EXPERIMENTAL AND COMPUTATIONAL INVESTIGATION OF PULSED LASER ENERGY TRANSMISSION THROUGH THE ATMOSPHERE

Abstract
An experimental study has been conducted and compared with a computed numerical model in order to determine the limitations induced by the air breakdown on the transmission of a high energy laser pulse through the standard atmosphere. The 10.6 µm CO₂ laser displays up to 300 J in a 2.5 µsec pulse with a high power peak (typically 5x10⁸ W ; 50 ns F W H M) followed by a high energy tail. The laser beam is focused by means of a 5 X telescope at 67.5 m (f/D = 135) outside the laboratory. Envelope of the beam and energy density distribution in the focal plane are presented. Aerosol concentration and size distribution measurements are obtained by means of a particle optical counter (Knollenberg axially scattering spectrometer probe : 0.5 µm < d > 45 µm). Energy and fluence transmitted through the air breakdown - induced plasma for given atmospherical conditions are measured as a function of time and incident fluence and then compared with results of a computed numerical hydrodynamic bi-dimensional model.