Electromagnetic pulses from high intensity laser experiments with gas-density plasma*

Radio frequency (RF) electromagnetic radiation in the form of an electromagnetic pulse (EMP) resulting from high intensity laser plasma experiments has the potential to damage scientific diagnostics in experiments. Although solid-target laser EMP has been thoroughly studied, there is a dearth of published research with respect to to gas-density targets, even though EMP can still be catastrophic in such cases. Here we compare the EMP generated in a direct laser acceleration (DLA) experiment at the Texas Petawatt laser facility to that in a laser-wakefield acceleration (LWFA) experiment at the HERCULES laser facility at the University of Michigan, elucidating the mechanisms for the purpose of understanding the physics and developing mitigation strategies. In the Texas Petawatt, a 150-fs, 100 J laser pulse focused with a f/40 parabola on a supersonic hydrogen gas jet target with density from 10^18 cm^-3 to 10^19 cm^-3. In HERCULES, a 39 fs, 9 J laser pulse was focused with an f/40 parabola into a gas cell of nitrogen-doped helium with a measured electron density of about 4 x 10^18 cm^-3. The relative contribution of beam-electrons and non-beam electrons to the EMP will be discussed for both cases, as well as PIC simulations with experiment-relevant parameters