High-spatial-resolution one-dimensional rotational coherent anti-Stokes Raman spectroscopy imaging using counterpropagating beams

A counterpropagating phase-matching geometry is employed for high-spatial-resolution one-dimensional (1D) imaging of temperature and O₂-to-N₂ concentration ratio using picosecond pure-rotational coherent anti-Stokes Raman spectroscopy (RCARS) over a large field (20 mm). A single-shot 1D RCARS image of more than 20 mm in length is thus acquired at 300 K in air. High-resolution 1D RCARS flame measurements are demonstrated using a custom-built burner and a premixed methane/air flame (Φ=0.6). This phase-matching scheme improves the spatial resolution by approximately 1 order of magnitude when compared to the standard small-angle BOXCARS phase-matching schemes typically employed in CARS measurements. Additionally, for a 20 mm 1D image, signal levels are increased by 10² because of the higher irradiance provided in the current scheme.