Nonlinear increase in the interaction efficiency of a second pulse with a target upon excitation of a plasma by a train of pulses from a Nd:YAG laser

The efficiency of hole drilling in an aluminium plate was studied experimentally upon excitation of a plasma on its surface in air by a train of pulses from a Nd:YAG laser, the interval between pulses being 15 — 20 μs. It was found that the crater depth increases nonmonotonically with each successive pulse of the train. A nonlinear, more than by a factor of six, increase in the depth was detected upon interaction of the second pulse with the target. The mechanism explaining this increase in the interaction efficiency of the second pulse in the train with the target is proposed.