Void Investigations using Laser Diagnostics
Résumé
A particular feature of a 3D dust particle cloud trapped in a plasma, is the usual appearance in its centre of a dust-free region, the void. This region is defined by the equilibrium between an inward electrostatic force and an outward ion drag force. The plasma characteristics inside the void are drastically different than those of the surrounding dusty plasma. Experimentally it is easily observed through an enhanced plasma emission and a slightly different plasma colour. In this work, the void appears in a dust particle cloud grown from material sputtering in a capacitively-coupled rf discharge in Argon. The void is the place of many complex phenomena (dynamics, self-excited oscillations, growth of dust particle successive generations). In order to get reliable information about the plasma inside the void, non intrusive diagnostics must be used. For that purpose, optical emission spectroscopy and laser diagnostics are the most suitable. They can provide local information with a good spatial resolution. In some extent, spatiotemporal plasma changes can also be investigated. In this work we present preliminary results obtained by laser absorption and Laser Induced Fluorescence (LIF) on the void properties.