高功率光纤激光部分相干合成的可行性及效果分析

提出部分相干合成的概念,论证了谱线宽度和偏振特性并不是影响高功率光纤激光部分相干合成的瓶颈.与完全相干合成的理想情形相比,随着光束线宽的增大,部分相干合成光束的远场光斑图样基本保持不变,但峰值强度和斯特尔(Strehl)比随之减小,光斑能量越来越分散.利用数值计算的方法对部分相干合成与非相干合成光束的远场效果进行了比较分析.计算结果表明,尽管线宽的存在降低了部分相干合成的效果,但与非相干合成相比,部分相干合成的光束仍具有较大优势.     

光纤激光相干合成中两种相位控制方法的比较

主振荡功率放大器(MOPA)相干合成是实现大数量光纤激光器相干合成的一条有效途径,而相位控制是其中的关键。对MOPA方案的两种相位控制方法——外差探测法和多抖动法进行了比较分析。并在此基础上,提出了一种新的相位控制方法。新方法增加了相干合成的光束数目,降低了实验操作难度。通过Matlab软件仿真表明,采用新方法进行64路光束相干合成时,相位均方根误差小于0.08λ,而使用多抖动法进行30路光束相干合成时,相位均方根误差为0.15λ。     

高功率光纤激光的时间部分相干性对相干合成的影响

 将多个光纤激光器的输出光束进行相干合成是获得高功率、高光束质量激光的有效途径。利用准部分相干光(PPCB)模型,计算了高功率光纤激光器阵列发出的部分相干光在远场的能量分布,分析了激光的时间部分相干性对相干合成的影响。计算结果表明,随着单根激光器输出光束线宽的增大,远场光斑的图样基本保持不变,但峰值功率和Strehl比随之减小。对于采用的算例,要保证远场光斑的Strehl比大于0.8,单根光纤激光器的线宽不能超过5 nm。     

光纤激光相控阵相干合成技术研究进展

主要介绍了近年来光纤激光相控阵相干合成技术的发展现状,总结了中国科学院光电技术研究所在这方面的最新研究成果,包括基于振幅调制的光纤激光相控阵相干合成能力优化、光纤激光相控阵实现收发一体相干合成、光纤激光相控阵的目标在回路相干合成、光纤激光相控阵在大气湍流下实现耦合接收光束的共相合束、基于多孔径波前探测的相干合成方法、基于自适应光纤准直器和微透镜阵列的光束大角度高精度连续寻址扫描等。以上研究工作将促进光纤激光相控阵技术朝向更多单元、更高功率、更远距离等方向演进,并推动其与激光大气传输、空间激光通信、自适应光学等理论和应用的结合与发展。     

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。     

高功率光纤激光的时间部分相干性对相干合成的影响

将多个光纤激光器的输出光束进行相干合成是获得高功率、高光束质量激光的有效途径。利用准部分相干光(PPCB)模型,计算了高功率光纤激光器阵列发出的部分相干光在远场的能量分布,分析了激光的时间部分相干性对相干合成的影响。计算结果表明,随着单根激光器输出光束线宽的增大,远场光斑的图样基本保持不变,但峰值功率和Strehl比随之减小。对于采用的算例,要保证远场光斑的Strehl比大于0.8,单根光纤激光器的线宽不能超过5 nm。     

光纤激光相干合成高速高精度相位控制器

基于随机并行梯度下降算法（SPGD）和现场可编程逻辑阵列（FPGA）设计制作了相干合成（CBC）相位控制器。理论分析表明,该控制器单次迭代速率大于1.125 MHz,对于2路和16路相干合成,其平均控制带宽的理论值分别大于70 kHz和9 kHz,与现有的SPGD算法相位控制器相比有了量级上的提高。利用该控制器进行了验证性实验,表明该控制器能够实现高速高精度相位控制。当利用相位控制器对两路激光的相位进行锁定时,目标圆孔内能量提高了1.51倍,远场光斑对比度提高了5.29倍。     

光纤激光相干合成高速高精度相位控制器

基于随机并行梯度下降算法（SPGD）和现场可编程逻辑阵列（FPGA）设计制作了相干合成（CBC）相位控制器。理论分析表明,该控制器单次迭代速率大于1.125 MHz,对于2路和16路相干合成,其平均控制带宽的理论值分别大于70 kHz和9 kHz,与现有的SPGD算法相位控制器相比有了量级上的提高。利用该控制器进行了验证性实验,表明该控制器能够实现高速高精度相位控制。当利用相位控制器对两路激光的相位进行锁定时,目标圆孔内能量提高了1.51倍,远场光斑对比度提高了5.29倍。

     

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。     

User Workshop on High-Power Lasers at the Linac Coherent Light Source

A two-day international workshop on the physics and integration of high-power lasers with the Linac Coherent Light Source was held in Stanford, California, USA, on October 1–2, 2013. The workshop was co-organized by UC Berkeley, Lawrence Berkeley, Lawrence Livermore, and SLAC National Accelerator Laboratories. More than 150 scientists, including 30 students and postdocs who are working in high-intensity laser-matter interactions, fusion research, and dynamic high-pressure science, came together from North America, Europe, and Asia. The group discussed the most promising and important new physics experiments that will be enabled by the unique combination of high-power lasers and the world-class LCLS free-electron laser X-ray beam.     

Coherent Beam Combination Using a General Model-Based Method

Coherent beam combination techniques can increase the output laser power from a single gain medium. We demonstrate coherent beam combination using the general model-based wavefront error correction method. The experiments for wavefront error correction are performed by using a 7-segment deformable mirror. Both the gen- eral model-based method and the stochastic parallel gradient descent algorithm are used to correct the wavefront error generated by a turbulent simulator. The experimental results show that the residual error is obviously reduced in comparison with that by using the SPGD method.     

Second User Workshop on High-Power Lasers at the Linac Coherent Light Source

The second international workshop on the physics enabled by the unique combination of high-power lasers with the world-class Linac Coherent Light Source (LCLS) free-electron X-ray laser beam was held in Stanford, CA, on October 7–8, 2014. The workshop was co-organized by UC Berkeley, Lawrence Berkeley, Lawrence Livermore, and SLAC National Accelerator Laboratories. More than 120 scientists, including 40 students and postdoctoral scientists who are working in high-intensity laser-matter interactions, fusion research, and dynamic high-pressure science came together from North America, Europe, and Asia. The focus of the second workshop was on scientific highlights and the lessons learned from 16 new experiments that were performed on the Matter in Extreme Conditions (MEC) instrument since the first workshop was held one year ago.     

Fourth User Workshop on High-Power Lasers at the Linac Coherent Light Source

The fourth international user workshop focusing on high-power lasers at the Linac Coherent Light Source (LCLS) was held in Menlo Park, CA, USA, on October 3–4, 2016 [1 R. Falcone, S. Glenzer, and S. Hau-Riege, Synchrotron Radiation News 27(2), 56–58 (2014).[Taylor &; Francis Online] , [Google Scholar]–3 C. Bolme, S. Glenzer, and A. Fry, Synchrotron Radiation News 29(2), 14–17 (2016).[Taylor &; Francis Online] , [Google Scholar]]. The workshop was co-organized by Los Alamos National Laboratory and SLAC National Accelerator Laboratory (SLAC), and garnered the attendance of more than 110 scientists. Participants discussed the warm dense matter and high-pressure science that is being conducted using high-power lasers at the LCLS Matter in Extreme Conditions (MEC) endstation. During the past year, there have been seven journal articles published from research at the MEC instrument [4 L. B. Fletcher et al., Review of Scientific Instruments 87(11), 11E524 (2016).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–10 P. Sperling et al., Physical Review Letters 115(11), 115001 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. The specific topics discussed at this workshop were experimental highlights from the past year, current status and future commissioning of MEC capabilities, and future facility upgrades that will enable the expanded science reach of the facility.     

Third User Workshop on High-Power Lasers at the Linac Coherent Light Source

On October 5–6, 2015, the third international user workshop focusing on high-power lasers at the Linac Coherent Light Source (LCLS) was held in Menlo Park, CA, USA [1 R. Falcone, S. Glenzer, and S. Hau-Riege, Synchrotron Radiation News 27(2), 56–58 (2014).[Taylor &; Francis Online] , [Google Scholar], 2 P. Heimann and S. Glenzer, Synchrotron Radiation News 28(3), 54–56 (2015).[Taylor &; Francis Online] , [Google Scholar]]. The workshop was co-organized by Los Alamos National Laboratory and SLAC National Accelerator Laboratory. More than 110 scientists attended from North America, Europe, and Asia to discuss high-energy-density (HED) science that is enabled by the unique combination of high-power lasers with the LCLS X-rays at the LCLS-Matter in Extreme Conditions (MEC) endstation.     

Coherent Beam Combination of Eight Watt-Level Polarization-Maintained Fiber Amplifiers

We demonstrate the coherent beam combination of eight Watt-level polarization-maintained fiber amplifiers. The phase control signal of each amplifier is generated by running a stochastic parallel gradient descent algorithm on a digital signal processor （DSP）. The experimental result shows that the whole system in close-loop performs well for long-time observation. Energy encircled in the target pinhole is 6.68 times more than that in open-loop. The combination efficiency is as high as 84.5%.     

高能固态激光阵列光束合成技术浅析

建立了高能固态激光阵列合成的模型,对相干合成型和非相干合成型的高能固态激光系统进行了分析和比较.引入光束传输因子(BPF)作为评价合成光束的光束质量,对湍流大气对板条激光器和光纤激光器相干合成与非相干合成远场光束质量的影响进行了定量分析.计算模型和结果为工程实际中合成方案的选择和评估提供了参考.     

二维固体激光阵列逆达曼光栅相干合束技术模拟研究

采用逆达曼光栅将二维锁相相干的激光阵列进行相干合束并进行孔径装填是获得远场单一主瓣大功率高光束质量激光输出的一种有效技术方案,将其应用于大尺寸5×5固体激光相干阵列相干合束中,并进行了固体激光阵列合束孔径装填的理论分析和原理性验证实验,测量了系统的实际合束效率,同时进行了后焦面逆达曼光栅的加工和放置误差对合束效率影响的详细分析。实验结果表明,逆达曼光栅用于固体激光阵列相干合束是一种有效的技术方案,且可以通过调节光栅周期和傅里叶透镜焦距来适应系统对激光阵列占空比的要求。这对于开发基于逆达曼光栅相干合束的高功率高光质量的全固态激光系统具有重要的意义。     

Coherent Beam Combination of Three Fiber Amplifiers with Multi-dithering Technique

Coherent beam combination of three W-level fiber amplifiers with multi-dithering technique is demonstrated. The multi-dithering technique is used for phase control in two channels. In the experiment, two channels are modulated by sine wave with 70 kHz and 100 kHz respectively, and two regular commercial DSP lock-in amplifiers and an industrial computer are used for electric signal processing in the feedback loop. The fringe contrast is advanced from 12% to 81%, and 78% coherent combination efficiency is obtained when the feedback loop is closed.     

Coherent Beam Combination of Two Polarization Maintaining Ytterbium Fibre Amplifiers

We investigate coherent beam combination of fibre laser beams by phase locking. Phase noise of a polarization maintaining ytterbium fibre amplifier is inspected with a fibre interferometer. In a feed back control loop, two fibre polarization maintaining ytterbium amplifiers are phase locked and coherent combined when the phase noise is properly controlled by a LiNO3 phase modulator.