Detection of atomic oxygen and its electronic coherence decays using time-resolved ultrafast coherent Raman...

Area of Science:

• Spectroscopy
• Physical Chemistry
• Plasma Physics

Background:

• Atomic oxygen is a crucial reactive species in combustion and plasma processes.
• Accurate detection and characterization of atomic oxygen are essential for understanding these environments.
• Existing methods for atomic oxygen detection can be limited in sensitivity and scope.

Purpose of the Study:

• To report the detection of atomic oxygen using time-resolved hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (CARS).
• To quantitatively measure electronic Raman coherence decays of atomic oxygen in flames and low-temperature plasmas.
• To enhance signal-to-noise ratios (SNRs) for atomic oxygen detection and improve contrast with molecular oxygen signals.

Main Methods:

• Utilized time-resolved hybrid femtosecond/picosecond CARS spectroscopy.
• Employed Raman transitions between spin-orbit coupled triplet ground states of atomic oxygen.
• Generated atomic oxygen in an H2/O2/Ar diffusion flame and an O2/Ar pulsed plasma discharge.
• Measured coherence decays for O(3P2)-O(3P1) and O(3P2)-O(3P0) Raman transitions.

Main Results:

• Successfully detected atomic oxygen and measured its electronic Raman coherence decays.
• Observed single exponential decays for specific atomic oxygen Raman transitions.
• Obtained atomic oxygen Raman linewidths across a pressure range in plasma and at atmospheric pressure in a flame.
• Achieved enhanced atomic oxygen SNRs, up to sevenfold, by exploiting electronic triplet coherence beating.
• Found that vibrational excitation minimally impacts dephasing rates of diatomic molecular rotational CARS transitions.

Conclusions:

• Time-resolved hybrid femtosecond/picosecond CARS is effective for detecting atomic oxygen and measuring its coherence decays.
• The technique provides valuable data on atomic oxygen linewidths and dephasing dynamics in flames and plasmas.
• Exploiting coherence beating significantly improves SNR, enabling more sensitive atomic oxygen detection.
• Results support the assumption that vibrational excitation does not influence diatomic molecular rotational CARS dephasing.