chapter 1, Optical Wave Propagation in Random Media: Background Review

Excerpt

1.1 Introduction

When an optical wave propagates through the atmosphere of the earth, it experiences distortions caused by small temperature variations related to the sun's heating of the earth and the turbulent motion of the air due to winds and convection. The most well-known manifestation of this phenomenon is the twinkling of stars, observed long before the invention of the laser.

Laser beam propagation through the atmosphere, which is of great interest to a variety of scientists and engineers, is a subset of the more general study of optical wave propagation through random media. By random medium, we mean one whose basic properties are random functions of space and time. Astronomers (including Sir Isaac Newton) were among the first scientists to show interest in certain atmospheric effects, like the quivering of the image of an astronomical object at the focus of a telescope and temporal fluctuations in received irradiance (intensity), the latter commonly called scintillation. During the 1950s, Russian scientists Obukhov [1] and Tatarskii [2] began theoretical studies of scintillation. These early theoretical studies were soon followed by a series of measurements of optical scintillation, the results of which were published mostly in astronomy journals. With the invention of the laser in 1960, theoretical investigations of optical wave propagation went beyond the interest of astronomers by focusing on characteristics of laser beams propagating through atmospheric turbulence. A brief history of scintillation studies by Russian scientists throughout the decades of the 1950s, 1960s, and 1970s can be found in an article by Gurvich [3].

A complete rigorous theory of optical wave propagation through random media is not yet available, but the general theory is fairly well understood in certain asymptotic regimes.