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Time-domain modelling and thermometry of the CH4[formula omitted] Q-branch using hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering.
- Source :
-
Combustion & Flame . Feb2021, Vol. 224, p183-195. 13p. - Publication Year :
- 2021
-
Abstract
- We present time-domain measurements and modelling of the CH 4 ν 1 vibrational Q-branch, as well as simultaneous temperature acquisition from the CH 4 and N 2 vibrational Q-branches using broadband hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS). Accurate measurements with fs/ps CARS require knowledge of the time-domain response of the probed molecule at different temperatures and pressures. In this work, a fs/ps CARS model was developed for the CH 4 ν 1 Q-branch and validated using time-resolved probe delay scans at pressures between 70 and 600 Torr and temperatures between 295 and 1000 K. A simplified modified exponential energy gap model was used to determine the linewidths of the Raman transitions within the Q-branch. Total Q-branch linewidths for the entire explored parameter space were also determined from the probe delay scans. This enabled quantitative measurements of CH 4 with fs/ps CARS as well as the temperature through the hot bands of the CH 4 ν 1 Q-branch. With a broadband fs laser pulse in a two-beam phase matching scheme, the N 2 Q-branch and CH 4 ν 1 Q-branch were simultaneously measured in a heated cell, and the temperatures from each molecule's spectra was evaluated. The fitted temperatures corresponded well with differences ranging from 4 to 17%. It was also shown that exchanging 90% of CH 4 for N 2 or Ar at 295 K and 500 Torr did not significantly impact the normalized time-domain signal prior to a 100 picosecond probe delay. Spatially resolved one-dimensional (1-D) thermometry using the CH 4 Q-branch was also demonstrated with an imaged spatial resolution of 40 µm. With the developed model, 1-D quantitative measurements of CH 4 concentration and temperature can be measured with time resolution of tens of picoseconds. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00102180
- Volume :
- 224
- Database :
- Academic Search Index
- Journal :
- Combustion & Flame
- Publication Type :
- Academic Journal
- Accession number :
- 148123489
- Full Text :
- https://doi.org/10.1016/j.combustflame.2020.11.017