Ro-vibrational spectroscopy in hybrid fs/ps- CARS for N 2 thermometry

Ro-vibrational CARS spectroscopy is performed on the Q-branch of N 2 in the hybrid fs/ps regime. A new optical setup has been mounted using a single laser source and a spectral filtering stage based on a volume Bragg grating and a Fabry-Perot etalon, in order to achieve a good enough resolution. CARS spectra are recorded in ambient air at a 1 kHz repetition rate. However, a CH 4 /air flame is probed at 2 Hz, in order to obtain a strong enough signal to enable thermometry. The theoretical treatment is also detailed and provides the calculated spectrum, properly compared to experimental profiles in order to retrieve the temperature. The accuracy of the hybrid fs/ps CARS thermometry is satisfactory as regards the state of the art, but further experiments are in progress to increase the repetition rate of the measurement in hot gases.