伽马辐照对掺镱光纤材料特性影响的研究

掺镱光纤是高功率激光器的核心材料,但在高能射线辐照后其应用性能会显著下降,因此有必要对掺镱光纤材料在辐照环境下的性能变化进行深入研究。采用改进型化学气相沉积法结合稀土螯合物掺杂制备了系列光纤预制棒及光纤,测试了光纤在不同剂量下射线辐照前后的高功率输出性能,以及光纤预制棒辐照前后的吸收光谱及镱离子荧光寿命。结果表明:小剂量辐照后掺镱光纤的高功率输出显著下降,通过预制棒吸收光谱可看出主要是因为伽马辐照后使掺镱光纤材料中Al的相关缺陷浓度增多,在可见光区域吸收损耗增加。Ce离子的掺杂通过缓减辐致铝氧空位中心(Al-OHC)色心缺陷的增加,减少Yb离子荧光寿命的下降,可在一定程度上抑制高功率掺镱光纤的辐致暗化。     

高功率连续波掺镱光纤激光器研究进展

高功率连续波掺镱光纤激光器因具有电光效率高、光束质量好、热管理方便等优点,在工业加工、军事国防、科学研究等领域得到广泛应用,但是高功率条件下的非线性效应和热效应限制了其输出功率的进一步提升。基于此,本文重点分析了受激拉曼散射非线性效应和热致模式不稳定现象的形成机理和抑制方法,为高功率光纤激光系统的设计与集成提供了参考,并详细介绍了2015年以来为克服两种因素的影响所取得的最新研究成果,最后展望了高功率连续波掺镱光纤激光器的发展趋势。     

用于高功率系统的掺镱石英光纤研究进展及发展趋势

掺镱石英光纤是掺镱光纤激光器及放大器的重要基础元件.掺镱光纤性能提升是促进掺镱光纤激光器系统功率进一步攀升的关键.本文回顾了高功率掺镱光纤激光器系统功率攀升情况及功率限制性问题,简述了针对激光功率攀升的瓶颈问题所提出的改善性方案.重点阐述了掺镱光纤制备技术、光纤材料、结构性设计在改善功率限制性方面所取得的研究进展,并对未来掺镱石英光纤的研究及发展趋势进行了展望.     

国产纺锤形渐变掺镱光纤实现6 kW宽谱激光输出

高功率高光束质量光纤激光器在工业加工等领域有着广泛的应用,然而光纤中的非线性效应和模式不稳定效应限制着高光束质量光纤激光器的功率提升,采用新型结构大模场增益光纤在同时抑制非线性效应和模式不稳定效应方面具有较大潜力。报道了基于单位自研的纺锤形渐变掺镱光纤激光成功实现6 kW功率、高光束质量激光输出。激光器采用主振荡功率放大结构,放大级采用双向981 nm泵浦纺锤形渐变掺镱光纤,在总泵浦功率为7.68 kW时,输出功率达到6.02 kW,光束质量M2因子约为1.9。通过进一步优化纺锤形掺镱光纤制作工艺及结构参数,有望实现更高功率、近单模光束质量的光纤激光输出。     

高功率掺镱光纤激光器的非线性效应和研究进展

高功率掺镱光纤激光器在精密加工、国防、科研等领域有重要的应用价值,然而随着功率的提升,光纤内部的非线性效应开始凸显。在此,详细分析了受激布里渊散射(SBS)、受激拉曼散射(SRS)、非线性折射率、横模不稳定(TMI)等非线性效应的产生过程,并提出抑制方法。另外,从光纤振荡器和主振荡功率放大器两个角度,简述了近几年学者们在抑制非线性效应基础上不断提升掺镱光纤激光器输出功率的研究进展。目前,全光纤结构的掺镱振荡器输出功率达到8kW;单纤主振荡功率放大器激光系统输出功率已突破20kW。     

光纤激光宽温度范围运行研究进展

简要回顾了高功率掺镱光纤激光器的发展历程,指出宽温运行光纤激光器的需求与应用场景。综述已有关于光纤激光器在变温条件下的研究成果,在高功率光纤激光器的发展中,工作温度对光纤激光器造成的影响将进一步显现。介绍了利用现有光纤器件以及传统光纤激光器设计的宽温运行光纤激光器案例。通过系统设计和结构优化,本课题组已成功实现千瓦级的宽温运行光纤激光器,整机运行温度从常温拓展到-30℃。进一步的功率提升和温度范围拓展还需要对光纤激光器工作机理、光纤器件温度特性等方面进行深入研究。此外,展望了宽温运行光纤激光器的发展趋势,研究结果为高功率宽温运行光纤激光器的发展提供了参考。     

中子辐照对掺镱光纤材料光学特性的影响

采用改进型化学气相沉积法结合稀土螯合物掺杂制备了系列掺镱光纤预制棒及光纤,并测试了光纤(预制棒)辐照、退火前后的光学性能.结果表明:中子辐照后掺镱光纤材料中与Al相关的缺陷浓度增多,导致光纤材料在可见光区域吸收损耗增加.Ce离子的掺杂可缓减铝氧空位中心(Al-OHC)等色心缺陷的增加,从而有效抑制掺镱光纤的辐致暗化效应.热退火可降低中子辐致色心缺陷的浓度从而降低光纤材料的吸收,在一定程度上消除暗化效应.     

1μm全光纤MOPA结构激光器输出特性研究

主振荡功率放大（main oscillation power amplification, MOPA）结构由于其光束质量良好和参数可调的优点,已成为高功率光纤激光器的主流设计之一。为了改善高功率掺镱光纤激光器（ytterbium-doped fiber laser, YDFL）的输出性能,提高系统的光-光转换效率,文中报道了一台基于915 nm泵浦激光器和双包层掺镱光纤（ytterbium-doped fiber, YDF）的MOPA结构全光纤高功率激光器。该高功率光纤激光器由电调制激光二极管（laser diode, LD）泵浦的种子激光器和掺镱光纤放大器（ytterbium-doped fiber amplifier, YDFA）组成。连续光（continuous wave, CW）工作模式下,激光种子源经过YDFA后,实现了中心波长为1 069.96 nm的激光输出,最大平均输出功率可达945.9 W,MOPA激光器整机的斜率效率高达74.12%,具有良好的稳健性。该研究方案对研制高功率MOPA光纤激光器具有参考意义。     

自主研发的976nm波段全光纤激光器实现了100W量级功率输出

正976nm波段掺镱光纤激光器可作为高功率掺镱/铒光纤激光器的高亮度泵源,在蓝光和紫外光源等领域也有良好的应用前景,因而备受关注。不过,由于其三能级跃迁特性导致的泵浦阈值高、放大自发辐射强等问题,该激光器的功率提升面临巨大挑战。现阶段,国际上976nm波段光纤激光器的输出功率达到100 W量级,而国内976nm波段光纤激光器的输出功率仅为20 W量级。国防科技大学针对影响该激光器功率提升的     

自研20μm/400μm保偏光纤基于振荡器种子实现4 kW突破

高功率窄线宽光纤激光器在相干合成、光谱合成以及非线性频率转换等领域发挥了重要的作用，吸引了大量国内外研究人员的广泛关注。近年来，华中科技大学武汉光电国家研究中心光纤激光技术团队持续进行优秀的国产化高功率窄线宽线偏振光纤激光技术的研究工作，2022年，课题组采用基于振荡器的种子源加自研的保偏掺镱光纤先后实现单正向1.2 kW和单反向3.2 kW的线偏振窄线宽光纤激光输出。近期，课题组进一步优化保偏掺镱光纤的掺杂组分，并改良振荡器种子源设计来抑制窄线宽保偏放大过程中的TMI和受激布里渊散射（SBS）效应，最终实现了输出功率4.1 kW的窄线宽线偏振全光纤激光输出。     

High-power continuous-wave output of master oscillator power amplifier system at 1053 and 1083 nm

We report the efficient generation of high-power laser radiation at 1053 and 1083 nm wavelength by using of a hybrid master oscillator fiber power amplifier system, consisting of a diode-pumped Yb-doped oxyorthosilicate solid state laser as the master oscillator and an Yb-doped large-mode-area fiber as the power amplifier. Efficient tunable diode-pumped Yb-doped oxyorthosilicate lasers at 1053 and 1083 nm have been constructed, which was scaled up to a maximum output power of 34.5 W at 1053 nm and 30.2 W at 1083 nm by a fiber power amplifier, corresponding to a slope efficiency of 93.9 and 87.8%, respectively.     

分布反馈光纤激光器阵列中外腔反馈特性研究

以半导体激光器中的复合腔模型和实测的分布反馈光纤激光器的外腔端面反射率为基础,对不同反射率条件下分布反馈光纤激光器的输出功率进行了仿真,同时搭建了二基元分布反馈光纤激光器阵列实验平台,对仿真结果进行了验证.仿真与实验结果表明:外腔反馈光重新注入分布反馈光纤激光器会增加激光器的输出功率,降低了阵列的输出功率平坦性.并且外腔端面反射率越大,这种平坦性降低的效果越明显.在构建分布反馈光纤激光器阵列时,应考虑外腔反馈对阵列输出功率平坦性造成的影响,尽量选择外腔端面反射率较小的激光器进行组阵.     

Environmentally stable ytterbium figure-of-eight fiber laser producing 177-fs pulses

Pulses of 177 fs and 1035 nm, with average power of 1.2 mW, have been generated directly from a passively mode-locked Yb-doped figure-of-eight fiber laser, with a nonlinear optical loop mirror for mode-locking and pairs of diffraction gratings for intracavity dispersion compensation. To our knowledge, these are the shortest pulses ever to come from a passively mode-locked Yb-doped figure-of-eight fiber laser. This represents a 5-fold reduction in pulse duration compared with that of previously reported passively mode-locked Yb-doped figure-of-eight fiber lasers. Stable pulse trains are produced at the fundamental repetition rate of the resonator, 24.0 MHz.     

1018 nm短波长掺镱光纤激光高功率自组织相干合成

搭建了两台高功率、低量子损耗的1018 nm短波长掺镱光纤激光器,进行了全光纤结构下两路光纤激光器的相干合成实验。获得了功率为55 W、合成效率为90.2%的相干输出,这是当前严格单模1018 nm光纤激光器的最高功率水平。同时,验证了Michelson腔自组织相干合成技术能够实现光纤激光器的高功率单模输出。     

掺镱双包层光纤激光器典型参数对斜线效率的影响

 分析了双包层光纤激光器(DCFL)耦合方程的解析解，并对信号光散射损耗、后腔镜泵浦反射率等影响掺镱DCFL斜线效率的典型参数进行了理论研究。结果表明，斜线效率并不是随着后腔镜泵浦反射率的升高而单调增大，因为泵浦反射率的升高会影响光纤的最佳长度，从而降低斜线效率。所以在优化斜线效率时应该考虑到泵浦反射率和光纤最佳长度之间的匹配。同时，提高纤芯掺杂浓度、减小信号光散射损耗也能增大斜线效率。     

10-W cladding-pumped fiber laser with single transverse mode output

A Yb-doped double-clad fiber laser is demonstrated with a measured power output of 10.6 W and a fundamental spatial mode. The optical-to-optical conversion efficiency is 44% and the slope efficiency is 86% closed to quantum efficiency of optical conversion. In our laser system, a D-shape (340 μm/400 μm) inner cladding Yb-doped fiber is used as the gain material within the Fabry-Perot cavity. Multimode diode pump radiation is injected into the cladding through an end facet of the composite fiber.     

Optimization of pumping mode for double-clad fiber lasers

A theoretical modeling of Yb-doped double-clad fiber lasers under various pumping modes including arbitrary numbers of end-pump and side-pump is introduced. Approximate analytic expressions of distributed lasers along the whole fiber are derived, and their accuracies are investigated. The effect of the pumping mode on the output performance of fiber lasers is discussed. The numerical results show that the approximate analytic solution is in excellent agreement with the exact numerical solution of the rate equations, the output power in the side-pump scheme is lower than that in end-pumping scheme, and more uniform distributions of laser and pump powers can be achieved by adopting the distributed pump mode and optimizing the arrangement of pump powers. However, further flattening the pump distribution by using more pump points can degrade the laser efficiency.     

Yb-doped passively mode-locked fiber laser with Bi_2Te_3-deposited

In this study we present an all-normal-dispersion Yb-doped fiber laser passively mode-locked with topological insulator(Bi2Te3) saturable absorber. The saturable absorber device is fabricated by depositing Bi2Te3 on a tapered fiber through using pulsed laser deposition(PLD) technology, which can give rise to less non-saturable losses than most of the solution processing methods. Owing to the long interaction length, Bi2Te3 is not exposed to high optical power, which allows the saturable absorber device to work in a high power regime. The modulation depth of this kind of saturable absorber is measured to be 10%. By combining the saturable absorber device with Yb-doped fiber laser, a mode-locked pulse operating at a repetition rate of 19.8 MHz is achieved. The 3-d B spectral width and pulse duration are measured to be 1.245 nm and317 ps, respectively.     

Fiber fuse behavior in k W-level continuous-wave double-clad field laser

In this study, original experimental data for fiber fuse in k W-level continuous-wave(CW) high power double-clad fiber(DCF) laser are reported. The propagating velocity of the fuse is 9.68 m/s in a 3.1-k W Yb-doped DCF laser. Three other cases in Yb-doped DCF are also observed. We think that the ignition of fiber fuse is caused by thermal mechanism,and the formation of bullet-shaped tracks is attributed to the optical discharge and temperature gradient. The inducements of initial fuse and formation of bullet-shaped voids are analyzed. This investigation of fiber fuse helps better understand the fiber fuse behavior, in order to avoid the catastrophic destruction caused by fiber fuse in high power fiber laser.