Maher W E
Appl Opt. 1972 Feb 1;11(2):249-56. doi: 10.1364/AO.11.000249.
Pulsed laser beam propagation through the atmosphere is described by a model that contains the transient effects of air wave development. This study considers the initial stages in the propagation of a laser beam; the computer calculation follows the process during the time regime in which pressure gradients are important. Energy absorbed by the medium from the beam during a time increment is added to the existing internal energy in the form of excited molecular states. Deactivation rates are specified by pressure, temperature, and component species such as CO(2) and H(2)O. Absorption and deactivation processes change the temperature of the air and cause the buildup of the cylindrically symmetric air waves. A Richtmyer-von Neuman finite difference scheme follows the waves' development, and a pseudoviscosity term is used to smooth steep pressure gradients. During the growth of the related gradients in the index of refraction the equations for power flow in the initially diffraction-limited beam are continually changed to allow for refraction. Power densities in the focal plane are obtained as a function of time, atmospheric constitution, power, beam source aperture diameter, range, and radius from the beam axis in the focal plane.
脉冲激光束在大气中的传播由一个包含气波发展瞬态效应的模型来描述。本研究考虑激光束传播的初始阶段；计算机计算跟踪压力梯度起重要作用的时间段内的过程。在一个时间增量期间介质从光束吸收的能量以激发分子态的形式添加到现有的内能中。失活速率由压力、温度以及诸如CO₂和H₂O等组分种类确定。吸收和失活过程改变空气温度并导致圆柱对称气波的形成。一种Richtmyer-von Neuman有限差分格式跟踪气波的发展，并且使用一个人工粘性项来平滑陡峭的压力梯度。在折射率相关梯度增长期间，最初衍射受限光束中的功率流方程不断变化以考虑折射。焦平面中的功率密度作为时间、大气组成、功率、光束源孔径直径、距离以及焦平面中距光束轴的半径的函数获得。
