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1
Content available remote

Kinetic Energies in the Direct Double Photoionization of Helium and the Electron-Electron Correlation

100%
Bauer J.
Acta Physica Polonica A
|
2000
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vol. 97
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issue 4
629-637
EN
We present a simple model describing kinetic energy probability distributions of outgoing electrons in the direct double photoionization of helium. The model applies to photons of energy greater than the binding energy of the atom and to radiation intensities extending from perturbation regime to the strong-field one. It appears that the shape of probability distribution is mainly determined by the electron-electron correlation in their final state. For nonperturbative intensities the distribution depends strongly on polarization of incident radiation.
2
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Strong-Field Phenomena in Atoms - Quasiclassical Approach

100%
Fedorov M. V.
Acta Physica Polonica A
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1994
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vol. 86
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issue 1
235-243
EN
A quasiclassical (WKB) approach is used to construct a theory of atomic transitions induced by a strong light field. This approach is used to find the "Coulomb-Volkov" solutions of the Schrödinger equation in which both the Coulomb and light fields are taken into account. These solutions are shown to be applicable in a region of low light frequencies, low electron energies and angular momenta. The found solutions are used to describe two kinds of processes: strong-field photoionization from highly excited (Rydberg) atomic levels, and field-assisted electron-ion scattering. In the photoionization problem the strong-field complex quasi-energies of an atom are found. A problem of the strong-field stabilization of an atom, as well as the expected behavior of the ionization time in its dependence on the light field strength are discussed.
3
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High Order Harmonic Generation and Atomic Stabilization in Ultra-Intense Laser Pulses

100%
Maquet A., Millack T., Véniard V.
Acta Physica Polonica A
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1994
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vol. 86
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issue 1
191-199
EN
We present results of recent numerical simulations on the non-linear response of a single-electron atom submitted to an intense laser pulse. We address both the questions of the light scattered by the atom and the possible stabilization against ionization. One of the results of our simulations is the the presence of hyper-Raman lines in the high-order harmonic spectra. We suggest that these lines could be a signature of atomic stabilization.
4
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Laser-Matter Interaction with Intense Short Laser Pulses

100%
Lompré L. A.
Acta Physica Polonica A
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1994
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vol. 86
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issue 1
135-150
EN
Laser-matter interaction in rare gases (He, Ne, Ar and Xe) has been investigated using a 1 ps Nd-glass laser pulse at 1053 nm with intensities between 10^{13} to 10^{18} W/cm^{2}. Three aspects of the interaction have been studied: the creation of multiply charged ions, the energy of the ejected electron and the propagation in an underdense plasma. At the maximum laser intensity, all electrons of the outer shell are removed, except in Ne for which charge states up to 7+ are observed. Comparison of experimental data with Ammosov et al. tunneling model shows a very good agreement, indicating that ionization with a 1 ps pulse in the near infrared light mainly occurs in tunneling regime. Electrons created in a low-density medium with energies up to 5 keV have been detected. These energies are far above the energy acquired during the ionization process, indicating that at high laser intensities electron energy is governed by ponderomotive force. Finally, the study of the propagation of an intense laser pulse in an underdense plasma shows that it is not possible to obtain simultaneously high laser intensity (10^{17}-10^{18} W/cm^{2}) and high electron density (10^{19}-10^{20} cm^{-3}). Best conditions for solving this problem will be discussed.
5
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The Spatial Region of Photoionization in a Strong Laser Field

100%
Bauer J.
|
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.
6
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Use of Bersons-Kulsh Form Factor of Short-Pulse Approximation in Rydberg-State Physics

100%
Parzyński R., Sobczak M.
Acta Physica Polonica A
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2003
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vol. 103
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issue 1
13-23
EN
The experiments on high Rydberg states interacting with short electromagnetic pulses were hitherto mainly explained by using numerical integration of the time-dependent Schrödinger equation in a restricted state basis. In this study we apply a different approach based on the Bersons-Kulsh analytical form factor of the short-pulse approximation. This analytical approach is shown to well reproduce the recent experimental results and those of numerical integration of the time-dependent Schrödinger equation both in the case of terahertz half-cycle pulses and optical many-cycle pulses. This fact enables a recommendation of the analytical Bersons-Kulsh form factor as an alternative and efficient method of quantum calculations of electromagnetically induced Rydberg state redistribution.
7
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Fractional Revival of Rydberg Wave Packets in Twice-Kicked One-Dimensional Atoms

100%
Chatterjee S., Saha A., Talukdar B.
Acta Physica Polonica A
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2011
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vol. 120
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issue 3
438-442
EN
We study revival and fractional revival phenomena of wave packets in a one-dimensional Rydberg atom irradiated by two time-delayed half-cycle pulses using an autocorrelation function characterized by electronic transition probabilities as weighting factors rather than modeling them by a Gaussian or Lorentzian distribution. If the momentum (q_2) delivered to the atom by the second kick is much smaller than that (q_1) imparted by the first one, the times of revival and fractional revival coincide with those of the single kicked atom. For q_2 ≥ q_{1}/4 appearance of revival and fractional revival depends on both the values of q_2 and time delay t_1 between the pulses but more sensitively on t_1. The number of fractional revivals tends to become numerous as the value of t_1 increases.
8
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One-Dimensional versus Three-Dimensional Approaches to the Rydberg Wave Packet Dynamics

100%
Kopyciuk T., Parzyński R.
Acta Physica Polonica A
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2006
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vol. 110
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issue 1
41-49
EN
We show that a one-dimensional approximation to a real three-dimensional atom offers good results for a selected group of the Rydberg states. It is demonstrated in the context of evolution of the Rydberg wave packets produced by the so-called half-cycle pulses.
9
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The Initial-value Problem in the Quasi-classical Theory of Strong-field Photoionization of Rydberg Atoms

100%
Tikhonova O., Fedorov M.
Acta Physica Polonica A
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1998
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vol. 93
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issue 1
77-85
EN
Photoionization of Rydberg atoms is considered in the quasi-classical (WKB) approach. The total nonlinear strong-field ionization rate is found and investigated. The time of ionization, as a function of a growing field-strength amplitude, is shown to approach asymptotically the Kepler period t_{k}. Interference stabilization of Rydberg atoms is confirmed to exist in the case of short pulses (shorter than the Kepler period).
10
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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.
11
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Hyperfine Structure Constants in the 10^{2}D_{3/2} and 11^{2}D_{3/2} States of ^{85}Rb

100%
Głódź M., Kraińska-Miszczak M.
Acta Physica Polonica A
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1993
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vol. 83
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issue 2
161-165
EN
The magnetic-dipole interaction constants A and the electric-quadrupole interaction constants B of two n^{2}D_{3/2} states of ^{85}Rb were measured by the quantum beat method. The results are - for n = 10: |A| = 0.393(8) MHz, |B| = 0.141(13) MHz, for n = 11: |A| = 0.283(6) MHz, |B| = 0.100(11) MHz, and positive ratio B/A for both states.
12
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Content available

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.
13
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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
|
2004
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vol. 106
|
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.
14
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
|
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.
15
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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.
16
Publication available in full text mode
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On Argon-Induced Pressure Shifts of ^{198}Hg Spectral Lines Associated with Quasi-Rydberg Transitions

80%
Trawiński R.
Acta Physica Polonica A
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2006
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vol. 110
|
issue 1
51-56
EN
The extended Omont-Kaulakys-Ueda treatment of collisional effects on quasi-Rydberg states, in which the perturbation of the lower state is taken into account, is applied to mercury-argon system. The pressure shift coefficients of 6p-ns and 6p-nd spectral lines are calculated and compared with available experimental data.
17
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Content available

Electron Energy Spectra from the Strong-Field Double-Ionization of Xenon

80%
Chaloupka J., Lafon R., Rudati J., Sheehy B., Agostini P., Kulander K., DiMauro L.
Acta Physica Polonica A
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2002
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vol. 101
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issue 3
337-346
EN
The electron energy spectra correlated to the strong-field double-ionization of xenon are presented at three laser intensities. The double-ionization electrons are on average more energetic than those generated from single-ionization. This difference in energy is not manifested as a simple scaling to higher electron energies, but rather as a change in the shape of the spectra. This trend is observed at all intensities. Most notably, the comparison between single- and double-ionization spectra is very similar at low and high peak laser intensities. This could imply that a sequential double-ionization process dominates at all intensities, even where the double ion yield is enhanced.
18
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Towards Attosecond Pulses with High Harmonics

80%
Agostini P., Paul P., Breger P., Toma E., Muller H., Mullot G., Augé F., Balcou P.
Acta Physica Polonica A
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2002
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vol. 101
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issue 3
313-324
EN
The high harmonics produced by focusing an intense femtosecond laser in a gas are theoretically shown to be locked in phase. The physics of this locking is discussed and a new method based on quantum interference in two-photon, two-color ionization allowing to retrieve the relative phase of harmonic pairs is described. The main result is that the 5 harmonics of orders 11-19 produced in argon generate a train of subfemtosecond pulses with a period of 1.35 fs and a duration of 250 attoseconds.
19
Content available remote

Circularly Polarized Laser Fields, with Different Z, Including Non-Zero Initial Momentum

80%
Ristić V., Miladinović T., Stevanović J.
Acta Physica Polonica A
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2011
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vol. 119
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issue 6
761-763
EN
In this paper, by estimating the influence of different atom charge Z to the transition rate in tunnel ionization of atoms in strong laser fields we are devoloping further the observations from our earlier work. That is in the process of tunnel ionization including non-zero momentum into calculation of the transition rate gives result in lower transition rates for ejecting electrons from atoms by low-frequency laser fields, indicating that much of the photons are engaged in transferring energy to the free electron and thus unable to contribute to the effect of ionization. This is a conclusion that needs further experimental testing, which would clarify the mechanisms of tunnel ionization.
20
Content available remote

Radiation Amplification near an Autoionizing State

80%
Lambropoulos P., Zhang J., Van Enk S. J.
Acta Physica Polonica A
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1994
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vol. 86
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issue 1
61-69
EN
We present an internally consistent theory of amplification near the minimum of autoionizing states with quantitative application to calcium. We have included a completely specified three-photon pumping and we find certain unusual aspects of the system. We find conditions under which the system remains in a steady state, although being coupled to the continuum. For incoherent pumping we obtain quantitative results for the gain. Our results and their extensions are also discussed in the context of present-day experimental possibilities.
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