Suppression of Raman-resonant interferences in rotational coherent anti-Stokes Raman spectroscopy using time-delayed picosecond probe pulses.

We measure time-dependent pure-rotational coherent anti-Stokes Raman spectroscopy (CARS) spectra for room-temperature N(2), O(2), CO(2), C(2)H(4), and C(3)H(8), as well as in a C(3)H(8) diffusion flame, using picosecond lasers. Because Raman coherences for N(2) and O(2) persist significantly longer than those for the other species, delayed probing can significantly reduce unwanted resonant contributions to rotational coherent anti-Stokes Raman spectroscopy spectra, enabling temperature and relative O(2)/N(2) concentration determination in fuel-rich gas mixtures. Delayed probing also eliminates interference from smeared vibrational CARS. Probe delay affects both the temperature and relative O(2)/N(2) concentrations inferred from rotational spectra when using a standard frequency-domain analysis.