HIGH INTENSITY LASER PROPAGATION IN THE ATMOSPHERE
TRW SYSTEMS REDONDO BEACH CA QUANTUM PHYSICS LAB
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The research reported here involves the thermal self-defocusing effect, which occurs in the case of high energy laser beam propagation in the atmosphere. Two subjects are investigated, namely, heating mechanisms, and the dynamics of the propagating laser beam. The heating mechanism study is concerned specifically with photo-absorption in the far wings of pressure broadened CO2 vibration-rotation bands, while the beam dynamics analysis treats the effects of target motion on the degree of self-defocusing of the laser beam. A theory of far-wing pressure broadening is developed in which the basic broadening mechanism is assumed to arise from perturbations of the absorbers rotational motion via a short range repulsive interaction with a colliding molecule. The theory predicts a far-wing spectral behavior described by a product of a Lorentz line shape and an exponentially decreasing factor, in general agreement with recent measurements. In the beam dynamics work a convenient closed form expression has been obtained for the maximum flux which the thermal self-defocusing effect permits one to transmit through the atmosphere. This analysis takes into account the effect of target motion. The expression for the maximum flux depends upon such parameters as the initial beam intensity, the initial beam diameter, the target distance, the rotational rate of the beam, and the effective absorption coefficient for heating of air by light at the laser frequency.
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