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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Calculation of nonlinear resonant Raman effect cross sections in intense laser and magnetic fields

T. Ya. Karagodova

Published May 10, 1996• 0 citations
Publisher

Abstract

The method of computer simulations on nonlinear resonant magnetooptical effects developed for the first time for real multilevel atoms in the two laser fields of arbitrary intensity and external magnetic field is applied for Raman-effect cross section calculations and investigations of the dependence on magnetic field strength, intensities, detunings of laser fields for alkaline atoms, thallium. Calculations of nonlinear resonant Raman-effect cross- sections in the intense laser fields resonant to adjacent transitions and magnetic field show the opportunity of appearing of the new effects in Raman scattering in atomic gases.

DOI
10.1117/12.239692

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Oct 21, 1998•0 citations
The method of computer simulations on nonlinear resonant magnetooptical effects developed for the first time for real multilevel atoms in the two laser fields of arbitrary intensity and external magnetic field is applied for Raman-effect cross section calculations and investigations of the dependence on magnetic field strength, intensities, detunings of laser fields for alkaline atoms, thallium. Calculations of nonlinear resonant Raman-effect cross- sections in the intense laser fields resonant to adjacent transitions and magnetic field show the opportunity of appearing of the new effects in Raman scattering in atomic gases.
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.
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.
The method of computer simulations on nonlinear resonant magneto-optical 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, polarizations and detunings of laser fields for alkaline atoms. The essence of the method consists in simulations and analysis of the plots of dependence of quasienergies on parameters (detunings and intensities of radiation fields, magnetic field strength), which are obtained with the help of sorting subprogram, and selection of suitable algorithms for calculations of characteristics of nonlinear resonant magneto-optical 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 dicohroizm of different types are predicted. The results show the agreement with known experiments. Such calculations of nonlinear resonant magneto-optical 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.
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.
Theory and methods of computer simulations permit investigation of the interaction of high-power laser radiation, up to GW/cm2, with atoms having both small and large fine-structure intervals compared with interactions with a laser field and an external magnetic field. The modifications of the energies and population of atomic levels due to such interactions lead to nonlinear effects. Besides modifications in the Raman effect and new effects of rotation of the plane of polarization and circular dichroism that were investigated earlier, there are such nonlinear effects as the modification of the number, positions, intensities, and polarizations of the lines in the resonant fluorescence spectrum. Numerical experiments permit investigation of the characteristics of resonant fluorescence and comparison with known experimental results.PACS Nos.: 32.50, 78.20.L, 42.65, 42.50.H
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.