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

Experiments on the excitation of propagating surface plasmons (SPs) by ultrashort, high intensity laser interaction with "grating" targets are reviewed. At intensities exceeding $10^{19}~\mbox{W cm}^{-2}$ on target, i.e. in the strongly relativistic regime of electron dynamics, multi-MeV 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 $\simeq $660 picoCoulomb. Intense XUV high harmonics (HH) diffracted by the grating are observed when a plasma with sub-micrometer scale is produced at the target surface by a controlled prepulse. When the SP is excited, the HH are strongly enhanced in a direction quasi-parallel to the electrons. Simulations show that the HH 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 rotating wavefront. This latter technique may be capable to produce nearly single-cycle SPs.