Interference-free hybrid fs/ps vibrational CARS thermometry in high-pressure flames.

Abstract

Interference-free hybrid femtosecond/picosecond vibrational coherent anti-Stokes Raman scattering (CARS) of nitrogen is reported for temperature measurements of 1300-2300K in high-pressure, laminar H2-air and CH4-air diffusion flames up to 10bar. Following coherent Raman excitation by 100fs duration pump and Stokes pulses, a time-asymmetric probe pulse is used for the detection of spectrally resolved N2 CARS signals at probe delays as early as ∼200-300 fs. This allows for full rejection of nonresonant contributions while being independent of collisions for single-shot precision of ±2% at elevated pressures. The effects of collisions at longer probe-pulse delays are also investigated to determine the feasibility of varying the detection timing from 200fs to 100ps.