Nonstationary ponderomotive self-focusing of a Gaussian laser pulse in a plasma

Tripathi, Deepak; Bhasin, Lalita; Uma, R.; Tripathi, V. K.
November 2010
Physics of Plasmas;Nov2010, Vol. 17 Issue 11, p113113
Academic Journal
A model of relaxing ponderomotive nonlinearity is developed to study the nonstationary self-focusing of a Gaussian laser pulse in a plasma. The ponderomotive force acts on the electrons instantaneously but the plasma density redistribution via the process of ambipolar diffusion is taken to evolve on the time scale τR≅r0/cs, where r0 is the laser spot size and cs is the sound speed. The paraxial ray approximation is used to solve the wave equation. The focusing is stronger at the rear of the pulse than at the front, causing considerable distortion of the pulse when pulse duration is comparable to nonlinearity relaxation time. The saturation effect of nonlinearity leads to focusing of any portion of the pulse to a minimum spot size r0fmin at an optimum distance zop and then the spot size increases. fmin and zop depend on the intensity of the portion of the pulse.


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