Laser frequency broadening by atmospheric turbulence

The temporal coherence degradation or frequency broadening of laser irradiance propagating through atmospheric turbulence was studied. The laser power spectral density is expressed in terms of various turbulent parameters. The full width at half maximum of the laser power spectral density after propagating through a turbulent medium was derived for two limiting cases. Typical results for 10 m/sec wind velocity are 2,300 rad/sec for vertical propagation and 45,000 rad/sec for horizontal propagation of 10 km. It is concluded that this broadening is important for coherent radar ranges larger than 10 km.