By means of the numerical study of the dynamics of a plasma irradiated by a
n ultraintense laser beam, we analyze two major effects induced by the rela
tivistic dynamics of the target's particles. First, we show how the magneti
c term in the Lorentz force leads to inhomogeneities in the plasma surface-
charge density. We demonstrate that the induced inhomogeneities are regular
when the impinging field intensity has a uniform transversal profile. This
regularity gives rise to a grating-like structure, which may be detected b
y observation of the held reflected by the plasma target. The second effect
studied is linked with the anisotropic character of the Lienard-Wiechert f
ields associated with the plasma particles. This velocity-dependent anisotr
opy enhances plasma oscillations as the plasma particles quiver in response
to the incident electromagnetic wave. The result of this plasmon enhanceme
nt may be observed by inspection of the harmonic intensities of the light t
ransmitted by a thin plasma slab irradiated by a high-intensity laser beam.