Opto-acoustic phenomena accompanying the propagation of high-power pulsed laser radiation in the atmosphere

Abstract

Opto-acoustic phenomena accompanying the propagation of high-power pulsed laser radiation in the atmosphere are used for remote determination of the energetic and geometric parameters of laser radiation. The amplitudes and shapes of acoustic pulses have been calculated for the following typical temporal behavior of Gaussian beams: a triggering pulse, short laser pulse, and harmonically modulated radiation disregarding the effect of kinetic cooling in the laser beam propagation channel. Numerical calculations allow one to determine experimentally the radiation power and the absorption coefficient in air for the chosen mode of laser radiation, because the difference between the calculated dimensionless and measured normalized sound pressure levels remains constant for each temporal behavior and is a function of the sought-after parameters. It is experimentally demonstrated that the geometric and energetic characteristics of laser beams measured by opto-acoustic methods agree well with the results of contact bolometer measurements. The standard deviation does not exceed 15% for the laser energy density W ≤ 13 J/cm 2 . For W > 13 J/cm 2 , the observed discrepancy of the results is explained by nonlinearity of bolometer sensors. An algorithm of reconstructing the spatial structure of laser beams from the data of wire bolometer sensors is suggested and realized. The optimal number of initial projections and readings for each projection has allowed us to reconstruct the beam spatial structure in real time. The algorithm is efficient when the noise level does not exceed 20%. The nonlinear extinction coefficient of laser radiation in the atmosphere also can be retrieved from opto-acoustic measurements without additional information about optical and meteorological situation.