Author Affiliations
Abstract
1 College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China
2 Nanhu Laser Laboratory, National University of Defense Technology, Changsha 410073, China
3 Hunan Provincial Key Laboratory of High Energy Laser Technology, National University of Defense Technology, Changsha 410073, China
A low-numerical-aperture (NA) concept enables large-mode-area fiber with better single-mode operation ability, which is beneficial for transverse mode instability and nonlinear effects suppression. In this contribution, we reported a high-power fiber amplifier based on a piece of self-developed large-mode-area low-NA fiber with a core NA of 0.049 and a core/inner cladding diameter of 25/400 µm. The influence of the pump wavelength and fiber length on the power scaling potential of the fiber amplifier is systematically investigated. As a result, an output of 4.80 kW and a beam quality factor of ∼1.33 were finally obtained, which is the highest output power ever reported in a fiber amplifier exploiting the low-NA fiber. The results reveal that low-NA fibers have superiority in power scaling and beam quality maintenance at high power levels.
high power fiber lasers ytterbium-doped fiber low-numerical-aperture fiber mode instability Chinese Optics Letters
2024, 22(4): 041404
王鹏 1,2,3孟祥明 1,2,3吴函烁 1,2,3叶云 1,2,3[ ... ]陈金宝 1,2,3,*
1 国防科技大学 前沿交叉学科学院,长沙 410073
2 国防科技大学南湖之光实验室,长沙 410073
3 国防科技大学 高能激光技术湖南省重点实验室,长沙 410073
半导体激光(LD)泵浦的高功率光纤激光器具有效率高、体积小、重量轻、稳定性好等优点,在工业加工等诸多领域都有着广泛的应用。为了提高泵浦光吸收率,传统光纤激光器常用915 nm和976 nm波段的LD作为激光的泵浦源。在该类LD泵浦的光纤激光器中,由于量子亏损和泵浦吸收系数相对较高,光纤激光器的热致模式不稳定(TMI)阈值相对较低。为了提高量子效率和潜在的TMI阈值,提出采用大于1010 nm波段的LD直接泵浦光纤激光器,产生高量子效率激光。搭建了振荡放大一体化的全光纤激光器,采用总泵浦功率为2.56 kW的1010 nm波段LD泵浦,首次获得输出功率2.05 kW、光束质量M2约1.7的激光。后续将通过进一步增大泵浦功率、优化光纤特性以实现更高功率、更优光束质量的光纤激光输出。
光纤激光器 量子亏损 振荡放大一体化 模式不稳定 fiber laser quantum defect oscillating-amplifying integrated laser transverse mode instability 强激光与粒子束
2024, 36(3): 031001
1 国防科技大学前沿交叉学科学院,湖南 长沙 410073
2 国防科技大学南湖之光实验室,湖南 长沙 410073
3 国防科技大学高能激光技术湖南省重点实验室,湖南 长沙 410073
模式不稳定是限制当前高功率光纤激光器功率提升的主要因素。在近单模光纤激光器中,一般采用减小光纤弯曲直径的方法增加高阶模损耗、提升模式不稳定阈值;然而,少模光纤激光器中存在多个高阶模式,会导致动态模式不稳定(TMI)阈值随着弯曲直径减小而降低的反常模式不稳定现象。基于纤芯/包层直径为30/600 μm的双包层掺镱光纤以及具有不同直径的光纤水冷柱,设计了一台后向泵浦的高功率光纤放大器,研究了该激光器中的反常模式不稳定现象。结果表明:当采用中心波长为976 nm的稳波长激光二极管(LD)作为泵浦源时,随着增益光纤弯曲直径由13 cm增加至16 cm,激光器的TMI阈值由1650 W提升至3740 W,提升幅度约为1.27倍,输出激光的相对亮度提升了87%。光纤弯曲直径的增加虽然会带来输出激光光束质量的轻微退化,但输出激光的相对亮度能够大幅提升。最终,结合光纤弯曲以及泵浦波长优化,实现了7.1 kW高亮度光纤激光输出,相对亮度为1293。
光纤光学 光纤放大器 反常模式不稳定 光纤弯曲 泵浦波长优化
1 国防科技大学前沿交叉学科学院,湖南 长沙 410073
2 国防科技大学南湖之光实验室,湖南 长沙 410073
3 国防科技大学高能激光技术湖南省重点实验室,湖南 长沙 410073
由于自激振荡的限制,单级超荧光光纤光源的功率提升十分困难,目前仅达到百瓦量级。基于主振荡功率放大(MOPA)方案,使用1018 nm光纤激光级联泵浦1080 nm波段的超荧光,实现了6.2 kW高功率输出。最高功率下的光光转换效率为81.5%,没有出现横模不稳定(TMI),功率提升受限于受激拉曼散射(SRS)。
光纤光学 超荧光光源 高功率 级联泵浦 受激拉曼散射 横模不稳定 中国激光
2023, 50(22): 2215001
强激光与粒子束
2023, 35(8): 081003
1 国防科技大学 前沿交叉学科学院,湖南 长沙 410073
2 国防科技大学 南湖之光实验室,湖南 长沙 410073
LD泵浦掺镱光纤激光器具有低成本、高效率、高光束质量等优点,在工业、科研、**等领域有着广泛的应用。在大部分实际应用中,由功率和光束质量决定的亮度是影响光纤激光器实际作用性能的核心指标。受到非线性效应(尤其是受激拉曼散射)和模式不稳定效应的限制,当前高亮度掺镱光纤激光器输出功率提升遭遇了明显的技术瓶颈。为了抑制非线性效应和模式不稳定效应,在传统方法的基础上,提出了变纤芯直径光纤和优化泵浦波长等成体系的方法以提升光纤激光器的输出功率;为了有效提高对光纤激光器的设计研发能力,提出并开发了具有自主知识产权的光纤激光仿真软件SeeFiberLaser。首先,介绍了影响宽谱高功率掺镱光纤激光器亮度提升的主要限制因素,给出了各个限制因素的抑制方法;其次,利用自研光纤激光仿真软件SeeFiberLaser对提升光纤激光器功率的方法进行优化设计,并对工业常用的振荡器和高亮度光纤激光放大器进行仿真优化;然后,介绍课题组采用后向泵浦、变纤芯直径光纤和优化泵浦波长等方法提升激光功率,实现的6~10 kW高亮度功率光纤激光器;最后,对更高亮度光纤激光器的技术方案进行讨论和展望,提出了无源器件集成化、增益传能光纤一体化等思路,提出了基于变纤芯直径增益传能一体化光纤和集成化无源器件的新型高功率近单模光纤激光器技术方案。
光纤激光器 非线性效应 模式不稳定 激光亮度 仿真软件 fiber lasers nonlinear effects mode instability laser brightness simulation software 红外与激光工程
2023, 52(6): 20230242
Jiexi Zuo 1,2,3,4Haijuan Yu 1,2,3,4Shuzhen Zou 1,4Zhiyong Dong 1,4[ ... ]Xuechun Lin 1,2,3,4,*
Author Affiliations
Abstract
1 Laboratory of All-Solid-State Light Sources, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China
2 Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing, China
3 College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing, China
4 Beijing Engineering Technology Research Center of All-Solid-State Lasers Advanced Manufacturing, Beijing, China
Achieving an all-fiber ultra-fast system with above kW average power and mJ pulse energy is extremely challenging. This paper demonstrated a picosecond monolithic master oscillator power amplifier system at a 25 MHz repetition frequency with an average power of approximately 1.2 kW, a pulse energy of approximately 48 μJ and a peak power of approximately 0.45 MW. The nonlinear effects were suppressed by adopting a dispersion stretched seed pulse (with a narrow linewidth of 0.052 nm) and a multi-mode master amplifier with an extra-large mode area; then an ultimate narrow bandwidth of 1.32 nm and a moderately broadened pulse of approximately 107 ps were achieved. Meanwhile, the great spatio-temporal stability was verified experimentally, and no sign of transverse mode instability appeared even at the maximum output power. The system has shown great power and energy capability with a sacrificed beam propagation product of 5.28 mm $\cdot$ mrad. In addition, further scaling of the peak power and pulse energy can be achieved by employing a lower repetition and a conventional compressor.
fiber laser nonlinear optics picosecond pulse transverse mode instability High Power Laser Science and Engineering
2023, 11(2): 02000e22
Author Affiliations
Abstract
College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha, China
In this work, a confined-doped fiber with the core/inner-cladding diameter of 40/250 μm and a relative doping ratio of 0.75 is fabricated through a modified chemical vapor deposition method combined with the chelate gas deposition technique, and subsequently applied in a tandem-pumped fiber amplifier for high-power operation and transverse mode instability (TMI) mitigation. Notably, the impacts of the seed laser power and mode purity are preliminarily investigated through comparative experiments. It is found that the TMI threshold could be significantly affected by the seed laser mode purity. The possible mechanism behind this phenomenon is proposed and revealed through comprehensive comparative experiments and theoretical analysis. Finally, a maximum output power of 7.49 kW is obtained with the beam quality factor of approximately 1.83, which is the highest output power ever reported in a forward tandem-pumped confined-doped fiber amplifier. This work could provide a good reference and practical solution to improve the TMI threshold and realize high-power high-brightness fiber lasers.
confined-doped fiber fiber laser good beam quality high power transverse mode instability mitigation High Power Laser Science and Engineering
2022, 10(6): 06000e44
王鹏 1,2,3,4杨保来 1,2,3张汉伟 1,2,3,*奚小明 1,2,3[ ... ]吕品 4
1 国防科技大学前沿交叉学科学院,湖南 长沙 410073
2 脉冲功率激光技术国家重点实验室,湖南 长沙 410073
3 高能激光技术湖南省重点实验室,湖南 长沙 410073
4 中国科学院自动化研究所,北京 100190
为研究掺镱光纤(YDF)光子暗化效应对高功率高亮度光纤激光器的影响,利用25/400 μm大模场YDF和915 nm半导体泵浦源搭建了光纤激光振荡器,输出功率可达5 kW,输出激光为近单模。对该光纤激光振荡器进行满功率拷机时出现了光子暗化现象,激光器输出功率急剧下降,输出激光时域中呈现出强烈的横向模式不稳定性(TMI)现象。经过多次测试后发现:后向泵浦时该光纤激光振荡器的TMI效应对应的泵浦功率阈值和输出功率阈值均出现一定程度的下降(约为14%),与传统理论相符;前向泵浦时TMI效应对应的泵浦功率阈值和输出功率阈值出现一定程度的上升(约为15%),这与传统理论不相符,需进一步开展研究。最终,该光纤激光振荡器输出功率受到光子暗化效应的影响无法维持在5 kW功率水平。
光纤光学 掺镱光纤 光子暗化 光纤激光振荡器 横向模式不稳定 光学学报
2022, 42(23): 2306001
强激光与粒子束
2022, 34(12): 121001