Laser-induced fluorescence measurements deformation of neutrals distribution function in the vicinity of a surface

Sheath region is of great interest for all plasma reactors and applications. Because this region is restricted to a few Debye lengths, it is impossible to make measurements with classical intrusive diagnostics like Langmuir probes. Laser Induced Fluorescence is a good way to access to the Argon neutral velocity distribution function in the vicinity of a conductive surface. We have made such measurements in a multipolar plasma device. Nevertheless, some artifacts can be present and must be taken into account. For example, the laser power absorption plays a significant role for high neutrals density. The non-elastic collision coefficient of neutrals with the surface is calculted with respect to the distance to the surface with a spatial definition of $0.1$mm. A neutral fluid acceleration with the distance to the surface is also observed which still remains to be explained.