Saturation behavior of nonlinear refraction

提出了一种测量非线性折射率的新方法，包括高强度下的光谱色散和饱和。这种方法大大超过了现有的z-扫描方法的能力，并且通常适用于介电材料，无论它们是固体、液体还是气体。具体地说，该方法还允许将对非线性折射率的瞬时贡献与具有集成响应的瞬时贡献分开，例如，由于自由电子的形成。我们计划将这种方法应用于两类宽带隙介质：稀有气体和固体。前者，特别是氦，是相关的，因为它们允许与已建立的理论模型进行直接比较。以前已经证明过在Ar中的克尔饱和，并引起了一场关于丝化背后的机制的有争议的辩论。使用略微改进的测量装置，我们计划在泵浦-探测实验中明确地研究飞秒成丝的场景，从而实现对丝内沿传播轴的强度和电子密度的直接时间分辨测量。对克尔饱和效应的准确了解是改进成丝、气体、体介质体和光纤中产生超连续谱模型的重要前提，也可能在被动锁模技术中发挥重要作用。作为这个项目的结果，将为克尔效应的所有这些非常重要的应用提供可靠的数据，提高我们对提高强度下的非线性光学的理解，并通过实验结果详细描述被称为非线性光学的范式变化。

A novel method for measuring the nonlinear refractive index, including its spectral dispersion and its saturation at high intensities, is proposed. The method widely exceeds the capabilities of the established z-scan method and is generally applicable to dielectric materials regardless whether they are solid, liquid, or gaseous. In particular, the method also allows for the separation of instantaneous contributions to the nonlinear refractive index from those with an integrated response, e.g., due to the formation of free electrons. We plan to apply this method to two classes of wide-bandgap dielectrics: noble gases and solids. The former and in particular helium are relevant as they allow for a direct comparison with established theoretical models. Kerr saturation in argon has been demonstrated before and gave rise to a controversial debate concerning mechanisms behind filamentation. Using a slightly modified version of the measurement set-up, we plan to explicitly investigate the scenario of femtosecond filamentation in a pump-probe experiment, enabling the direct time-resolved measurement of intensity and electron density along the propagation axis inside the filament. The exact knowledge of Kerr saturation effects is an important prerequisite for improved models of filamentation, supercontinuum generation in gases, bulk dielectrics, and fibers and may also play an important role in passive mode-locking techniques. As a result of this project, there will be reliable data for all these highly important applications of the Kerr effect, improving our understanding of nonlinear optics at elevated intensities and detailing by experimental results what has been referred to as a paradigm change in nonlinear optics.