Propagation of an intense Laser pulse in a cold electron-ion plasma is cons
idered. Starting with the fully relativistic equations, for pancake-shaped
pulses, a one-dimensional nonlinear Schrodinger equation is derived. It is
shown, in quasi-stationary stage, both localized and cusp solution exist an
d relativistic effects cause solitons to move slower as their amplitude inc
reases. These observations indicate particle-like behavior for localized so
lutions.