共查询到20条相似文献,搜索用时 15 毫秒
1.
K. Drese M. Holthaus 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(1):119-134
We develop adiabatic perturbation theory for quantum systems responding to short laser pulses, with or without a frequency
chirp. Our approach rests on lifting the time-dependent Schr?dinger equation to an extended Hilbert space, then applying standard
perturbational techniques to Floquet states in this extended space, and finally projecting back to the physical Hilbert space.
The same strategy also allows us to construct superadiabatic bases for monitoring the quantum evolution in the course of a
pulse. These bases provide a diagnostic tool for improving the efficiency of pulse-induced population transfer. The formalism
is applied to the selective excitation of molecular vibrational states by chirped laser pulses, which exploit either successive
single-photon resonances or a multiphoton resonance, and by a STIRAP-like process.
Received: 23 June 1998 / Revised: 18 August 1998 / Accepted: 25 August 1998 相似文献
2.
D. G. Arbó K. T?kési J. E. Miraglia 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(3):303-312
We present a theoretical study of the ionization of hydrogen atoms as a result of the interaction with an ultrashort external electric field. Doubly-differential momentum distributions and angular momentum distributions of ejected electrons calculated in the framework of the Coulomb-Volkov and strong field approximations, as well as classical calculations are compared with the exact solution of the time dependent Schr ödinger equation. We show that in the impulsive limit, the Coulomb-Volkov distorted wave theory reproduces the exact solution. The validity of the strong field approximation is probed both classically and quantum mechanically. We found that classical mechanics describes the proper quantum momentum distributions of the ejected electrons right after a sudden momentum transfer, however pronounced the differences at latter stages that arise during the subsequent electron-nucleus interaction. Although the classical calculations reproduce the quantum momentum distributions, it fails to describe properly the angular momentum distributions, even in the limit of strong fields. The origin of this failure can be attributed to the difference between quantum and classical initial spatial distributions. 相似文献
3.
V. Berardi M. Armenante R. Bruzzese F. Esposito S. Solimeno N. Spinelli S. Bakhramov 《Il Nuovo Cimento D》1991,13(4):423-433
The intensity dependence of the multiphoton ionization spectra of Xe atoms has been investigated with an improved accuracy
and well-controlled laser parameters. In particular, we have examined the ionization rates for X3+, X2−, X+ as functions of the laser intensity and the pressure in the target chamber. The apparatus used for these measurements is
characterized by a high-energy resolution (better than 200 meV) and a completely digital acquisition system. The time-of-flight
spectra clearly show the contributions of the different isotopes present in Xe gas. The laser pulses have been characterized
with great accuracy by monitoring the energy, pulse width and divergence shot by shot. The ionization rates of the different
ions have been used for testing the basic assumption of the Geltman theory of multiple ionization based on the single electron
ionization model. We have found that for the small intensity range investigated the quantity (dXe
+/dI)·(dXe
3+/dI)/(dXe
2+/dI)2 appears to be quite close to the value 0.5 predicted by this model. 相似文献
4.
N.V. Vitanov B.W. Shore K. Bergmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(1):15-29
The well-known process of stimulated Raman adiabatic passage (STIRAP) provides a robust technique for achieving complete population
transfer between the first and last state of a three-state chain, with little population, even transiently, in the intermediate
state. The extension of STIRAP to general N-state chainwise-linked systems continues to generate interest. Recently Malinovsky and Tannor (Phys. Rev. A 56, 4929 (1997)) have shown with numerical simulation that a resonant pulse sequence, which they term “straddle STIRAP”, can
produce (under appropriate conditions, including specific pulse areas) complete population transfer with very little population
in intermediate states. Their proposal supplements a pair of counterintuitively ordered delayed laser pulses, driving the
first and last transition of the chain and corresponding to the pump and Stokes pulses in STIRAP, with one or more additional
strong pulses of longer duration which couple the intermediate transition(s) and overlap both the pump and the Stokes pulses.
In this paper, we modify the “straddling” Malinovsky-Tannor pulse sequence so that the intermediate couplings are constant (and strong), at least during the times when the pump and Stokes pulses are present, and the intermediate states therefore
act as a strongly coupled subsystem with constant eigenvalues. Under this condition, we show that the original N-state chain is mathematically equivalent to a system comprising N-2 parallel -transitions, in which the initial state is coupled simultaneously to N-2 dressed intermediate states, which in turn are coupled to the final state. The population transfer is optimized by suitably
tuning the pump and Stokes frequencies to resonance with one of these dressed intermediate states, which effectively acts
as the single intermediate state in a three-state STIRAP-like process. We show that tuning to a dressed intermediate state
turns the system (for both odd N and even N) into a three-state system - with all of the properties of conventional STIRAP (complete population transfer, little transient
population in the intermediate states, insensitivity to variations in the laser parameters, such as pulse area). The success
of the tuning-to-dressed-state idea is explained by using simple analytic approaches and illustrated with numerical simulations
for four-, five-, six- and seven-state systems.
Received: 17 April 1998 / Accepted: 15 June 1998 相似文献
5.
N. Hay R. de Nalda T. Halfmann K.J. Mendham M.B. Mason M. Castillejo J.P. Marangos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):231-240
We have studied high-order harmonic generation (HHG) from organic molecules irradiated with near-infrared high intensity laser
pulses of 70 fs and 240 fs duration. The molecular systems studied were the aromatics benzene and naphthalene and the alkanes
cyclopropane and cyclohexane (cyclic) and n-hexane (linear). Harmonic intensities were measured both as a function of laser intensity (in the range 5×1013-5×1015 W cm-2) and as a function of ellipticity of the laser field polarisation. The results were compared with those from the xenon atom.
For 70 fs pulses, harmonic generation from the organic systems was similar to that of xenon, revealing an atom-like behaviour
for molecules when the laser pulse duration is shorter than the fragmentation timescale of the molecule. We note significant
differences between molecules with respect to HHG efficiencies and the suppression of HHG in larger species. We discuss these
differences in the context of the molecular properties, electronic structure and behaviour of ionisation and fragmentation
that result in enhancement of field ionisation in larger systems. Study of the polarisation ellipticity dependence of HHG
shows that the harmonic yield in molecules is less sensitive to the polarisation than for atoms (xenon). This is consistent
with the expected behaviour given the larger recollision cross-section presented by the core in the molecular system compared
to the atom. Our results suggest that study of HHG from molecules exposed to ultra-short pulses is potentially a powerful
tool for understanding the electron dynamics of molecules exposed to an intense field.
Received 14 September 2000 and Received in final form 6 December 2000 相似文献
6.
K. Drese M. Holthaus 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(1):73-86
With the help of superadiabatic techniques for quantum systems depending slowly on time, we demonstrate how the total transition
amplitude, tracked in time in the usual adiabatic basis, can be decomposed into a perturbative part consisting of terms proportional
to powers of the adiabaticity parameter, and a nonperturbative component. The interference of both components underlies the
oscillations that accompany transitions in the adiabatic basis. Whereas for traditionally considered systems the final nonadiabatic
transition probability is determined by the nonperturbative part alone, this is no longer correct for models describing stimulated
Raman adiabatic passage (STIRAP). We explain the recently discovered breakdown of the Dykhne-Davis-Pechukas formula on general
grounds, and provide simple, but accurate approximations for transition amplitudes in STIRAP systems.
Received: 22 January 1998 / Revised: 17 March 1998 / Accepted: 31 March 1998 相似文献
7.
G. Li S. Wu P. Zhou 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(2):267-277
The dressed-state populations and the resonance fluorescence spectrum of a V-type three-level atom driven by a strong coherent
field and a weak stochastic one simultaneously are investigated. There can be significant population inversion due to the
effect of the stochastic field. The atomic resonance fluorescence spectrum can be controlled by adjusting the frequency difference
between the coherent field and the stochastic one and the coherent Rabi frequency. Peak suppression and line narrowing occur
under appropriate conditions.
Received 23 June 2000 and Received in final form 18 January 2001 相似文献
8.
M. H. Naderi M. Soltanolkotabi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(3):471-479
We investigate the effect of a static electric field on
photoionization of the He atom in the ground 1S and low-lying 2S
and 2P excited states. The field-affected ionization potential and
photoionization cross-section are determined from the complex
eigenvalues of the time-dependent Schr?dinger equation solved by the
complex rotation method in the Floquet ansatz. Accuracy of the method
is enhanced by the use of the Hylleraas basis set. For the ground
state of helium, we find that the total photoionization cross-section
remains constant or decreases as a function of the DC field strength
until this field reaches a certain critical value. For the low-lying
excited states, effect of the static field is similar to the ordinary
DC Stark effect. 相似文献
9.
H.-F. Zhang J.-H. Wu J.-Y. Gao 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):443-447
A five-level system to control the wavelength of the in-line amplifier by the quantum interference is proposed. It is found
that the gains of the first and the second probe can be adjusted by changing the coherent field and the incoherent pumping.
The new scheme may find its application in optical switch and optical communications.
Received 9 October 2002 Published online 24 April 2003
RID="a"
ID="a"e-mail: qol@mail.jlu.edu.cn 相似文献
10.
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
11.
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
12.
K. Jin Z. C. Wang Q. Zhang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):325-332
We study the absorption spectra of a degenerate V-type
atom, where a resonant driving field and a probe field drive
different branches of transitions and a dc field is applied to
drive the transition between two excited states. The effects of
vacuum induced coherence (VIC) on the absorption spectra are
investigated. It is demonstrated that in some special cases the
VIC can lead to the depression of absorption and narrow resonance.
The origin of these features are discussed. When the pump field
and the dc field have the same intensity, it is interesting to
find that the whole absorption spectrum comes mainly from the
absorptions induced by the interferences among different
transitions between dressed states. 相似文献
13.
X.-M. Su Z.-C. Zhuo Z.-H. Kang L.-J. Wang J.-Y. Gao 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):395-398
We investigate the conditions in which the propagation of an electromagnetic wave is changed from transparency to cutoff in
a non-uniform plasma. The allowed frequency range of the driving wave is obtained for the case that the probe frequency is
above the plasma frequency. The effect of the power of the driving field on the range is analyzed.
Received 23 May 2001 相似文献
14.
M. M. Hossain S. Mitra S. Chakrabarti D. Bhattacharyya B. Ray P. N. Ghosh 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(2):141-146
We report the experimental observation of electromagnetically induced transparency (EIT) in a Doppler broadened rubidium vapour
at room temperature for different probe intensities at a fixed pump intensity in a five-level Λ-type system formed by the
D2 transition of 85Rb. For a constant pump intensity, we find that the EIT width and height change with the variation of probe intensity. We
observe a nonlinear variation of the height of the EIT peak and a linear variation of the width (FWHM) of the EIT signal with
probe intensity. In the Doppler broadened multilevel system, we also observe the velocity selective dips along with the EIT
signal. A numerical simulation of the probe response signal based on density matrix representation in a five-level system
is carried out to reproduce the experimentally observed spectra. 相似文献
15.
A. M. Ishkhanyan B. Joulakian K.-A. Suominen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(3):397-404
Two distinct strongly non-linear scenarios of molecule formation in an atomic Bose-Einstein condensate (either by photoassociation
or Feshbach resonance) corresponding to large and small field detuning are revealed. By examining arbitrary external field
configurations, we show that the association process in the first case is almost non-oscillatory in time while in the second
case the evolution of the system displays strongly pronounced Rabi-type oscillations. We construct highly accurate approximate
solutions for both limit cases. We show that at strong coupling limit the non-crossing models are able to provide conversion
of no more than one third of the initial atomic population. Finally, we show that for constant-amplitude models involving
a finite final detuning the strong interaction limit is not optimal for molecule formation. 相似文献
16.
Q. Xu X. M. Hu J. W. Yin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(2):267-273
The atomic coherence in a three-level Λ atom is studied, in which each optical transition is driven by a coherent field and
the metastable states are coupled to each other via a microwave field. It’s shown that the atomic coherence crucially depends
on the relative phase delay between the envelopes of the amplitudes of the three coupling fields. In particular, when the
phase delay is adjusted to 0 or π, the maximal atomic coherence arises, while the maximal atomic coherence doesn’t occur once
the phase delay is changed to π/2. The maximal atomic coherence is attributed to the trapping of the population in the lower
sublevels. 相似文献
17.
S. Ring B. Schmidt H. Baumgärtel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(2):155-158
We have studied the ionization of Rydberg-excited xenon atoms in THz-laser fields and by quantum dynamical calculations. The
experimental threshold laser field strength for 10% ionization probability follows an n*-1.68 (1.04 THz) dependence (n* effective principal quantum number) with additional weak resonance structures and shows that ionization does not occur by
a Landau-Zener mechanism. At scaled frequencies of to 5.6 the simulated threshold fields for ionization in oscillatory fields show a dependence on the principal quantum number
n of n-4.1 to n-1.35.
Received: 17 February 1998 / Revised: 20 April 1998 / Accepted: 21 April 1998 相似文献
18.
A. Settimi S. Severini C. Sibilia M. Bertolotti A. Napoli A. Messina 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(3):379-391
The present paper discusses the stimulated emission, in strong coupling
regime, of an atom embedded inside a one dimensional (1D) Photonic Band Gap
(PBG) cavity which is pumped by two counter-propagating laser beams. Quantum
electrodynamics is applied to model the atom-field interaction, by
considering the atom as a two level system, the e.m. field as a
superposition of normal modes, the coupling in dipole approximation, and the
equations of motion in Wigner-Weisskopf and rotating wave approximations. In
addition, the Quasi Normal Mode (QNM) approach for an open cavity is adopted, interpreting the local density of states (LDOS)
as the local density of
probability to excite one QNM of the cavity; and therefore rendering this
LDOS dependent on the phase difference of the two laser beams. In this paper
we demonstrate that the strong coupling regime occurs at high values of the
LDOS. In accordance with the results of the literature, the emission
probability of the atom decays with an oscillatory behaviour, so that the
atomic emission spectrum exhibits two peaks (Rabi splitting). The novelty of
this work is that the phase difference of the two laser beams can produce a
coherent control of both the oscillations for the atomic emission
probability and, as a consequence, of the Rabi splitting in the emission
spectrum. Possible criteria to design active delay lines are finally
discussed. 相似文献
19.
J. H. Li X. X. Yang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):563-569
We theoretically investigate the features of two-photon absorption
in a five-level atomic system with interacting dark resonances. It
is found that two-photon absorption can be completely suppressed
at two different frequencies due to the application of two
coherent coupling fields and the atomic system exhibits double
electromagnetically induced transparency windows against
two-photon absorption. The position and width of the double
two-photon transparency windows can be controlled via properly
adjusting the frequency detuning and the intensities of the two
coupling fields. In addition, one enhanced narrow central line can
be observed in the two-photon absorption spectra, which may find
applications in high-precision spectroscopy. Form a physical point
of view, we explicitly explain these results in terms of quantum
interference induced by three different two-photon excitation
channels in the dressed-state picture. 相似文献
20.
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