Suppression of Raman-resonant interferences in rotational coherent anti-Stokes Raman spectroscopy using time-delayed...

Area of Science:

• Molecular spectroscopy
• Laser-based diagnostics
• Combustion analysis

Background:

• Coherent anti-Stokes Raman spectroscopy (CARS) is a powerful technique for gas-phase analysis.
• Accurate temperature and concentration measurements are crucial for understanding combustion processes.
• Traditional CARS methods can be affected by resonant interference and spectral smearing.

Purpose of the Study:

• To investigate the impact of time-dependent, delayed probing on pure-rotational CARS spectra.
• To assess the feasibility of using delayed probing for accurate temperature and concentration measurements in gas mixtures and flames.
• To minimize resonant contributions and vibrational interference in rotational CARS.

Main Methods:

• Picosecond lasers were used to measure time-dependent pure-rotational CARS spectra.
• Spectra were acquired for various gases (N(2), O(2), CO(2), C(2)H(4), C(3)H(8)) at room temperature and in a C(3)H(8) diffusion flame.
• Delayed probe techniques were applied to isolate rotational coherences.

Main Results:

• Raman coherences for N(2) and O(2) were observed to persist significantly longer than for other species.
• Delayed probing effectively reduced unwanted resonant contributions to rotational CARS spectra.
• Interference from smeared vibrational CARS was eliminated by delayed probing.
• Probe delay influenced the inferred temperature and relative O(2)/N(2) concentrations.

Conclusions:

• Delayed probing is a valuable technique for enhancing the accuracy of temperature and concentration measurements using pure-rotational CARS.
• This method enables precise determination of O(2)/N(2) concentrations in fuel-rich environments.
• The findings are significant for advanced combustion diagnostics and chemical kinetics studies.