基于高效率布里渊放大的高能量窄脉冲可调控涡旋激光技术研究

This project presents a method of direct generation and high-efficency amplification of a switchable vortex laser based on a liquid-core optical fiber or liquid-core simple photonic crystal fiber Brillouin amplifier. It provides a new feasible approach to obtain a high-energy narrow-pulse vortex laser with orbital angular momentum and porlarization switch. In this project, we investigate the generation of a stable vortex laser with switchable orbital angular momentum and polarization state as well as high-efficiency Brillouin amplification of narrow-pulse swithcable vortex laser. The latter includes the study of the theory of Brillouin amplification of a vortex laser, the generation of narrow-pulse Stokes signal beam and the control of characteristics of amplified vortex laser. We will focus on the the key scientific problems such as the switch of orbital angular momentum and polarization state, the control of spatial and temporal behavior characteristics in the generation and amplification of a vortex laser as well as stability analysis. Thus, high-energy narrow-pulse switchable vortex laser technology will be developed, and the technological difficulties in the tranditional optical fiber technology will be solved. It is expected to achieve a switchable vortex laser with the energy of greater than 1mJ, the pulse width of less than 5ns, and the energy extraction efficiency of larger than 40%. The research results will provide important application reference for laser processing, encryption optical communication, high-density plasma confinement, and so on.

本项目提出采用液芯光纤或液芯简化光子晶体光纤布里渊放大器直接产生并高效率放大轨道角动量和偏振状态可调控涡旋激光的方法，为获得高能量窄脉冲可调控涡旋激光提供一条新的切实可行的技术途径。项目拟开展以下研究内容：轨道角动量和偏振状态可调控稳定涡旋激光的产生；窄脉冲可调控涡旋激光的高效率布里渊放大，包括涡旋激光布里渊放大理论、窄脉冲Stokes信号光的产生和放大后涡旋激光特性调控等方面。重点解决涡旋激光产生与放大过程中轨道角动量和偏振状态的调控机理和方法、涡旋激光的空域和时域行为特性控制，以及稳定性分析等关键科学问题。开拓高能量窄脉冲可调控涡旋激光新技术，解决传统光纤激光技术难以实现窄脉冲可调控涡旋激光高效率放大的技术瓶颈。期望获得能量大于1mJ，脉冲宽度小于5ns，能量转换效率大于40%的可调控涡旋激光。其成果将为激光加工、加密光通信和高密度等离子体约束等领域提供重要的应用参考。

带有轨道角动量（OAM）的涡旋光场和具有非均匀偏振的柱对称矢量（CV）涡旋光场在高分辨率成像、显微、光操控和激光加工等领域具有广泛的应用。此外，其塑造聚焦特性能力在高能领域中更有前景，尤其是单纵模矢量脉冲。然而，目前一些产生上述结构光场的模式转换器损伤阈值较低，无法直接应对强激光脉冲的情况。针对这一问题，本项目从可调控空心光束和CV光场的产生、OAM光场和CV涡旋脉冲布里渊光-声参量放大两方面开展研究，并在研究中发现OAM可逆布里渊光-声传输，从而实现OAM态在光场与声场间的可逆参量转换。提出了激光束斜入射大芯径和小芯径多模液芯光纤产生空心光束的方法，分别获得了暗斑尺寸和环状光束宽度可控的高质量空心光束和CV涡旋光束，产生效率达37％。以此为基础，系统研究了OAM光场在受激布里渊放大（SBA）介质中的非线性传播特性，证明了利用SBA能够产生高能量单纵模CV超短脉冲，实验中获得了100 mJ量级300 ps脉冲宽度的CV单纵模脉冲，转换效率达40%以上。通过对放大后种子脉冲的相位和横向分布偏振层析进行测量，发现种子脉冲的相位和偏振结构能够被高保真保持。这些结果表明SBA是一种产生高功率CV光的可行方法，通过进一步将该结构拓展到多泵浦组束系统有望产生超高强度的CV脉冲，甚至可在等离子基的SBS系统中实现超高能量CV飞秒脉冲的产生。