Extreme high field plasmonics: Electron acceleration and XUV harmonic generation from ultrashort surface plasmons

Experiments on the excitation of propagating surface plasmons (SPs) by an ultrashort, high intensity laser interaction with grating targets are reviewed. At intensities exceeding 10¹⁹ W cm⁻² on target, i.e., in the strongly relativistic regime of electron dynamics, multi-megaelectronvolt electrons are accelerated by the SP field as dense bunches collimated in a near-tangent direction. By the use of a suitable blazed grating, the bunch charge can be increased up to ≈660 pC. Intense extreme ultraviolet high harmonics (HHs) diffracted by the grating are observed when a plasma with a submicrometer scale is produced at the target surface by a controlled prepulse. When the SP is excited, the HHs are strongly enhanced in a direction quasi-parallel to the electrons. Simulations suggest that the HHs are boosted by nanobunching in the SP field of the electrons which scatter the laser field. Besides the static and dynamic tailoring of the target density profile, further control of electron and HH emission might be achieved by changing the SP duration using a laser pulse with a rotating wavefront. The latter technique may allow the production of nearly single-cycle SPs.