Collision-induced resonances in Doppler-broadened systems

Vladilen S Letokhov, Veniamin P. Chebotayev

Peng Zhou, S. Swain

We investigate the effects of collisional dephasing and Doppler broadening on the quantum beats, narrow resonances, and probe transparency induced by quantum interference in a Vee-type atom consisting of an excited doublet coupled to a single ground level by the vacuum. We show that the amplitudes of the quantum-beat oscillations are greatly reduced, and the narrow resonances are substantially suppressed and broadened, for even very small dephasing rates and Doppler broadening. Fluorescence quenching and the previously reported probe transparency can never occur in the presence of dephasing collisions and Doppler broadening.

R. Corbalán, Gaspar T. Orriols, L. Roso +2 more

Jing Liu, Duncan G. Steel

We report a series of measurements of the nearly degenerate four-wave-mixing response in atomic sodium in the presence of a helium buffer gas. The results show the line shape associated with both the ground-state and excited-state dynamics. The line shape evolves as a function of pressure from a dip at a pressure of 0 Torr to a spike at a few Torr due to the presence of collisions. The width of the spike is determined by residual Doppler broadening. At higher pressure (\ensuremath{\ge}10 Torr), the width of the spike is further narrowed below the residual Doppler width. The additional reduction is due to a form of Dicke narrowing associated with the dynamics of the lower- and upper-level excitations. The results are in qualitative agreement with a perturbation solution of the density-matrix equations which include the effects of velocity-changing collisions and state-changing collisions.

M. Anil Kumar, Suneel Pratap Singh

We present a theory of electromagnetically induced transparency (EIT) and slow light in a Doppler broadened three-level ladder (cascade) system incorporating residual Doppler broadening of two-photon coherence and velocity-changing and dephasing collision effects of a buffer gas. Both regimes of wave-vector mismatch occurring when either the probe frequency is higher than that of the (strong) control field or vice versa are considered. It is found that the velocity-changing collisions in general cause narrowing of EIT resonance linewidths which, in a particular wave-vector mismatch regime, can lead to large transparency and slow light generation at relatively low control field intensities. Large collisional dephasing of two-photon coherence in a ladder system, however, tends to mask these effects. A reduction in group velocity by more than 3 orders of magnitude is predicted in the regime where the probe frequency is lesser than that of the control field and in the absence of collisions.

E. Arimondo, R. Corbalán, Gaspar T. Orriols +2 more