Demonstrating the accuracy of terahertz absorption spectroscopy and cavity ringdown spectroscopy by a comparison of atomic oxygen density measurements

This work presents a comparison of absolute ground-state atomic oxygen densities measured with terahertz (THz) absorption spectroscopy and cavity ringdown spectroscopy (CRDS). All measurements were performed on the same capacitively coupled radio frequency oxygen discharge, for applied powers in the range of 20–100 W and gas pressures of 70 and 130 Pa. When preconditioning of the reactor walls was taken into account to ensure reproducibility of the results, the atomic oxygen densities obtained with THz absorption spectroscopy and CRDS were found to be in excellent agreement. It can be concluded that both of these techniques can be reliably used to measure line-of-sight integrated atomic oxygen densities with high accuracy.