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1
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Suppression of Excited-Atom Two-Photon Ionization due to Rabi Oscillations between the Excited and a Lower State

100%
Grudka A., Parzyński R.
Acta Physica Polonica A
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2001
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vol. 99
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issue 2
257-265
EN
Optical resonance between the initially occupied excited atomic state and some lower lying state is shown to be a suppressor of two-photon ionization from this excited state via near-threshold Rydberg states because of Rabi oscillations between the resonantly coupled states.
2
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N-Level Atoms in Multiple Laser Fields, the Long and the Short of It

100%
Eberly J.
Acta Physica Polonica A
|
1994
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vol. 85
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issue 4
685-692
EN
The interaction of multi-level atoms with several to many lasers simultaneously is examined in two regimes, the "short" regime of resonant atomic response to prescribed laser fields, and the "long" regime of resonant pulse propagation in which several to many laser pulses pass through an active medium composed of many-level atoms. Results obtained with I. Białynicki-Birula et al. in the short regime are reviewed, and new results in the long regime are described.
3
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The Spatial Region of Photoionization in a Strong Laser Field

100%
Bauer J.
Acta Physica Polonica A
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2008
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vol. 114
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issue 4
739-750
EN
In the framework of the Keldysh-Faisal-Reiss theory in the velocity gauge we investigate the magnitude of the space region, where photoionization in a strong laser field takes place. We find substantial differences between the short-range and the long-range (Coulomb) potentials, and between linear and circular polarizations of incident radiation. It appears that only for the initial state in the Coulomb potential the region of space, where ionization is held, expands significantly with increasing intensity for a typical optical frequency and non-relativistic but strong circularly polarized laser field. As a result of our considerations, we suggest to modify the idea of Reiss and Krainov of a certain simple Coulomb correction to the Volkov wave function. We show that photoionization rate calculated for the H(1s) atom, using our approach, is in better agreement with other theoretical results for moderately strong circularly polarized laser field.
4
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Quantum-classical Correspondence in Intense Laser Field-atom Interactions

100%
Bowden C., Pethel S., Rosenberger A., Sung C.
Acta Physica Polonica A
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1998
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vol. 93
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issue 1
31-43
EN
High-field ionization suppression in a classical Kepler ensemble is discussed in terms of optimization with respect to pulse turn-on rate as well as pre-pulse preparation. It is argued that high-field ionization suppression is best understood in terms of reduced probability of ionization for pulsed fields, whereas for a quasi-steady field, high-field ionization suppression implies a reduced ionization rate at higher intensities. The classical ensemble is used to calculate the high-field ionization rate of a one-dimensional atomic model using a Gaussian short-range potential and the results are compared with high-frequency Floquet theory results recently reported by other authors. Better than qualitative agreement is found and the results are compared and discussed in terms of quantum superposition and classical interference. Finally, high-field ionization suppression is discussed in relation to statistical relative stability of classical orbits of the ensemble, and classical interference for both short- and long-range potentials. Correspondence with quantum superposition is interpreted in relation to quantum-classical correspondence.
5
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Chaos Assisted Tunneling and Nonspreading Wave Packets

80%
Zakrzewski J., Delande D., Buchleitner A.
Acta Physica Polonica A
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1998
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vol. 93
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issue 1
179-186
EN
Consider an initial state lying on a primary resonance island. The state may tunnel into the chaotic sea surrounding it and further escape to infinity via chaotic diffusion. Properties of transport in such a situation are studied on an exemplary system - the hydrogen atom driven by microwaves. We show that the combination of tunneling followed by chaotic diffusion leads to peculiar large scale fluctuations of the AC Stark shift and ionization rates. An appropriate random matrix model describes accurately these statistical properties.
6
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Atoms and Molecules in a Strong Laser Field

80%
Busuladžić M., Gazibegović-Busuladžić A., Hasović E., Milošević D., Becker W.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
516-518
EN
We investigate high-order above-threshold ionization of diatomic molecules and their companion atoms by linearly polarized strong laser field using improved molecular (atomic) strong-field approximation. The most noticeable feature of the molecular spectra is the existence of minima that are absent in atomic case. We have derived an analytical formula for their position which is independent of the molecular symmetry.
7
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Polarization Dependence of Microwave "ionization" of Excited Hydrogen Atoms

80%
Koch P.
Acta Physica Polonica A
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1998
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vol. 93
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issue 1
105-133
EN
After a brief review of the ionization of excited hydrogen atoms by a linearly polarized field, we discuss experimental results for the polarization dependence of this process. Experiments at ω/2π = 9.904 GHz used two different ranges of principal quantum number n_{0} between 29 and 98. At low scaled frequencies, Ω ≲ 0.1, ionization data for certain narrow ranges of n_{0} exhibit striking sensitivity to fields with elliptical polarization not too far from circular polarization. Classical calculations reproduce this behavior and show it to be the result of 2ω driving terms that appear when the Hamiltonian is transformed to a frame rotating at ω. It shows how higher-dimensional dynamics can influence the ionization and be used to control it when the polarization departs from linear or circular polarization. At higher scaled frequencies, 0.6 ≲ Ω_{0} ≲ 1.4, near the onset of ionization circularly and elliptically polarized data show surprising similarities with linearly polarized data in a parameter regime where the ionization dynamics is dominated by the influence of the pendulumlike resonance zone centered at scaled frequency n_{0}^{3}ω ≡ Ω_{0} = 1. The stabilizing influence of this zone can be understood classically, but nonclassical stability associated with quantal separatrix states at its edge is a semiclassical effect.
8
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Content available

Explosion of Atom Clusters in a Free-Electron Intense Laser Pulse

80%
Rusek M., Orłowski A.
Acta Physica Polonica A
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2004
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vol. 105
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issue 5
425-436
EN
The explosion of rare-gas atomic clusters induced by short, intense X-ray pulses generated by a free-electron laser is studied. A numerical approach for an explicitly time-dependent description of small to medium size clusters in 3D is developed within the Thomas-Fermi model. Such an approach, though strongly simplified in comparison to fully quantum-mechanical schemes, is nevertheless expected to yield a qualitatively correct description of the electronic and ionic dynamics of these systems, at a much lower computational cost.
9
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Resonance Fluorescence Spectrum of Two-Level Atoms Driven by Two Noncollinear Classical Fields

80%
Łobodziński B.
Acta Physica Polonica A
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1997
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vol. 92
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issue 3
501-506
EN
The resonance fluorescence spectrum of an ensemble of two-level atoms driven by two classical, frequency degenerate and noncollinear laser beams is investigated. It has been found that the spatially-averaged resonance fluorescence spectra differ significantly from the spectra of two-level atoms calculated for the single-beam excitation. The differences were noticed in the number of peaks, their positions and shapes and in their dependences on an angle between wave vectors of the incident beams.
10
Content available remote

Experiments with a Mesomaser

80%
Lange W., Walther H.
Acta Physica Polonica A
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1994
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vol. 86
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issue 1
7-28
EN
We investigated the dynamically modified interaction between Rydberg atoms and a single mode of a microwave cavity driven by a strong external field. With a monochromatic injected field we observed dynamic suppression of spontaneous emission, when the intracavity Rabi frequency exceeds the cavity linewidth. We discuss a theoretical model using non-Markovian decay rates, which is in excellent agreement with experiment. When a bichromatic driving field is used, enhanced decay reappears in narrow resonance zones as the detunings and injected intensities are varied. These results are interpreted in terms of cavity-modified transitions between the Floquet states of a two-level atom. Striking aspects of these transitions are their small linewidth and an asymmetry between emission and absorption.
11
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Multiphonon Absorption and Photon Avalanche Criterion in Erbium Doped Materials

80%
Auzel F.
Acta Physica Polonica A
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1996
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vol. 90
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issue 1
7-19
EN
The photon avalanche effect has been recently observed at room temperature in erbium doped fluoride glasses and crystals, in a particularly clear way, displaying simultaneously all the typical features of this effect: (i) existence of a threshold for transmission at the excitation wavelength, (ii) up-conversion excitation threshold, (iii) long delay for threshold establishment. Analysing the first step of the avalanche effect as an anti-Stokes multiphonon absorption, it can be shown why this effect is so clearly observed at room temperature in our erbium studies. Our results are compared with other cases of avalanche, with cases which have been called "looping effects" and "quasi-avalanche" ones.
12
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Population Inversion on Transition into the Ground State of Atoms Induced by Optical Excitation and Collisions

80%
Markov R., Plekhanov A., Shalagin A.
Acta Physica Polonica A
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2002
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vol. 101
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issue 1
77-88
EN
Lasing on the sodium resonance transitions (D_1 and D_2 lines) at the superluminosity regime was observed upon the non-resonance excitation in the presence of a buffer gas. Dependences of the lasing intensity on the pump radiation intensity and its frequency detuning from the frequencies of resonance transitions were examined. It was found that under the specific experimental conditions (high buffer gas pressure, sufficiently high intensity of pump radiation) upon the large positive frequency detuning of pump radiation with respect to the frequency of resonance ("working") transition, contrary to ingrained conceptions, population inversion for the "working" transition is raised. That results in the observed phenomena.
13
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Investigation of Radiation Trapping in Atomic Vapour Excited by Weak Resonant Laser Pulses

80%
Chorąży J., Stacewicz T.
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vol. 96
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issue 3-4
383-390
EN
We present results of our investigations on radiation trapping in sodium vapour excited to 3P level by weak laser pulses. The evolution of the fluorescence signal as well as the evolution of excited atoms distribution were studied using the Monte Carlo method. Some predictions of these investigations were checked experimentally.
14
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Extreme Nonlinear Optics in Terms of Riccati-Type Equation

80%
Parzyński R., Plucińska A.
Acta Physica Polonica A
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2005
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vol. 108
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issue 6
959-969
EN
In an approach based on the nonlinear Riccati-type differential equation for the ratio of the level population amplitudes, rather than on the optical Bloch equations, we describe the response of a two-level system to a few-cycle light pulse of intensity from the regime of extreme nonlinear optics, i.e., when the Rabi and transition frequencies are comparable. Emphasis is put on the dependence of the spectra of the scattered light on the carrier-envelope phase, duration and strength of both resonant and off-resonant pulses.
15
Content available remote

Correlation? What Correlation?

80%
Eberly J. H.
Acta Physica Polonica A
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1994
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vol. 86
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issue 1
151-157
EN
We describe recent developments in the theory of multi-electron atoms in strong radiation fields, with particular focus on the degree of e-e correlation accompanying a laser-atom interaction.
16
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On the Time Dependent Features of the Two-Colour Light Pulses Propagation in the Sodium Vapour

80%
Alhasan A., Fiutak J.
Acta Physica Polonica A
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2006
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vol. 109
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issue 2
143-157
EN
The phase and group velocities of the pulsed light are suitably defined and calculated. So are the duration of both pulses, probe and coupling, and their energies as a function of the travelled distance. The time evolution, for a given distance, of the dressed atom state is described by the Liouville-von Neumann equation for the density matrix.
17
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An Iterative Method for Extreme Optics of Two-Level Systems

80%
Parzyński R., Sobczak M., Plucińska A.
Acta Physica Polonica A
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2004
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vol. 106
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issue 6
827-842
EN
We formulate the problem of a two-level system in a linearly polarized laser field in terms of a nonlinear Riccati-type differential equation and solve the equation analytically in time intervals much shorter than half the optical period. The analytical solutions for subsequent intervals are then stuck together in an iterative procedure to cover the whole scale time of the laser pulse. Very good quality of the iterative method is shown by recovering with it a number of subtle effects met in earlier numerically calculated photon-emission spectra from model molecular ions, double quantum wells, atoms, and semiconductors. The method is used to describe novel, carrier-envelope offset phase effects in the region of extreme nonlinear optics, i.e., when two-level systems are exposed to pulses of only a few cycles in duration and strength ensuring the Rabi frequency to approach the laser light frequence.
18
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Comparison Between Standard and Modified Judd-Ofelt Theories in a Pr^{3+}-Doped Fluoride Glass

80%
Goldner P., Auzel F.
Acta Physica Polonica A
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1996
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vol. 90
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issue 1
191-196
EN
A method which takes into account normalized oscillator strengths is detailed for the calculation of parameters in Judd-Ofelt theory (B.R. Judd, Phys. Rev. 127, 750 (1962), G.S. Ofelt, J. Chem. Phys. 37, 511 (1962)). In the case of a Pr^{3+} -doped fluorozirconate glass, the Judd-Ofelt parameters obtained in this way do not depend strongly on the transitions included in the fit. Particularly, it is no longer necessary to exclude the ^{3}H_{4} → ^{3}P_{2} transition from the analysis. Three modified theories (F. Auzel, S. Hubert, P. Delamoye, J. Lumin. 26, 251 (1982), A.A. Kornienko, A.A. Kaminskii, E.B. Dunina, Phys. Status Solidi B 157, 267 (1990)) are also considered but do not improve the calculated intensities when the energy of the 5d level is set to its experimentally determined value. Finally, in connection with 1.3 μ amplification, the 1.3 μ reabsorption (^{1}G_{4} → ^{1}D_{2}) oscillator strength is computed from the various models as well as the 1.3 μ emission branching ratio (^{1}G_{4} → ^{3}H_{5}/^{1}G_{4} → ^{3}H_{6}). The best agreement with experiment is obtained with the standard Judd-Ofelt theory.
19
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Dynamics of Argon Clusters in an Intense Laser Pulse: Bloch-Like Hydrodynamic Model

80%
Rusek M., Orłowski A.
Acta Physica Polonica A
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2004
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vol. 106
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issue 1
3-12
EN
The dynamics of small (<55 atoms) argon clusters ionized by an intense, infrared, femtosecond laser pulse is studied using a Bloch-like hydrodynamic model. Evolution of both free electrons and ions formed in the cluster explosion process is examined. Oscillations of the electron cloud in a rare-gas atomic cluster are described as a motion of a fluid obeying Bloch-like hydrodynamic equations. Our theoretical approach includes all possible ionization mechanisms: tunnel (or field) ionization both by an external laser field, and by an internal field due to the space-charge distribution inside the cluster, as well as electron-impact (or collisional) ionization. The results of our simulations are compared both with experimental findings and with predictions of other theoretical models.
20
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Three-Colour Excitation of D_1 Transition in Cold Rubidium Atoms

80%
Alhasan A.
Acta Physica Polonica A
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2007
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vol. 111
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issue 3
299-321
EN
We analyse the three-colour electromagnetically induced transparency for the D_1 transition in cold ^{87}Rb atoms. We report an enhancement of the electromagnetically induced emission of a drive field as an exclusive enhancement of the third- and fourth-rank components of the density matrix. Moreover, the gain experienced by the drive field is attributed to the influence of the quantum switching effect on the increased absorption of the probe field. The electromagnetically induced emission effect is employed to generate slow light Gaussian-wave trains with shape preserving. These soliton trains were not only generated in the drive channel as has been designated but also in the switch channel which reveals multiple-light storage phenomenon.
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