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报道了基于锯齿波脉冲抑制自相位调制(SPM)的高功率窄线宽单频脉冲光纤激光放大器. 通过优化掺镱(Yb)石英有源光纤的长度, 在保证输出功率和转换效率的同时提高单频光纤激光放大器中的受激布里渊散射阈值, 并采用脉冲波形为锯齿波的种子光, 利用其光强对时间的变化率为常数的特性有效抑制了SPM效应导致的激光光谱展宽现象. 主放大级泵浦功率为11.3 W时获得了平均输出功率为3.13 W、脉冲重复频率为20 kHz的1064 nm单频激光输出; 此时脉冲宽度为6.5 ns, 对应峰值功率为24 kW, 测得光谱线宽仅为83 MHz, 接近变换极限水平. 与采用常规高斯波形脉冲种子光的对照实验相比, 锯齿波形脉冲对SPM所致的光谱展宽具有显著抑制效果, 为高功率窄线宽脉冲光纤激光放大器提供了一种行之有效的方法.Fiber laser system in master oscillator power amplifier (MOPA) scheme is a promising technique for high-power narrow-linewidth laser output. With modulation-generated pulsed seed laser, the fiber MOPA benefits the flexible temporal behavior. However, the spectral linewidth broadening induced by self-phase modulation (SPM) is the main obstacle to achieving high-power single-frequency laser output with narrow spectral linewidth, especially for pulsed fiber MOPA in which the kilowatts level peak power results in strong nonlinearity. The SPM induced linewidth broadening is related to the derivative of light intensity with respect to time (dI/dt). Theoretically, if the dI/dt of the laser pulse is a constant, the SPM process will not generate any new frequency components. Hence, the linewidth broadening can be suppressed. In this work, we demonstrate a high-power single-frequency Yb fiber amplifier at 1064 nm, in which a sawtooth laser pulse is employed to suppress the SPM induced linewidth broadening, for obtaining the output with near-transform-limited narrow linewidth. The sawtooth-shaped seed pulse train is generated through using an electro-optic intensity modulator to modulate the continuous-wave (CW) output of a single-frequency fiber laser. After being pre-amplified, the seed laser with a pulse repetition rate of 20 kHz is coupled into the main amplifier, in which a piece of 0.9-m-long Yb-doped silica fiber with core and clad diameters of 35 μm and 250 μm, respectively, is used as a gain medium. The seed laser is enhanced to an average power value of 3.13 W under a launched 976-nm pump power value of 11.3 W before the onset of stimulate Brillouin scattering. The pulse energy 157 μJ and the pulse width 6.5 ns give a peak power of 24 kW. The spectral linewidth measured using a scanning Fabry-Perot interferometer at the maximum power is only 83 MHz, which is quite close to the 76-MHz transform-limited linewidth of the 6.5-ns sawtooth-shaped pulse. For comparison, we also conduct an experiment with a common Gaussian-shaped seed laser, in which the spectral linewidth is broadened significantly with a peak power value of only 1.5 kW. The results here reveal that the using of the sawtooth-shaped pulse is a promising technique to suppress the SPM induced spectral linewidth broadening in high-peak-power fiber amplifiers and acquire near-transform-limited narrow-linewidth laser output.
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Keywords:
- single-frequency fiber laser /
- pulsed fiber laser /
- self-phase modulation /
- narrow-linewidth laser
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图 2 不同有源光纤长度时光纤激光MOPA的平均输出功率曲线, 进入放大器种子光功率为220 mW, 重复频率为20 kHz
Fig. 2. Average power of the fiber MOPA with different active fiber lengths as a function of launched pump power with 220 mW seed power at a PRF of 20 kHz.
图 3 平均输出功率为3.13 W、脉冲重复频率为20 kHz时的激光光谱
Fig. 3. Laser spectrum power recorded at the average output power of 3.13 W and the PRF of 20 kHz.
图 4 (a)调制产生的脉冲种子源的波形; (b)经过预放大进入主放大级之前的波形; (c)主放大器最高输出功率时的波形
Fig. 4. Oscilloscope traces of the (a) modulated seed pulse, (b) pulse after being pre-amplified, and (c) main amplifier output at the maximum power.
图 5 (a)使用锯齿波形时主放大器最高输出功率为24 kW时的激光线宽; (b)使用高斯波形时预放大级输出的激光线宽(脉宽7.5 ns, 峰值功率1.5 kW)
Fig. 5. Measured spectral linewidths of (a) the sawtooth pulse at the maximum peak power of 24 kW and (b) the Gaussian-shaped pulse after being pre-amplified to a peak power of 1.5 kW with a pulse width of 7.5 ns.
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[1] 漆云凤, 刘驰, 周军, 陈卫标, 董景星, 魏运荣, 楼祺洪 2010 物理学报 59 3942
Google Scholar
Qi Y F, Liu C, Zhou J, Chen W B, Dong J X, Wei Y R, Lou Q H 2010 Acta Phys. Sin. 59 3942
Google Scholar
[2] Wang X L, Zhou P, Leng J Y, Du W B, Xu X J 2013 Chin. Phys. B 22 044205
Google Scholar
[3] Fu S J, Shi W, Feng Y, Zhang L, Yang Z M, Xu S H, Zhu X S, Norwood A R, Peyghambarian N 2017 J. Opt. Soc. Am. B 34 A49
Google Scholar
[4] Malinowski A, Vu T K, Chen K K, Nilsson J, Jeong Y, Alam S, Lin D J, Richardson J D 2009 Opt. Express 17 20927
Google Scholar
[5] Steinhausser B, Brignon A, Lallier E, Huignard P J, Georges P 2007 Opt. Express 15 6464
Google Scholar
[6] 来文昌, 马鹏飞, 肖虎, 刘伟, 李灿, 姜曼, 许将明, 粟荣涛, 冷进勇, 马阎星, 周朴 2020 强激光与粒子束 32 121001
Google Scholar
Lai W C, Ma P F, Xiao H, Liu W, Li C, Jiang M, Xu J M, Su R T, Leng J Y, Ma Y X, Zhou P 2020 High Power Laser and Particle Beams 32 121001
Google Scholar
[7] Petersen E, Shi W, Chavez-Pirson A, Peyghambarian N 2012 Appl. Opt. 51 531
Google Scholar
[8] Broderick R G N, Offerhaus L H, Richardson J D, Sammut A R, Caplen J, Dong L 1999 Opt. Fiber Technol. 5 185
Google Scholar
[9] Shi W, Petersen B E, Leigh M, Zong J, Yao Z D, Chavez-Pirson A, Peyghambarian N 2009 Opt. Express 17 8237
Google Scholar
[10] Yang C, Chen D, Xu S, Deng H, Lin W, Zhao Q, Zhang Y, Zhou K, Feng Z, Qian Q, Yang Z 2016 Opt. Express 24 10956
Google Scholar
[11] Robin C, Dajani I 2011 Opt. Lett. 36 2641
Google Scholar
[12] Tino E, Christian W, Cesar J, Fabian S, Florian J, Hans-Jürgen O, Oliver S, Thomas S, Jens L, Andreas T 2011 Opt. Express 19 13218
Google Scholar
[13] Boggio C M J, Marconi D J, Fragnito L H 2005 J. Lightwave Technol. 23 3808
Google Scholar
[14] Zhang L, Hu J M, Wang J H, Feng Y 2012 Opt. Lett. 37 4796
Google Scholar
[15] Shi C, Zhang H W, Wang X L, Zhou P, Xu X J 2018 High Power Laser Sci. 6 e16
Google Scholar
[16] Fang Q, Shi W, Kieu K, Petersen E, Chavez-Pirson A, Peyghambarian N 2012 Opt. Express 20 16410
Google Scholar
[17] Su R T, Zhou P, Ma P F, Lü H B, Xu X J 2013 Appl. Opt. 52 7331
Google Scholar
[18] Zhou P, Huang L, Xu J M, Ma P F, Su R T, Wu J, Liu Z J 2017 Sci. China Technol. Sci. 60 1784
Google Scholar
[19] Agrawal P G 2001 Nonlinear Fiber Optics (New York: Academic Press) pp329–334
[20] Su R T, Ma P F, Zhou P, Chen Z L, Wang X L, Ma Y X, Wu J, Xu X J 2019 High Power Laser Sci. Eng. 7 51
Google Scholar
[21] Huang L, Ma P F, Su R T, Lai W C, Ma Y X, Zhou P 2021 Opt. Express 29 761
Google Scholar
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