Analysis of the joint impact of atmospheric turbulence and refractivity on laser beam propagation

Victor A Kulikov,Mikhail A Vorontsov

doi:10.1364/oe.25.028524

Abstract

A laser beam propagation model that accounts for the joint effect of atmospheric turbulence and refractivity is introduced and evaluated through numerical simulations. In the numerical analysis of laser beam propagation, refractive index inhomogeneities along the atmospheric propagation path were represented by a combination of the turbulence-induced random fluctuations described in the framework of classical Kolmogorov turbulence theory and large-scale refractive index variations caused by the presence of an inverse temperature layer. The results demonstrate that an inverse temperature layer located in the vicinity of a laser beam’s propagation path may strongly impact the laser beam statistical characteristics including the beam wander and long-exposure beam footprint, and be a reason for refractivity-induced spatial anisotropy of these characteristics.

Highlights

Propagation of a laser beam in the Earth’s atmospheric boundary layer can be influenced by refractive index spatial inhomogeneities resulting from complicated dynamics of air masses [1,2,3,4]
In the numerical analysis of laser beam propagation, refractive index inhomogeneities along the atmospheric propagation path were represented by a combination of the turbulence-induced random fluctuations described in the framework of classical Kolmogorov turbulence theory and large-scale refractive index variations caused by the presence of an inverse temperature layer
In this paper we introduced a physics-based Wave-Optics Ray-Tracing Extension (WORTEX) model for numerical analysis of laser beam propagation in atmosphere which accounts for the combined effects of turbulence and refractivity

Summary

Introduction

Propagation of a laser beam in the Earth’s atmospheric boundary layer can be influenced by refractive index spatial inhomogeneities resulting from complicated dynamics of air masses [1,2,3,4]. Further simplification can be made for laser systems operating over relatively short (typically a few kilometers) distances and in absence of strong refractivity gradients in vicinity of the laser beam propagation path, e.g. caused by inversed temperature layers In these cases the refractivity term in Eq (1) can be considered as a constant [ nrefr (r) = const ]. For a spatially coherent, monochromatic or quasi-monochromatic laser beam, the impact of both atmospheric turbulence and refraction can be accounted for in the parabolic approximation of the diffraction theory In this approximation, evolution of the optical field complex amplitude A(r, z) along the laser transmitter optical axis (oz -axis) can be described by the following parabolic equation [7]: 2ik. The system of Eqs. (4)-(7) represents the WORTEX model describing laser beam propagation in presence of both atmospheric turbulence and refractivity

Atmospheric turbulence and refractivity models

Conclusion