Saturation behavior of nonlinear refraction

点击翻译按钮获取中文摘要

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.