Wohlers M R
Appl Opt. 1972 Jun 1;11(6):1389-98. doi: 10.1364/AO.11.001389.
Consideration is given to certain physical phenomena that can attenuate the intensity of a laser beam by refractively spreading or scattering the beam as it propagates. The total attenuation caused by these effects can be well above the usual geometric spreading and absorption losses. Two specific phenomena are analyzed: the nonlinear thermal blooming of the beam (thermal lens effect) and the spreading caused by random variations of the index of refraction of the medium in which the beam is propagating (turbulence effects). The intent of the investigation is to obtain reasonably simple analytic expressions that can be used to estimate or set bounds on the extent of the attenuation. Such expressions are obtained for both the transient and the steady-state effects of thermal blooming when the medium is moving relative to the laser beam, and various estimates are also obtained for the turbulence-induced attenuation of the peak intensity of a beam. For comparison, estimates are also given of the effective attenution of the beam when it is viewed by a fixed observer, if there are random variations in its direction of propagation.
考虑某些物理现象，这些现象会在激光束传播时通过折射扩展或散射光束来减弱其强度。由这些效应引起的总衰减可能远高于通常的几何扩展和吸收损耗。分析了两种具体现象：光束的非线性热晕效应（热透镜效应）以及光束传播介质的折射率随机变化所导致的扩展（湍流效应）。研究的目的是获得合理简单的解析表达式，可用于估计衰减程度或设定其界限。当介质相对于激光束移动时，针对热晕效应的瞬态和稳态效应都得到了这样的表达式，并且还获得了关于光束峰值强度的湍流诱导衰减的各种估计值。为作比较，还给出了如果光束传播方向存在随机变化时，固定观察者所观察到的光束有效衰减的估计值。
