Degradation of a laser beam by a two-dimensional turbulent jet

A laser beam traversing turbulence undergoes an intensity reduction which is correlated with the statistical behavior of refractive index perturbations. The analytical relation predicts degradation as a function of beam diameter, path length, wave number and wave structure function. Refractive index perturbations are approximated via the equations of state, using temperature and velocity perturbations. An experiment was conducted in which visible wavelength lasers traversed a well documented two-dimensional jet. Temperature perturbations vary from 0.25 to 1.89 K and velocity fluctuations range from 9.2 to 30.8 m/sec. Measured central spot intensities are as low as 18% of the undisturbed beam, depending on jet Mach number, beam position relative to the jet exit and wavelength. The average difference between theory and experiment is two percent in terms of far field intensity.