共查询到20条相似文献,搜索用时 15 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.
A.-S.F. Obada A.M. Abdel-Hafez M. Abdelaty 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(3):289-294
Phase properties of the field interacting with a two-level atom in a lossless cavity Jaynes-Cummings model, taking into account
the level shifts produced by Stark effect with an additional Kerr medium for one-mode are studied using the phase formalism
of Pegg and Barnett. It is shown in particular that phase properties of the field reflect the collapse and revival phenomena.
The results for the time evolution of the phase probability distribution and the phase fluctuations are obtained. The effect
of Stark shift on the phase properties in both the absence and presence of a Kerr medium is analyzed. Phase localization is
found for certain choice of the parameters.
Received: 27 March 1998 / Revised: 8 June 1998 / Accepted: 9 June 1998 相似文献
3.
S. Cohen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(1):31-38
Approximate analytical formulae describing the energy variation of line intensities, autoionization widths and lineshape asymmetries,
are derived for a Phase-Shifted Multichannel Quantum Defect Theory model composed of two closed interacting channels coupled
to two effective continua. This is accomplished by putting the two compatibility equation solutions, for the common phase
shifts of the two open channels, in such a form so the resonant behavior is attributed to one of them, the other accounting
for an energy dependent background. Then, the well-known procedures for the simpler case where only one continuum is considered
are applied, using only the resonant solution. The method is quite general and applicable to any MQDT model with two or more
open channels. The resulting analytical formulae are tested on experimental spectra of Sr, Ba and Cu and it is shown that
they are valid as long as: i) The resonances are non-overlapping, ii) The direct closed channel coupling is much stronger
than the indirect one through the continua and (when excitation matrix elements are involved) iii) The open channels excitation
strength is smaller or at least comparable to the closed channels one.
Received: 26 May 1998 / Accepted: 1st July 1998 相似文献
4.
I. A. Ivanov A. S. Kheifets 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(2):249-255
We apply a non-perturbative procedure for the calculation of the total
photoionization cross-section of two-electron atomic systems. The procedure is based on the Floquet-Fourier representation
of the time-dependent Schr?dinger equation. With the use of the Hylleraas-type basis functions, the total photoionization
cross-sections obtained are within the accuracy of a fraction of a percent, which, we believe, is the most accurate estimate
for the cross-sections available. The total photoionization cross-sections for neutral helium deviate notably from the benchmark
experimental data [J.A.R. Samson et al., J. Phys. B 27, 887 (1994)]. 相似文献
5.
M.A. Baig M. Yaseen Raheel Ali Ali Nadeem S.A. Bhatti 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(2):201-209
We report new measurements on laser-assisted molecular dissociative sequential excitation and ionization spectra of strontium
vapor. A single Nd:YAG pumped dye laser in conjunction with an atomic beam apparatus have been used to investigate the even
parity 5snd
3,1
D
2
Rydberg series resulting from the 5s5p
1
P
1
resonance level. The relative intensities changes among the 5snd
3
D
2
and 1
D
2
Rydberg series are attributed to the interactions with the 4d6s
1,3
D
2
perturbers, respectively. The interchannel interactions between the 5snd
1
D
2
series and the 4d6s
1
D
2
level and among the 5snd
3
D
1,2,3
series and the 4d6s
3
D
1,2,3
intruders have been separately parameterized using the two-channel quantum defect theory.
Received: 10 September 1998 / Received in final form: 16 December 1998 相似文献
6.
P. Müller B.A. Bushaw W. Nörtershäuser K. Wendt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):33-44
Isotope shifts and hyperfine structure have been measured in 4snp 1 P1 and Rydberg states for all stable calcium isotopes and the radioisotope 41Ca using high-resolution laser spectroscopy. Triple-resonance excitation via
Rydberg state was followed by photoionization with a CO2 laser and mass selective ion detection. Isotope shifts for the even-mass isotopes have been analyzed to derive specific mass
shift and field shift factors. The apparent isotope shifts for 41Ca and 43Ca exhibit anomalous values that are n-dependent. This is interpreted in terms of hyperfine-induced fine-structure mixing, which becomes very pronounced when singlet-triplet
fine-structure splitting is comparable to the hyperfine interaction energy. Measurements of fine-structure splittings for
the predominant isotope 40Ca have been used as input parameters for theoretical calculation of the perturbed hyperfine structure. Results obtained by
diagonalizing the second-order hyperfine interaction matrices agree very well with experimentally observed spectra. These
measurements allow the evaluation of highly selective and sensitive methods for the detection of the rare 41Ca isotope.
Received 17 December 1999 and Received in final form 29 March 2000 相似文献
7.
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
8.
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
9.
M. A. Baig S. Mahmood M. A. Kalyar M. Rafiq N. Amin S. U. Haq 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):9-16
We report new measurements of the oscillator strengths of the 3p
2P3/2 ↦nd 2D5/2, 3/2 and 3p 2P1/2 ↦
nd 2D3/2 Rydberg transitions of sodium using a thermionic diode ion
detector in conjunction with the Nd:YAG pumped dye lasers. The ns
2S1/2 and nd 2D5/2,3/2 Rydberg series have been recorded
via two-step excitation, from the 3p 2P3/2 and 3p 2P1/2
intermediate states. Employing the saturation technique, the photoionization
cross sections from the 3p 2P3/2 and 3p 2P1/2 intermediate states at the first ionization threshold are determined as 7.9(1.3) Mb and 6.7(1.1) Mb respectively. The f-values
of the Rydberg transitions are calibrated with the photoionization cross section measured at the first ionization threshold
and compared with the earlier data. 相似文献
10.
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
11.
S. Assimopoulos A. Bolovinos E. Luc-Koenig S. Cohen A. Lyras P. Tsekeris M. Aymar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(3):243-254
We report the even parity J
=4,5 autoionizing spectra of calcium below the 3d threshold, investigated by two-step laser excitation from the 3d4s metastables
through the 3d4p , intermediate states and subsequent optogalvanic detection. The 3d4s states are populated by electronic collisions in a d.c.
glow discharge sustained in a Ca heat-pipe. More than a hundred resonant transitions have been measured with an accuracy of
for the narrow ones using standard laser calibration techniques. The high lying levels are assigned to all expected autoionizing series. Moreover, some levels are observed. The theoretical interpretation is achieved by a combination of the nearly ab initio eigenchannel R-matrix and multichannel quantum-defect (MQDT) methods as well as by an empirical determination of the MQDT parameters in
the phase-shifted formulation. Theoretical energy level positions and excitation profiles are compared with the experimental
data confirming the identification of the observed structures. Strong mixing between series is found, while the ones do not couple with the series. Further insight into the strong channel mixing in the studied energy range is provided by a comprehensive review
of the excitation profiles in the vicinity of the 4p5p perturber as obtained from a number of intermediate levels used in the present and in earlier experiments. Systematic electron
correlation trends for series of , and are discussed.
Received: 20 November 1997 / Accepted: 15 January 1998 相似文献
12.
13.
T. Cheng J. Liu S. Chen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):19-26
In this paper, we investigate the dynamics of a hydrogen atom in high-frequency (several atomic units) super strong (up to
several tens of atomic units) laser fields within the high frequency Floquet theory framework. The ionization rate, ionization
spectrum, angular distribution and high-order harmonic generation are all investigated. Our studies reveal the universal behavior
of the total ionization rate, excess-photon ionization spectrum and angular distribution of the ionization rate in the stabilization
regime, and achieve a deep insight into the dynamics of high-order harmonic generation in the stabilization regime.
Received 6 June 2001 and Received in final form 31 August 2001 相似文献
14.
L. Feng Y.-k. Ho 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(1):25-30
In this paper, ion-atom and ion-ion collisions in the presence of intense laser fields are qualitatively studied by Classical
Trajectory Monte Carlo (CTMC) simulations. It is found that in contrast to the field-free collisions, the colliding ion and
the target nucleus could absorb energy from the applied laser fields when the electrons escape from the collision system.
This result is explained in terms of Coulomb explosion induced by the enhanced ionization at the so-called critical internuclear
distance. Also, the corresponding energy gain cross-sections are evaluated.
Received: 7 October 1998 / Received in final form: 28 January 1999 相似文献
15.
V. N. Lokhman D. D. Ogurok E. A. Ryabov 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):59-67
We report about effective ionization of iodine atoms and CF3I molecules under the action of intense XeCl laser radiation (308 nm). The only ion fragment resulting from the irradiation
of the CF3I molecules is the I+ ion. We have studied the influence of the intensity, spectral composition, and polarization of the laser radiation used on
the intensity
of the ion signal and the shape of its time-of-flight peak. Based on the
analysis of the results obtained, we have suggested the mechanism of this
effect. The conclusion drawn is that the ionization of the iodine atoms by
the ordinary XeCl laser with a nonselective cavity results from a three- (2 + 1)-photon REMPI process. This process is in
turn due to the presence of accidental two-photon resonances between various spectral components of the laser radiation and
the corresponding intermediate excited states of the iodine atom. The probability of ionization of the atoms from their ground
state I(2P3/2) by the radiation of the ordinary XeCl laser is more than two orders of magnitude higher than the probability of their ionization
from the metastable state I*(2P1/2). The ionization of the CF3I molecules by the XeCl laser radiation occurs as a result of a four-photon process involving the preliminary one-photon dissociation
of these molecules and the subsequent (2 + 1)-photon REMPI of the resultant neutral iodine atoms. 相似文献
16.
L.B. Madsen L.A.A. Nikolopoulos P. Lambropoulos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(1):67-79
Ab initio time-dependent (TD) calculations of the behavior of positronium (Ps) under strong subpicosecond laser pulses are presented.
The results are compared with results in H through scaling. It is found that a substantial amount of the population can be
found in excited states after the pulse. In the perturbative regime, generalized multiphoton ionization cross-sections are
extracted from the results of the time-dependent calculations. The generalized cross-sections are used to predict the response
of Ps to nanosecond laser pulses at wavelengths of current experimental interest. Beyond the application to Ps, the generality
of the method for extracting generalized cross-sections from TD nonperturbative calculations is discussed.
Received 8 June 1999 相似文献
17.
M. Yaseen R. Ali A. Nadeem S.A. Bhatti M.A. Baig 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):177-189
We report new studies of the odd parity autoionizing Rydberg series of strontium attached to the 4d( 2
D
3/2, 5/2) ionic limits possessing J = 1-3 based on the two-color three photon resonant excitation technique in conjunction with an atomic beam apparatus. Using
the 4d
23
P
0 intermediate levels, we have been able to record the autoionizing Rydberg series of J = 1 whereas, from the 4d
23
P
2 intermediate level the series of Rydberg levels possessing J = 1, 2 and 3 have been observed. The level assignments and the line shapes simulations of the autoionizing resonances have
been made using the multichannel quantum defect theory.
Received 21 November 2001 / Received in final form 2 May 2002 Published online 19 July 2002 相似文献
18.
We present a technique for state-selective position
detection of cold Rydberg atoms. Ground state Rb atoms in a
magneto-optical trap are excited to a Rydberg state and are
subsequently ionized with a tailored electric field pulse. This
pulse selectively ionizes only atoms in e.g. the 54d state and not
in the 53d state. The released electrons are detected after a slow
flight towards a micro channel plate. From the time of flight of
the electrons the position of the atoms is deduced. The state
selectivity is about 20:1 when comparing 54d with 53d and the
one-dimensional position resolution ranges from 6 to 40 μm
over a range of 300 μm. This state selectivity and position
resolution are sufficient to allow for the observation of coherent
quantum excitation transport. 相似文献
19.
Summary In the present paper we derive a new integral equation for the non-perturbative evaluation of transition matrix elements for
high-intensity multiphoton processes. Our method will be partly based on the Kramers-Henneberger transformation. In the course
of the development of our theory we shall relate our approach to previous investigations along similar lines. As a specific
example we shall apply our integral equation to the problem of light scattering and present a multiphoton generalization of
the Kramers-Heisenberg dispersion formula. We shall then apply this general formula to the study of higher-harmonic generation
from a short-range potential with a single bound state, and evaluate the ratesR
n
of then-th-order harmonic for a set of specifically chosen parameters.
This work has been supported by the East-West Program of the Austrian Academy of Sciences under Project Nr. 45.174/1-46a/93
of the ?sterreichische Bundesministerium für Wissenschaft und Forschung. 相似文献
20.
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