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We report the development of a simple and sensitive two-beam hybrid femtosecond/picosecond pure rotational coherent anti-Stokes Raman scattering (fs/ps CARS) method to simultaneously measure the rotational and vibrational temperatures of diatomic molecules. Rotation–vibration non-equilibrium plays a key role in the chemistry and thermalization in low-temperature plasmas as well as thermal loading of hypersonic vehicles. This approach uses time-domain interferences between ground state and vibrationally excited N2molecules to intentionally induce coherence beating that leads to apparent non-Boltzmann distributions in the pure rotational spectra. These distortions enable simultaneous inference of both the rotational and vibrational temperatures. Coherence beating effects were observed in single-shot fs/ps CARS measurements of a 75 Torr N2DC glow discharge and were successfully modeled for rotational and vibrational temperature extraction. We show that this method can be more sensitive than a pure rotational fs/ps CARS approach using a spectrally narrow probe pulse. Lastly, we experimentally measured the beat frequencies via Fourier transform of the time-domain response and obtained excellent agreement with the model.
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Comparison of rotational and vibrational thermometry of detonation in microchannels
Vibrational and rotational temperatures in various detonation conditions involving diluted hydrogen-oxygen mixtures were studied in a microscale detonation tube using hybrid fem- tosecond/picosecond Coherent anti-Stokes Raman scattering (hybrid fs/ps CARS). Measured temperatures at various locations behind the shockwave were compared to Chapman-Jouguet conditions as predicted by equilibrium calculations. Simultaneous shadowgraphy was also employed to establish timing between the detonation wave and laser beams. Comparison between vibrational nitrogen and oxygen thermometry were made for detonations in the same gas mixture. Oxygen rotational temperature was measured and compared to vibrational temperature measured in a similar gas mixture.
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- Award ID(s):
- 1839551
- PAR ID:
- 10517951
- Publisher / Repository:
- American Institute of Aeronautics and Astronautics
- Date Published:
- Journal Name:
- AIAA SCITECH 2023 Forum
- ISBN:
- 978-1-62410-699-6
- Format(s):
- Medium: X
- Location:
- National Harbor, MD & Online
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.2514/6.2023-2254
