Waves, Solitons and Turbulence in Optical Systems - Abstract

Brée, Carsten

Intensity clamping in femtosecond filaments and the role of multiphoton resonances

It is well-examined that the optical intensity in a femtosecond filament cannot be increased to arbitrary values by increasing the input optical power. Rather, the intensity eventually clamps as the input power exceeds a critical threshold. As a time-averaged model of nonlinear beam propagation reveals, this behavior is closely linked to the saturation of the nonlinear refractive index due to the onset of self-induced ionization. Employing exact quantum calculations of the optical response, we show that besides the global saturation behavior, the nonlinear refractive index exhibits local dips. These dips stem from atomic multiphoton resonances and can significantly alter the beam propagation dynamics. In particular, we observed intermediate intensity clamping, giving rise to a step-like increase of the optical intensity with increasing input power.