Diagnostics of laser-produced plasmas

Laser-produced plasmas are used for a variety of studies, relevant for both basic physics and applications, and are of course essential within the study of inertial confi nement approach to nuclear fusion. Because of this large interest, a large variety of diagnostics have been developed and are routinely used to unveil the physical processes at work during plasma process and laser-plasma interaction. Nevertheless, the diagnostics of laser-produced plasmas poses several challenges. First of all, laser-produced plasmas have a small volume and short duration. Typically, the size is comparable to the laser spot dimension (micrometer to millimeter) and the lifetime is also comparable to the laser pulse duration (after the end of the laser pulse the plasma rapidly cools down and vanishes). Hence, diagnostics usually need to have high spatial and temporal resolution. But indeed, the main challenge arises from the fact that the temperature and density of laser-produced plasmas span over several orders of magnitude and is characterized by the presence of very distinct plasma ‘regions’, which are all simultaneously present. 1) First, we have the ‘undercritical region’ (or plasma corona), which is defi ned by having a density smaller than the laser critical density, in practical units: