Laser-induced fluorescence spectroscopy of and absolute density calibration by Rayleigh scattering in capacitively coupled rf discharges

Laser-induced fluorescence spectroscopy (LIF) was applied to measure absolute densities of the first metastable state in capacitively coupled rf discharges at 13.56 MHz. The metastable state was transferred to the B 3 Π g , v = 3 state with a dye laser at 687.44 nm and the fluorescence of the transition to the state was observed at 762 nm. The time-depending LIF signal was investigated and the effective lifetime of the B 3 Π g , v = 3 state was determined by eliminating the delay due to the photomultiplier circuit. The absolute density calibration was done by comparison with Rayleigh scattering at the laser wavelength of 687 nm. Therewith, axial density profiles were measured and their dependence on pressure and power was investigated. The metastable densities vary between 10 12 and 10 13 cm −3 for pressures from 40 to 1000 Pa. Furthermore, small amounts of oxygen (0.5–2%) were added and the influence on the metastable density is discussed.