Spatial profiles of metastable densities and electric field strengths in parallel-plate radio frequency discharges

Metastable densities and sheath electric field strengths have been measured in 13.56-MHz parallel-plate helium discharges. Absorption spectroscopy was used to measure the helium singlet metastable density throughout the volume of the discharge. The singlet metastable density appeared to be depleted near the center of the discharge region, particularly at higher powers. Spatially and temporally resolved sheath electric field strength was determined from laser-induced fluorescence measurements of the Stark structure of the n=11 singlet Rydberg manifold. Two-dimensional (2-D) maps of the electric field strength indicate that the field is uniform across a large fraction of the electrode diameter.