The effect of atmospheric turbulence on the quality of complete and partially coherent of flat-topped beam with circular, rectangular and elliptical symmetry

Abstract

The laser beam propagation in irregular environments (e.g. atmosphere and ocean) has many applications, especially in free-space optical (FSO) communication systems. The growing use of such communications in applications such as laser, optical telecommunication radars and some information processing techniques has caused the growth and advancement of researchers in this field. The study of the properties of laser-emission in a turbulent atmosphere is a fundamental issue in laser physics and its applications. It is necessary to investigate the influence of atmospheric turbulence on the quality factor (M2-factor or propagation factor) of laser beams with various symmetries to control the types of laser beams in a turbulent atmosphere. In this article, the M2-factor of complete and partially coherent of flat-topped (PCFT) beams with circular, rectangular and elliptical symmetries are investigated in turbulent atmosphere. The results show that the intensity of three beams, with the propagation in the turbulent atmosphere becomes less and with the lower coherence length the intensity gets less. With an increasing wavelength of beams, M2-factor decreases and thus the quality of the beams is improved. The effect of the turbulent atmosphere on the partially coherent beam is much less than a complete coherent beam, thus the coherent reduction of the laser space is proposed as an approach to decrease the effects of the atmosphere. By decreasing the refractive index structure, the M2-factor of the beams becomes less so the quality of the beam becomes better. The investigations show that the PCFT beams have the best quality with elliptical symmetry and the worst quality with the circular symmetry in the turbulent atmosphere. In a complete unlike partially coherent at the beginning of the path, circular beam quality is better than rectangular and elliptical beams but circular beam quality becomes worse after a distance.