Fermi pencil beams and off-axis laser detection

TL;DR

This paper develops models for narrow laser beam propagation in turbulent atmospheres using Fermi pencil equations, and proposes a framework for reconstructing beam properties from off-axis measurements, simplifying parameter estimation.

Contribution

It introduces macroscopic Fermi pencil beam models for laser propagation and a novel off-axis measurement framework for reconstructing beam direction and source location.

Findings

Effective modeling in small mean-free-path regimes.

Simplified parameter reconstruction compared to detailed radiative transfer.

Framework successfully reconstructs beam direction and source location.

Abstract

This paper concerns the reconstruction of properties of narrow laser beams propagating in turbulent atmospheres. We consider the setting of off-axis measurements, based on light detection away from the main path of the beam. We first model light propagation in the beam itself by macroscopic approximations of radiative transfer equations that take the form of Fermi pencil beam or fractional Fermi pencil beam equations. Such models are effective in the small mean-free-path, large transport-mean-free path regime. The reconstruction of their constitutive parameters is also greatly simplified compared to the more accurate radiative transfer equations or (fractional) Fokker-Planck models. From off-axis measurements based on wide-angle single scattering off the beam, we propose a framework allowing us to reconstruct the main features of the beam, and in particular its direction of propagation and the location of the emitting source.