Coulomb broadening of electromagnetically-induced transparency peak in CW argon ion laser

In spite of fast evolution of the solid-state and fiber lasers, argon ion lasers remain to be the most powerful sources of short-wave CW radiation with high spatial coherence. At the same time, the active media of argon ion lasers -- low-temperature plasma -- is a good object for study nonlinear spectroscopic phenomena. In this work, the Autler-Townes doublet corresponding to the field splitting of ionic energy levels and the peak of EIT (electromagnetically induced transparency) induced by high-power radiation of the single-frequency argon argon laser have been studied. The effects are observed in the absorption spectrum at adajacent transition in 3-level Λ-scheme of ArII by probe-field technique. In the argon-laser plasma the shape of the EIT resonance is influenced by ion-ion Coulomb scattering. It leads to a broadening of resonant structures that is added to the field broadening. The measured EIT peak appears about 1.5 times wider than theoretical one taking into account corresponding power broadening. It is shown that the 1.5 times difference is due to the Coulomb broadening.