title: Probe-pulse optimization for nonresonant suppression in hybrid fs/ps coherent anti-Stokes Raman scattering at high temperature.
abstract: Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) offers accurate thermometry at kHz rates for combustion diagnostics. In high-temperature flames, selection of probe-pulse characteristics is key to simultaneously optimizing signal-to-nonresonant-background ratio, signal strength, and spectral resolution. We demonstrate a simple method for enhancing signal-to-nonresonant-background ratio by using a narrowband Lorentzian filter to generate a time-asymmetric probe pulse with full-width-half-maximum (FWHM) pulse width of only 240 fs. This allows detection within just 310 fs after the Raman excitation for eliminating nonresonant background while retaining 45% of the resonant signal at 2000 K. The narrow linewidth is comparable to that of a time-symmetric sinc2 probe pulse with a pulse width of ~2.4 ps generated with a conventional 4-f pulse shaper. This allows nonresonant-background-free, frequency-domain vibrational spectroscopy at high temperature, as verified using comparisons to a time-dependent theoretical fs/ps CARS model.
authors: Department of Mechanical Engineering, Iowa State University, Ames, IA 50011, USA.
authors: Joseph D
authors: JD
authors: Miller
authors: Mikhail N
authors: MN
authors: Slipchenko
authors: Terrence R
authors: TR
authors: Meyer
mesh_terms: D003198:Computer Simulation; D008027:Light; D008962:Models, Theoretical; D012542:Scattering, Radiation; D013059:Spectrum Analysis, Raman / Q000379:methods*