共查询到20条相似文献,搜索用时 31 毫秒
1.
Xun-Li Feng Zhao-Yang Chen Zhi-Zhan Xu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(1):117-121
The nondegenerate two-photon interaction of a two-level atom with a broadband multimode squeezed vacuum is investigated. We
find that in the two-photon process the squeezed vacuum has a driving effect on the atom which can lead to an ac Stark effect
when the average photon number of the squeezed vacuum is larger than a critical value.
Received: 2 February 1999 / Received in final form: 20 April 1999 相似文献
2.
J. Peřina Jr. 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(2):235-242
The dependence of one- and two-photon characteristics of pulsed entangled two-photon fields generated in spontaneous parametric
down-conversion on the pump-pulse properties (shape of the pump-pulse spectrum and its internal structure) is examined. It
is shown that entangled two-photon fields with defined properties can be generated. A general relation between the spectra
of the down-converted fields is established. As a special case the interference of two partially overlapping pulsed two-photon
fields is studied. The fourth-order interference pattern of entangled two-photon fields is investigated in the polarization
analog of the Hong-Ou-Mandel interferometer.
Received: 23 December 1998 / Received in final form: 14 April 1999 相似文献
3.
M.C. Marques J.F.F. Mendes 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):123-127
We propose and study a model where two aspects are present: parity conservation and infinitely many absorbing states. Whereas
steady-state simulations show that the static critical behaviour is not affected by the presence of multiple absorbing configurations,
the influence of the initial state associated with the presence of slowly decaying memory effects is clearly displayed in
time dependent simulations. We report results of a detailed investigation of the dependence of critical spreading exponents
on the initial particle density.
Received 13 January 1999 and Received in final form 7 April 1999 相似文献
4.
A. Ekers M. Głódź J. Szonert B. Bieniak K. Fronc T. Radelitski 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(1):49-58
The results of an experimental study of population dynamics following excitation of [0pt] and [0pt] states of rubidium are reported. Excitation transfer and quenching cross-sections in collisions with ground state rubidium
atoms, and natural lifetimes have been measured. The experiment was performed in a vapour cell, using pulsed two-photon excitation
and photon counting detection. The analysis of time dependent signals was based on a rate equation model in which transitions
induced by thermal radiation have been accounted for. The measurements yielded following results: (1) [0pt] state J-mixing cross-section: [0pt] ; (2) cross-sections for [0pt] excitation transfer process: [0pt] ; (3) quenching cross-sections: [0pt] , [0pt] , [0pt] ; [0pt](4) radiative lifetimes: [0pt] ns, [0pt] ns, [0pt] ns.
Received 1st December 1998 and Received in final form 17 May 1999 相似文献
5.
Z.-C. Wang Z.-Y. Chen Y. Xu 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):185-190
A theoretical study is made of the steady-state populations of a three-level atom in a ladder configuration, driven by a superposition
of a monochromatic laser wave with a broad-band squeezed vacuum. The master equation for the system and the atomic Bloch equations
are derived. The steady-state populations are calculated numerically and shown graphically as functions of two-photon detuning
for various cases of the squeezed vacuum. It is shown that, the atomic populations depend strongly on the relative phase of
the driving field and the squeezed vacuum. When the phase matching condition is fulfilled, there will be a strong two-photon
resonant absorption from the squeezed vacuum, a characteristic different from absorption of photons from a classical field.
Received: 28 May 1997 / Revised and Accepted: 10 December 1997 相似文献
6.
J. Ruostekoski D.F. Walls 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(3):335-339
Two Bose-Einstein condensates in different Zeeman sublevels can be decoupled from driving light fields in coherent population
trapping. A condensate pair with a deterministic entanglement and a controllable value of the relative phase may be prepared
by selecting the phase difference between the coherent light fields. The rate of the condensate phase diffusion may be determined
from the two-photon resonant absorption of radiation.
Received: 29 June 1998 / Revised: 10 October 1998 / Accepted: 19 October 1998 相似文献
7.
S.M. Kirkpatrick J.W. Baur C.M. Clark L.R. Denny D.W. Tomlin B.R. Reinhardt R. Kannan M.O. Stone 《Applied Physics A: Materials Science & Processing》1999,69(4):461-464
Molecular excitation via the simultaneous absorption of two photons can lead to improved three-dimensional control of photochemical
or photophysical processes due to the quadratic dependence of the absorption probability on the incident radiation intensity.
This has lead to the development of improved three-dimensional fluorescence imaging, optical data storage, and microfabrication.
The latter of these involves the fabrication of three-dimensional structures using a spatial variation in the incident intensity
within a photopolymerizable resin. In the past, the translation of the focal plane of a tightly focused laser beam was used
to induce localized photopolymerization and fabrication of three-dimensional structures. Here we report the first successful
demonstration of large-area patterning via ultrafast holography-based two-photon polymerization of a commercially available
optical resin and a large two-photon cross-section dye (AF380). This opens tremendous possibilities for the wide-spread use
of two-photon absorption for the three-dimensional control of photoinduced processes.
Received: 21 June 1999 / Accepted: 23 June 1999 / Published online: 8 September 1999 相似文献
8.
C. Mavroyannis 《Applied physics. B, Lasers and optics》2001,73(1):39-50
We have considered the interference spectra that occur at the three-photon generated frequency arising from the interaction
of three laser fields with a four-level atom, where two of the laser fields are on two-photon resonance with the three levels
forming a “λ” scheme while the third laser operates between the second ground and the second excited state of the atom. At
low intensities of all three laser fields, the overall intensity of the peak at the three-photon generated frequency, describing
the spectrum of an electron in the second excited state, depends on the strength of the combined field of the two laser fields
that are on two-photon resonance and it takes negative values. This indicates that light amplification without population
inversion is likely to occur at the three-photon generated frequency. The combined field of the three laser fields induces
multiphoton excitations near the three-photon generated frequency, whose peaks are characterized by linewidths which are much
less than the natural linewidths of the atoms. These excitations describe absorption or stimulating emission processes depending
on the values of the detunings of the laser fields. The derived results are graphically presented and discussed.
Received: 24 January 2001 / Published online: 8 June 2001 相似文献
9.
We report a simplified Z-scan technique based on a study on the symmetric features of a typical Z-scan curve. The contributions
from the two-photon absorption (TPA) and the nonlinear refraction (NLR) are easily separated from a closed-aperture Z-scan
curve using this method. And the determination of the two nonlinearities is simplified and unambiguous. We demonstrate this
method on ZnSe, CdS, and ZnTe semiconductors with 120-fs laser pulses. And the influence from the uncertainty of the focal
plane (Z=0) position is discussed. It is also found that the TPA coefficient can be obtained independently without knowing
the exact location of the focal point.
Received: 8 July 1999 / Published online: 3 November 1999 相似文献
10.
M. Weber F. Rickermann F. Abbing G. von Bally 《Applied physics. B, Lasers and optics》1999,68(5):1069-1072
A holographic double-exposure interferometer for quasi real-time analysis is realized, utilizing a photorefractive BTO:Cd
crystal for hologram recording. Heating of the crystal reduces the time required to reach the steady-state working situation.
Light-induced absorption losses are reduced by heating as well. Additionally, the diffraction efficiency is increased by this
method. A sixfold increase in the light intensity of the reconstructed interferogram is achieved.
Received: 2 December 1998 / Revised version: 28 January 1999 / Published online: 7 April 1999 相似文献
11.
A. Lakhlifi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(2):211-222
Ammonia monomers have been adsorbed on argon clusters at low temperature K by Rohmund and Huisken [#!frfh97!#] using the pick-up technique. They measured the spectrum of the NH3 molecules in the region of the umbrella mode. Two broad bands centered around 970 and 1000 cm-1 with finer details were observed. The authors attempted to interpret the obtained spectrum on the basis of the free rotation
motions of the molecules. In this paper semi-empirical atom-atom potential energy calculations are performed for the ammonia
monomer adsorbed on a rigid face-centered-cubic (fcc)-type surface of the argon cluster. In the equilibrium position of the rigid molecule on the cluster surface the orientational
potential energy surface exhibits two quasi-equivalent minima separated by a potential barrier of about 100 cm-1. The symmetry of the molecular vibration-inversion double-well potential is destroyed; the inversion motion is then forbidden
in the ground state. On the basis of the two adsorption orientations, the vibrational frequency shifts are calculated and
the obtained infrared bar-spectrum agrees with the experimental one.
Received 6 April 1999 and Received in final form 19 July 1999 相似文献
12.
M. Weinelt 《Applied Physics A: Materials Science & Processing》2000,71(5):493-502
Quantum-phase and population decay of image-potential states have been investigated by two-photon photoemission with femtosecond
time resolution. The influence of steps and defects on quasielastic and inelastic scattering processes is illustrated for
a vicinal Cu(119) surface and diluted adsorbate layers of CO and Cu on Cu(001).
Received: 19 April 2000 / Accepted: 2 September 2000 / Published online: 12 October 2000 相似文献
13.
Y. Kobayashi T. Ohno T. Sekikawa Y. Nabekawa S. Watanabe 《Applied physics. B, Lasers and optics》2000,70(3):389-394
Pulse widths of the 7th and 9th harmonics of a Ti:sapphire (TiS) laser have been measured by an autocorrelation technique
using two-photon and three-photon ionization of He and Ar as nonlinear phenomena. The pulse widths of the 7th and 9th harmonics
were 47 fs and 27 fs, respectively, where the pulse width of the fundamental pulse was 34 fs. The pulse width of the 9th harmonic
depends strongly on the peak intensity of the fundamental pulse. These results can be explained by quantum theory by taking
into account the temporal and spatial distribution of the fundamental beam.
Received: 15 June 1999 / Revised version: 8 October 1999 / Published online: 2 February 2000 相似文献
14.
R.E. Nettleton 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):429-437
Robertson has found a projection operator which, applied to the Liouville equation, yields an exact equation for , the information-theoretic phase-space distribution. If the Robertson equation is multiplied by a set [0pt]{} of functions representing physical fluxes, odd under momentum reversal and even under configuration inversion, a set of
evolution equations is obtained for time-dependent ensemble averages which are variables of extended thermodynamics. In earlier work, a perturbation calculation was developed, assuming just
one variable , for an operator [0pt] occurring in the Robertson equation. This calculation is extended here to the case where there are variables. The coefficients in the evolution equations depend on {} and explicitly on time t at short times. It is shown here that these coefficients exhibit Onsager symmetry at long times, after the transient explicit
t-dependence has disappeared, to .
Received 13 September 1999 and Received in final form 4 April 2000 相似文献
15.
G. Sharma S. Ghosh 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(2):301-307
Based on hydrodynamic model of plasmas an analytical investigation of frequency modulational interaction between copropagating
high frequency pump and acoustic mode and consequent amplification (steady-state and transient) of the modulated waves is
carried out in a magnetised piezoelectric semiconductor medium. The phenomenon of modulational amplification is treated as
four wave interaction process involving cubic nonlinearity of the medium. Gain constants, threshold-pump intensities and optimum-pulse
duration for the onset of modulational instabilities are estimated. The analysis has been performed in non-dispersive regime
of the acoustic mode, which is one of the preconditions for achieving an appreciable initial steady-state growth of the modulated
signal wave. It is found that the transient gain constant diminishes very rapidly if one chooses the pump pulse duration beyond
the maximum gain point. Moreover, the desired value of the gain can be obtained by adjusting intensity and pulse duration
of the pump and doping concentration of the medium concerned.
Received 12 August 1999 and Received in final form 17 December 1999 相似文献
16.
The field-induced carrier redistribution between the subbands of a semiconductor superlattice is treated using the density
matrix approach. The unit cell of the superlattice consists of one quantum well with three occupied subbands. Carrier scattering
on polar-optical phonons is described within the microscopic bulk phonon model. At the tunneling resonance, an intrinsic population
inversion is observed. The temperature dependence of the population inversion is determined.
Received 25 October 2002 / Received in final form 27 November 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: kl@pdi-berlin.de 相似文献
17.
E. Carlon M. Henkel U. Schollwöck 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):99-114
The density matrix renormalization group ( DMRG) is applied to some one-dimensional reaction-diffusion models in the vicinity
of and at their critical point. The stochastic time evolution for these models is given in terms of a non-symmetric “quantum
Hamiltonian”, which is diagonalized using the DMRG method for open chains of moderate lengths (up to about 60 sites). The
numerical diagonalization methods for non-symmetric matrices are reviewed. Different choices for an appropriate density matrix
in the non-symmetric DMRG are discussed. Accurate estimates of the steady-state critical points and exponents can then be
found from finite-size scaling through standard finite-lattice extrapolation methods. This is exemplified by studying the
leading relaxation time and the density profiles of diffusion-annihilation and of a branching-fusing model in the directed
percolation universality class.
Received 2 February 1999 相似文献
18.
W.D. Heiss 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(1):1-4
Avoided level crossings are associated with exceptional points which are the singularities of the spectrum and eigenfunctions,
when considered as functions of a complex coupling parameter. It is shown that the wave function of one state changes sign but not the other, if the exceptional point is encircled in the complex plane. An experimental setup is
suggested where this peculiar phase change could be observed.
Received: 7 January 1999 / Received in final form: 15 March 1999 相似文献
19.
Photobleaching and stabilization of. fluorophores used for single-molecule analysis. with one- and two-photon excitation 总被引:2,自引:0,他引:2
Fluorescence spectroscopic measurements at the single-molecule level usually require large absorption cross sections and fluorescence
quantum yields for the dyes under study. In addition to these parameters, the collectable number of fluorescence photons and,
thus, the signal-to-noise ratio of the measurement, is influenced by processes like triplet-state population and photobleaching,
shifting the saturation threshold of the dye to lower excitation intensities. Confocal fluorescence correlation spectroscopy
(FCS) is a versatile method to precisely determine photon emission rates of single molecules but also gives access to rate
constants of dynamic bleaching and intersystem crossing. In recent FCS studies in solution and living cells, two-photon excitation
with its inherent spatial sectioning has proven to be a very valuable alternative to minimize background and cumulative signal
loss. However, there is evidence that in many dye systems, the photobleaching rates with two-photon excitation are significantly
enhanced with respect to one-photon excitation at comparable photon-emission yields. The reasons have so far remained mainly
speculative. In the present study, potential photobleaching pathways are investigated by adding chemical stabilizers and by
working at different oxygen concentrations. The results suggest that the population of triplet states does not appear to be
responsible for the limited emission rate with two-photon excitation. Rather, photobleaching pathways via the formation of
radicals seem to be plausible causes for the signal limitation. Favorable conditions are discussed to maximize the overall
photon-collection yield in two-photon experiments.
Received: 4 July 2001 / Published online: 23 November 2001 相似文献
20.
V. Bystritsky W. Czapliński M. Filipowicz E. Guła N. Popov 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(1):75-83
The time-dependence of the population of muonic hydrogen states in hydrogen-helium mixtures is calculated for principal quantum
number n. The number of muons transferred to helium nuclei is also determined. The dependence of the population of the ground state
of muonic hydrogen on time and target density and the helium concentration is also considered. The results are in agreement with recent experimental
data. The comparison of the calculated yield of K lines of X-ray in pure hydrogen and deuterium with experimental data indicates the essential role of the Coulomb deexcitation
process. Possible Stark mixing is also analysed.
Received 17 February 1999 and Received in final form 9 June 1999 相似文献