Abstract

Nonlinear refraction is the key nonlinear optical process in transparent dielectric materials, giving rise to processes like self-phase modulation, four-wave mixing, and self-focusing. These processes play an important role in the creation of optical filaments, which are normally understood as arising from a balance of self-focusing Kerr action and defocusing contributions from a self-generated plasma. This perspective has been recently challenged by experimental results [1] that clearly indicate a strong saturating influence from higher-order contributions n₄I², n₆I³ etc. to nonlinear refraction. In particular, Ref. [1] indicated that Kerr saturation precedes similar effects from a self-generated plasma, which would indeed be a paradigm shift in the understanding of filament formation. In the following, we present an independent theoretical approach for the prediction of Kerr saturation from experimentally well secured multiphoton ionization models. Our model allows computation of the nonlinear refractive index including its full dispersion deep into the uv from the single parameter of ionization energy. Results agree with experimental data within about 20% precision for the inert gases. Moreover, the formalism can be extended to compute higher-order indices, which widely concurs with the experimental findings of Loriot et al.

© 2011 IEEE