Subthreshold two-pulse time-delayed laser ionization of Cu

Two collinear frequency-doubled Nd:YAG laser pulses were used to study the temporal evolution of ion generation in Cu targets. The method is based on the decoupling of the total ionization energy using two individual laser beams operating at fluences below the ionization threshold. A maximum in the ion signal generated corresponding to a laser interpulse delay of 60 ns has been determined.