Quantitative measurements of atomic oxygen using hybrid fs/ps CARS

Atomic radicals play a key role in plasma-enhanced deposition and etching of materials in semiconductor processing. However, there are few alternatives to two-photon laser-induced fluorescence for quantifying atomic species in situ. Here, we present hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) measurements of atomic oxygen using Raman transitions between ground state spin-orbit split energy levels. We demonstrate localized 1-D spatial distributions of rotational temperature and atomic oxygen profiles of nanosecond-pulsed pin-to-pin discharges in O₂/Ar mixtures. The use of hybrid fs/ps CARS enables the measurement of the Raman coherence decay times and associated linewidths of atomic oxygen. A strategy to enhance the relative signal-to-noise ratio of atomic oxygen by leveraging molecular oxygen electronic coherence beating will be discussed.