Optical communications in the earth´s atmosphere

The main reasons for the present interest in the potentialities of the laser for communication system applications lie in the coherent nature of the radiation and the short wavelength. The property of coherence, as considered in this article, is the ability of an electromagnetic wave to interfere with itself. The phenomenon is characterized by the ability to form a highly collimated beam, which leads to the ability to achieve communications over great distances. However, the perturbing effects of the earth´s atmosphere on coherent optical radiation raise a serious obstacle to the use of lasers in earthbound communication systems. Space and interplanetary communications applications appear more promising as atmospheric effects are eliminated.