Probability of error in an atmospheric laser communication line

An investigation was made of the probability of error in an atmospheric laser communication line. A duplex communication system with a helium-neon laser transmitted discrete information (in combination with pulse-code modulation equipment or with a computer) under conditions of orthogonal polarization modulation. The probability of an error in the system depended strongly on the degree of turbulence of the atmosphere. A comparison was made of the influence of intensity fluctuations and spatial variations of the laser beam on the error probability. This probability was found to be governed not only by the intensity fluctuations but also by the fluctuations of the laser beam cross section at the point of reception; the influence of beam wandering could be eliminated by automatic beam alignment.