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Journal of Contemporary Physics (Armenian Academy of Sciences)

Determination of polarization relaxation times of atomic levels

G. G. Adonts, Eghine G. Kanetsyan, Mikayel Arzakantsyan

Published Sep 1, 2012• 1 citation
Publisher

Abstract

Rotation of polarization plane of a probe signal under influence of a time-advanced intense pulse is investigated taking into account optical pumping of atoms in a resonant medium. A formula is derived for the angle of rotation of polarization plane of the probe signal. It follows from this formula that modification of the polarization plane is caused by two processes: radiative decay of atoms and collision-induced redistribution of atoms over magnetic sublevels. It is shown that this method enables direct measuring long times of atomic collisions on the background of short times of the radiation decay.

DOI
10.3103/s1068337212050052

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Journal of Physics B Atomic and Molecular Physics•Jan 28, 1986•7 citations
Rotation of polarization plane of a probe signal under influence of a time-advanced intense pulse is investigated taking into account optical pumping of atoms in a resonant medium. A formula is derived for the angle of rotation of polarization plane of the probe signal. It follows from this formula that modification of the polarization plane is caused by two processes: radiative decay of atoms and collision-induced redistribution of atoms over magnetic sublevels. It is shown that this method enables direct measuring long times of atomic collisions on the background of short times of the radiation decay.
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The propagation of strongly polarized electromagnetic waves through a resonance medium, with arbitrary angular momenta of the levels, is investigated in the adiabatic-following approximation. Exact wavefunctions of the two-level atomic system with degenerate levels in the field of a circularly (linearly) polarized wave are constructed and the picture of the shift of energy level splittings is discussed. Exact formulae for the nonlinear refractive index of the medium in the field of the circularly (linearly) polarized wave are found. The propagation of counterpropagating polarized waves—an intense pump wave and a probe light signal—through the resonance medium is studied. The studies are carried out in the scope of a two-level (one-photon resonance) and a three-level (one- and two-photon resonances) medium. Formulae are found for the induced rotation of the plane of polarization for the probing signal that are exact in terms of the intensity of the pump wave. The spectral dependence of the angle of rotation is studied, and it is shown that a series of Stark-shifted resonance poles of atomic absorption and a three-photon scattering process arise.
The propagation of a strongly polarised electromagnetic wave through a resonance medium with arbitrary angular momenta of the levels is investigated in the adiabatic following approximation. Exact wavefunctions of the two-level atomic system with degenerate levels in the field of a circularly (linearly) polarised wave are constructed and the picture of the energetic level splitting and shift is discussed. Exact formulae for the non-linear refractive index of the medium in the field of the circularly (linearly) polarised wave are found. The propagation of counterpropagating polarised waves-an intense pump wave and a probe light signal-through the resonance medium is studied. The studies are carried out in the scope of a two-level (one-photon resonance) and a three-level (one- and two-photon resonances) medium. Formulae are found for the induced pump angle of rotation of the ellipse (plane) of polarisation for the probing signal that are exact in terms of the intensity of the pump wave. The spectral dependence of the angle of rotation is studied, and it is shown that a series of Stark-shifted resonance poles of atomic absorption and a three-photon scattering process arise.
Abilities of the method of accumulation of coherent unstable response of a medium for amplification of the rotated component of the probe wave’s polarization in the atomic medium of three-level atoms are studied. Probe wave is examined in frames of the perturbation theory and its frequency is considered near to one photon resonance from the ground to the first excited level. The intense monochromatic pump field connects two excited energy levels and propagates through the medium without a change. The broadening of spectral lines caused by the relaxation processes and the Doppler broadening are included into the calculations. It is shown that by multiple consistent instantaneous change of input probe field’s phase from 0 to π and back, it is possible to obtain, in the tail part of the rotated component of the probe field, a separate narrowed light pulse along with the increase in intensity by more than an order of magnitude with respect to the input field.
The general nonstationary theory of propagation of an elliptically polarized pulse resonantly interacting with the 1/2–1/2 transition is presented. The theory that takes into account relaxation processes is developed in terms of irreducible tensor operator representation allowing diagonalization of the relaxation matrix and introduction of effective decay times governing relaxation of both population and coherence between magnetic sublevels of the resonant system. It is shown that interference of magnetic sublevels in the field of polarized radiation that optically pumps the atoms can result in inversionless amplification of radiation.
The modified stimulated photon echo is proposed as a method for the investigation of elastic collisions of excited atoms with non-excited foreign gas atoms, which induce the redistribution of the excited atoms in Zeeman sublevels. Such collisions cause the difference in the population, orientation and alignment relaxation times of a resonant level. It is shown that the proper choice of mutual orientation of the exciting-light polarisation vectors makes it possible to determine the relaxation times for the population, orientation and alignment of a resonant level. It is found that the formulae, derived in the limit of exciting-pulse small areas, are the most attractive for spectroscopic purposes, as in this case the polarisation properties of the modified stimulated photon echo do not depend on the exciting-pulse shapes, nor on their areas. A detailed discussion of the experimental results of Hartmann and collaborators (1979) and of Keller and Le Gouet (1984), mainly concerned with the investigation of the modified stimulated photon echoes in gases, is carried out.