The idea of S. G. Rautian to represent the middle part of the profile of an isolated spectral line as the interference of resonant (the central part of the line) and nonresonant (the peripheral part) interactions is realized for the version based on kinetic equations.
Abstract Under the conditions of the Markov approximation, a master kinetic equation is derived that describes the transfer of the state of a single-photon packet to the state of a solitary object, depending on the nature of the latter. A single-photon excitation is a broadband packet with a Gaussian frequency distribution (an information signal) that interacts nonresonantly with a selected high-Q cavity mode (an intermediary). The latter also interacts nonresonantly with an absorber whose natural frequency is resonant to the central frequency of the packet.
Modern resonance spectroscopic experiments on the measurement of transition frequencies in atoms have reached a level where a meticulous description of all aspects of the studied processes has become obligatory. The precision achieved has led to the fact that the determination of the transition frequency on the basis of measured data is substantially refined by theoretical treatment of the observed spectral line profile. Thus, a large impact of effects arising beyond the resonance approximation, in particular due to the effect of quantum interference, is found experimentally. We show that the picture becomes even more complicated when the observed spectral line profile is ``identified'' with one of the processes---emission or absorption. An accurate determination of the transition frequency requires a description of the absorption line profile inseparable from the emission process, and vice versa. The theoretical aspects discussed in this paper create prerequisites for more accurate experiments.
The Rautian-Sobelman approach describing the collision-Doppler shape of spectral line that takes into account both soft and hard velocity-changing collisions is extended to the case when correlation between Doppler and collision broadening as well as the dispersion line asymmetry should be considered. Numerical calculations show that speed-dependent effects can produce the additional line narrowing as well as broadening and also the line asymmetry. It is shown that speed-dependent profiles based on the soft and hard collision models differ much more one from another than those which omit the speed-dependent effects.