Time resolved spectroscopy

Emission spectroscopy is very often used as a diagnostic tool in the study of discharges, for example in recognising the presence of particular species within the discharge. Inferring even the relative concentrations of discharge species from emission measurements alone is however very difficult. This difficulty arises because the emission strength of specific lines or bands from the atoms or molecules of interest depends on a number of parameters. These include the radiative strength of the different lines, the quenching of the excited state by collisions within the plasma and the energy distribution of the electrons which determines the rate of collisional excitation of the state. If the atomic data is available and a particular electron energy distribution, usually Maxwellian, is assumed then often emissions measurements are used to estimate the relative concentrations of species. We have studied the sheath dynamics of a 13.56 MHz capacitively driven hydrogen discharge. This is a parallel plate device and was operated with pressures ranging from 6.7 to 133 Pa and at powers up to 150 W