EAGER: Overcoming the Saturation Limit of High Intensity, Fully Coherent Raman Backscattering Laser

美国国家科学基金会使用探索性研究的早期概念拨款（EAGER）资助机制来支持在未经测试但具有潜在变革性的研究思路或方法的早期阶段的探索性工作。这个EAGER项目是由于Dear Colleague Letter NSF 16-080邀请来自历史上的黑人学院和大学的申请者提交提案，以加强该机构教师的研究能力而获得的。特拉华州立大学的这个项目旨在研究通过受激拉曼后向散射（SRBS）技术将超短激光脉冲输出能量提高100倍以上的可行性。如果这个项目成功，它可以转化超高强度激光，这反过来又会产生巨大的技术和科学影响。该项目将加强研究能力，并为等离子体物理领域的学生提供教育机会。该项目由数学和物理科学理事会资助。目前高功率激光啁啾脉冲放大的替代方案是受激拉曼后向散射（SRBS）方案，其中等离子体中的共振相互作用相干地介导能量从长泵浦转移到更短的种子。反向散射的短种子应该同时经历放大和压缩，由于等离子体不受光学损伤的影响，并且具有独特的色散特性，它的功率可以增长到非凡的水平。从理论上和实验上论证了SRBS激光器的可行性。然而，尽管在过去十年中取得了一些进展，但由于早期饱和，最大放大脉冲能量被限制在毫焦耳水平。本项目通过理论、计算和实验相结合的方法解决SRBS中的障碍，旨在对早期饱和的潜在机制建立坚实的理论认识，并通过模拟和实验验证；制定了克服饱和极限的方案，并证明了饱和障碍是可以解决的；并演示如何通过一毫米长的等离子体中的移动孤子腔产生相干的、单尖峰的、单周期的千瓦特激光脉冲。

The National Science Foundation uses the Early-concept Grants for Exploratory Research (EAGER) funding mechanism to support exploratory work in its early stages on untested, but potentially transformative, research ideas or approaches. This EAGER project was awarded as a result of the invitation in the Dear Colleague Letter NSF 16-080 to proposers from Historically Black Colleges and Universities to submit proposals that would strengthen research capacity of faculty at the institution. The project at Delaware State University aims to examine the feasibility of increasing the output energy in ultra-short laser pulses by over 100 times via the Stimulated Raman Backscattering (SRBS) technique. If this project succeeds, it could transform ultra-high intensity lasers, which in turn would have great technological and scientific impact. The project will strengthen research capacity and provide educational opportunities to students in the area of plasma physics. This project is funded by the Directorate for Mathematical and Physical Sciences.An alternative to the present chirped pulse amplification for high power laser is the Stimulated Raman Backscattering (SRBS) scheme, where a resonant interaction in plasma coherently mediates energy transfer from the long pump into the much shorter seed. The backscattered short seed should undergo simultaneous amplification and compression, and since plasma is impervious to optical damage and has unique dispersion properties, its power can grow to extraordinary levels. Feasibility of SRBS lasers was demonstrated theoretically and experimentally. Still, despite some progress over the past decade, the maximum amplified pulse energy was limited to milli-joule levels due to early saturation. This project addresses obstacles in SRBS through an integrated theoretical, computational, and experimental approach, and aims to develop a solid theoretical understanding of the underlying mechanism for the early saturation, verified by simulation and confirmed with experiments; develop a scheme to overcome the saturation limit and prove that the saturation barrier can be resolved; and demonstrate how a coherent, single spiked, and single cycled petawatt laser pulse can be generated via a moving soliton cavity in a millimeter-long plasma.