Ultrabroadband coherent anti-Stokes Raman scattering for gas temperature and concentration measurements

The aim of this work was to investigate and extend the capability of the ultrabroadband CARS technique for temperature and concentration measurements for multiple species and a wide range of practical applications, especially for gasification diagnostics. Practical gasification or combustion devices mainly work under high pressures. Therefore, a sufficiently short probe pulse (~2 ps) was utilized for collision-free measurements. In order to simultaneously excite multiple gas species with Raman shifts up to ~4200 cm-1, a ~7 fs pump/Stokes beam was used. Both beams are generated by a 200 kHz BBO-based OPCPA system. Based on this configuration, the experimental methods and the theoretical framework for temperature and concentration determination were developed. The accuracy and precision of this technique was at first determined in a gas oven with controlled temperatures and gas flows. In this way, temperature measurements at temperatures from 295 K up to ~1300 K were performed with excellent accuracies within ~4%. The CO detection limit in CO2 atmosphere was extended to 0.5% at room temperature and 2% at 1073 K at a pressure of 1.4 bar. Temperature and concentration measurements were further extended to 20 bar and 10 bar, respectively. The influence of the ultrabroadband spectrum on the excitation efficiencies was investigated in detail. Subsequently, ultrabroadband CARS technique was applied for the first time for coal gasification investigations. Successful CARS analytical results were obtained even for the gasification process of a single coal particle.