High resolution laser induced fluorescence Doppler velocimetry utilizing saturated absorption spectroscopy

Area of Science:

• Plasma Physics
• Atomic and Molecular Physics

Background:

• Understanding neutral particle dynamics is crucial for plasma process control.
• Electron-cyclotron-resonance (ECR) plasmas are widely used in materials processing and fusion research.
• Accurate measurement of neutral flow velocity is challenging.

Purpose of the Study:

• To develop a high-resolution laser induced fluorescence (LIF) system for measuring neutral particle flow velocity.
• To achieve high accuracy in velocity determination using Doppler shift.
• To investigate neutral particle flow in an ECR argon plasma.

Main Methods:

• Developed a high-resolution laser induced fluorescence (LIF) system.
• Integrated a saturated absorption spectroscopy unit for precise wavelength calibration using Lamb dip and Fabry-Perot fringes.
• Measured Doppler shift of LIF spectra from argon metastable atoms to determine velocity distribution function.

Main Results:

• Achieved a minimum detectable flow velocity of +/-2 m/s with stable long-time performance.
• The system accurately determines flow velocity via Doppler shift, proportional to the velocity distribution function.
• Radial measurements revealed an inward flow of neutral particles associated with neutral depletion.

Conclusions:

• The developed LIF system offers high accuracy and sensitivity for neutral flow velocity measurements in ECR plasmas.
• The findings indicate an inward neutral particle flow, contributing to neutral depletion phenomena.
• This technique provides valuable insights into neutral transport mechanisms in plasmas.