Saturation behavior of nonlinear refraction

提出了一种测量非线性折射率的新方法，包括其光谱色散和高强度下的饱和度。该方法大大超出了现有的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。特别是，该方法还允许将非线性折射率的瞬时贡献与那些具有积分响应的贡献分离，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频隙介质：惰性气体和固体。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。克尔饱和在氩气中已经被证明，并引起了一个有争议的争论，关于机制背后的长丝。使用稍微修改的测量装置，我们计划在泵浦探针实验中明确研究飞秒灯丝的场景，从而实现沿灯丝内部传播轴的强度和电子密度的直接时间分辨测量。克尔饱和效应的确切知识是改进成丝、气体、体电介质和纤维中超连续谱产生模型的重要先决条件，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，克尔效应的所有这些非常重要的应用将有可靠的数据，提高我们对高强度非线性光学的理解，并通过实验结果详细说明被称为非线性光学范式变化的东西。

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.