Hard-collision broadening of the probe-field spectrum in a -system

The probe-field spectrum of a three-level Λ-gas with hard collisions between particles is studied. The shape and positions of components of the Autler–Townes doublet are obtained at different collision frequencies. When the Doppler broadening is much greater than the collision frequency the width of the peaks is found to be proportional to the collision frequency. In contrast when collisions are elastic the peaks are shown to narrow due to the Dicke effect.