1-D imaging of rotation-vibration non-equilibrium from pure rotational ultrafast coherent anti-Stokes Raman scattering

• Published in: Optics letters 2020-08, Vol.45 (15), p.4252-4255
• Main Authors: Chen, Timothy Y., Goldberg, Benjamin M., Patterson, Brian D., Kolemen, Egemen, Ju, Yiguang, Kliewer, Christopher J.
• Format: Article
• Language: English
• Subjects: Coherent scattering; Doppler effect; Energy levels; Energy transfer; Hypersonic flow; Low temperature; Molecular rotation; Nitrogen plasma; Plasmas (physics); Raman spectra; Red shift; Rotational spectra; Spatial distribution; Spatial resolution; Vibration measurement
• ISSN: 0146-9592; 1539-4794
• DOI: 10.1364/OL.394122

We present one-dimensional (1-D) imaging of rotation-vibration non-equilibrium measured by two-beam pure rotational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS). Simultaneous measurements of the spatial distribution of molecular rotation-vibration non-equilibrium are critical for understanding molecular energy transfer in low temperature plasmas and hypersonic flows. However, non-equilibrium CARS thermometry until now was limited to point measurements. The red shift of rotational energy levels by vibrational excitation was used to determine the rotational and vibrational temperatures from 1-D images of the pure rotational spectrum. Vibrational temperatures up to 5500 K were detected in a C H 4 / N 2 nanosecond-pulsed pin-to-pin plasma within 2 mm near the cathode. This approach enables study of non-equilibrium systems with 40 µm spatial resolution.