Single‐beam coherent anti‐Stokes Raman scattering (CARS) spectroscopy of gas‐phase CO₂ via phase and polarization shaping of a broadband continuum

Abstract

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.

Hybrid fs/ps rotational CARS temperature and oxygen measurements in the product gases of canonical flat flames

“…The present work additionally provides a quantitative assessment of single-shot species measurements (O 2 /N 2 ) in flames using femtosecond CARS. Previous work [17,35,48,49,34] has provided demonstration of species detection in low-temperature gas cells and furnaces with well-defined mixtures, or qualitative species imaging [50,51]. This study extends the technique to quantitative concentration monitoring in flame environments with simultaneous temperature measurement.…”

Communication: Comment on the effective temporal and spectral resolution of impulsive stimulated Raman signals

“…3,4 Pulse shaping techniques have been used for manipulating these signals. [5][6][7] Impulsive stimulated Raman scattering uses femtosecond pulses to measure simultaneously molecular vibrations over a broad bandwidth. [8][9][10] It has been argued that by using a combination of a femtosecond and a picosecond pulse it is possible to achieve both high spectral and temporal resolution that exceed the fundamental transform limit.…”

Chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering concentration measurements

“…Related to concentration measurements, the effect of gas-phase composition on fs CARS temperature measurements has been investigated [26]. Single-beam fs CARS has been demonstrated for high repetition rate, single laser shot concentration measurements of diatomic nitrogen [27] and carbon dioxide [28]. Binary phase shaping with single-beam fs CARS has also been demonstrated for selective excitation of carbon dioxide, oxygen, and nitrogen [29] and to measure group velocity dispersion in combustion-related gases at elevated pressures [30].…”