Generation of an ion-acoustic pulse by two electromagnetic pulses at difference frequencies in a collisionless plasma

Abstract

This paper presents an investigation of the generation of an ion-acoustic pulse by two electromagnetic (EM) pulses in a collisionless hot unmagnetized plasma at the difference frequency of the two EM pulses. On account of the interaction of the two EM pulses, a ponderomotive force at the difference frequency becomes finite and leads to the generation of an ion-acoustic pulse. When the two EM pulses have a Gaussian intensity distribution in time and uniform intensity distribution in space, the generated ion-acoustic pulse is also Gaussian in time with a pulse width $={[\frac{{t}_{10}^{2}{t}_{20}^{2}}{({t}_{10}^{2}+{t}_{20}^{2})}]}^{\frac{1}{2}}$, where ${t}_{10}$ and ${t}_{20}$ are the initial pulse widths of the incident EM pulses. Moreover, if the incident EM pulses have a Gaussian intensity distribution in space and time, the nonuniform intensity distribution of the EM pulses in a plane transverse to the direction of propagation leads to the redistribution of electrons and ions, and transient (time-dependent) cross focusing of the pulses may occur for appropriate initial powers of the EM pulses. The ion-acoustic-pulse generation is seen to be drastically modified by cross focusing of the two EM pulses.