  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.
