A structure-based
laser accelerator harnesses technological progress developed by laser
and optical fiber industries, potentially facilitating a compact and
efficient system. In the optical regime, dielectrics sustain higher
electric fields and gradients of the order of a few GV/m may become
available, but the acceleration structures are different than those
used in the microwave regime. Various dielectric structures have been
analyzed and from the pure accelerator parameters perspective (gradient,
interaction impedance, group velocity, wake-fieldss), their performance
is of great promise. Operation similar to current linear accelerators
may lead to a prohibitively low efficiency therefore, including a feedback
attached to each module may improve the efficiency from a few percents
to higher than 90% -- in fact, the efficiency is limited only by the
constraints on the stability of the optical system. Single mode operation
in the optical regime imposes that at least one of the dimensions of
each micro-bunch ought to be sub-micronic leading to a stringent constraint
on the emittance and thus on the luminosity. Attempting to increase
the latter, imposes high energy density in the vacuum tunnel as well
as in its adjacent dielectric layer(s). This in turn is bounded by the
maximum stress dielectrics can sustain at these scales, temperature
increase and head dissipation as well as non-linearities. Beam-stability
considerations in the configurations of interest will be discussed as
well.