  It is well known that Brunel's vacuum heating mechanism is operative for
laser energy absorption when the target plasma density rises sharply. For
non-relativistic laser intensities and planar targets it is also necessary that
the laser should strike the target at oblique incidence. The laser electric
field at oblique incidence has a component normal to the surface to extract
electrons from the target in the vacuum region for Brunel's mechanism to be
operative. At relativistic laser intensities, oblique incidence is not
necessarily required as the J x B force is significant and can extract
electrons from the target even when the laser is at normal incidence. In this
manuscript, the interaction of short and intense laser pulse with structured
overdense plasma targets have been studied using 2D particle-in-cell
simulations. It is shown that for structured targets the absorption increases
many fold. A detailed study and understanding of the absorption process for the
structured targets in terms of structure scale length and amplitude have been
provided.
