共查询到20条相似文献,搜索用时 625 毫秒
1.
M. Fifirig A. Cionga 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):33-39
We study the “coherent phase control” between the three-photon ionization by a fundamental laser field and the one-photon
ionization by its third harmonic for a hydrogen atom in its ground state. The relative phase δ of the harmonic field with
respect to the fundamental laser radiation “modulates” the interference between the two ionization channels, which is important
near the crossing points between the ionization rates of the two individual processes. Numerical results for the total ionization
rate and for the angular distribution of the photoelectrons as a function of the phase δ are presented for frequencies located
in the vicinity of the atomic resonances corresponding to the absorption of two laser photons.
Received 31 August 2000 and Received in final form 6 February 2001 相似文献
2.
L.A.A. Nikolopoulos Takashi Nakajima P. Lambropoulos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):297-304
Calculations of intense field (around 1016 W/cm2) single- and double-ionization processes in helium at XUV wavelengths are presented. The laser wavelength is chosen near
the | 2s2p
1
P autoionization structure and the dynamics are explored. Single and double ionization yields, as well as the photoelectron
energy spectrum for photon energies around the autoionization structure are calculated. In the case of a pulse of few femtoseconds
duration, no significant enhancement of the double ionization yield has been found in tuning the photon frequency around the
peak of the resonance. It is also shown that in the case of a long pulse (and hence narrow compared with the relevant autoionization
width), the branching ratio of double to single ionization yield can be relatively enhanced by tuning to the absorption minimum
of the resonance.
Received 19 February 2002 / Received in final form 2 May 2002 Published online 19 July 2002 相似文献
3.
M. Fifirig A. Cionga F. Ehlotzky 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):333-336
The two-photon ionization of the hydrogen atom from its ground state by a two-colour electromagnetic field consisting of two
odd harmonics of the same IR laser is analyzed. The influence of the state of polarization of the bichromatic field on the
azimuthal angular distribution and the dependence of the elliptic dichroism on the photon frequencies are reported.
Received 11 December 2002 Published online 29 April 2003
RID="a"
ID="a"e-mail: fritz.ehlotzky@uibk.ac.at 相似文献
4.
S. Kazamias F. Weihe D. Douillet C. Valentin T. Planchon S. Sebban G. Grillon F. Augé D. Hulin Ph. Balcou 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(3):353-359
We report a systematic study of high order harmonic generation with an infrared laser apertured by an iris, as a function
of the aperture size. Measurements were made of harmonic generation efficiency for different gas species, laser energies and
focal geometries. Harmonic efficiencies as a function of aperture show a characteristic peaked shape, which is independent
of gas species and harmonic order. A one dimensional, time dependent simulation of harmonic generation in a gas cell, taking
into account experimentally measured transverse coherence of the laser, closely reproduces the observed behaviours. We show
that the aperture diameter which maximizes harmonic yield is the result of a compromise between considerations of focal geometry
and ionization (which favour small apertures); and harmonic dipole amplitude and phase (which favour large apertures).
Received 31 May 2002 Published online 24 September 2002
RID="a"
ID="a"e-mail: kazamias@ensta.fr
RID="b"
ID="b"UMR 7639 du CNRS 相似文献
5.
M.A. Kornberg J.E. Miraglia 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):45-51
We present numerical results for the photoelectron spectrum in double ionization by keV photons in the quasiequal-energy sharing
region. In this region of the spectrum, the relevant ionizing mechanism is due to a mutual sharing of the photon momentum
by both electrons, with small momentum transferred to the atomic nucleus. Calculations were performed for photon energies
of 25 and 50 keV, where retardation effects are fundamental, while final-state correlations are of minor importance. The spectra
present a two-peak structure, with maxima located at the photoelectron energies , with the photon energy in atomic units. We discuss the general features of the spectrum in terms of the picture of the photoionization
of two free electrons, and we propose a way of detecting the contribution by experiments.
Received 24 January 2000 相似文献
6.
A. Flettner J. König M.B. Mason T. Pfeifer U. Weichmann R. Düren G. Gerber 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(1):115-119
High harmonic generation is compared in the dependence on the ellipticity of the fundamental laser radiation for an atomic
and a molecular system. In particular argon and nitrogen are compared employing molecular beams and intense ( 3×1014 W/cm2) and ultrashort (80 fs) 800 nm laser pulses. It turns out that for all the harmonics under investigation (H5, H13 and H21)
the harmonic yield decreases slower with the ellipticity for the molecule than for the atom. This indicates differences in
atomic and molecular high harmonic generation.
Received 24 April 2002 Published online 24 September 2002 相似文献
7.
Ultrahigh Harmonic Generation from an Atom with Superposition of Ground State and Highly Excited States 总被引:1,自引:0,他引:1 下载免费PDF全文
We investigate the high-order harmonic generation from an atom prepared in a superposition of ground state and highly excited state. When the atom is irradiated by an ultrashort pulse, the cutoff position of the plateau in the harmonic spectrum is largely extended compared with the case that the atom is initially in the ground state. The physics of the extension of the high-order harmonic plateau can be interpreted by the spatial structure of the atomic initial wave packet. We can optimize the generation of high-order harmonics by substituting the excited state for a particular coherent superposition of some highly excited states to form a spatially localized excited wave packet. 相似文献
8.
U. Kentsch T. Werner G. Zschornack F. Grossmann V.P. Ovsyannikov F. Ullmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):297-305
Irq+ ( 41≤q≤64) ions with open-shell configurations have been produced in the electron beam of the room-temperature Dresden Electron
Beam Ion Trap (Dresden EBIT) at electron excitation energies from 2 keV to 13 keV. X-ray emission from direct excitation processes
and radiative capture in krypton-like to aluminium-like iridium ions is measured with an energy dispersive Si(Li) detector.
The detected X-ray lines are analyzed and compared with results from multiconfigurational Dirac-Fock (MCDF) atomic structure
calculations. This allows to determine dominant produced ion charge states at different electron energies. The analysis shows
that at the realized working gas pressure of 5×10-9mbar for higher charged ions the maximum ion charge state is not preferently determined by the chosen electron beam energy
needed for ionization of certain atomic substates, but by the balance between ionization and charge state reducing processes
as charge exchange and radiative recombination. This behaviour is also discussed on the basis of model calculations for the
resulting ion charge state distribution.
Received 12 July 2001 and Received in final form 10 September 2001 相似文献
9.
T. Mercouris C.A. Nicolaides 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):241-248
By implementing a time-independent, nonperturbative many-electron, many-photon theory (MEMPT), cycle-averaged complex eigenvalues
were obtained for the He atom, whose real part gives the field-induced energy shift, Δ(ω
1, F
1;ω
2, F
2,ϕ), and the imaginary part is the multiphoton ionization rate, Γ(ω
1, F
1;ω
2, F
2,ϕ), where ω is the frequency, F is the field strength and ϕ is the phase difference. Through analysis and computation we show that, provided the intensities
are weak, the dependence of Γ(ω
1, F
1;ω
2, F
2,ϕ) on ϕ is simple. Specifically, for odd harmonics, Γ varies linearly with cos(ϕ) whilst for even harmonics it varies linearly
with cos(2ϕ). In addition, this dependence on ϕ holds for Δ(ω
1, F
1;ω
2, F
2,ϕ) as well. These relations may turn out to be applicable to other atomic systems as well, and to provide a definition of
the weak field regime in the dichromatic case. When the combination of (ω
1, F
1) and (ω
2, F
2) is such that higher powers of cos(ϕ) and cos(2ϕ) become important, these rules break down and we reach the strong field
regime. The herein reported results refer to Γ(ω
1, F
1;ω
2, F
2,ϕ) and Δ(ω
1, F
1;ω
2, F
2,ϕ) for He irradiated by a dichromatic ac-field consisting of the fundamental wavelength λ = 248 nm and its 2nd, 3rd and 4th
higher harmonics. The intensities are in the range 1.0×1012-3.5×1014 W/cm2, with the intensity of the harmonics being 1-2 orders of magnitude smaller. The calculations incorporated systematically
electronic structure and electron correlation effects in the discrete and in the continuous spectrum, for 1S, 1P, 1D, 1F, 1G, and 1H two-electron states of even and odd parity.
Received 9 July 2000 and Received in final form 2 November 2000 相似文献
10.
P. Schlagheck A. Buchleitner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):401-415
We provide a detailed quantum treatment of the spectral characteristics and of the dynamics of nondispersive two-electron
wave packets along the periodically driven, collinear frozen planet configuration of helium. These highly correlated, long-lived
wave packets arise as a quantum manifestation of regular islands in a mixed classical phase space, which are induced by nonlinear
resonances between the external driving and the unperturbed dynamics of the frozen-planet configuration. Particular emphasis
is given to the dependence of the ionization rates of the wave packet states on the driving field parameters and on the quantum
mechanical phase space resolution, preceded by a comparison of 1D and 3D life times of the unperturbed frozen planet. Furthermore,
we study the effect of a superimposed static electric field component, which, on the grounds of classical considerations,
is expected to stabilize the real 3D dynamics against large (and possibly ionizing) deviations from collinearity.
Received 7 November 2002 / Received in final form 2 December 2002 Published online 28 January 2003 相似文献
11.
E.G. Thrapsaniotis 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(2):239-247
The present paper deals with the motion of a Brownian particle on two identical but shifted potential surfaces, coupled via a tunneling matrix element in an external electric field. Dissipation is induced by a heat bath represented by an infinite
set of harmonic oscillators with a continuum range of frequencies. We derive a perturbative solution for the quantum coherence
term of the particle system after performing a small-polaron-like transformation. This is subsequently necessary for the extraction
of an equation that describes the reduced dynamics and the minimal action path of the Brownian particle. Finally we extract
expressions for the population relaxation rate and the pure quantum-dephasing rate of the two-level system.
Received 4 January 2001 and Received in final form 12 March 2001 相似文献
12.
Harmonic Enhancement Mechanism of a Superposition State Atom Irradiated by Short Pulses 总被引:1,自引:0,他引:1 下载免费PDF全文
We investigate the high-order harmonic generation (HHG) of a model atom whose initial state is prepared in a superposition of its ground state and an excited state irradiated by different duration laser pulses. Compared to the HHG generated from an atom whose initial state is in its ground state, its conversion efficiency obtains some enhancement. The enhancement originates from the higher ionization rate (rather than the ionization yield) of the atom with superposition initial state. 相似文献
13.
L. Sanchez-Palencia P. Horak G. Grynberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):353-364
We numerically study the spatial diffusion of an atomic cloud experiencing Sisyphus cooling in a three-dimensional linlin optical lattice in a broad range of lattice parameters. In particular, we investigate the dependence on the size of the
lattice sites which changes with the angle between the laser beams. We show that the steady-state temperature is largely independent
of the lattice angle, but that the spatial diffusion changes significantly. It is shown that the numerical results fulfill
the Einstein relations of Brownian motion in the jumping regime as well as in the oscillating regime. We finally derive an
effective Brownian motion model from first principles which gives good agreement with the simulations.
Received 8 August 2001 and Received in final form 6 November 2001 相似文献
14.
In Rydberg atoms subject to static and harmonic collinear electric fields, intrashell transition can be induced by the first
order perturbation from a small perpendicular electric or magnetic field, or by effects of the second order in the major fields.
Both mechanisms lead to resonances that are suppressed under certain conditions, and high-frequency interference oscillations
in case of non-adiabatic field switching. Recent measurements of microwave ionization signals show very rich and fascinating
structures similar to the ones predicted for intrashell mixing. We show that the observed ionization structures may be explained
by diabatic electric-field ionization and the consistent use of perturbation theory for intrashell mixing. In particular,
the dominant oscillation frequency is successfully interpreted in terms of interference between first and second order transition
amplitudes. New predictions are provided. The present approach gives a comprehensive picture of intrashell transitions, which
may be tested in future experiments designed to observe such transitions directly.
Received 2 May 2002 / Received in final form 23 September 2002 Published online 21 January 2003
RID="a"
ID="a"e-mail: Valentin.Ostrovsky@pobox.spbu.ru
RID="b"
ID="b"e-mail: horsdal@ifa.au.dk 相似文献
15.
16.
A. Buchleitner K. Sacha D. Delande J. Zakrzewski 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(2):145-157
We present a semiclassical analysis of the dynamics of Rydberg states of atomic hydrogen driven by a resonant microwave field
of linear polarization. The semiclassical quasienergies of the atom in the field are found to be in very good agreement with
the exact quantum solutions. The ionization rates of individual eigenstates of the atom dressed by the field reflect their
quasiclassical dynamics along classical periodic orbits in the near integrable regime, but exhibit a transition to nonspecific
rates when global chaos takes over in phase space. We concentrate both on the principal resonance where the unperturbed Kepler
frequency is equal to the driving field frequency and on the higher primary resonance The latter case allows for the construction of nondispersive wave packets which propagate along Kepler ellipses of intermediate
eccentricity.
Received: 23 June 1998 / Accepted: 10 November
1998 相似文献
17.
T. Halfmann K. Böhmer L.P. Yatsenko A. Horsmans K. Bergmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(1):113-123
We report the observation of pronounced coherent population trapping and dark resonances in Rydberg states of xenon. A weak
two-photon coupling with radiation of = 250 nm is induced between the 5p6
1
S
0 ground state of xenon and state 5p
56p[1/2]0, leading to (2+1) resonantly enhanced three-photon ionization. The state 5p
56p[1/2]0 is strongly coupled by radiation with ≃ 600 nm to 5p
5
ns[J
C]1 or 5p
5
nd[J
C]1 Rydberg states with principal quantum numbers n in the range 18 ?n? 23 and with the rotational quantum number of the ionic core J
C = 1/2 or J
C = 3/2. The ionization is monitored through observation of the photoelectrons with an energy resolution ΔE = 150 meV which is sufficient to distinguish the ionization processes into the two ionization continua. Pronounced and robust
dark resonances are observed in the ionization rate whenever is tuned to resonance with one of the ns- or nd-Rydberg states. The dark resonances are due to efficient population trapping in the atomic ground state 5p6
1
S
0 through the suppression of excitation of the intermediate state 5p
56p[1/2]0. The resolution is sufficient to resolve the hyperfine structure of the ns-Rydberg levels for odd xenon isotopes. The hyperfine splitting does not vary significantly with n in the given range. Results from model calculations taking the natural isotope abundance into account are in good agreement
with the observed spectral structures. Pronounced dark resonances are also observed when the dressing radiation field with
is generated from a laser with poor coherence properties. The maximum reduction of the ionization signal clearly exceeds
50%, a value which is expected to be the maximum, when the dip is caused by saturation of the transition rate between the
intermediate and the Rydberg state due to incoherent radiation. This work demonstrates the potential of dark resonance spectroscopy
of high lying electronic states of rare gas atoms.
Received 7 May 2000 and Received in final form 25 June 2001 相似文献
18.
L. Vernac M. Pinard E. Giacobino 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(1):125-136
We show the equivalence between an ensemble of two-level atoms driven by a squeezed vacuum field, and a harmonic oscillator
coupled to a squeezed field. We give the conditions for optimal squeezing transfer from the field to the atomic ensemble.
We show that EPR-type correlations are created between the atomic ensemble and the incoming field.
Received 23 January 2001 相似文献
19.
A. Wetzels A. Gürtler H.G. Muller L.D. Noordam 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):157-165
An optically excited Rydberg wavepacket can be generated by exciting the electron from a low-lying state to a coherent superposition
of high-lying states with a short broadband optical pulse. A special kind of Rydberg wavepacket is generated in the case of
a interaction of a weak THz half cycle pulse with a stationary Rydberg state, called the THz wavepacket. This THz wavepacket
is a coherent superposition of the initial Rydberg state and its neighbouring states. We have investigated the time evolution
of THz wavepackets by measuring the impact of two in time delayed half cycle pulses ( ≈ 200 V cm-1) on the population of a stationary (n = 40) Rydberg state in rubidium. The first half cycle pulse creates the THz wavepacket and the second half cycle pulse probes
the dynamics of the THz wavepacket. We support our experimental data by numerically solving the Schr?dinger equation and with
a semi-classical picture. Whereas an optically excited wavepacket is initially localized, a THz wavepacket is initially delocalized
and becomes localized after half a revival time.
Received 23 August 2000 and Received in final form 27 March 2001 相似文献
20.
M. Johansson A.M. Morgante S. Aubry G. Kopidakis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):279-283
Modulational instability of travelling plane waves is often considered as the first step in the formation of intrinsically
localized modes (discrete breathers) in anharmonic lattices. Here, we consider an alternative mechanism for breather formation,
originating in oscillatory instabilities of spatially periodic or quasiperiodic nonlinear standing waves (SWs). These SWs
are constructed for Klein-Gordon or Discrete Nonlinear Schr?dinger lattices as exact time periodic and time reversible multibreather
solutions from the limit of uncoupled oscillators, and merge into harmonic SWs in the small-amplitude limit. Approaching the
linear limit, all SWs with nontrivial wave vectors (0 < Q < π) become unstable through oscillatory instabilities, persisting for arbitrarily small amplitudes in infinite lattices.
The dynamics resulting from these instabilities is found to be qualitatively different for wave vectors smaller than or larger
than π/2, respectively. In one regime persisting breathers are found, while in the other regime the system thermalizes.
Received 6 October 2001 / Received in final form 1st March 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: mjn@ifm.liu.se 相似文献