Probing ultrafast magnetic-field generation by current filamentation instability in femtosecond relativistic laser-matter interactions

This paper presents experimental measurements of the femtosecond timescale generation of magnetic field fluctuations exceeding 1 kT in relativistic laser-solid interaction, using a probe electron beam generated in a laser wakefield accelerator. Three-dimensional particle-in-cell simulations demonstrate that such fluctuations originate from the current filamentation instability arising at submicron scales around the irradiated target surface, and that they grow in a few tens of femtoseconds to amplitudes strong enough to broaden the angular distribution of the probe electron bunch.