An overview of the limitations on the transmission of high energy laser beams through the atmosphere by nonlinear effects

The important nonlinear effects which limit high energy laser propagation through the atmosphere are reviewed. The two most important effects are thermal blooming (or thermal defocussing) and air breakdown within the beam. A third, less important effect is stimulated raman scattering. The possibility of transmitting laser beams through fogs, clouds or haze by boring holes through these atmospheric media with the laser beam is also reviewed. The laser's waveform is considered to be a train of pulses. It is shown that the waveform design and other important parameters such as range to the focal plane, aperture and focal spot size, pulse intensity, etc., can be chosen to avoid the thermal blooming of individual pulses and air breakdown. The limit on beam propagation is then caused by thermal blooming due to the cumulative heating by the pulses in the train. An added set of parameters then controls this multipulse blooming including beam slew rate, cross wind velocity, and interpulse spacing. Parametric tradeoffs required to satisfactorily control thermal blooming and quantitative results for several parametric choices are summarized.