Alexander I. Karagodov

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.

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.

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.

Computer simulations on the processes of resonantly excited radiation in the intense laser and magnetic fields

The theory and method of computer simulations created formerly permits to investigate the interaction of high power laser radiation up to gigawatt on centimeter to the second power with the atoms as well as with small so with large fine structure interval in the external magnetic field. The modifications of the energies and populations of atomic levels due to such interaction lead to the new nonlinear effects. Among them besides the modifications in Raman effect and new effects of rotation of plane of polarization and circular dichroism investigated before there are such new effects as the modifications of the number, intensities, polarizations of the lines at the excitation spectra and the scattering spectra of resonant fluorescence. The real atom is multilevel system. Usually the theoretical investigations of nonlinear resonant magnetooptical effects are limited by two- or three-level approximations or by using the perturbation theory. This is justified for considering the effects in the weak magnetic fields but not sufficient for revealing and investigation the characteristics of the new nonlinear magnetooptical effects taking place in the intense radiation and magnetic fields. Such effects are related to modifications of electronic structure of atoms (level shifts and splittings, populations modifications). As the considered media is atomic gas one can reach for power density up to gigawatt on centimeter to the second power. As the considered concentrations are small it is possible to neglect the collisional relaxation. For real atom the considered system is multilevel so only numerical solution is appropriated. The simulations permit to find some new effects in the excitation spectra of Raman effect and resonant fluorescence.

New nonlinear polarization effects for frequency selection

The method of computer simulations on nonlinear resonant magnetooptical effects developed for real multi-level atoms in the two laser fields of arbitrary intensity and external magnetic field is applied for the polarization effects of different types calculations and investigations of the dependence of the characteristics of these effects on magnetic field strength, intensities, polarization and detunings of laser fields for alkaline atoms. The essence of the method consists in simulations and analysis of the plots of dependence of quasi energies on parameters, which are obtained with the help of sorting subprogram, and selection of suitable algorithms for calculations of characteristics of nonlinear resonant magnetooptical effects. One photon and two photon resonant effects are investigated for wide range of magnetic field strength from Zeeman to Paschen Back effects. Some new features in the spectra of rotation of plane of polarization and circular dichroism of different types are predicted. The results show the agreement with known experiments. Such calculations of nonlinear resonant magnetooptical effects in the intense laser fields resonant to adjacent transitions and magnetic field show the opportunity of investigation the modifications of electronic structure due to intense radiation fields and strong external magnetic field in atomic gases and also may be used for the treatment of new methods of phase-polarization selection of modes of tunable lasers.