Generation of Femtosecond Vortex Beams, Self-channeling, and Filamentation in Gaseous Media

丝化，即强大的飞秒激光的自陷，在过去的五年中得到了非常迅速的发展，以至于出现了激光雷达和脉冲压缩等几种应用。这一看似简单的现象涉及飞秒激光脉冲复杂的空间和时间重塑。环绕在灯丝周围的包含大部分光能的背景光束在空间和时间上对光束的耗散效应起着举足轻重的作用，然而，确切的机制尚不清楚，其他方面，如灯丝强度的自稳定(钳位)更容易理解。当激光功率超过成丝的临界功率两个或更多个数量级时，观察到随机多成丝和光学湍流。对于细丝之间的相互作用以及它们与背景光束的相互作用知之甚少。我们建议在存在位错的情况下研究成丝现象。主要目标之一是通过使用不同构型的光学涡旋(例如，在晶格状结构中)来产生细丝的有序结构。这将使多个细丝可重复，从而更容易进行系统的实验研究。在这方面要解决的一个问题是，有序图案是否支持灯丝形成和范围，如果是，则支持灯丝形成和范围。此外，与规则的相错模式相结合的丝状化本身似乎是一个有趣的问题。仅从涡旋对背景光束的影响就可以推断出这一点，从而为实验提供了控制参数，也为理论建模提供了试验台。事实上，由于多重成丝不可避免地与对称性破缺联系在一起，似乎位错在多重成丝中发挥了作用，因此值得研究。我们还建议通过折射飞秒探测光束离开细丝来探索成丝的动力学。对于孤立和有序的多个细丝的情况，比较实验结果将不仅提供关于成丝本身的动力学的启发信息，而且还将提供关于细丝之间相互作用的作用的启发信息。虽然大多数实验将使用标准的10-MJ钛宝石飞秒激光系统，但中红外的飞秒激光光源的可用性为系统研究提供了额外的机会。此外，耶拿行波激光系统可以在高功率下展示新的效果。该项目利用了DFG研究单位532的专业知识和研究基础设施。尤其重要的是应用物理研究所(Tünnermann教授)的微结构能力，为实现用于飞秒涡旋产生的定制光学提供了独特的机会。同样重要的是固态理论和光学研究所成员(莱德尔教授)提供的理论支持。此外，我们还希望有序细丝结构与规则波导结构(教授、教授)的交叉链接。Nolte and Pertsch)将被确认。

Filamentation, i.e. self-trapping of powerful femtosecond laser beams has seen a very rapid development in the past five years to the point that several applications like LIDAR and pulse compression have emerged. The seemingly simple phenomenon involves complex spatial and temporal reshaping of the femtosecond laser pulses. The background beam surrounding the filament and containing the major part of the optical energy is known to play a pivotal role in the dissipative effects shaping the beam in space and time, however, the exact mechanisms are not known, other aspects like self-stabilization of the filament intensity (clamping) are much easier to comprehend. At laser powers exceeding the critical power for filamentation by two or more orders of magnitude, stochastic multiple filamentation and optical turbulence is observed. Little is known about the mutual interaction of the filaments and their interaction with the background beam.We propose to investigate filamentation in the presence of phase dislocations. One of the key goals is to generate ordered structures of filaments by using optical vortices in different configurations, e.g., in lattice-like structures. This will make multiple filamentation repeatable and thus more easily accessible to systematic experimental study. A question to address in this regard is whether ordered patterns, and if which, support filament formation and range. In addition, filamentation in conjunction with regular patterns of phase dislocations appears to be an interesting problem by itself. This can be inferred merely from the fact that vortices influence the background beam thus providing control parameters for experimentation and a test bed for theoretical modeling. In fact, as multiple filamentation is inevitably linked to symmetry breaking, it seems to be likely that phase dislocations play a role in multiple filamentation anyway and thus are worth being investigated.We also propose to probe the dynamics of filamentation by refracting a femtosecond probe beam off the filament. Comparing experimental results for the case of isolated and ordered multiple filaments will provide illuminating information not only on the dynamics of filamentation itself, but also on the role of the interaction of filaments.While most of the experiments will use a standard 10-mJ Ti:Sapphire femtosecond laser system, the availability of femtosecond laser sources in the mid-infrared provides additional opportunities for systematic investigations. Moreover, the Jena TW laser system can be used to demonstrate novel effects at high powers.The project takes advantage of the expertise and research infrastructure rounded up in the DFG Research Unit 532. Particularly important are the microstructuring capabilities at the Institute of Applied Physics (Prof. Tünnermann) providing unique opportunities for realizing customized optics for femtosecond vortex generation. Equally important will be the theoretical support through members of the Institute of Solid-State Theory and Optics (Prof. Lederer). In addition, we hope that cross links of ordered filament structures to regular wave guide structures (Profs. Nolte und Pertsch) will be identified.