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

在过去的五年中，强大的飞秒激光束的自俘获（即丝化）发展非常迅速，以至于出现了激光雷达和脉冲压缩等几种应用。这个看似简单的现象涉及飞秒激光脉冲复杂的时空重塑。众所周知，围绕在灯丝周围的背景光束和包含光能的主要部分在空间和时间上塑造光束的耗散效应中起着关键作用，然而，确切的机制尚不清楚，其他方面如灯丝强度的自稳定（夹紧）更容易理解。当激光功率超过成丝的临界功率两个或两个以上数量级时，观察到随机多重成丝和光湍流。人们对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。我们建议在相位错存在的情况下研究成丝。其中一个关键目标是通过使用不同构型的光学涡流，例如在晶格状结构中产生有序的细丝结构。这将使多个细丝可重复，从而更容易获得系统的实验研究。在这方面需要解决的一个问题是，是否有序的图案，如果是有序的图案，支持长丝的形成和范围。此外，与相位错的规则模式相结合的成丝本身似乎是一个有趣的问题。这可以仅仅从旋涡影响背景光束的事实中推断出来，从而为实验提供了控制参数，并为理论建模提供了测试平台。事实上，由于多丝化不可避免地与对称破缺有关，相位错似乎很可能在多丝化中发挥作用，因此值得研究。我们还建议通过折射飞秒探针光束来探测灯丝的动力学。比较孤立和有序的多细丝的实验结果，不仅可以对细丝本身的动力学，而且可以对细丝相互作用的作用提供有启发性的信息。虽然大多数实验将使用标准的10-mJ Ti:Sapphire飞秒激光系统，但中红外飞秒激光源的可用性为系统研究提供了额外的机会。此外，耶拿TW激光系统可用于演示高功率下的新效果。该项目利用了DFG研究单位532的专业知识和研究基础设施。特别重要的是应用物理研究所（Prof. t<s:1> nnermann）的微结构能力，为实现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，固体理论与光学研究所的成员（Lederer教授）将提供理论支持。此外，我们希望有序灯丝结构与规则波导结构的交联(prof .；Nolte和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.