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脉冲光纤激光的高亮度功率合成技术研究
其他题名Study on high brightness power combining technology of pulse fiber lasers
胡曼
学位类型博士
导师周军
2016
学位授予单位中国科学院上海光学精密机械研究所
关键词脉冲光纤激光器 受激布里渊散射 受激拉曼散射 被动相干合成技术 光谱合成技术
摘要由于高功率光纤激光器具有转换效率高、光束质量好、良好的热管理和结构紧凑等优点,在通信、传感、医疗、工业加工以及国防军事等领域均有广阔的应用前景。相比连续高功率光纤激光器,脉冲光纤激光器在相对低的平均功率下就可以获得更高的峰值功率和单脉冲能量,使得脉冲光纤激光器成为光纤激光领域一个重要的研究热点。特别是,近年来新型大模场面积光纤以及光子晶体光纤的不断出现,使得高功率脉冲光纤激光器和放大器的性能不断被提升。但是,随着工业应用需求和科学研究发展的不断深入,对脉冲激光源的亮度和单脉冲能量提出了越来越高的要求,而单纤脉冲激光器的输出功率和能量的进一步提升受到了各种非线性效应、端面损伤和热效应等因素的限制。基于多路脉冲合成的激光功率合成技术为突破单纤限制提供了新的思路和方案,目前也受到越来越多的关注。 第一章绪论部分首先对单纤的脉冲光纤激光器,及其在高功率提升方面遇到的非线性效应等问题进行了简要的回顾和介绍。针对脉冲光纤激光器几种典型的合成技术方案的发展现状进行了概述,给出了国内外一些研究机构重要的研究成果。 第二章对基于掺钐光纤可饱和吸收特性的全光纤化被动调Q脉冲光纤激光器进行了理论和实验的研究。在同一种激光腔结构下,通过改变输出端的反馈条件,实现了两种调Q模式(可饱和吸收体被动调Q和受激布里渊散射(SBS)快速自调Q)的脉冲运转。 第三章主要分析了光纤中的受激拉曼散射效应(SRS)。对于调Q脉冲光纤激光器中出现的SRS的阈值特性进行了对比实验研究,包括:传能光纤长度、偏振效应、泵浦方式以及温度特性等因素对SRS阈值的影响。针对高功率连续光纤放大器中出现的反常低阈值拉曼效应进行了理论和实验的研究,并探索了一种有效的抑制方法。 第四章主要研究了基于强度调制技术的纳秒脉冲光纤放大器。采用单频纳秒脉冲种子源,经过四级光纤放大,得到平均输出功率为211W,脉冲重复频率和脉宽分别为10MHz和5.6ns,峰值功率高达3.7kW的稳定脉冲序列,并实现了重复频率和脉宽均可调的纳秒脉冲光纤放大器。另外,针对脉冲放大过程中重复频率和脉宽对SBS阈值特性的影响进行了研究,结果表明:在脉宽小于10ns的情况下,脉宽越小,重复频率越低对应的SBS阈值功率越高。 第五章对两路全光纤化的环形腔结构脉冲光纤激光器进行了被动相干合成实验研究,搭建了基于全光反馈环形腔的被动相干合成系统,当单路输出脉冲重复频率均为3kHz,脉冲宽度分别为580ns和550ns,输出平均功率分别为37mW和43mW时,得到合成之后的总输出平均功率为200mW,重复频率仍为3kHz,脉宽压缩到454ns,相干效率为82.5%。合成之后的脉冲激光峰值功率相比单路时提升了近一个数量级。 第六章对两路基于强度调制技术的可调谐纳秒脉冲光纤激光器进行了光谱合成研究。实现了可调谐纳秒脉冲激光的三种光谱合成:1)具有相同重复频率和脉宽的两路脉冲激光在时域和空域上均保证完全重叠时,合成光的平均功率和峰值功率相比单路均提升了一倍;2)有相同重复频率和脉宽的两路脉冲激光仅在空域重叠时,可获得重复频率和脉宽可调谐范围均扩展一倍的合成脉冲激光;3)实现了两路脉宽不同或重复频率不同或脉冲能量不同的脉冲激光的任意组合,得到满足特殊应用需求的双脉冲激光输出。光谱合成技术能够发挥脉冲激光在时域上可任意组合的优势,为多脉冲激光的应用需求提供了更多的有效途径和手段。
其他摘要Due to high conversion efficiency, excellent beam quality, convenient heat management and compact structure, high power fiber laser has been widely used in many fields, such as, communications, sensing, medical, industrial processing, national defense and so on. Compared with the continuous high power fiber laser, pulse fiber laser can output higher peak power and more powerful pulse energy at a lower average power, which makes the pulse fiber laser being an important research topic. In particular, thanks to the birth of large mode area fiber and photonic crystal fiber in recent years, the performance of high power pulse fiber laser has been greatly promoted. However, with the development of industrial applications and scientific researches, the brightness and pulse energy of single pulse laser source are far away from the higher and higher requirements. The further improvement of single fiber laser is limited by all kinds of nonlinear effects, optical or thermal damages and thermal aberrations. The beam combing technology provides a potential solution to overcome these limits, which can scale fiber lasers to higher power levels and maintain the good beam quality. Lots of researches have been focused on this technology. The first chapter is an introduction part. It starts from an overview of the development of single pulse fiber laser. Nonlinear effects encountered in the high power situation are also analyzed. Then, several typical pulse beam combing technical solutions are summarized and some important research results reported by institutions are listed. The second chapter is a theoretical and experimental research of an all-fiber passively Q-switched fiber laser based on a Sm3+-doped saturable absorber (SA). Two Q-switched patterns (SA Q-switched and SBS self Q-switched) are obtained with a common laser cavity structure, just by changing the feedback conditions of output end. The third chapter is a research of stimulated Raman scattering (SRS) in fiber. For the SRS observed in the SBS Q-switched fiber laser, the threshold characteristics are analyzed by setting a series of contrast experiments, including influence factors of passive fiber length, polarization state, pumping schemes and fiber temperature. In addition, for an un-normal low threshold SRS effect generated in a kilowatt high power narrow band continuous fiber amplifier, studies are performed on and an effective method are proposed to suppress the un-normal low threshold SRS effect. The fourth chapter focuses on the research of a nanosecond pulse fiber amplifier based on an intensity modulator. A single frequency nanosecond pulse seed is input to a four-stage fiber amplifier. The maximum amplified output average power is 211W and the peak power is as high as 3.7kW. The repetition rate and pulse width of the amplified pulse laser is 10MHz and 5.6ns. Pulse lasers with tunable repetition rate and pulse width are also realized. Furthermore, the threshold characteristics of stimulated Brillouin scattering (SBS) generated during the amplifying process are studied. The influence factors are mainly focused on the repetition rate and pulse duration of the seed pulse laser. The results show that narrower pulse duration and lower repetition rate results in higher SBS threshold when the pulse duration is less than 10ns. The fifth chapter is an experimental research of a passively coherent beam combining (CBC) based on two all-fiber pulse lasers. The passive CBC system based on the all-optical feedback loop is established. When the repetition rates of single fiber lasers are both 3kHz and the pulse durations are 580ns and 550ns respectively and the average output powers are 37mW and 43mW, the combined average power is 200mW and the repetition rate is remained to 3kHz and the pulse duration is compressed to 454ns. The coherent combining efficiency is 82.5% and the peak power of the combined beam is nearly improved an order of magnitude compared to the single pulse lasers. The sixth chapter carried out a research of spectral beam combining (SBC) of two tunable nanosecond pulse lasers. The pulse lasers are referred to the laser researched in chapter four. Three SBC situations are discussed: 1) the pulses of single channels overlap in both temporal and spatial domain. Then, both the average power and peak power for combined laser can be doubled; 2) the pulses of single channels only overlap spatially but breaking joint temporally. The tuning range of repetition-rate and pulse duration for combined laser can be doubled; 3) two single pulse lasers with different pulse durations or different repetition rates are spectrally combined. The pulse energy of single lasers and the inter-pulse separation can both be set at one’s option. Then, the double-pulse laser represents two closely conjoint pulses with tunable pulse durations and tunable repetition rates and tunable pulse energies and tunable inter-pulse separations are obtained. The SBC technique takes advantage of the arbitrary combination of pulse lasers in temporal domain and it provides a new method for generation of double-pulse laser.
语种中文
文献类型学位论文
条目标识符http://ir.siom.ac.cn/handle/181231/15948
专题学位论文
推荐引用方式
GB/T 7714
胡曼. 脉冲光纤激光的高亮度功率合成技术研究[D]. 中国科学院上海光学精密机械研究所,2016.
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