Spectrum of an anti-Stokes Raman ion laser in Λ-schemes with various level parameters

The dependence of the Raman-laser output power in a standing-wave mode on the pump frequency located near the resonance with ionic levels is studied. The emission spectra in two Λ-schemes of Ar II with different lifetimes of the final levels are compared. In the scheme with a long-lived final state, a sharp peak with an amplitude exceeding the amplitude of a broad contour by a factor of 1.5 — 2 is observed at the exact resonance, whereas no spectral features are observed near the resonance in the scheme with a short-lived final level. The effect is analysed within the framework of a model taking into account the Coulomb scattering of ions. It is shown that the peak forms due to a difference in the broadening of the Bennett structures in the population distribution of the operating levels over velocities. In the second Λ-scheme, the contribution of the final level is small in amplitude, and a sharp peak in the spectrum disappears in accordance with the predictions of the model.