Tamara Ya. Karagodova

Influence of a magnetic field on coherent population trapping in atomic systems of degenerated levels

Coherent population trapping effect is widely studied for simple three-level systems of different types ((Xi) 2, (Lambda) , V)1,2. For real atoms the situation is more complicated. Atomic levels are degenerated one and in the presence of external fields coupling of magnetic sublevels appears due to radiation, so magnetic fields leading to the systems of levels of the higher order. Our theory and method of calculation for interaction of multilevel atoms, with intense radiation fields in the presence of external magnetic fields have been applied for considering coherent population trapping effect for such systems. In the absence of magnetic field for considering sets of parameters, we can see the behavior of populations in function of time, detunings for both systems of coupled sublevels inherent to the coherent population trapping effect. In the presence of magnetic field, we can see novel features in the populations for the systems of coupled magnetic sublevels.

The pecularities of coherent population trapping resonances on fine structure levels for different light polarization

At the conditions of two-photon resonance the effect of coherent population trapping (CPT) can take place. The CPT may be observed as in absorption so in resonance fluorescence. The CPT is widely applied in high resolution spectroscopy, laser cooling, atomic optics and so on. Earlier the peculiarities of CPT resonances on fine structure levels of an atom have been considered on example of thallium atoms. It was shown that the form and number of resonances are influenced by geometry of experiment and initial conditions (initial level populations). As the investigations of CPT on fine structure levels are the object of interest last years, we have considered the numerical analysis of dependence the form of CPT resonances on fine structure levels of T1 atoms as lower levels of Λ-system on polarization of radiation fields. The cases of elliptical, linear and circular polarization have been considered.

Computer simulations on the influence of initial conditions and geometries of experiment on the resonances of coherent population trapping on fine structure levels of thallium atoms

We consider peculiarities of coherent population trapping (CPT) effect on magnetic sublevels of fine structure levels for Thallium (TI) atoms. The system of levels taken into account consists of eight levels. By considering spontaneous decay onto the levels of thermostat we have found the solutions of Schroedinger equation in resonant approximation and so we have found the populations of magnetic sublevels. We have considered different geometries of experiment. Among them there are the cases for which the polarization vectors of both components of radiation fields are parallel to each other and parallel or perpendicular to magnetic field, polarization vectors are perpendicular to each other (one of them is parallel to magnetic field). Also the orientation of magnetic field may be parallel or perpendicular to wave vector of radiation field. Also we have considered different initial populations of magnetic sublevels. In contrary to trivial initial populations of sublevels of the ground state of an atom we have considered the initial population of another metastable fine structure level of TI atom. This situation can take place for atomic photofragments produced in the photodissotiation of diatomic molecules.

Influence of magnetic field orientation and strength on the dynamics and dispersion of a multilevel system

The effect of coherent population trapping related to quantum interference of states now is well investigated for (Lambda) -systems in which the lower levels are generated by the hyperfine structure sublevels of the ground state of the atom. At present time the majority of experimental researches of resonances of CPT are made with alkaline atoms, for which hyperfine components of the ground state have typical interval of several gigahertz. We consider CPT in (Lambda) -systems in which the fine structure sublevels of the atom generate the lower levels. Our computer simulations have been made for the thallium atom for which the distance between sublevels of fine structure components is approximately 7792 cm-1. Theoretical and computer simulations of dynamics and dispersions of population of the considered multilevel system allow to detect new peculiarities of effect and demonstrate the influence of orientation and strength of magnetic field.

Nonlinear resonant magneto-optical effects in alkaline metal vapors in the strong bichromatic laser radiation field

In the paper there are presented the last results of computer simulations on the spectra of magneto-optical rotation (MOR) of plane of polarization for the both components of intense bichromatic laser radiation. Also the dependences of MOR on light intensity and magnetic field strength are investigated. The calculations are based on the theory and method, published earlier. The agreement of calculations for the cases investigated in the known experiments with experimental results permits to hope that new peculiarities of the MOR in alkaline vapors considered in our paper can be observed in the natural experiments.

Dynamics and dispersion of populations for multilevel systems in the intense-radiation and external magnetic fields

The theory of interaction of the elementary atomic systems with resonant laser fields is well known. At the same time multilevel systems are investigated in less details. We consider T1 atoms as multilevel system due to removal of degeneracy of levels with different magnetic quantum number in strong radiation and magnetic fields. It is known that recently investigated effect, connected with the quantum interference of states is coherent population trapping (CPT). We propose the method of numerical calculations of interaction of real atoms with strong radiation fields and magnetic field, valid in the case when the values of Rabi frequencies considerably exceed the line widths. This method can be applied to investigate the CPT effect and influence of the external magnetic field on it.

Numerical analysis of nonlinear resonant polarization phenomena in strong fields

The numerical analyses of polarization phenomena is developed for the radiation fields resonant with the transitions nS1/2-nP1/2,3/2 and nP1/2,3/2 -- (n+2)S1/2 of alkaline atoms. The method of computer simulation of nonlinear resonant polarization phenomena is used, which is based on the solution of the problem of interaction of the real multilevel atom with two laser fields of arbitrary intensity and polarization and with a constant magnetic field. This method is known to be successful applied for the investigation of the polarization phenomena in the atomic gases of the alkaline atoms Na and K. In present paper the whole alkaline group is considered. The represented spectra of rotation of plane of polarization are appear to be qualitatively different for different atoms since atom fine- structure intervals differ very much from each other. The obtained spectra for Rb are in good agreement with the experimental spectra.

Population dynamics for multilevel systems in the external magnetic field

Coherent population trapping effect is widely studied for simple three-level systems of different types ((Xi) , (Lambda) , V). For real atoms situation is more complicated. Atomic levels are degenerated one and in the presence of external fields coupling of magnetic sublevels appears due to as radiation, so magnetic fields, leading to the systems of levels of the higher order. Our theory and model of calculation for interaction of multilevel atom with intense radiation field at the presence of external magnetic field have been applied for considering coherent population trapping effect for such systems.

Two-photon magneto-optical effects in atomic gases in resonant laser and strong magnetic fields

The theory of interaction of intense bichromatic field of laser radiation with multilevel atomic system in the external magnetic field is considered. The magnitudes of interaction are much larger than the width of atomic levels. The vector-potential of radiation field consisting of two monochromatic components with the frequencies resonant to adjacent transitions is taken in electric dipole approximation. The eigenvalues and eigenstates of the Hamiltonian, including spin-orbit interaction and interactions with laser radiation and external magnetic fields, are found without perturbation theory using resonant approximation. When the effects of resonantly excited radiation are considered the Hamiltonian of interaction with the weak field of scattered radiation is included also. Its eigenfunctions are found with the help of perturbation theory. We consider tow types of effects: polarization effects and effects of resonantly excited radiation. As the atomic system is multilevel we use the numerical methods. The influence of the magnetic field on coherent population trapping effect for multilevel systems is considered. Some of our theoretical results coincide with known experimental ones.

Resonant fluorescence for multilevel systems in intense nonmonochromatic fields: possibilities for applications in laser medicine

The theory of resonant fluorescence of multilevel system in two monochromatic intense laser fields has been applied for investigating the temporal decay of magnetic sublevels of an atom. As for two-level system the triplet of resonant fluorescence is observed, for real atom being the multilevel system the multiplet of resonant fluorescence can be observed. The excitation spectra, defining the intensities of lines in the multiplet of resonant fluorescence, and shifts of components of spectra are shown. Typical temporal dependence of fluorescence intensity for magnetic sublevels of an atom having different relaxation constants is shown. The computer simulation of resonant fluorescence for simple systems can help to understand the regularities in temporal decay curves of atherosclerotic plaque, malignant tumor compared to normal surrounding tissue.