Magnetic field generation in plasma waves driven by co-propagating intense twisted lasers*

We present a new magnetic field generation mechanism in underdense plasmas driven by the beating of two, co-propagating, Laguerre-Gaussian (LG) orbital angular momentum (OAM) laser pulses with different frequencies and also different twist indices. Results of 3D particle-in-cell simulations show that the twisted ponderomotive force drives up an electron plasma wave with a helical rotating structure. For the case of 300 fs duration, 3.8×1017 W/cm2 peak laser intensity we observe magnetic field of up to 0.4 MG. We will also outline a theoretical model, based on cold electron fluid equations, that reproduces that pertinent features of the PIC simulations – including the axial magnetic field – in the appropriate limits and elucidates the mechanism and highlights its scaling with key parameters.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. Applications of this new method of magnetic field creation will be discussed.