Vibration–rotation interaction in time‐resolved coherent anti‐Stokes Raman scattering for gas‐phase thermometry

Abstract

Different approaches to the vibration–rotation (VR) interaction in time‐resolved intensities of coherent anti‐Stokes Raman scattering (CARS) of light homonuclear diatomics (namely H2, N2 and O2) are here compared in view of the diagnostic refinement of the technique that has an acknowledged thermometric potential for studies in combustion science. From this perspective, VR interaction is treated in agreement with past works about conventional or frequency‐resolved CARS, and although the current theoretical context refers to optical nonlinearities excited by ultrashort laser pulses, the results confirm the strong sensitivity of H2 CARS to the VR interaction quantified by means of the Herman–Wallis (HW) factor. Indeed, depending on the model of the interaction, time‐resolved H2 signals can be subject to indeterminations on the order of 10% leading to relevant thermometric inaccuracies. Heavier diatomics are less sensitive, but the choice of an appropriate HW factor can contribute to improve the confidence in CARS thermometry with ultrashort laser pulses. Copyright © 2012 John Wiley & Sons, Ltd.