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Enhancement of Doppler spectroscopy to transverse direction by using optical vortex
Hiroki Minagawa1, Shinji Yoshimura2,3, Kenichiro Terasaka4
1College of Industrial Technology, Nihon University, Narashino, Chiba, 275-8575, Japan.
Scientific Reports
|September 16, 2023
Summary
This study introduces optical vortex beams for tunable diode laser absorption spectroscopy (TDLAS), enabling particle flow velocity measurements perpendicular to the laser beam. This breakthrough overcomes limitations of conventional TDLAS in plasma-material interactions.
Area of Science:
- Plasma Physics
- Spectroscopy
- Fluid Dynamics
Background:
- Tunable diode laser absorption spectroscopy (TDLAS) is crucial for plasma diagnostics.
- Conventional TDLAS is limited to measuring flow velocities parallel to the laser beam.
- Observing perpendicular particle transport in plasma-material interactions requires new methods.
Purpose of the Study:
- To demonstrate the feasibility of measuring transverse particle flow velocities using TDLAS.
- To adapt TDLAS for applications in plasma-material interactions where perpendicular flow is dominant.
Main Methods:
- Replaced the conventional plane-wave probe beam with an optical vortex beam in TDLAS.
- Utilized the helical wavefront of the optical vortex to induce an azimuthal Doppler shift.
- Analyzed the sinusoidal variation of the azimuthal Doppler shift in the absorption spectrum.
Main Results:
- Successfully measured particle flow velocities perpendicular to the laser beam direction.
- Transverse flow velocity is determined from the amplitude of the azimuthal Doppler shift variation.
- Achieved measurement errors below 15% for velocities above 70 m/s, with a mean absolute percentage error under 8%.
Conclusions:
- Optical vortex beams enable TDLAS measurements of transverse flow velocities in plasmas.
- This technique overcomes the directional sensitivity limitations of conventional TDLAS.
- The method is particularly valuable for studying plasma-material interactions.
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