of pump laser. (b) Pulse waveform diagram of laser pulse with seeder injected (c) without seeder injected.
Fig. 4 shows the output pulse energy of each power amplifier. The theoretical values of the F-N equation are in good agreement with the test value. The output energy can up to 610 mJ of AMP3 at 200 Hz. Out of the amplification from AMP1, AMP2 and AMP3, the energy extract efficiency becomes 7.8%, 16.2% and
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30.0% respectively and the average optical efficiency of the 3-stage slab amplification module is 18.5%. It shows that the near-field beam intensity is uniformly distributed.
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Fig. 4 Theoretical and test values of the amplifier output energy as the function of pump energy. The input energy of (a) AMP1 is 17 mJ, (b) AMP2 is 80 mJ, (c) AMP3 is 280 mJ.
At 200 Hz operation, the more parameters of MOPA system are listed in Table 1. The laser pulse at 532 nm is narrowed to 4.8 ns during the AMP1, AMP2, AMP3 and LBO unit. Due to the thermal effect, the 5
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beam quality is reduced to 3.0 after the amplifiers. The peak power density is at most 280 MW/cm2, which
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is within the safe range of the optical film layer. Table 1 Laser parameters in the amplified chain Subsystem Oscillator Pre-AMP AMP1 AMP2 AMP3 LBO
Pump energy/mJ 35 40 800 1300 1100
Input/mJ
Output/mJ
Pulse width/ns
M2
Beam size/mm
7 17 80 280 610
7 17 80 290 610 320
7.0 7.0 6.2 5.3 5.8 4.8
1.1 1.2 1.5 1.9 3.0 3.0
φ1.2 φ1.5 2.5×2.5 5.0×5.0 6.0×6.0 7.0×7.0
Fig. 5 shows laser power stability and beam quality test data of 532 nm. The average power is 63.5 W and power stability (RMS) for 4 h reaches 1.0%. The laser is cooled by a water cooler with 5 kW cooling capacity. The near-field beam intensity is uniformly distributed and the far field spot is gaussian distributed. The beam quality of M2 in two axes are 2.8 (horizontal direction) and 3.0 (vertical direction), as shown in
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Fig. 5(d).
Fig. 5 (a) The power stability (RMS) at 532 nm for 4 h, (b) the near-field spot, (c) the far-field spot, and (d) the beam quality of M2
Fig.6 gives the frequency stability of oscillator that can reach to 4.2×10-9(RMS) @70 s. The frequency stability at 532 nm is 8.4×10-9 (RMS) @70 s. The pulse stability and frequency stability using Ramp-fire technology with bias feedback technology are very stable in a short time. The seeder injection success rate is 100% with good vibration shock resistance. The frequency stability will be worsened by external
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disturbances such as vibration, temperature, air disturbance. So Pound-Drever-Hall (PDH) frequency stabilization measures are still needed to maintain long-term frequency stability.
6
Fig. 6 The frequency stability of the oscillator at 1064 nm for 70 s.
4. Conclusion
A compact high-energy single-frequency laser for space debris observation was developed by using a seed injection and MOPA method. Because of high stability of NPRO laser and novel ramp-fire technology, the laser output a high stability single frequency pulse with the frequency stability of 4.2×10-9(RMS) for 70 s and energy stability of 1.0% (RMS) for 4 h. The output power 63 W of 532 nm with a total pulse energy of 310 mJ, beam quality M2 of 3.0 and pulse width of 4.8 ns was achieved at 200Hz. The average optical efficiency of bounce-pumped slab amplifier (AMP1, AMP2 and AMP3) is about 18.7%, which reduced thermal effects, cooling complexity and structure volume. Most importantly, the proposed MOPA system has been used for space debris observations successfully for the first time, which strongly indicates that it is a promising solution.
Acknowledgments
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This work was financially supported by the National Natural Science Foundation of China (Grant No. 6 1905119), the University Natural Science Research Project of Jiangsu Province (Grant No. 19KJB140013)
References
[1] H.F. Zhang, M.L. Long, H.R. Deng, Z.B. Wu, Z.E. Cheng, Z.P. Zhang, Space debris laser ranging with a 60W single-frequency slab nanosecond green laser at 200 Hz, Chin. Opt. Lett. 17 (2019) 051404. [2] Z.J. Kang, Z.W. Fan, Y.T. Huang, H.B. Zhang, W.Q. Ge, M.S. Li, X.C. Yan, 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) (2018) 6560-6571.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
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[3] Y. Xia, L.F. Du, X.W. Cheng, F.Q. Li, J.H. Wang, Z.L. Wang, Y. Yang, X. Lin, Y.C. Xun, S.S. Gong, G.T. Yang, Development of a solid-state sodium Doppler lidar using an all-fiber-coupled injection seeding unit for simultaneous temperature and wind measurements in the mesopause region, Opt. Express 25(5) (2018) 5264. [4] J.T. Guo, J.F Wang, H. Wei, W.F. Huang, T.R. Huang, G. Xia, W. Fan, Z.q. Lin, High-power, Joule-class, temporally shaped multi-pass ring laser amplifier with two Nd:glass laser heads, High Power Laser Sci. Eng. 7 (2019) e8. [5] J.S. Qiu, X.X. Tang, Z.W. Fan, H.C. Wang, 200 Hz repetition frequency joule-level high beam quality Nd:YAG nanosecond laser, Opt. Commun. 368 (2016) 68–72. [6] X. Fu, Q. Liu, P.L. Li, Z. Sui, T.H. Liu, M.L. Gong, High-efficiency 2 J, 20 Hz diode-pumped Nd:YAG active-mirror 7
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master oscillator power amplifier system, Appl. Phys. Express 8 (2015) 092702. [7] C. Baumgarten, M. Pedicone, H. Bravo, H. Wang, L.Yin, C. S. Menoni, J. J. Rocca, B. A. Reagan, 1 J, 0.5 kHz
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repetition rate picosecond laser, Opt. Lett. 41(14) (2016) 3339-3342.
[8] J. Liu, L. Li, X.C. Shi, R.F. Chen, J.L. Wang, W.B. Chen, High-beam-quality, 5.4 J, 5 Hz diode-pumped Nd:YAG active mirror laser amplifier, Chin. Opt. Lett. 16(12) (2018) 121402.
[9] X. Yu, L. Dong, B. Lai, P. Yang, Adaptive aberration correction of a 5 J/6.6 ns/200 Hz solid-state Nd:YAG laser, Opt. Lett. 42 (2017) 2730–2733.
[10] K. Tsubakimoto, H. Yoshida, N. Miyanaga, High-average-power green laser using Nd:YAG amplifier with stimulated Brillouin scattering phase-conjugate pulse-cleaning mirror, Opt. Express 24(12) (2016) 12557-12564.
[11] C.Y. Li, C.Q. Lu, C. Li, N. Yang, Y. Li, Z. Yang, S. Han, J.F. Shi, Z.W. Zhou, 2.36 J, 50 Hz nanosecond pulses from a diode side-pumped Nd:YAG MOPA system, Opt. Commun. 394 (2017) 1–5.
[12] X.X. Tang, J.S, Qiu, Z.W. Fan, H.C. Wang, H. Liu, Y.L. Liu, Z.J. Kang, Experimental study on SBS-PCM at 200 Hz repetition rate pumped with joule-level energy, Opt. Mater. 67 (2017) 64–69.
[13] C. Cui, Y.L. Wang, Z.W. Lu, H. Yuan, Y. Wang, Y. Chen, Z. Wang, Z.X. Bai, R.P. Mildren, Demonstration of 2.5 J, 10 Hz, nanosecond laser beam combination system based on non-collinear Brillouin amplification, Opt. Express 26(25) (2018) 32717-32727.
[14] G.Y. Guo, Y.Z. Chen, J.G. He, Y. Lang, W.R. Lin, X.X. Tang, H.B. Zhang, Z.J. Kang, Z.W. Fan, Diode-pumped large-aperture Nd:YAG slab amplifier for high energy nanosecond pulse laser, Opt. Commun. 400 (2017) 50-54.
[15] O. Lux, C. Lemmerz, F. Weiler, U. Marksteiner, B. Witschas, S. Rahm, A. Schafler, O. Reitebuch, Airborne wind lidar observations over the North Atlantic in 2016 for the pre-launch validation of the satellite mission Aeolus, Atmos. Meas. Tech. 11 (2018) 3297–3322.
[16] G. Goodno, H. Komine, S. McNaught, S. Weiss, S. Redmond, W. Long, R. Simpson, E. Cheung, D. Howland, P. Epp, Coherent combination of high-power, zigzag slab lasers. Opt. Lett. 31(9) (2006)1247-1249.
[17] F. Fitzpatrick, J. Rudd, M. Albert, K. Puffenburger, T. Schum, S. Litvinovitch, D. Jones, F. Hovis, Lifetime testing of a
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355-nm, space-qualifiable laser, Proc. SPIE 10779 (2018) 1077908.
[18] C. Lemmerz, O. Lux, O. Reitebuch, B. Witschas, C. Wuhrer, Frequency and timing stability of an airborne injection-seeded Nd:YAG laser system for direct-detection wind lidar, Appl. Opt. 56(32) (2017) 9057-9068.
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8
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*Credit Author Statement
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Credit Author Statement Jianyong Ding: Methodology, Software, Data Curation, Writing - Original Draft, Writing - Review & Editing.
Guangli Yu: Methodology, Visualization.
Ruilin Zheng: Writing - Review & Editing.
Jun Zhou: Software , Resources, Supervision.
Xiaolei Zhu: Conceptualization, Project administration. Weikuan Duan: Investigation.
Chunqi Fang: Validation, Investigation.
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Wei Wei: Conceptualization, Resources, Writing - Review & Editing, Funding acquisition.
PII: DOI: Reference:
S0030-4018(20)30160-7 https://doi.org/10.1016/j.optcom.2020.125534 OPTICS 125534
To appear in:
Optics Communications
Received date : 26 September 2019 Revised date : 1 February 2020 Accepted date : 14 February 2020 Please cite this article as: J. Ding, G. Yu, R. Zheng et al., A compact, high-power single-frequency laser based on Nd:YAG slab amplifier, Optics Communications (2020), doi: https://doi.org/10.1016/j.optcom.2020.125534. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
Journal Pre-proof
Highlights
lP repro of
Highlights: ·The laser for space debris observations for the first time. ·The novel method of ramp-fire with bias feedback.
·Theoretical simulation and experiment of slab amplification
·Conductively cooled bounce-pumped slab amplifier with more reliable
Jou
rna
and efficient.
Journal Pre-proof
*Manuscript Click here to view linked References
A compact, high-power single-frequency laser based on Nd:YAG slab
lP repro of
amplifier
Jianyong Ding1,2, Guangli Yu2, Ruilin Zheng1, Jun Zhou2,3, Xiaolei Zhu3, Weikuan Duan1, Chunqi Fang1, Wei Wei1*
(1College of Electronic and Optical Engineering, Nanjing University of Posts and Telecommunications, Nanjing, 210023, China) (2Nanjing Institute of Advanced Laser Technology, Chinese Academy of Sciences, Nanjing, 210038, China)
(3Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai, 201800, China)
Abstract: High-power all-solid-state lasers have received widespread attentions as the core component of space debris observing systems, however, the system's efficiency and thermal management constrain certain practical applications. A novel kind of master oscillator power-amplifier (MOPA) system with a high optical efficiency, compact structure and simple cooling system was proposed and demonstrated, which based on single-frequency seeder and diode bounce-pumped slab amplifier. By injecting a single frequency laser, the output pulse energy achieved is about 310 mJ (@532 nm, 200 Hz), which has excellent parameters including pulse duration of 4.8 ns, beam quality M2 of 3.0 and power stability (RMS) of 1.0% for 4 h. Most importantly, the proposed MOPA system has been successfully used for space debris observations for the first time, which strongly indicates that it is a promising solution.
Key words: Single-frequency, Nd:YAG slab amplifier, Solid-state laser, MOPA .
1. Introduction
Currently, with increasing threat to satellites and space stations from space debris, monitoring and warning of space debris has become a hot issue for the development of aerospace recently [1-2].
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High-power diode-pumped solid-state laser (DPSSL) is considered to be one of the most potential laser sources for laser ranging because of their high peak power and long life-time [3-5]. However, there are still some drawbacks of high-power DPSSL will restrict the beam quality, system efficiency and complexity of cooling system, such as thermal distortion, thermal depolarization and thermal management [6]. In order to solve these problems, a series of new laser systems including rod lasers, slab lasers, InnoSlab lasers and active-mirror lasers have been developed in recent years[7-9]. The side-pumped rod laser based on the master oscillator power-amplifiers (MOPA) are the most widely used for spot symmetry and high
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pump power. In addition, 4F image transmission, spatial filtering and wave-front correction technologies are adopted to improve the beam quality [10]. In 2017, Chaoyang Li reported on a nanosecond Nd:YAG MOPA system with pulse energy of 2.36 J at 50 Hz [11]. However, it is difficult to obtain the beam output close to the
diffraction
limit
by
the
thermal
compensation
or
spatial
filtering.
Recently,
the
stimulated-brillouin-scattering phase-conjugate mirror (SBS-PCM) is introduced to realize dynamic correction of beam wave-front distortions in high-power amplification [12-13]. Unfortunately, the fluorinert liquid (FC-770) used in SBS-PCM as medium is unreliable for its fluidity and volatility, which make SBS-PCM mainly used in experiment instead of in engineering lasers. Besides, these methods for improving 1
Journal Pre-proof
beam quality will greatly increase laser size and reduce reliability, which is disadvantageous for engineering applications, especially for mobile laser ranging systems. Zigzag slab lasers have shown advantages over
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conventional rod lasers in terms of beam quality and efficiency due to rectangular structure and zigzag optical transmission. In addition, the conduction cooling technology of slab crystals is more advantageous than convection cooling in terms of mechanical stability, compact structure, and water quality requirements [14-16]. The slab amplifier have developed rapidly for its compact size and efficient thermal management, especially in space laser field. In 2018, Floyd Hovis reported a 355 nm, space-qualified laser which achieved 100 mJ/pulse of single frequency 355 nm output at 150 Hz with an M2 of 3.0 [17]. The DPSSL carried by Aeolus is realized as a MOPA system, generating 60 mJ of single-frequency pulses at 355 nm wavelength, 50 Hz repetition rate and 20 ns pulse duration [18]. To the best of our knowledge, the slab laser exhibit outstanding performance in space-based lidar, but it is not reported in the space debris observation. Considering the high reliability and efficiency of observational requirement, MOPA system based on Nd:YAG slab amplifier is more advantageous to achieve high energy while maintaining a compact structure. In this work, we design a compact, high-power MOPA system based on single-frequency seeder and slab amplifiers for space debris observation for the first time, which delivers a 310 mJ high-energy pulse of 532 nm at 200 Hz. By injecting a single frequency laser, the oscillator adopted resonant detection and ramp-fire with bias feedback to achieve a single-frequency pulse. The bounce-pumped design and pumped waveguides were adopted in slab amplifier to increase amplification efficiency and pump uniformity. Simulations for slab amplifier have been implemented to choose the appropriate media parameter and pump power. The near-field and far-field beam qualities were excellent by thermal lens compensation. The proposed MOPA system has been successfully used for space debris observations for the first time, which strongly indicates that it is a promising solution.
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2. Experimental Setup
2.1 The laser system and parameters
The laser system is consisted of three parts: seed, master oscillator and amplifier unit, as shown in Fig.1. Seeder laser was a nonplanar ring oscillator (NPRO) laser with the power of 100 mW (CW) and line width of 3 kHz. Through high-precision drive and temperature control circuits, frequency stability of NPRO was less than 2 MHz in 2 min and it will become worse when working for a long time. The ramp-fire with bias feedback was used to generate a single frequency pulses with high stability of frequency and pulse. The
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oscillator length is controlled by two PZTs, PZT1 for scanning cavity by the ramp voltage at 200 Hz, PZT2 with DC bias for dynamic compensation. It could overcome the frequency jitter caused by nonlinear displacement of piezoelectric ceramics, reduce the difficulty of control system and improve mechanical stability.
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Fig. 1 Experimental setup of MOPA system. L: lens; I: isolator; M: mirror; AMP: amplifier; P: polarizer.
The peak power of fiber-coupled LD1-LD4 was 120 W at 808 nm and pumping beam was focused to 1.2 mm. Laser crystal size of oscillator and end-pump amplifier is Φ3 mm×20 mm with doping concentration 0.8%, which was cooled by TEC under the condition of 200 Hz repetition frequency. The cavity length was about 500 mm, which rear mirror with a transmission of 5% at 1064 nm and output mirror with a transmission of 60% at 1064 nm. The electric-optical Q-switch was composed of a KD*P electro-optic modulator, quarter wave (QW) plate, and polarizer. Two QW plates were inserted at both
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ends of the laser rod to eliminate space hole burning effect.
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Fig. 2 Modular design of the bounce-pumped slab amplifier (a) 3D illustration of the module, (b) Bounce-pumped structure, 1-LD G-stacks, 2-pump waveguide, 3-Nd: YAG slab.
After passing the end-pump double-pass amplifier and isolator, laser beam was shaped into Φ 2.5 mm by the beam expander. The bounce-pumped slab amplifier adopted a symmetric conductively cooled configuration and zigzag slab design with “pump on bounce” architecture, as shown in Fig. 2. G-stack 3
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array with 4 Bars or 6 Bars was installed at the reflection point of zigzag slab. A trapezoidal waveguide with a thickness of 5 mm was used to shape the pump spot to improve pump uniformity. In case of
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1 2 high-energy pumping, LD was cooled conductively by pure water, which improves the reliability of the 3 4 amplifier greatly. To prevent thermal deformation of the structure, a poly tetra fluoroethylene (PTFE) 5 material was used to isolate the heat of the amplifier. 6 7 The crystal size of the AMP1 was 5 mm ×5 mm×112 mm with doping concentration 1.0% pumped by 8 9 12 G-stacks(48 Bars) with total peak power 7200 W, pump pulse width 150 μs. The angle of slab AMP1 10 11 end face was cut into Brewster angle. The crystal size of the AMP2 was 6 mm×8 mm×121 mm with 12 doping concentration 0.8% pumped by 14 G-stacks (84 Bars) with total peak power 12600 W, pump pulse 13 14 width 150 μs. The crystal size of the AMP3 was 8 mm×10 mm×118 mm with doping concentration 1.0% 15 16 pumped by 12 G-stacks (72 Bars) with total peak power 10800 W, pump pulse width 150 μs. The angle of 17 slab AMP2 and AMP3 end face was cut into 45°. And, the angular deviation of crystal faces at both ends 18 19 was 3° to avoid self-oscillation. Two cylindrical mirrors were used to compensate for the thermal focal 20 21 length of slab crystal horizontally and vertically. Polarizer between amplifiers was used to increase the 22 23 degree of laser's polarization. The slab crystal was soldered to the heat sink with indium to improve 24 thermal conductivity. The optical components in the slab-amplified chain were placed at an angle to avoid 25 26 lens back-laser amplification and self-oscillation. 27 28 29 2.2 Theory and measurements 30 31 32 The laser amplification formula of bounce structure Nd:YAG amplifier could be expressed by the 33 34 Frantz-Nodvik equation, as shown in Equation 1 [12]. 35 (1) 36 37 38 Where E is the output energy, Es is the saturation fluence, Aact is the cross-sectional area of the propagating 39 40 laser beam, θ is the complementary angle to the angle of incidence at the total internal reflection surface, 41 42 Ein is the input energy, As is the cross-sectional area of the slab, f is the fill factor of slab, Estore is the total 43 stored energy of slab. 44 45 Waveforms of signal and pulse were detected by an oscilloscope (MDO3054, Tektronix, China) with a 1 46 47 GHz PIN photodiode. Laser power and power stability were recorded by using a laser power meter 48 (L500W, Ophir, Isreal). Near-field and far-field spots of laser were measured by a CCD (SP620U, Spiricon, 49 50 USA). The beam quality was detected by a beam quality analyzer (M2-200S-FW, Spiricon, USA). The 51 52 frequency stability was measured by a wavelength meter (WS7, HighFinesse, Germany). All 53 54 measurements were performed at room temperature. The wave-front distortion was measured by a laser 55 interferometer (GPIXP/D, Zygo, USA) to judging the stress distribution inside the slab Nd:YAG module. 56 57 The wave-front distortion of AMP1, AMP2 , AMP3 was 0.399 λ, 0.461 λ, 0.436 λ at 633 nm. 58 59 3. Results and discussions 60 61 The signal diagram of seed injection based on ramp-fire with bias feedback is showed in Fig.3 (a). 62 63 4 64 65
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When PZT is loaded with periodic scanning voltage, the interference waveform (sine wave) of seeder laser can be detected by PD. A TTL trigger signal (channel 2) is generated to the Q switch while the peak point
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is detected by circuit system. The position of peak point is stabilized in a 10 μs time window by PZT to improve stability. The PIN photodiode can obtain the waveform shown in Fig.3 when the PZT scans the cavity. The single-frequency pulse had a narrow linewidth (60 MHz) without intensity modulation after seeder injection, which can reduce the risk of component damage and improve system safety in energy amplification.
Fig.3.The signal diagram of ramp-fire (a) the channel 1 is used to test the pulse signal. Channel 2 is the trigger signal of the Q switch. Channel 3 is the interference signal of the seed laser. Signal amplitude increases rapidly at the peak where the Q switch is triggered. Channel 4 is the signal of pump laser. (b) Pulse waveform diagram of laser pulse with seeder injected (c) without seeder injected.
Fig. 4 shows the output pulse energy of each power amplifier. The theoretical values of the F-N equation are in good agreement with the test value. The output energy can up to 610 mJ of AMP3 at 200 Hz. Out of the amplification from AMP1, AMP2 and AMP3, the energy extract efficiency becomes 7.8%, 16.2% and
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30.0% respectively and the average optical efficiency of the 3-stage slab amplification module is 18.5%. It shows that the near-field beam intensity is uniformly distributed.
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Fig. 4 Theoretical and test values of the amplifier output energy as the function of pump energy. The input energy of (a) AMP1 is 17 mJ, (b) AMP2 is 80 mJ, (c) AMP3 is 280 mJ.
At 200 Hz operation, the more parameters of MOPA system are listed in Table 1. The laser pulse at 532 nm is narrowed to 4.8 ns during the AMP1, AMP2, AMP3 and LBO unit. Due to the thermal effect, the 5
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beam quality is reduced to 3.0 after the amplifiers. The peak power density is at most 280 MW/cm2, which
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is within the safe range of the optical film layer. Table 1 Laser parameters in the amplified chain Subsystem Oscillator Pre-AMP AMP1 AMP2 AMP3 LBO
Pump energy/mJ 35 40 800 1300 1100
Input/mJ
Output/mJ
Pulse width/ns
M2
Beam size/mm
7 17 80 280 610
7 17 80 290 610 320
7.0 7.0 6.2 5.3 5.8 4.8
1.1 1.2 1.5 1.9 3.0 3.0
φ1.2 φ1.5 2.5×2.5 5.0×5.0 6.0×6.0 7.0×7.0
Fig. 5 shows laser power stability and beam quality test data of 532 nm. The average power is 63.5 W and power stability (RMS) for 4 h reaches 1.0%. The laser is cooled by a water cooler with 5 kW cooling capacity. The near-field beam intensity is uniformly distributed and the far field spot is gaussian distributed. The beam quality of M2 in two axes are 2.8 (horizontal direction) and 3.0 (vertical direction), as shown in
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Fig. 5(d).
Fig. 5 (a) The power stability (RMS) at 532 nm for 4 h, (b) the near-field spot, (c) the far-field spot, and (d) the beam quality of M2
Fig.6 gives the frequency stability of oscillator that can reach to 4.2×10-9(RMS) @70 s. The frequency stability at 532 nm is 8.4×10-9 (RMS) @70 s. The pulse stability and frequency stability using Ramp-fire technology with bias feedback technology are very stable in a short time. The seeder injection success rate is 100% with good vibration shock resistance. The frequency stability will be worsened by external
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disturbances such as vibration, temperature, air disturbance. So Pound-Drever-Hall (PDH) frequency stabilization measures are still needed to maintain long-term frequency stability.
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Fig. 6 The frequency stability of the oscillator at 1064 nm for 70 s.
4. Conclusion
A compact high-energy single-frequency laser for space debris observation was developed by using a seed injection and MOPA method. Because of high stability of NPRO laser and novel ramp-fire technology, the laser output a high stability single frequency pulse with the frequency stability of 4.2×10-9(RMS) for 70 s and energy stability of 1.0% (RMS) for 4 h. The output power 63 W of 532 nm with a total pulse energy of 310 mJ, beam quality M2 of 3.0 and pulse width of 4.8 ns was achieved at 200Hz. The average optical efficiency of bounce-pumped slab amplifier (AMP1, AMP2 and AMP3) is about 18.7%, which reduced thermal effects, cooling complexity and structure volume. Most importantly, the proposed MOPA system has been used for space debris observations successfully for the first time, which strongly indicates that it is a promising solution.
Acknowledgments
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This work was financially supported by the National Natural Science Foundation of China (Grant No. 6 1905119), the University Natural Science Research Project of Jiangsu Province (Grant No. 19KJB140013)
References
[1] H.F. Zhang, M.L. Long, H.R. Deng, Z.B. Wu, Z.E. Cheng, Z.P. Zhang, Space debris laser ranging with a 60W single-frequency slab nanosecond green laser at 200 Hz, Chin. Opt. Lett. 17 (2019) 051404. [2] Z.J. Kang, Z.W. Fan, Y.T. Huang, H.B. Zhang, W.Q. Ge, M.S. Li, X.C. Yan, 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) (2018) 6560-6571.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
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[3] Y. Xia, L.F. Du, X.W. Cheng, F.Q. Li, J.H. Wang, Z.L. Wang, Y. Yang, X. Lin, Y.C. Xun, S.S. Gong, G.T. Yang, Development of a solid-state sodium Doppler lidar using an all-fiber-coupled injection seeding unit for simultaneous temperature and wind measurements in the mesopause region, Opt. Express 25(5) (2018) 5264. [4] J.T. Guo, J.F Wang, H. Wei, W.F. Huang, T.R. Huang, G. Xia, W. Fan, Z.q. Lin, High-power, Joule-class, temporally shaped multi-pass ring laser amplifier with two Nd:glass laser heads, High Power Laser Sci. Eng. 7 (2019) e8. [5] J.S. Qiu, X.X. Tang, Z.W. Fan, H.C. Wang, 200 Hz repetition frequency joule-level high beam quality Nd:YAG nanosecond laser, Opt. Commun. 368 (2016) 68–72. [6] X. Fu, Q. Liu, P.L. Li, Z. Sui, T.H. Liu, M.L. Gong, High-efficiency 2 J, 20 Hz diode-pumped Nd:YAG active-mirror 7
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master oscillator power amplifier system, Appl. Phys. Express 8 (2015) 092702. [7] C. Baumgarten, M. Pedicone, H. Bravo, H. Wang, L.Yin, C. S. Menoni, J. J. Rocca, B. A. Reagan, 1 J, 0.5 kHz
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repetition rate picosecond laser, Opt. Lett. 41(14) (2016) 3339-3342.
[8] J. Liu, L. Li, X.C. Shi, R.F. Chen, J.L. Wang, W.B. Chen, High-beam-quality, 5.4 J, 5 Hz diode-pumped Nd:YAG active mirror laser amplifier, Chin. Opt. Lett. 16(12) (2018) 121402.
[9] X. Yu, L. Dong, B. Lai, P. Yang, Adaptive aberration correction of a 5 J/6.6 ns/200 Hz solid-state Nd:YAG laser, Opt. Lett. 42 (2017) 2730–2733.
[10] K. Tsubakimoto, H. Yoshida, N. Miyanaga, High-average-power green laser using Nd:YAG amplifier with stimulated Brillouin scattering phase-conjugate pulse-cleaning mirror, Opt. Express 24(12) (2016) 12557-12564.
[11] C.Y. Li, C.Q. Lu, C. Li, N. Yang, Y. Li, Z. Yang, S. Han, J.F. Shi, Z.W. Zhou, 2.36 J, 50 Hz nanosecond pulses from a diode side-pumped Nd:YAG MOPA system, Opt. Commun. 394 (2017) 1–5.
[12] X.X. Tang, J.S, Qiu, Z.W. Fan, H.C. Wang, H. Liu, Y.L. Liu, Z.J. Kang, Experimental study on SBS-PCM at 200 Hz repetition rate pumped with joule-level energy, Opt. Mater. 67 (2017) 64–69.
[13] C. Cui, Y.L. Wang, Z.W. Lu, H. Yuan, Y. Wang, Y. Chen, Z. Wang, Z.X. Bai, R.P. Mildren, Demonstration of 2.5 J, 10 Hz, nanosecond laser beam combination system based on non-collinear Brillouin amplification, Opt. Express 26(25) (2018) 32717-32727.
[14] G.Y. Guo, Y.Z. Chen, J.G. He, Y. Lang, W.R. Lin, X.X. Tang, H.B. Zhang, Z.J. Kang, Z.W. Fan, Diode-pumped large-aperture Nd:YAG slab amplifier for high energy nanosecond pulse laser, Opt. Commun. 400 (2017) 50-54.
[15] O. Lux, C. Lemmerz, F. Weiler, U. Marksteiner, B. Witschas, S. Rahm, A. Schafler, O. Reitebuch, Airborne wind lidar observations over the North Atlantic in 2016 for the pre-launch validation of the satellite mission Aeolus, Atmos. Meas. Tech. 11 (2018) 3297–3322.
[16] G. Goodno, H. Komine, S. McNaught, S. Weiss, S. Redmond, W. Long, R. Simpson, E. Cheung, D. Howland, P. Epp, Coherent combination of high-power, zigzag slab lasers. Opt. Lett. 31(9) (2006)1247-1249.
[17] F. Fitzpatrick, J. Rudd, M. Albert, K. Puffenburger, T. Schum, S. Litvinovitch, D. Jones, F. Hovis, Lifetime testing of a
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355-nm, space-qualifiable laser, Proc. SPIE 10779 (2018) 1077908.
[18] C. Lemmerz, O. Lux, O. Reitebuch, B. Witschas, C. Wuhrer, Frequency and timing stability of an airborne injection-seeded Nd:YAG laser system for direct-detection wind lidar, Appl. Opt. 56(32) (2017) 9057-9068.
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*Credit Author Statement
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Credit Author Statement Jianyong Ding: Methodology, Software, Data Curation, Writing - Original Draft, Writing - Review & Editing.
Guangli Yu: Methodology, Visualization.
Ruilin Zheng: Writing - Review & Editing.
Jun Zhou: Software , Resources, Supervision.
Xiaolei Zhu: Conceptualization, Project administration. Weikuan Duan: Investigation.
Chunqi Fang: Validation, Investigation.
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Wei Wei: Conceptualization, Resources, Writing - Review & Editing, Funding acquisition.