Atmospheric Propagation of Two C02 Laser Pulses

An experimental investigation has been conducted to study the propagation of a high-energy laser beam (0£ >10 W/cm; FB >10 J/cm) in the atmosphere. At these intensities and fluence levels air breakdown can occur because of the interaction of the intense radiation with the aerosol particles naturally suspended in the path of the beam. An air plasma is created, which expands rapidly and consequently can have a detrimental effect on the energy propagation. This paper reports, first, the energy transmitted through the breakdown plasma as a function of the incident average energy density (ET/Ej 300 J/cm) and second, the possibility of increasing the transmission of the incident energy by the application of a precursor pulse as a function of the double-pulse separation time (controllable from a few microseconds to 1/10 s). In our particular experiment, the maximum increase (by a factor of three) is observed for At= 100-200 j*s, an effect due to the cleaning effect of the first pulse by vaporizing aqueous aerosol particles.