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Hybrid fs/ps coherent anti-Stokes Raman scattering (CARS) is employed to investigate the vibrational temperature evolution of N2 in lean methane flames exposed to pulsed microwave irradiation. Vibrational temperature during and post microwave illumination by a 2 μs, 30 kW peak power, 3.05 GHz pulse is monitored in flames diluted with N2, N2 and CO2 , and N2 and Ar. Electric field strengths inside the microwave cavity are monitored directly using electric field probes. Temperature increases up to 140 K were observed in flames with additional Ar and CO2 dilution, whereas temperature increases by 80 K were observed in mixtures diluted with only N2 . The microwave energy deposition to excited states begins to thermalize over scales of 100 μs, however, equilibrium is not reached before excited combustion products convect out of the probe volume on the order of several 1 ms. Understanding the impact of varying bath gases on microwave interaction, magnitude of temperature rise and thermalization timescales is critical for the development and validation of new kinetic models for applications exhibiting significant degrees of thermal non-equilibrium, such as high-speed reentry flows and plasma-assisted combustion.
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This content will become publicly available on January 3, 2026
Coherent Control for Selective Excitation of Combustion Species in a Benchtop Flame Using fs/ps CARS
Hybrid fs/ps coherent anti-Stokes Raman scattering employing coherent control is presented for selective excitation of combustion-relevant species. Femtosecond pulse shaping is accomplished experimentally using a 4-f pulse shaper with a spatial light modulator at the Fourier plane. A feedback-controlled genetic algorithm for adaptive pulse shaping is used to optimize for the selective excitation of CO2 (near 1388 cm−1) and O2 (near 1556 cm−1) rovibrational transitions in a non-reacting flow. 0D fs/ps CARS measurements acquired in a near-adiabatic flame demonstrate the use of coherent control in a combustion environment.
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- Award ID(s):
- 2033675
- PAR ID:
- 10632742
- Publisher / Repository:
- American Institute of Aeronautics and Astronautics
- Date Published:
- ISBN:
- 978-1-62410-723-8
- Format(s):
- Medium: X
- Location:
- Orlando, FL
- Sponsoring Org:
- National Science Foundation
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