Vibrational femtosecond/picosecond coherent anti-Stokes Raman scattering with enhanced temperature sensitivity for flame thermometry from 300 to 2400K

Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) of N-2 has recently been demonstrated for gas-phase thermometry in reacting flows, enabling frequency-domain detection at high repetition rates with excellent chemical specificity and independence from the effects of collisions and nonresonant background. In this work, we overcome the limited sensitivity of vibrational fs/ps CARS thermometry of N-2 below 1200K by spectrally resolving J-dependent rovibrational coherence revivals that occur 32ps after initial excitation. The N-2 rovibrational coherence is excited using broadband, 100-fs pump and Stokes pulses and probed as a function of time using a narrowband, 5.8-ps probe pulse (bandwidth of 2.5cm(-1)). The rovibrational features exhibit sufficient temperature sensitivity below 1200K for accurate thermometry using a simple, time-dependent phenomenological model. Specifically, three distinct spectral features at a single probe delay of 32.5ps are analyzed, corresponding to rovibrational revivals with mean rotational quantum numbers of < J >=3.5, 14, and 28. Good agreement is found between simulated and measured fs/ps CARS spectra in an adiabatic flat-flame burner from 298 to 2400K. Copyright (c) 2015 John Wiley & Sons, Ltd.