Influence of collisions on saturated-absorption profiles of the 557 nm line of Kr I

Saturated-absorption profiles of the lines at lambda =557 nm involving the lowest metastable level of krypton show intense and broad Gaussian backgrounds due to thermalising collisions. These backgrounds are greatly reduced by the addition of xenon atoms which quench the metastable level. The variation of the amplitude of the background relative to the amplitude of the narrow absorption resonance versus pressure is quadratic in pure krypton and linear in mixtures of krypton and xenon. An interpretation of the results is given taking into account transit-time effects, while making use of published results for the quenching cross section.