Single-shot ultrafast coherent anti-Stokes Raman scattering of vibrational/rotational nonequilibrium

The study of internal molecular energy transfer is important for a variety of nonequilibrium and nonthermal environments, including plasma-based manufacturing and materials treatment, medical device treatment applications, and plasma-assisted combustion. In the current work, hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering spectroscopy is demonstrated for simultaneous, single-shot measurement of pure-rotational and rovibrational energy distributions in the highly nonequilibrium environment of a dielectric barrier discharge plasma. Detailed spatial distributions and shot-to-shot fluctuations of rotational temperatures spanning 325–450 K and corresponding vibrational temperatures of 1200–5000 K are recorded across the plasma and surrounding flow with high precision and accuracy. This approach allows concise measurements of vibrational/rotational energy distributions in nonequilibrium environments at kilohertz rates that are free of nonresonant background and minimize interference from molecular collisions.