Statistical parameters of femtosecond laser pulse post-filament propagation on a 65  m air path with localized optical turbulence

Abstract

High-power femtosecond laser radiation propagates nonlinearly in air, exhibiting pulse self-focusing and strong multiphoton medium ionization, which leads to the spatial fragmentation of laser pulses into highly localized light channels commonly called filaments. Filaments are characterized by high optical intensity and reduced (even zero) angular spreading and can contain laser plasma or be plasmaless (postfilaments). The presence of optical turbulence on the propagation path dramatically changes pulse filamentation dynamics and in some cases causes pulse fragmentation enhancement and collapse arrest. For the first time, to the best of our knowledge, we experimentally and theoretically investigate the transverse profile of Ti:sapphire femtosecond laser radiation nonlinearly propagating a 65 m air path to the region of postfilament evolution after passing through an artificial localized air turbulence. We show that when a turbulence layer is placed before the filamentation region, the average number of high-intensity local fluence maxima (“hot points”) in the beam profile and their sizes grow as the turbulence strength increases, and then saturates at some levels. On the contrary, the deposition of a turbulence screen within the filamentation region has almost no effect on either the number or the average diameter of postfilaments.

Postfilament-Induced Two-Photon Fluorescence of Dyed Liquid Aerosol Enhanced by Structured Femtosecond Laser Pulse

“…Optionally, a laser pulse may experience specific modulation using a thin layer of heated turbulent air, which imposes stochastic phase modulation of the optical pulse when passing through it. Recently [16], our experimental studies on the influence of turbulence on laser beam filamentation showed that the application of a thin but intense turbulent layer in the optical path of high-power laser radiation propagation leads to the intensity redistribution in the beam cross section due to the inhomogeneities of air refractive index, which initiates small-scale stochastic optical beam nucleation and the formation of high-intensity hot spots during the propagation. As an example, Figure 2a,b demonstrate the images of the transverse structure of a 35mJ femtosecond laser beam travelling a 100-m air path (a) without a turbulent layer and (b) when a turbo-heater is switched-on.…”

Vortex Beam in a Turbulent Kerr Medium for Atmospheric Communication

“…In this case, in order to simplify the calculations the spectral density function of turbulent inhomogeneities, ε t is modeled by a step function: θ(k − k g )•τ. Here, k g is the upper cut-off spatial frequency of the pulse spectrum and τ is a free parameter associated with the amplitude of the turbulence [16].…”