Investigations of laser plasmas dynamics by means of real and virtual Langmuir Probes

In this paper we propose a novel technique for LPP-Laser Produced Plasmas investigation, combining high time resolved measurements using compact Langmuir Probes with the output of a theoretical model called HYBLAS developed on purpose, which is able to simulate the charged particles collected by a so-called virtual probe. It will be shown that with an appropriate experimental set-up and with the use of a Matlab software able to accurately analyze the experimental I-V curves, laser plasmas can be investigated properly even if the probe is placed very close to the target surface. This permits not only to study the plume expansion with a high temporal resolution, but also to estimate correctly the self-generated coulomb electric field inside the plume and to detect the inner structure of the the first upcoming expanding plasma. HYBLAS is able to predict and describe the plume expansion at relatively low power densities and is a powerful method to compare directly the experimental current signals with the numerical results if the initial conditions are setted properly. A direct comparison of the theoretical data with the experimental ones realized on different metal targets shows that our method is able to predict properly the overall plasma expansion in the nanosecond laser pulse duration regime. The virtual probe method was moreover tested by comparing the numerical results with another numerical code called MULTI, which simulate the expansion by combining the hydrodynamics equations to a multigroup method in order to include the radiation transport.