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8The 30th International Conference on Advanced Laser Technologies LD-I-5
ALT'23
Diode-laser spectroscopy of metastable atoms of heavy inert gases in
high-frequency discharge plasma
A. Chernyshov, P. Mikheyev, E. Fomin
Samara Branch of P.N. Lebedev Physical Institute of the Russian Academy of Sciences (SB LPI), 221, Novo-Sadovaya, Samara, 443011, Russian Federation
chak@fian. smr. ru
Determination of gas-discharge plasma parameters, such as gas temperature, electron number density and population of levels, by noninvasive spectral methods is simplified if the collision broadening and shift coefficients of the relevant spectral lines of the plasma-forming inert (or rare) gas are known. In 2012, lasers with optical pumping of metastable atoms of heavy rare gases, which are produced in a low-power electric discharge (OPRGL), were proposed [1]. At present, OPRGL is extensively studied as a chemically inert alternative to powerful diode pumped alkali metal vapor lasers. The interest in OPRGL aroused the need for reliable determination of the collision broadening and shift coefficients of infrared lines of rare gases, and especially for those transitions that are included in the laser cycle.
0 2 Av, GHz 0 20 40 PR Torr
Fig. 1. Neon line 703.2 nm: a) Processed absorption signal for a natural mixture of isotopes and transmission resonances of the reference interferometer (FSR = 750 MHz); b) Dependence of the Lorentzian line width WLCorr for the 20Ne isotope on the partial pressure of the disturbing gases. The coefficient of determination R2 close to unity confirms the linearity of the graphs.
The report discusses the technique for collisional broadening and shift coefficients measurements of the Ar*, Ne* and Kr* IR lines by diode-laser absorption spectroscopy. In particular, inaccuracy due to temperature gradients that occur in the discharge region of the measuring cell with flowing gas is estimated. The possibility of reducing the Stark broadening to the line width to a negligibly low level when inert gas atoms are excited to a metastable state using an RF discharge is discussed [2]. A probing radiation source with a continuous tuning range up to 100 GHz is proposed, consisting of a quantum-well diode laser with an additional dual-plate external reflector [2-4]. The use of fluorescent lamp starters as reference cells for measuring of Ar* and Ne* line shifts is described [3]. The report also discusses a data processing technique [2-5] that accounts for the existence of Ne and Kr isotopes and their influence on the profiles of the studied lines Fig.1. The developed technique eliminates the need to use expensive isotopically enriched rare gases for spectroscopic measurements. The assessment of the reliability of the obtained collisional broadening and shift coefficients was made by comparing their values with relevant data from literature and calculations.
[1] P. Mikheyev. Optically pumped rare-gas lasers, Quantum Electronics, vol. 45, pp. 704-708, (2015).
[2] P. Mikheyev, A. Chernyshov, N. Ufimtsev et al. Pressure broadening of Ar and Kr (n+1)s[3/2]2 ^ (n+1)p[5/2]3 transition in the parent gases and in He, J. Quant. Spectrosc. Radiat. Transfer., vol. 164, pp. 1-7, (2015).
[3] A. Chernyshov, P. Mikheyev, N. Ufimtsev. Measurement of pressure shift and broadening for Ar and Kr 4s[3/2]2 ^ 4p[5/2]3 transition in rare gases using diode-laser spectroscopy, J. Quant. Spectrosc. Radiat. Transfer., vol. 222, pp. 84-88, (2019).
[4] A. Chernyshov, P. Mikheyev, N. Ufimtsev. Measurement of pressure shift and broadening coefficients for Ne 3s[3/2]2 ^ 3p[5/2]3 transition in Ne and He using diode-laser absorption spectroscopy, J. Quant. Spectrosc. Radiat. Transfer., vol. 258, pp. 107368, (2021).
[5] A. Chernyshov, P. Mikheyev, N. Ufimtsev. Collisional broadening and shift coefficients for (n+1)s[3/2]2 ^ (n+1)p[1/2] 1 argon and neon lines in parent and foreign rare gases, J. Quant. Spectrosc. Radiat. Transfer., vol. 293, pp. 108381, (2022).
