<title>Atmospheric effects modeling for high-energy laser systems</title>

High energy laser (HEL) beams propagating through the earth's atmosphere are influenced by a wide variety of effects which, in general, reduce the beam irradiance (or, power concentration) at the target. In this paper an overview of atmospheric effects modeling for HEL systems is presented. The most important atmospheric propagation effects for cw HEL systems include transmission losses, turbulence, and thermal blooming. The general characteristics of these effects are described including scaling parameters and models useful for estimating their effects on HEL beam propagation. The wavelength dependence for propagation of an uncompensated cw HEL beam over a sea level path is shown by comparing the peak target irradiance for seven laser wavelengths ranging from the 0.337 micrometers N₂ laser to the 10.59 micrometers CO₂ laser. The use of adaptive optics for compensation of turbulence and thermal blooming effects is discussed and its effectiveness compared for near- field/ground-to-space and distributed/horizontal path propagation effects. Adaptive optics compensation is shown to be much more effective and the system requirements less stressing for near-field rather than distributed propagation paths since the turbulence induced scintillation effects tend to be smaller and the compensation is less likely to increase the blooming effects for near-field paths.