Transit effects in saturated absorption resonances

An important problem in saturated absorption spectroscopy is discussed: the width of a nonlinear absorption resonance in a low-pressure gas in a standing wave field. It is shown that the results reported by A. N. Titov et al. are incorrect. These authors stated that at weak saturations the resonance width is of the order of the reciprocal transit time of an atom traveling at the thermal velocity across a light beam. The specific source of the error is indicated, which is an incorrect mathematical treatment of the correct initial equations. It is also shown that the saturated absorption line profile in the transit limit is almost independent of the laser field configuration.