Pulse dynamics control in passively mode-locked high energy solid state laser oscillators

产生高重复频率的飞秒脉冲的锁模激光振荡器变得越来越强大。采用最先进的技术，如基于薄盘或板材的方案，激光振荡器直接产生了10微焦耳范围内的脉冲能量。与此同时，在这一发展过程中，人们意识到脉冲持续时间的大幅增加远远超出了增益带宽限制，这至少部分地抵消了高能量；我们在这里将其称为比例问题。对于采用半导体可饱和吸收体的孤子锁模激光振荡器--这是最常见的类型--众所周知，吸收镜中的双光子吸收过程构成了主要的限制过程。然而，克服这一限制的令人信服的概念尚未得到证明。这将是本提案的主题：在对脉冲整形机制进行简要分析的基础上，研究并实现了一种导致来自高能振荡器的更短脉冲的FPGA控制概念。令人惊讶的是，具有净正色散的啁啾脉冲振荡器(CPO)也存在定标问题，其中脉冲在振荡器往返过程中一直处于啁啾状态。由于存在啁啾，吸振器中的过度非线性模型不能简单地适用于这种情况。在这个参数范围内的尺度问题还没有得到系统的探讨，这也是本项目的主题。最后，我们将对高能固体激光振荡器中的非线性脉冲传输、它们的局限性以及激光动力学的外部控制有新的基本认识。我们将探索克服定标问题的概念，并产生比现在短得多的高能脉冲，这反过来将对物理学和其他领域的许多应用具有相关性。

Mode-locked laser oscillators emitting femtosecond pulses with high repetition rates become more and more powerful. Employing state-of-the-art techniques such as thin-disk or slab based schemes, pulse energies in the 10 µJ range have been generated directly from the laser oscillator. At the same time during this development, people realized a substantial increase of pulse duration well beyond the gain bandwidth limitations which at least partially counteracts the high energy again; we refer it here the scaling problem. From the solitary mode-locked laser oscillator employing a semiconductor saturable absorber - which is the most common type - it is well known that two-photon absorption processes in the absorber mirror form the main limiting process. Nevertheless, a convincing concept for overcoming this limitation was not yet demonstrated. This shall be the subject of this proposal: On the base of a concise analysis of the pulse shaping mechanisms an FPGA control concept is investigated and implemented leading to much shorter pulses from high energy oscillators. Surprisingly enough, the scaling problem is also known from chirped-pulse oscillators (CPO) with net positive dispersion where the pulses are chirped all the time during the oscillator roundtrip. Due to the chirp the model of excessive nonlinearity in the absorber cannot be simply adapted to this case. The scaling problem in this parameter range is not yet explored systematically which shall be subject of this project as well. At the end we will gain new fundamental insight into the nonlinear pulse propagation in high energy solid-state laser oscillators, into their limitations, and into the external control of laser dynamics. We will explore concepts to overcome the scaling problem and to generate high-energy pulses much shorter than now which in turn will be of relevance for many applications in physics and beyond.