Time and frequency-domain FS/PS cars measurements and modelling of the ch4 V₁ vibrational q-branch

With the increased interest in CH4 as a fuel for power generation, propulsion, and catalytic reforming, spatially and timeresolved quantitative measurements of CH4 are increasingly needed to advance these technologies. Hybrid fs/ps coherent anti-Stokes Raman scattering (fs/ps CARS) has been demonstrated to measure temperature and chemical species concentrations with tens of microns of spatial resolution on the picosecond time scale. However, accurate time-domain and frequency-domain models are necessary to understand the effect of probe delay on the fs/ps CARS signal. In this work, a time-domain model was developed for the CH4 1₁ vibrational Q-branch validated by delay scans across pressures ranging from 70 Torr to 600 Torr and furnace setpoint temperatures up to 1000 K. A simple modified exponential energy gap (MEG) law was implemented to fit to the room temperature delay scans to approximate the Q-branch linewidths. It was also found that changing the collisional partner did not influence the time-domain decay of the CH4 Q-branch signal prior to 100 picosecond probe delays. Comparison between simultaneously measured N2 Q-branch and CH4Qbranch spectra showed good agreement with evaluated temperatures.