[en] The propagation in a rarefied plasma (n_e < or approx. 10¹⁵ cm^-3) of collisionless shock waves and ion-acoustic solitons, excited following the interaction of a long (τ_L∼470 ps) and intense (I∼10¹⁵ W cm^-2) laser pulse with solid targets, has been investigated via proton probing techniques. The shocks' structures and related electric field distributions were reconstructed with high spatial and temporal resolution. The experimental results were interpreted within the framework of the nonlinear wave description based on the Korteweg-de Vries-Burgers equation