Improvement of the precision of coherent anti-Stokes rotational Raman scattering for oxygen and oxygen containing gas mixtures

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Combustion based on pure oxygen instead of air as an oxidizer is getting more and more important for industrial processes, since this is a possibility to reduce the release of large quantities of climate changing CO2 into the atmosphere. In addition the lack of N2 results in a significant reduction of the NOx emissions. A further optimization of such processes requires a detailed knowledge and understanding of the oxy-fuel combustion process. Therefore experimental data with high temporal and spatial resolution are required. Non-invasive laser based measurement techniques like e.g. CARS are very well qualified for such measurement problems. Beside vibrational CARS nowadays rotational CARS is getting more and more into focus, since it can directly be used for a multi species detection. Nevertheless for a data evaluation a precise modeling of the rotational CARS spectra is necessary. Here is still a strong need for unknown S-branch Raman linewidths. These data are available for pure N2 but not for O2 and combustion relevant gas mixtures.The main objective of this project is to close this gap. By using the time delayed picoseconds rotational CARS technique it is possible to measure the decay rate of the Raman coherence for pure O2 and gas mixtures with O2. These decay rates can be used to calculate the corresponding S-branch Raman linewidths. These data will then help to improve the precision of the rotational CARS Technique for processes involving O2. In addition these correct linewidth information can be used to fit the empirical parameters within the CARS collision models.