Polarization suppression of the nonresonant background in femtosecond coherent anti-Stokes Raman scattering for flame thermometry at 5 kHz.

Coherent anti-Stokes Raman scattering (CARS) spectra are acquired at 5 kHz in steady and unsteady flames while suppressing the nonresonant background by polarization techniques. Broadband femtosecond (fs) pump and Stokes pulses efficiently excite many Raman transitions in diatomic nitrogen which subsequently interfere and decay. Single-laser-shot measurements are performed as the decay of the Raman coherence is mapped to the frequency of the CARS signal by a chirped-probe pulse (CPP).