Hybrid fs/ps Rotational CARS Temperature and Concentration Measurements Using Two Different ps-Duration Probe Beams

A hybrid fs/ps pure-rotational CARS scheme is characterized for thermometry in furnace-heated air at temperatures from 290 to 800 K. Impulsive femtosecond excitation is used to prepare a rotational Raman coherence that is probed with a ps-duration beam generated from an initially broadband fs pulse that is bandwidth limited using air-spaced Fabry-Perot etalons. CARS spectra are generated using 1.5- and 7-ps duration probe beams with corresponding coarse and narrow spectral widths. The spectra are fitted using a simple phenomenological model for both shot-averaged and single-shot measurements of temperature and oxygen mole fraction. Our single-shot measurements exhibit high levels of precision when the spectrally coarse 1.5-ps probe beam is used. This systematic assessment of the hybrid CARS technique demonstrates its utility for practical application in moderatetemperature gas-phase systems.