Experimental validation of a phase screen propagation model for nanosecond laser pulses travelling through turbulent atmospheres

Applications involving the outdoor use of pulsed lasers systems can be affected by atmospheric turbulence and scintillation. In particular, deterministic prediction of the risk of injury or damage due to pulsed laser radiation can be difficult due to uncertainty over the focal plane fluence of radiation that has traversed through a turbulent medium. In this study, focussed beam profiles of nanosecond laser pulses are recorded for visible laser pulses that have traversed 1400m paths through turbulent atmospheres. Beam profiles are also taken under laboratory conditions. These pulses are characterised in terms of their peak focal plane fluence, total collected energy and Strehl ratio. Measured pulses are then compared statistically to pulse profiles generated by a two-dimensional phase screen propagation model based on the Von Karman power spectrum distribution. The model takes into account the refractive index structure constant (??2), the wavelength, the path geometry and macroscopic beam steering. Analysis shows good correlation between the measured and simulated data, inferring that the Von Karman phase screen model can be used to predict focal plane fluence distributions for outdoor applications.