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E-Verhandlungen 2001
Programm und Abstracts der Sitzung A 20

Direct observation of nonadiabatic transitions in Na + Molecule differential optical collisions

C. Figl¹, •R. Goldstein¹, A. Grimpe¹, A. Grosser¹, O. Hoffman¹, M. Jungen², F. Rebentrost³ und D. Wöß ner^1
3Max-Planck Institut für Quantenoptik, Garching
¹Institut für Atom- und Molekülphysik, Abteilung Atomare Prozesse, Universität Hannover
²Institut für Physikalische Cemie, Universität Basel

In a differential scattering experiment, we study the dynamics in optical collisions:

Giant dipole states of multi-electron atoms in crossed electric and magnetic fields

•Peter Schmelcher
Theoretische Chemie, Physikalische Chemie, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany

Giant dipole states of singly and doubly excited multi-electron atoms in crossed electric and magnetic fields are investigated. A gauge-independent approach to the separation of the center of mass yields a generalized multi-electron potential in crossed fields which serves as a basis for the study of the dipole states. For doubly excited systems a new class of highly symmetric decentred configurations is found and the properties of the corresponding resonances are determined. An outline on multiply excited systems is given.

Tunneling of Rydberg electrons in crossed electric and magnetic fields

•Wolfgang Ihra
Theoretical Quantum Dynamics, University Freiburg, Germany

Rydberg states of hydrogen in crossed electric and magnetic fields below the Stark saddle point energy have a finite decay width due to tunneling into asymptotic states. We study the tunneling dynamics semiclassically by using the imaginary time method. The dominant tunneling orbit for the motion in the plane perpendicular to the magnetic field is identified for different strength of the electric and magnetic fields. Implications concerning trends in the total decay width of quantum states as a function of the energy and the field parameters are discussed.

[1] S.C. Creagh and N.D. Whelan, Phys. Rev. Lett. 4975 (1996).

Chaotic ionization of non-hydrogenic alkali Rydberg states

•Andreas Krug^1,2 und Andreas Buchleitner^1
1Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Str. 38, D-01187 Dresden
²Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, D-85748 Garching b. München

We present the first ab initio treatment of microwave driven alkali Rydberg states. We find that nonhydrogenic atomic initial states - with no uniquely defined classical analogon - exhibit fingerprints of classically chaotic motion, and identify the relevant frequency scale that accounts for the experimentally observed [1] considerable discrepancies in the ionization yield of microwave driven alkali Rydberg states as compared to atomic hydrogen.

Our method combines the Floquet theorem, complex dilation of the Hamilton operator, and quantum defect theory. An efficient parallel implementation of our numerical code on the largest supercompter available in the academic realm (HITACHI SR8000-F1 at LRZ Munich) allows for an exact treatment of typical experimental quantum numbers (n @ 30...80), which define a multiphoton ionization process of the order of 15...120.

[1] P. M. Koch, and K. A. H. Leeuwen, Phys. Rep. 255, 289 (1995).

Laser-Atom Interaction at strongly relativistic intensities

•Ernst Lenz, Martin Dörr und Wolfgang Sandner
Max-Born-Institut, 12489 Berlin

We investigate the interaction of a charged particle in a potential with an ultra-strong and ultra-short field pulse. We consider a one-dimensional model for ionization and potential scattering. We compare the solutions of the time dependent Dirac (D)-, Klein-Gordon (relativistic Schrödinger, RS)- and the non relativistic Schrödinger equation. In the absence of a static potential the D and RS are equivalent, so a solution of the D equation is not necessary. The D equation becomes relevant if one deals with (a) deeply bound states in highly charged ions or (b) pair creation effects.
References:

Bottcher, C. and Strayer, M.R., 1986, Ann. Phys. 175, 64; Braun, J.W., Su, Q. and Grobe, R., 1999, Phys. Rev. A 59, 601; Dombey, N. and Calogeracos, A., 1999, Phys. Rep. 315, 41; Lenz, E., Dörr, M. and Sandner, W. , 2001, Laser Phys., 11; Lenz, E., Dörr, M. and Sandner, W. , 2001, Proceedings of the conference on Super-Intense Laser-Atom Physics, Piraux, B., ed., Kluwer; Rathe, U.W., Keitel, C.H., Protopapas, M. and Knight, P.L., 1997, J. Phys. B 30, 531

Dynamical localization in the 3-D kicked Rydberg atom

•Emil Persson¹, Shuhei Yoshida¹, Xiao-Min Tong², Carlos Reinhold³ und Joachim Burgdörfer^1
1Institute for Theoretical Physics, Vienna University of Technology, A 1040 Vienna, Austria
²Cold Trapped Ions Project, ICORP, JST, AXIS 3F, 1-40-2 Fuda Chofu, Tokyo 182-0024, Japan
³Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6373, USA

The dynamical localization for the 3D periodically kicked Rydberg atom is analyzed. For the 1D kicked atom, earlier work shows dynamical localization as the quantum suppression of classically fast ionization associated with unbounded chaotic trajectories. For the experimental observation, the crucial question is the dependence of the dynamical localization on the dimension. As the first step, we simulate the full 3D evolution of an extreme parabolic initial state elongated in the direction of the unidirectional kicks. We compare this simulation with the 1D model and find signatures of localization also in 3D. Implications for the experiment will be discussed.

Research funded by the FWF - SFB016, by NSF and by DOE-BES.

Peculiarities of cyclotron radiation from fast atomic ions.

•Vladimir Melezhik
P.N.T.P.M., Universite Libre de Bruxelles, Campus Plaine CP229, B-1050 Brussels, Belgium

In work [1] we have shown that atomic ions moving in a magnetic field generate monochromatic radiation with the cyclotron frequency w=QB/M, depending on the field strength B and the ion mass M and charge Q. The origin of the effect is the interaction of the bound electron with the oscillating field of the Stark term coupling the center of mass and electronic motions of an ion due to the nonseparability of the collective and internal degrees of freedom in the system. It was estimated that the radiation power for the He+ ion moving in field B= 4 a.u. exceeds by a few order of magnitude the synchrotron radiation (SR) power from the structureless pseudoparticle with mass of He+ and unit charge and considerably exceeds the SR from the electron moving with the same velocity in the same B. In the present report we discuss the ionic radiation for lower magnetic fields accessible at present-day laboratories and the possibility to use the effect as an amplifier of the cyclotron radiation. [1] V.S. Melezhik, Phys. Rev. A59, 4833 (1999)

Relativistic precession of elliptic wave packets

•Piotr Rozmej¹, Robert Arvieu², Ilya Averbukh³ und Marcin Turek^4
1Technical University, 65-246 Zielona Góra, Poland
²Institut des Sciences Nucléaires, 38026 Grenoble-Cedex, France
³Weizmann Institute of Science, 76100 Rehovot, Israel
⁴University MCS, 20-031 Lublin, Poland

We present a theoretical description of the precession of the elliptic wave packet (EWP) built from eigenstates of the Dirac equation for the hydrogenic atom. In 1989 by Gay, Delande and Bommier [1] have constructed coherent elliptic wave packets (EWPs). The probability density for this state, composed from states with the same n but different l,m quantum numbers, is fairly localized on a Kepler orbit (classical ellipse) with given average value of angular momentum l_av.

In non-relativistic theory such a state doesn't move in time as all partial waves gain a common phase factor related to non-relativistic energy. In relativistic theory the situation is different. Phases of partial waves vary with l and the probability density moves slowly. For relatively short time the relativistic precession of the classical ellipse, where the probability density was initially concentrated, is observed. The precession period is given by

T_prec = (2p(^h/_2p))/(\fracdEdl) _{l = lav} = T_Kep(2 l_av²)/(Za)² = T_LS , where T_Kep is the classical period of the electron in state n. This period is also the period of spin-orbit motion T_LS, discussed by us already for relativistic circular wave packets [2].
1. J-C. Gay, D. Delande and A. Bommier, Phys. Rev. A 39, 6587 (1989).
2. R. Arvieu, P.Rozmej and M. Turek, Phys. Rev. A 62, 022514 (2000).

MAGNETIC-FIELD INDUCED QUENCHING OF METASTABLE ³P₂ AND ³P₀ STATES IN INERT ATOMS

•E. Tchaplyguine¹, V. Ovsiannikov¹ und ^2
1Faculty of Physics, Voronezh State University, 394693 Voronezh, Russia
²

The first excited states of the inert atoms include two metastable j₁⁽⁰⁾ = |(n+1)s[\frac32]₂ñ and j₃⁽⁰⁾ = |(n+1)s¢[\frac12]₀ñ and two resonant states j₂⁽⁰⁾ = |(n+1)s[\frac32]₁ñ and j₄⁽⁰⁾ = |(n+1)s¢[\frac12]₁ñ. To determine the wave function of an excited atom in field we diagonalize the atom - magnetic field interaction within the fine-structure manifold including the metastable sublevel. So the resonance states are mixed to the metastable states and thus determine the possibility of radiative quenching for the latter. The two resonant lines of a free atom are splitted by field into ten lines: two p- and two s-lines from the lower doublet and two p- and two-times-two s-lines from the upper doublet. The probability for emission of the field-induced lines may be presented in terms of probabilities for the resonant-line emission. The intensities of forbidden lines in Neon may become comparable to those of the allowed lines in the field of several tens of Tesla. The calculated results show the dependence of the line intensities on the magnetic quantum number M of the initial state. This kind of ``circular dichroism'' differs for different atoms.

Third order Stark effect on the hydrogen line intensity

• A.A. Kamenski und V.D. Ovsiannikov
Department of Physics, Voronezh State University, 394693 Voronezh, Russia

The factors determining the intensity of radiation emitted by an atom from the state |nñ to the state |n¢ñ depend on the electric field F. So the intensity dependence on field is also evident:

The effect provides an additional spectroscopic information on the atomic structure which may be used in practice for optical diagnostics of dc fields exerted on atoms and to control the emission and absorption of light by atoms in field.

[1] Kamenski A. A. and Ovsiannikov V. D.J.Phys. B: At. Mol. Opt. Phys. 2000. 33 491-505; ibid. J.Phys. B: At. Mol. Opt. Phys. 2001.34 1-18

Finite-difference calculations for atoms and simple diatomic molecules in strong magnetic and static electric fields

•Mikhail Ivanov
Institute of Precambrian Geology and Geochronology (IPGG), Russian Academy of Sciences, Nab. Makarova 2, St.Petersburg, 199034, Russia

Fully numerical mesh solution of 2D and 3D quantum equations of the Schroedinger and Hartree-Fock type allows us to work with wavefunctions which have much more flexible geometry than the wavefunctions in the traditional basis-set approach. This flexibility is important for calculations of atoms and molecules in strong external electric and magnetic fields. For the magnetic fields we provide Hartree-Fock calculations for He, Li, Be, B, and C [1-2] including the first comprehensive investigation of the ground state configurations of these atoms in fields from B = 0 up to B = 2.35·10⁹T and a study of all the atoms with 1 £ Z £ 10 and their ions A⁺ in the high-field fully spin-polarised regime. The results on strong electric fields are the correct solution of the Schroedinger equation for the H₂⁺ ion (energies and decay rates) and the hydrogen atom in strong parallel electric and magnetic fields.

[1] M.V. Ivanov, J. Phys. B: At. Mol. Opt. Phys., 27, 4513 (1994); 31, 2833 (1998); Phys. Lett. A, 239, 72 (1998)

[2] M.V. Ivanov and P. Schmelcher, Phys. Rev. A, 57, 3793 (1998); 60, 3558 (1999); 61, 022505 (2000)

ATOMS AND MOLECULES IN A STRONG LASER FIELD. MULTI-PHOTON RESONANCES AND SCATTERING OF LIGHT. IONIZING RADIATION BIOCELLULAR EFFECT

•Alexander Glushkov
Atom.-Nucl.-Mol. Spectr. Centre and Inst. Appl. Math. OHMI, P.O. Box 108, Odessa-9, 65009, Ukraine

QED approach based on S-matrix Gell-Mann and Low formalism is used for studying the interaction of the atoms and molecules with a strong laser field. The kphoton emission and absorption lines are calculated for the Lorentz and Gauss (single-, multi-mode) laser pulse shape. Multi-photon resonance and ionization profiles in H, Na, Cs atoms are calculated. The phenomenon of the above threshold ionization is studied. Comparison with the eigen-channel R-matrix calculations of Luc-Koenig et al for Mg is given. Method is generalized for description of the multi-photon processes and applied to analysis of multi-photon resonances in SF₆ molecule. QED theory for the Rayleigh and Raman vibrational scattering of light on the metastable molecular levels is developed. The polarizability, depolarization degree estimates for Rayleigh and Raman light scattering at frequencies of Nd and Rb lasers are presented for H₂,HD, D₂ molecules.

The finite temperature version of S-matrix formalism is developed and used in study of radiation action mechanism on biological targets.

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