Coulomb broadening in a three-level system is studied. Interference resonances are not broadened by collisions, differing from saturation resonances in this regard. Experimental spectra of generation on adjacent ion transitions and resonance fluorescence are interpreted. An increase in the output power of ion Raman lasers is predicted.
Coherent preparation of quantum states of atoms and ions by laser light can lead to electromagnetically induced transparency and related effects. In particular, the standing wave at the adjacent transition induces a new type of nonlinear resonance in the probe-field spectrum of a three-level system. The resonance is due to the effect of high-order harmonics of atomic coherence. However, the resonance is broadened and the reason of the broadening was unclear. The paper describes how the velocity changing collisions broaden the resonance. The analytic theory taking into account up to 4-th order of the perturbation theory is presented. The numerical calculations are described. The analytical formulas are shown to describe the experiment qualitatively while the numerical computation demonstrates quantitative agreement. The Coulomb dephasing is discussed as the physical mechanism of the broadening.
The Coulomb broadening of a magneto-optical resonance of degenerate two-level ions in the field of a standing wave is calculated. Under the conditions of linear polarisation of this wave, of the normal Zeeman effect, and of weak saturation, the broadening is described by familiar expressions for multistage and two-photon resonances in separate three-level subsystems and the coefficients in these expressions depend on the angular momenta. The profile of a nonlinear resonance in the dependence of the output power of a single-frequency Zeeman ionic laser on the applied magnetic field consists of a narrow central interference peak, a wide diffusion part, and Lorentzian wings. It is shown that, in the case of a broad lower active level, the J → J+1 transitions are more favourable for the observation of a two-photon resonance and the relative amplitude of the resonance is not less than 2/7.
Coherent preparation of quantum states of atoms and ions by laser light can lead to electromagnetically induced transparency and related effects. In particular, the standing wave at the adjacent transition induces a new type of nonlinear resonance in the probe-field spectrum of a three-level system. The resonance is due to the effect of high- order harmonics of atomic coherence. However, the resonance is broadened in experiment and the reason of the broadening was unclear. The paper describes how the velocity changing collisions broaden the resonance. The analytic theory taking into account up to 4-th order of the perturbation theory is presented. The numerical solution of density matrix equations is discussed. The analytical formulas are shown to describe the experiment qualitatively while the numerical computation demonstrates quantitative agreement. The Coulomb dephasing is shown to be the physical mechanism of the broadening.
Continuous-wave generation of an anti-Stokes Raman laser on a number of blue-green argon-ion lines (4p-4s and 4p-3d) has been demonstrated with optical pumping from metastable levels 3d∣IH2G and 3d4F. It is found that the population transfer rate is increased by a factor of 3--5 (and hence the output power of the Raman laser) owing to Coulomb diffusion in the velocity space. The excitation and relaxation rates for the metastable level have been measured. The Bennett hole on the metastable level has been recorded using the probe field technique. It has been shown that Coulomb diffusion changes the shape of the contour to an exponential cusplike profile. Its width exceeds the Lorentzian one by 100 times and is close to the Doppler width. Such a giant broadening is also confirmed by the shape of the absorption saturation curve.
The problem of probe-field spectrum is considered for a three-level ion placed in a field of an intense standing light wave. The ion interaction with plasma and the velocity-changing Coulomb scattering are taken into account within the weak-collision model. The system of kinetic equations for the density matrix is solved by the expansion in spatial harmonics and eigenfunctions of the collision operator. The profile of nonlinear addition to the probe-wave absorption is determined for various values of the effective ion-ion collision frequencies and various amplitudes and frequencies of standing wave. It is shown that the broadening of the central nonlinear structure in the spectrum is caused by the Coulomb dephasing effect. The computational results are in qualitative agreement with the available experimental data.
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.