Ion energy distributions in laser-produced plasmas with two collinear pulses

Abstract

The formation and expansion dynamics of laser-produced plasmas was studied by means of the effect of a second delayed laser pulse upon the ion kinetic energy of the plasma created by the first one. Two types of measurements were carried out: ion kinetic energy distributions and overall ion time of flight (t.o.f.). Ion energy distributions were obtained with an electrostatic energy analyser, which allowed the observation of the energy distributions of each charge state separately while the ion t.o.f. signal was measured with an ion probe. Laser power densities ranged from 2 × 108 to 2 × 109 W cm−2 with 532 nm photons, and studies were extended to Al, Cu and Co targets. The effects of the second laser pulse on the plasma created by the first were very different depending on the interpulse delay. At low delays (from 0 to 10 ns) the second pulse produced an increase of the plasma average charge state and the maximum ion kinetic energy, while at higher delays (>20 ns) it produced a strong enhancement on the low charge yield (especially the single-charge ions) leaving unaltered the energies and yields of the high charges. An analysis of variations in both ion yield and kinetic energy produced interesting results regarding fundamental understanding of plasma formation and expansion dynamics, as well as possible improvements in technological applications based on laser-produced plasmas.