The proton and deuteron yields from thin targets irradiated by a picosecond laser pulse with an average radiation intensity of ≤4 × 10 ¹⁸ W/cm² at the target were measured in the megaelectron-volt energy range. A ring structure was observed for the outgoing ions, and the angular ion-beam divergence was found to be extremely small (0.5°). The fast-ion generation mechanism allowing for the appearance of ring structure is discussed, and the characteristic energies and spatioangular ion-beam distribution are estimated.