Pressure broadening of 772.376 and 772.421 nm argon lines and kinetics of argon metastable atoms

Abstract

Tunable diode laser absorption spectroscopy is used for recording the spectrally mixed profiles of argon 772.376 nm (2p7–1s5) and 772.421 nm (2p2–1s3) lines at different argon background pressures between 0.3 and 1 atmosphere. The absorbing atoms in the Ar*(1s5) and Ar*(1s3) metastable states are produced in a plane-to-plane dielectric barrier glow discharge operating at 20 kHz. The pressure broadening coefficient w and wavelength shift, s of the lines, deduced from the analysis of their variation versus pressure of recorded profiles, are w1=28.3 ± 2.0 pm (14.2 ± 1.0 GHz) and s1=11.5 ± 0.8 pm (-5.8 ± 0.4 GHz) for 772.376 nm line and w2=36.3 ± 0.5 pm (18.2 ± 0.3 GHz) and s2=12.8 ± 0.7 pm (-6.4 ± 0.4 GHz) for 772.4207 nm line, at 1 bar and 300 K. The progressive enhancement with argon pressure of the peak densities ratio [Ar*(1s3)]/[Ar*(1s5)], reaching 0.3 at 1 bar, reveals the importance of Ar-induced collisions for the population transfer from resonant 1s2 to the metasTable 1s3 state. Also, the time variation of Ar*(1 s) densities indicates the presence of a weak excitation channel outside the discharge current pulse initiated by the breakdown. This channel results from the heating of electrons by the electric field seen by the gas in the DBD gap.