INTENSE MAGNETIC-FIELD GENERATION BY RELATIVISTIC PONDEROMOTIVE FORCE IN AN UNDERDENSE PLASMA

It is shown that the relativistic ponderomotive force exerted by an ultra intense laser pulse launched in a plasma could generate a very strong low frequency (with index lf hereafter) magnetic field B(lf) with a maximum value of the order of B(lf)/B(l) = omega(pe)/omega, where omega(pe) is the electron plasma frequency and omega the laser one, and B(l) the high frequency magnetic field of the laser pulse. We derive the mechanism for this B(lf)-field creation in an underdense plasma and show how to diagnose its presence and propose an experimental set-up to achieve the measurement. We also stress the universality of this detection as far as picosecond pulses and the far infrared radiation range (FIR) are concerned. The great influence of this B(lf)-field on related important phenomena, such as relativistic self-focusing and wakefield generation by short laser pulses, is briefly underlined.