Femtosecond dynamics of energetic electrons in high intensity laser-matter interactions

Abstract

Highly energetic electrons are generated at the early phases of the interaction of short-pulse high-intensity lasers with solid targets. These escaping particles are identified as the essential core of picosecond-scale phenomena such as laser-based acceleration, surface manipulation, generation of intense magnetic fields and electromagnetic pulses. Increasing the number of the escaping electrons facilitate the late time processes in all cases. Up to now only indirect evidences of these important forerunners have been recorded, thus no detailed study of the governing mechanisms was possible. Here we report, for the first time, direct time-dependent measurements of energetic electrons ejected from solid targets by the interaction with a short-pulse high-intensity laser. We measured electron bunches up to 7 nanocoulombs charge, picosecond duration and 12 megaelectronvolts energy. Our ’snapshots’ capture their evolution with an unprecedented temporal resolution, demonstrat- ing a significant boost in charge and energy of escaping electrons when increasing the geometrical target curvature. These results pave the way toward significant improvement in laser acceleration of ions using shaped targets allowing the future development of small scale laser-ion accelerators.

Review on TNSA diagnostics and recent developments at SPARC_LAB

“…Figure 14(c) shows data captured from the tip target: the interaction with the laser produced a much larger number of fast electrons (about 7 nC), carrying also higher energies (about 12 MeV). Direct evidence of charge and energy boosts when using sharp tips can be (c) to avoid saturation of the CCD camera [28] . Figure 15.…”

“…In the following, we provide a review of the different diagnostics employed in laser-target interaction experiments related to electron, proton and ion acceleration. Finally, we present our recently developed non-destructive, single-shot, temporally resolved diagnostic [28][29][30][31] based on electro-optical sampling (EOS) [32] , able to record with femtosecond resolution ultrashort EMPs and fast electrons emitted from solid targets during the interaction, previously adopted just in accelerator physics. Our diagnostic is able to provide a more detailed picture of this phenomenon at the sub-picosecond timescale, highlighting its ultra-fast dynamics.…”

Electro-optic spatial decoding on the spherical-wavefront Coulomb fields of plasma electron sources

“…The wavefront of the Coulomb field signal has an incident angle of θ s = 0 to the EO crystal surface. In such a geometry, a linear temporal mapping relationship c Δ τ = Δ ξ tan θ p was utilized to deduce the timing information from the measured EO signal 28 , 30 , 33 , 35 , where Δ τ is the timing difference, Δ ξ denotes the observed displacement on the CCD and θ p is the relative angle between probe laser and electron beams. Up to now, non-destructive single-shot EO spatial decoding diagnostics and the corresponding temporal mapping relationship in LWFA have not yet been investigated.…”

Mapping the Damping Dynamics of Mega-Ampere Electron Pulses Inside a Solid

“…In particular, their "transit time" effectively determines the efficiency of energy transfer and the duration of emissions arising from the interaction. There have, however, been some attempts to measure dynamics of energetic electrons at rear of thin targets using (a) time-resolved reflectivity [14], (b) interferometry [15], or (c) measurement of the electric field [16]. There have also been studies of the dynamics inside the target using x-ray spectroscopy [17].…”