Single-beam coherent anti-Stokes Raman scattering (CARS) spectroscopy of gas-phase CO_2 via phase and polarization shaping of a broadband continuum

摘要

Coherent anti-Stokes Raman scattering (CARS) spectroscopy of gas-phase CO_2 is demonstrated using a single femtosecond (fs) laser beam. A shaped ultrashort laser pulse with a transform-limited temporal width of ～7 fs and spectral bandwidth of ～225 nm (～3500 cm~(?1)) is employed for simultaneous excitation of the CO_2 Fermi dyads at ～1285 and ～1388 cm~(?1). CARS signal intensities for the two Raman transitions and their ratio as a function of pressure are presented. The signal-to-noise ratio of the single beam–generated CO_2 CARS signal is sufficient to perform concentration measurements at a rate of 1 kHz. The implications of these experiments for measuring CO_2 concentrations and rapid pressure fluctuations in hypersonic and detonation-based chemically reacting flows are also discussed.