Speaker
Description
The generation of strong, transient magnetic fields is a defining characteristic of relativistic laser-solid interactions, playing a pivotal role in phenomena ranging from Target Normal Sheath Acceleration (TNSA) to micro-turbulent plasma instabilities. When high-intensity laser pulses irradiate overdense plasma targets, they drive complex, high-current electron dynamics that rapidly manifest as strong volumetric magnetic fields. Because these fields evolve on femtosecond timescales and at submicron spatial dimensions, capturing their detailed spatiotemporal dynamics has long posed a significant diagnostic challenge. Understanding these field generation mechanisms is essential, as they profoundly influence fast-electron transport, particle acceleration efficiency, and can provide a controlled platform for exploring laboratory astrophysics.
To resolve these ultrafast structures, we carried out a series of experimental campaigns at the Laboratoire d'Optique Appliquée (LOA) using a 100-TW, 1-Hz laser system1,2. We implemented a pump-probe scheme where laser-wakefield-accelerated (LWFA) electron beams were utilized as synchronized, low-emittance relativistic probes. By passing these high-energy electron bunches through the interaction zone, the strong magnetic fields deflected the probe particles, mapping the volumetric field profile directly onto the beam’s angular distribution. This deflectometry technique successfully captured the femtosecond-scale evolution of strong magnetic-field fluctuations. Complementary, fully relativistic particle-in-cell (PIC) simulations confirmed that these fluctuations grow to amplitudes capable of significantly broadening the probe bunch distribution just tens of femtoseconds after the laser pulse peak.
These results demonstrate the power of synchronized LWFA electron beams as a high-resolution, ultrafast diagnostic tool for extreme high-field plasma environments. By showing that relativistic electron probes can faithfully resolve transient field structures, these campaigns establish a robust framework for investigating the real-time dynamics of laser-driven plasma instabilities and particle acceleration mechanisms. Ultimately, these capabilities open new pathways for optimizing laser-driven ion sources, mitigating detrimental transport effects in fusion-relevant schemes, and deeping our understanding of cosmic magnetic field generation through scaled laboratory experiments.