Using conventional methods, a laser pulse can be focused down to around $6–8\mu \mathrm{m}$, but further reduction of the spot size has proven to be difficult. Here it is shown by particle-in-cell simulation that with a hollow cone an intense laser pulse can be reduced to a tiny, highly localized, spot of around $1\mu \mathrm{m}$ radius, accompanied by much enhanced light intensity. The pulse shaping and focusing effect is due to a nonlinear laser-plasma interaction on the inner surface of the cone. When a thin foil is attached to the tip of the cone, the cone-focused light pulse compresses and accelerates the ions in its path and can punch through the thin target, creating highly localized energetic ion bunches of high density.

• Received 2 January 2008

DOI:https://doi.org/10.1103/PhysRevE.78.036405