Spatial characterization of laser-induced plasmas: distributions of neutral atom and ion densities

Spatial distributions of temperature and relative number densities of Fe neutral atoms and ions in a laser-induced plasma have been measured by time- and space-resolved emission spectroscopy. The deconvolution of the intensity spectra has been carried out to obtain the local emissivity of neutral atom and ion lines as a function of the axial (z) and radial (r) coordinates. The plasma was generated with a Fe-Ni-Al alloy in air at atmospheric pressure using a Nd:YAG laser. The distributions present a dark region with negligible neutral atom and ion emissivities and densities, situated close to the sample surface at axial distances z≤1 mm. In the emitting region, the temperature has its maximum at the plasma axis (16000 K) and shows a monotonous decrease towards the border (6000 K). The neutral atoms and ions occupy regions corresponding to a great extent to different radial positions. At an axial distance z=1.8 mm, at which the maximum emissivities are produced, the maximum of the ion density is at r≅0.6 mm, whereas the neutral atom density maximum is at r≅1.3 mm.