Magnetic Field Generation in Plasma Waves Driven by Copropagating Intense Twisted Lasers

We present a new magnetic field generation mechanism in underdense plasmas driven by the beating of two, copropagating, Laguerre-Gaussian orbital angular momentum laser pulses with different frequencies and also different twist indices. The resulting twisted ponderomotive force drives up an electron plasma wave with a helical rotating structure. To second order, there is a nonlinear rotating current leading to the onset of an intense, static axial magnetic field, which persists over a long time in the plasma (ps scale) after the laser pulses have passed by. The results are confirmed in three-dimensional particle-in-cell simulations and also theoretical analysis. For the case of 300 fs duration, 3. 8×10^17 W/cm^2 peak laser intensity we observe magnetic field of up to 0. 4 MG. This new method of magnetic field creation may find applications in charged beam collimation and microscale pinch.