Studies of energy Strehl ratio of a collimated Gaussian beam in turbulent atmosphere

Abstract

With the wide application of laser beams in the atmosphere, such as optical communications, the propagation of high-power laser beams and laser ranging, the propagation of laser beams in turbulent atmosphere has been studied extensively for many years. The atmospheric turbulence severely influences the beam quality and therefore the efficiency of the technology. Up to now, there have been many studies in random effects on laser beams propagation through atmosphere. Typically, M² factor which is a very important parameter for characterizing the laser beam quality is widely investigated. In this paper, energy Strehl ratio was utilized to characterize the laser beam quality. The propagation of a collimated Gaussian beam through atmospheric paths was numerically simulated using phase screens by the FFT method. And the effects of various factors such as atmosphere turbulent parameter C²_n, the inner scale, the outer scale and meteorological parameters on energy Strehl ratio were analyzed by means of probability statistics. The results show that the mean of energy Strehl ratio decreases with the transmission distance increasing, and it is the same with strong refractive index fluctuation. However, the beam quality may be improved in shorter distance when energy Strehl ratio is larger than 1. The energy density of the laser beam after propagating through turbulent atmosphere in the radius of that in vacuum can be calculated by energy Strehl ratio. It may represent the accepting states of the laser beam in a short distance.