We study plasmonic excitations in structured targets and their impact on laser-target coupling in a regime of high short pulse laser fields (~30fs) at irradiation intensities (1019-20 W/cm2) several orders of magnitude higher than the typical values used in ordinary plasmonics and such that nonlinear and relativistic effects play a major role. We aim at tuning the features of the SPW driven electron bunches in order to build and validate an ultra-short synchronized light and electron source, with potential applications in probing ultrafast electronic processes in systems of interest in chemistry, biology and material science
The theory of SPW excitation and resonance is well known only in the linear regime and most experiments so far have been restricted to intensities below 1016 W/cm2, unable to drive relativistic SPW because of the intense prepulses inherent to high-power laser systems which can lead to an early disruption of the necessary target structuring. Nonetheless, exploiting the ultra-high contrast 100 TW laser facility UHI100 in Saclay we recently observed, for the first time at our knowledge, the acceleration of an electron beam driven by SPW along the target surface (figure 1) and a strong enhancement of both the energy and the number of electrons emitted from gratings irradiated at an incidence angle close to the resonant value for SPW excitation when compared to flat targets (figure 2). High current (more than 600 pC) electron emission is concentrated in a narrow cone close to the target surface, with energy spectra peaking at 5-8 MeV and reaching up to ~20 MeV that we succeeded to reproduce with massively parallel 2D and 3D numerical simulations (fig. 2 in joint document). Building on this, our last year experimental activity was devoted to clear away most experimental bottlenecks concerning future characterization (i.e. bunch duration determination) and application devoted (i.e. SPW driven high order harmonics emission) experiments.
References :
Cantono, G.; Sgattoni, A.; Fedeli, L.; et al. Extensive study of electron acceleration by relativistic surface plasmons PHYSICS OF PLASMAS, 25, 031907 (2018)
Sgattoni, A.; Fedeli, L.; Cantono, G.; et al. High field plasmonics and laser-plasma acceleration in solid targets PLASMA PHYSICS AND CONTROLLED FUSION, 58, 014004 (2016)
Fedeli, L.; Sgattoni, A.; Cantono, G.; et al. Electron Acceleration by Relativistic Surface Plasmons in Laser-Grating Interaction PHYSICAL REVIEW LETTERS, 116, 015001 (2016)
Ceccotti, T.; Floquet, V.; Sgattoni, A.; et al. Evidence of Resonant Surface-Wave Excitation in the Relativistic Regime through Measurements of Proton Acceleration from Grating Targets PHYSICAL REVIEW LETTERS, 111, 185001 (2013)