Absolute atomic chlorine densities in a Cl ₂ inductively coupled plasma determined by two-photon laser-induced fluorescence with a new calibration method

Absolute densities of chlorine atoms were determined in an inductively coupled plasma in pure chlorine gas as a function of gas pressure and RF power by two-photon laser-induced fluorescence. A new technique is proposed to put the relative two-photon laser-induced fluorescence (TALIF) measurements on an absolute scale, based on photolysis of Cl ₂ gas (without plasma) with a tripled Nd:YAG laser at 355nm. Because the dissociation cross-section and photo-dissociation laser beam energy density are well known, the absolute densities can be determined with high accuracy. We find that the ratio of the Cl atom density normalized to the Cl ₂ gas density without plasma at the reactor centre increases with RF power and decreases with gas pressure, reaching 20% at 2mTorr 500W _RF.