Overtone spectroscopy in the blue region by cavity-enhanced absorption spectroscopy with a mode-locked femtosecond laser: application to acetylene

The wide spectral coverage and high sensitivity of mode-locked cavity enhanced absorption spectroscopy (ML-CEAS) are illustrated by the observation of a very high overtone transition of C2H2 in the blue spectral region (420 nm, 8 quanta of CH stretch excitation), which was easily accessed by frequency-doubling a mode-locked femtosecond Ti:Sa laser. The detection limit is about 10−8/cm. The rotational analysis of this Σu+–Σg+ parallel band, centred at 23 813.244 cm−1, is presented and the vibrational assignment is discussed.