  In the frame of laser-driven wakefield acceleration, the main characteristics
oflaser propagation and plasma wave excitation are described, with an emphasis
onthe role of propagation distance for electron acceleration. To
optimizeinteraction length and maximize energy gain, operation at low plasma
density isthe most promising regime for achieving ultra-relativistic energies.
Among thepossible methods of extending propagation length at low plasma
density, laserguiding by grazing incidence reflection at the wall of dielectric
capillarytubes has several assets. The properties of laser guiding and the
measurement ofplasma waves over long distances are presented.
