<title>Scintillation Of Laser Radiation Due To Propagation Through Atmospheric Turbulence, Measurements, And Theoretical Calculations</title>

Abstract

Work on scintillation of laser light over open grassland has been motivated by the need to provide safety clearance for the use by the Army of various laser equipments (eg rangefinders). The scintillation strength may be characterised by the parameter n, n2 = 0.5 Cn2 K7/6 Lll/6 Here Cn is the Turbulent Refractive Index Constant K is the wavenumber of the radiation L is the range. For values of n2 (in weak scintillation n2 is the variance of the log irradiance) greater than 0.5, ie for ranges 0.5Km for visible or near IR lasers in Summer conditions the scintillation may no longer be described by the weak fluctuation theory (due to Rytov) . For medium and strong scintillation it is not at present possible to predict either the mean irradiance or the mean square irradiance fluctuations by analytical formulae. However, it is possible to obtain an integral expression for the mean irradiance I . In the present investigation this expression has been evaluated by numerical integration on a 1906A ICL computer. The mean square fluctuation of irradiance is more difficult to calculate, as it involves expressions for the fourth order moment of the field. In this case, it has not yet been possible to even derive closed expressions for the solution of the differential equation for the fourth moment of the field. However a number of possible numerical approaches have yielded results which compare favourably with experimental results in some cases. The results of some of these computations will be presented later.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.