On the interaction of turbulence intensity and its scales with various diameter laser beams at high temperatures

Abstract

Laser based missile defence systems (DIRCM) are being increasingly employed on aircraft. In certain circumstances the laser must pass through the exhaust plume of the aircraft engines. In order to predict the degree of divergence and dispersion of the laser beam an understanding of the exhaust gas structure and its influence is required. Specifically the effect of parameters such as temperature, carbon dioxide, turbulent intensity and turbulence scale sizes within the flow are of interest, in addition to the laser beam wavelength and beam size. A parametric study under controlled laboratory conditions was undertaken to examine these effects. The results of beam propagation through a high temperature turbulent flow at various turbulence intensity levels are presented in this paper. Beams with wavelengths 632.8 nm and 4.67 µm at various beam diameters are used to study laser beam interaction with various turbulence intensity and eddy scales. The effect of the relative size of the beam diameter with respect to the turbulence scale is also reported. It was found that the beam displacement was strongly related to turbulence intensity and beam diameter. Scale lengths, path length and turbulence intensity were found to influence beam displacement. Quantifying these parametric effects at high temperatures will assist with development of a parametrically based laser beam propagation model.