Transmission of a GaAs Laser Beam Through the Atmosphere

The mean intensity distribution in a GaAs laser beam (lambda = 9050 A; 66 x 5 microrad initially) was observed at distances of L = 130 m, 650 m, 1.3 km, and investigated at 4.5 km mainly as a function of the meteorological range. With increasing distance and decreasing meteorological range beam spreading increases and the spot structure of the laser-diode emission pattern decreases. Even at median meteorological ranges atmospheric aerosol scattering, not atmospheric turbulence, is the main reason for beam spreading. It was proved further that the probability distribution of the fluctuating intensity generally can be approximated with log-normal distribution functions. The fluctuations increase with increasing distance from the beam axis.