Ion and Atom Distributions Probing in Plasma via Wavelength-Modulated Laser-Induced Fluorescence

Laser-Induced Fluorescence (LIF) spectroscopy is a powerful tool for measuring spectral line profiles of ions or atoms in complex plasma conditions[1], commonly found in laboratory and industrial environments. These spectral line profiles represent Velocity Distribution Functions (VDFs), revealing crucial thermodynamic properties of plasma[2,3]. However, interpreting VDFs can be difficult due to overlapping distributions, various broadening mechanisms, or substantial background emission. We investigates the use of Wavelength Modulation (WM) spectroscopy, [4] a robust derivative spectroscopy technique[5], to address these challenges. Modern diode lasers, with their fast wavelength modulation capability, are ideal for obtaining derivative spectra through WM spectroscopy. The study combines modeling and experimental measurements to explore the use of WM spectroscopy for LIF measurements in plasma. The modeling demonstrated that WM LIF provides more reliable fitting in situations with low signal-to-noise ratio and complex VDF profiles, leading to more accurate identification of plasma dynamics. These modeling results were confirmed experimentally by examining weakly collisional argon plasmas with non-equilibrium VDFs using a tunable diode laser. The findings highlight the effectiveness of the WM approach in providing a more rigorous method for VDF analysis.

References

[1] J. Amorim, G. Baravian, and J. Jolly, J. Phys. D: Appl. Phys. 33, R51 (2000).

[2] S. Mazouffre, Plasma Sources Sci. Technol. 22, 013001 (2012).

[3] I. Romadanov and Y. Raitses, Review of Scientific Instruments 94, 073002 (2023).

[4] G. C. Mathews and C. S. Goldenstein, Opt. Lett. 42, 5278 (2017).

[5] D. G. Cameron and D. J. Moffatt, Appl. Spectrosc., AS 41, 539 (1987).