Single-laser-shot femtosecond coherent anti-Stokes Raman scattering thermometry at 1000 Hz in unsteady flames

Temperature measurements at 1000 Hz in driven and turbulent flames are performed using single-laser-shot femtosecond coherent anti-Stokes Raman scattering (fs-CARS). A Hencken burner H2–air flame is driven at 10 Hz by means of a piston actuator in the air supply line. Temperature measurements are performed by fitting single-laser-shot fs-CARS spectra of N2. The probe pulse is chirped to map the temporal shape of the Raman coherence into the frequency domain of the CARS signal. The probe pulse is delayed by approximately 2 picoseconds (ps) compared to the simultaneous arrival of the pump and Stokes pulses at the probe volume. The method for calculating theoretical fs-CARS spectra is presented and the procedure for fitting theoretical to experimental spectra is explained. Previous fs-CARS measurements were performed in a heated gas cell and in laminar adiabatic flames. Measurements in a driven H2–air flame and a turbulent methane–air flame are discussed in this paper. fs-CARS spectra are acquired with excellent signal-to-noise ratios. Temperature excursions in the driven flame due to the movement of the piston actuator in the air line are clearly evident, as well as the fluctuations in the turbulent flame.