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International Journal of Quantum Chemistry

The influence of orientation and strength of external magnetic field on the time dependences of populations of atomic levels for Lamda systems

T. Ya. Karagodova

Published Jun 15, 2004• 2 citations
Publisher

Abstract

Abstract The theory of interaction of intense laser fields with multilevel atoms in external constant magnetic fields is applied to analysis of the dependences of the populations on time, on detuning of laser frequency, on magnetic field orientation, and strength for spontaneous decay on the levels of thermostat. Solving the Schrödinger equation for the “atom in magnetic field + radiation field” system in resonant approximation we have obtained the probability of the population of common level for a generalized Λ system (e.g., 6P1/2‐7S1/2‐6P3/2 levels of Tl atoms). The results of computer simulations permit the investigation of the peculiarities of coherent population trapping in such system. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

DOI
10.1002/qua.20045

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Abstract The theory of interaction of intense laser fields with multilevel atoms in external constant magnetic fields is applied to analysis of the dependences of the populations on time, on detuning of laser frequency, on magnetic field orientation, and strength for spontaneous decay on the levels of thermostat. Solving the Schrödinger equation for the “atom in magnetic field + radiation field” system in resonant approximation we have obtained the probability of the population of common level for a generalized Λ system (e.g., 6P1/2‐7S1/2‐6P3/2 levels of Tl atoms). The results of computer simulations permit the investigation of the peculiarities of coherent population trapping in such system. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
The influence of the orientation and strength of a magnetic field on the dynamics and dispersion of the populations of the multilevel Λ system upon spontaneous decay into thermostat levels is considered. The radiation field consists of two components and is specified by the vector-potential in the electric dipole approximation. From the solution of the Schödinger equation for a system consisting of an atom in a magnetic field + radiation field, the probability of populating a common level for the generalized Λ system is determined in the resonance approximation. The calculation of the dynamics and dispersion of the populations demonstrates their dependence on the orientation of the magnetic field vector with respect to the light field polarization vector and on the relationship between the magnetic field strength and radiation field intensities. The coherent population trapping occurs only in the case when Rabi frequencies either exceed or are comparable to the Zeeman splitting of magnetic sublevels. By varying the orientation of the magnetic field, it is possible to change the dynamics and dispersion of the populations, thus affecting the coherent population trapping.
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.
The interaction of high power laser radiation with the atoms in the external magnetic field leads to the new nonlinear effects due to modifications of populations of the states of the system 'atom plus field.' From one side it can be followed by new peculiarities in the effect of the coherent population trapping and from other -- the effects of the population modifications are important for explanation of regularities of nonlinear magneto-optical effects. The modification of population dynamics due to the parameters of the system -- radiation field intensities, detunings, polarizations, magnetic field strength and orientation, relaxation constants leads to the new features in polarization effects, resonant fluorescence and resonant Raman effects. The new features of the considered theory are that it is built for multilevel atoms and has not restrictions on the probe intensity compared to the pump intensity. The theory and method permit to investigate the populations modifications depending on modifications of the parameters of the system and to find the relation between population dynamics and new nonlinear resonant magneto-optical effects. The considered system consists of atomic gas of low concentration in the constant magnetic field and two monochromatic laser fields of different intensities and polarizations. Analytically the influence of magnetic field on population dynamics of three-level systems have been considered. For real multilevel atom the computer simulations show the dependence of population dynamics on relaxation constants and the differences of this dynamics for different magnetic sublevels of the excited states of the atom. The results agree with known theoretical and experimental works.
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.
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.
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.