Laser-Driven Ultrafast Field Propagation on Solid Surfaces

The interaction of a 3×1019  W/cm2 laser pulse with a metallic wire has been investigated using proton radiography. The pulse is observed to drive the propagation of a highly transient field along the wire at the speed of light. Within a temporal window of 20 ps, the current driven by this field rises to its peak magnitude ∼104  A before decaying to below measurable levels. Supported by particle-in-cell simulation results and simple theoretical reasoning, the transient field measured is interpreted as a charge-neutralizing disturbance propagated away from the interaction region as a result of the permanent loss of a small fraction of the laser-accelerated hot electron population to vacuum

Impulsive electric fields driven by high-intensity laser matter interactions

The interaction of high-intensity laser pulses with matter releases instantaneously Ultra-large currents of highly energetic electrons, leading to the generation of highly-transient, large-amplitude electric and magnetic fields. We report results of recent experiments in which Such charge dynamics have been studied by using proton probing techniques able to provide maps of the electrostatic fields with high spatial and temporal resolution. The dynamics of ponderomotive channeling in underdense plasmas have been Studied in this way, as also the processes of Debye sheath formation and MeV ion front expansion at the rear of laser-irradiated thin metallic foils. Laser-driven impulsive fields at the surface of solid targets can be applied for energy-selective ion beam focusing

Relativistic Current Dynamics Investigations By Proton Probing

The proton probing technique has been used to investigate the incidence of a mid-l019 W cm-2 pulse with metalhc wire and laminar foam targets. Electric fields ∼ l010 V-m-1 are measured on the surface of the 125 μm-diameter wire in the wake of the laser interaction as it charges and discharges within a 20 ps temporal window, whilst the employment of a novel experimental technique permits the observation of the propagation of a charging front at ∼ c away from the point of interaction. In the foam shots, meanwhile, the behaviour of the hot electrons generated by the interaction pulse is probed inside the target. Evidence of electric inhibition effects and filamentation is found