Optical vortex-based spectroscopy for particle diagnostics

抄録

This study presents an approach for plasma flow diagnostics employing optical vortex beams with helical wavefronts. Although flow velocities perpendicular to the optical axis cannot be measured using conventional laser spectroscopy, this limitation is overcome herein by applying the azimuthal Doppler effect inherent in optical vortices. Specifically, we demonstrate quantitative velocity measurements of argon metastable atoms in a radio-frequency plasma using optical vortex laser absorption spectroscopy. Moreover, by introducing asymmetry into the beam intensity distribution, the asymmetric optical vortex laser-induced fluorescence method enables the determination of three-dimensional flow velocity vectors from a single laser path. Overall, these results indicate the promise of this diagnostic approach for complex plasma flows with limited optical access.