• coherent anti-Stokes Raman scattering;
  • ultrafast spectroscopy;
  • concentration measurement;
  • gas sensing

Hybrid femtosecond/picosecond (fs/ps) vibrational coherent anti-Stokes Raman scattering was demonstrated for high-speed, in-situ measurements of CH4/N2 mole fractions in binary gas mixtures with temporal nonresonant suppression. A single broadband, 100-fs laser source was used to simultaneously excite CH4 and N2 vibrational Raman transitions, characterized by a spectral separation of ~584 cm−1, followed by frequency-domain detection with a time-delayed ps probe pulse. In this manner, the temporal evolution of the nonresonant background and vibrational wavepackets of CH4 and N2 could be evaluated to maximize signal and minimize interferences. A typical accuracy of ~95% was achieved for experimental CH4 mole fractions between 0.02 and 0.70, and a precision of ~4% was achieved by maximizing relative excitation energy through induced chirp in the pump and Stokes pulses. It was further shown that mole-fraction measurements were not affected by variations in bi-molecular broadened linewidths over a wide range of mixture fractions. Copyright © 2013 John Wiley & Sons, Ltd.