Propagation of Pulsed Laser Energy Through the Atmosphere

An experimental investigation has been conducted to study pulsed laser energy propagation over long distance through the atmosphere. Typical gain switched pulse of the CO2 cold cathode electron gun laser (160 J, 2.5 /AS) shows an initial high-power spike (5.6 x 108 W, 50 ns FWHM) followed by a high-energy tail (130 J). The laser beam is focused by means of of a 5 X telescope outside the laboratory. Spatial and temporal distributions of intensity and energy density are measured in the breakdown area by burning of thermosensiti ve paper (envelope of the focused laser beam) and by use of calibrated Kalvar film (focal spot). Experimental determination of the air breakdown average threshold (l-2x!08 W/cm2, 3-5 J/cm2) leads to the conclusion that such a phenomenon is initiated on the spike of the pulse by > 4-^m-diam aerosol particles. A particle optical counter is used for in situ measurements of aerosol distribution (axially scattering spectrometer probe, calibrated in the 0.5 ftm <c?<45 iim range), to determine the number in the focal volume.