The condition of collapse stopping during propagation of high-power femtosecond laser pulses in an optical medium
A.A. Zemlyanov, O.V. Minina
V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, Tomsk, Russia
Keywords: femtosecond laser pulses, air, self-focusing, diffraction, intensity collapse, absorption
Abstract
The criterion for stopping the intensity collapse is established in the approximation of the nonlinear Schrödinger equation for the problem of self-focusing of high-power femtosecond laser radiation in an optical medium. Using propagation of a femtosecond laser pulse in air as an example, it is shown that the collapse stops when the role of diffraction increases due to a decrease in the radius of the laser beam, and occurs not at a point, but at an interval in front of the nonlinear focus, where the self-phase modulation of the radiation due to the plasma nonlinearity prevails over the Kerr effect. The result (collapse stop criterion) makes it possible to take into account the features of the nonlinear activity of various optical media during the propagation of high-power femtosecond laser pulses; in particular, the role of nonlinear absorption is determined under the conditions considered.
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