共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
This paper reports a theoretical design of chirped mirrors in 1.3-μm double-section semiconductor lasers to achieve high reflectivity
and dispersion compensation over a broad bandwidth. Analytic expressions for reflectivity, group delay and group delay dispersion
are derived. We use for the first time chirped air/semiconductor layer pairs as mirrors for higher-order dispersion compensation
in semiconductor lasers. Our optimised calculations demonstrate that the broad-band mirrors designed consist of a total of
only 12 air/semiconductor layers and achieve a reflectivity higher than 99.8%, a smooth group delay and almost stable dispersion
in the laser cavity over a 100-nm bandwidth. Due to a high index contrast of both types of the layers, n
l = 1, n
h~ 3.5, a high-reflectivity bandwidth of > 700 nm is obtained in 1.3-μm semiconductor lasers. We also compare our results with
that of a commercial simulation program and show a good agreement between them. As a conclusion, we assume from the theoretical
results that air/semiconductor layer pairs with varying thicknesses used at one end of double-section semiconductor lasers
can lead to femtosecond optical pulse generation using mode-locking techniques.
An erratum to this article can be found at . 相似文献
3.
Christophe Hecquet Franck Delmotte Marie-Fran?oise Ravet-Krill Sébastien de Rossi Arnaud Jérome Fran?oise Bridou Fran?oise Varnière Evgueni Meltchakov Frédéric Auchère Angelo Giglia Nicola Mahne Stefano Nanaronne 《Applied Physics A: Materials Science & Processing》2009,95(2):401-408
In this paper, we present a study on two-channel multilayer mirrors which can operate at two wavelengths in Extreme Ultraviolet
(EUV) spectral range. We propose a new method to design two-channel EUV multilayer mirrors with enhanced spectral selectivity.
The mirror structure is a stack of two periodic multilayers separated by a buffer layer. We have defined the main parameters
which allow adjustment of the distance between different order Bragg’s peak and of wavelength positions of reflectivity minima.
Two mirrors have been designed and deposited for solar EUV telescope applications by using this method. The first mirror reflects
Fe IX–X line (17.1 nm) and Fe XVI (33.5 nm) lines with attenuation of the He II line (30.4 nm). The second mirror reflects
Fe IX–X and He II lines with attenuation of Fe XV (28.4 nm) and Fe XVI lines. Measurements with synchrotron radiation source
confirm that, in both cases, for these mirrors, we are able to adjust reflectivity maxima (Bragg peak position) and minima.
Such multilayers offer new possibilities for compact design of multi-wavelength EUV telescopes and/or for high spectral selectivity. 相似文献
4.
A. Lambrecht M.T. Jaekel S. Reynaud 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(1):95-104
We calculate the photon emission of a high finesse cavity moving in vacuum. The cavity is treated as an open system. The field
initially in the vacuum state accumulates a dephasing depending on the mirrors motion when bouncing back and forth inside
the cavity. The dephasing is not linearized in our calculation, so that qualitatively new effects like pulse shaping in the
time domain and frequency up-conversion in the spectrum are found. Furthermore we predict the existence of a threshold above
which the system should show self-sustained oscillations.
Received: 10 December 1997 / Received in final form: 27 March 1998 / Accepted: 27 March 1998 相似文献
5.
S. K. Srivastava 《International Journal of Theoretical Physics》2007,46(6):1702-1709
Here, an accelerated phantom model for the late universe is explored, which is free from future singularity. It is interesting
to see that this model exhibits strong curvature for all time in future, unlike models with ‘big-rip singularity’ showing
high curvature near singularity time only. So, quantum gravity effects grow dominant as time increases in late universe too.
More importantly, it is demonstrated that quantum corrections to FRW equations lead to non-violation of ‘cosmic energy conditions’
of general relativity, which are violated for accelerating universe without these corrections. 相似文献
6.
A. Albersdörfer E. Sackmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):663-672
In this paper we study the effect of monovalent and divalent ions on the swelling behavior and viscoelastic parameters of ultrathin layers of the natural polyelectrolyte hyaluronic acid
covalently coupled to glass substrates. A colloidal probe technique is applied for this purpose based on latex beads, hovering over the polymer cushion. By analyzing the vertical Brownian motion of these beads with reflection
interference contrast microscopy (RICM) we determined the equilibrium layer thickness (with 3 nm vertical resolution), the
interfacial interaction potential, and the characteristic mesh size limiting the hydrodynamic flow within the polyelectrolyte
film as a function of the ionic strength. The experimental results are interpreted in terms of three different theoretical
models: the polyelectrolyte brush approximation of Pincus [#!ref1!#], a modified polyelectrolyte brush approximation in the
high salt concentration limit of Ross and Pincus [#!ref2!#] and the simple scaling approximation for neutral adsorbed polymers
of de Gennes [#!ref3!#]. Within experimental error all of these different models fit our experimental data and yield comparable
results for the equilibrium layer thickness. Moreover we determine a thickness dependent, effective surface coverage from
both brush models. The hydrodynamic properties of the films are interpreted in terms of the Brinkmann model of elastic porous
media by assuming an effective mesh size, which depends linearly on the Debye screening length. The salt induced condensation
of the polyelectrolyte films can be described microscopically in terms of a progressive contraction of the mesh size with
increasing salt concentration.
Received 10 September 1998 and Received in final form 30 November 1998 相似文献
7.
P. Hello 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(3):373-383
In this paper we study several means of compensating for thermal lensing which, otherwise, should be a source of concern for
future upgrades of interferometric detectors of gravitational waves. The methods we develop are based on the principle of
heating the cold parts of the mirrors. We find that thermal compensation can help a lot but can not do miracles. It seems
finally that the best strategy for future upgrades (“advanced configurations”) is may be to use thermal compensation together
with another substrate materials than silica, for example sapphire.
Received 26 April 2001 相似文献
8.
A. Gadomski 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):569-571
In this Rapid Note, we show that the problem of growth of molecular superlattice in a fully hydrated dipalmitoylphosphatidylcholine (DPPC) membrane
during the gel-to-subgel phase transformation process is a problem of time scale. There are, in fact, two time scales. The
first is an “integrated” or, in some sense, stagnant time scale, that reflects the well-known isotropic growth effect in the
d-dimensional space, but assigns the problem to be still in a category of Debye relaxation kinetics. The fraction of old (parent)
phase does not suit the Paley-Wiener criterion for relaxation functions, and the time behavior is exclusively due to the geometrical
characteristics of the kinetic process. The second (multi-instantaneous) time scale, in turn, is recognised to be a “broken”
(fractional time derivative) or memory-feeling (dynamic) scale, which carries some very essential physics of the phenomenon
under study, and classifies the problem to be of non-Debye (viz., stretched exponential) nature. It may, in principle, contain all the important effects, like small scale coexistence, presence
of collisions between domains, with possible annihilation and creation of domain boundaries, and/or a headgroup packing, hydration
against lipid mobility behavior, and finally, a multitude of quasi-crystalline states. It turns out, that within the range
of validity of the dynamic scale approximation proposed, the criterion for relaxation functions is very well fulfilled.
Received 30 November 1998 相似文献
9.
We study the director field around a spherical particle immersed in a uniformly aligned nematic liquid crystal and assume
that the molecules prefer a homeotropic orientation at the surface of the particle. Three structures are possible: a dipole,
a Saturn-ring, and a surface-ring configuration, which we investigate by numerically minimizing the Frank free energy supplemented
by a magnetic-field and a surface term. In the dipole configuration, which is the absolutely stable structure for micron-size
particles and sufficiently strong surface anchoring, a twist transition is found and analyzed. We show that a transition from
the dipole to the Saturn ring configuration is induced by either decreasing the particle size or by applying a magnetic field.
The effect of metastability and the occurrence of hysteresis in connection with a magnetic field are discussed. The surface-ring
configuration appears when the surface-anchoring strength W is reduced. It is also favored by a large saddle-splay constant K24. A comparison with recent experiments [#!itapdb:Poulin1997!#,#!itapdb:Poulin1998!#] gives a lower bound for W, i.e., for the interface of water and pentylcyanobiphenyl (5CB) in the presence of the surfactant sodium dodecyl sulfate.
Received 2 November 1998 相似文献
10.
M. Block O. Rehm P. Seibert G. Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(3):461-465
We have measured the lifetime of the metastable 3D
5/2
level in Ca+ using the “quantum jump" technique on a single stored and laser cooled ion in a linear Paul trap. We found a linear dependence
of the measured decay rate on the power of the laser which repumps the ions from the long lived 3D
3/2
level. This can be explained by off-resonant depletion of the 3D
5/2
level. The proper lifetime of this level is obtained by a linear extrapolation of the measured lifetime to zero laser power.
We obtain 1100(18) ms in agreement with theoretical calculations. The observed systematic change of the decay rate resolves
discrepancies between earlier experiments in which this effect had not been considered. Measurements on a linear chain of
10 laser cooled ions showed unexpected frequent coincidences of quantum jumps within our observation time of 20 ms. This indicates
a so far unexplained correlation between the ions in the chain at large distances.
Received 3 March 1999 相似文献
11.
B. Lamine M.-T. Jaekel S. Reynaud 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):165-176
We study the decoherence of atomic interferometers due to the scattering of stochastic gravitational waves. We evaluate the
“direct” gravitational effect registered by the phase of the matter waves as well as the “indirect” effect registered by the
light waves used as beam-splitters and mirrors for the matter waves. Considering as an example the space project HYPER, we
show that both effects are negligible for the presently studied interferometers.
Received 15 February 2002 / Received in final form 12 April 2002 Published online 19 July 2002 相似文献
12.
L.F. Rybaltchenko N.L. Bobrov V.V. Fisun I.K. Yanson A.G.M. Jansen P. Wyder 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):475-480
The influence of electric fields and currents has been investigated in the high- superconductors YBaCuO and BiSrCaCuO using a point-contact geometry with Ag as the counterelectrode, which reveal switching
transitions between states of a different resistance. The origin of this effect in point contacts is associated with electromigration
of the oxygen, driven by the electric field as well as by the current-induced “electron wind”. The switching effect preserves
its basic features at elevated temperatures up to room temperature and in high magnetic fields up to 10 T.
Received 23 November 1998 相似文献
13.
E.G. Mishchenko M. Patra C.W.J. Beenakker 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(2):289-297
A theory is presented for the frequency dependence of the power spectrum of photon current fluctuations originating from a
disordered medium. Both the cases of an absorbing medium (“grey body”) and of an amplifying medium (“random laser”) are considered
in a waveguide geometry. The semiclassical approach (based on a Boltzmann-Langevin equation) is shown to be in complete agreement
with a fully quantum mechanical theory, provided that the effects of wave localization can be neglected. The width of the
peak in the power spectrum around zero frequency is much smaller than the inverse coherence time, characteristic for black-body
radiation. Simple expressions for the shape of this peak are obtained, in the absorbing case, for waveguide lengths large
compared to the absorption length, and, in the amplifying case, close to the laser threshold.
Received 8 August 2000 相似文献
14.
The pulse shape of a passively Q-switched microchip laser 总被引:2,自引:0,他引:2
T. Erneux P. Peterson A. Gavrielides 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(3):423-431
The shape of the intensity pulse of a passively Q-switched microchip laser is investigated numerically and analytically. Our
analysis is motivated by independent microchip laser experiments exhibiting nearly symmetric pulses in the case of a semiconductor
saturable absorber and asymmetric pulses in the case of a solid state saturable absorber. Asymptotic methods are used to determine
limiting behaviors of the pulse shape for both symmetric and asymmetric pulses. In the first case, we determine a sech2 solution parametrized by one parameter which can be determined by solving two coupled nonlinear algebraic equations. In the
second case, the pulse solution is decomposed into two distinct approximations exhibiting different amplitude and time scales
properties. We review earlier approximations of the repetition rate and the pulse width.
Received 2 August 1999 相似文献
15.
M. Gartz C. Keutgen S. Kuenneke U. Kreibig 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(1):127-131
In this paper a detailed experimental study of Coherent Population Trapping (CPT) effect on sodium induced by a dye-laser
operating in a three-mode regime is presented and a detailed analysis of the role of velocity changing collisions is made.
These collisions show a very small relaxation effect on the dark resonances which are visible even at high pressures. For
the first time we demonstrate the persistence of the ground state coherence to pressures up to one atmosphere for a relatively
“heavy” buffer gas like argon. The experimental results have been compared with theory and a very good agreement has been
obtained. Preliminary results on the effect of Na-N2 collisions on Coherent Population Trapping are presented.
Received: 5 October 1998 / Received in final form: 3 December 1998 相似文献
16.
S. Roux J.F. Muzy A. Arneodo 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(2):301-322
Swirling turbulent flows display intermittent pressure drops associated with intense vorticity filaments. Using the wavelet
transform modulus maxima representation of pressure fluctuations, we propose a method of characterizing these pressure drop
events from their time-scale properties. This method allows us to discriminate fluctuations induced by just formed (young)
as well as by burst (old) filaments from background pressure fluctuations. The statistical characteristics of these filaments
(core size, waiting time) are analyzed in details and compared with previously reported experimental and numerical findings.
Their intermittent occurrence is found to be governed by a pure Poisson's law, the hallmark of independent events. Then we
apply the wavelet transform modulus maxima (WTMM) method to the background pressure fluctuations. This study reveals that,
once removed all the filaments, the “multifractal” nature of pressure fluctuations still persists. This is a clear indication
that the statistical contribution of the filaments is not important enough to account for the intermittency phenomenon in
turbulents flows.
Received 27 July 1998 and Received in final form 23 November 1998 相似文献
17.
M. S. Johansen P. Alstrom J. Borg M. T. Levinsen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):665-676
Significant statistical bias in LDA measurements and how to adequately deal with it is a subtle problem when dealing with
turbulent flows. In order to attempt a clarification we have performed measurements on a non-standard “grid experiment” where
a clear bias effect is found. We have investigated the effect of several corrective measures and find that best results, in
the sense of having the first moment converge to zero, are obtained when using the time between events as statistical weights.
The corrected time series have been used to check for extended self-similarity (ESS). Even though no scaling regime is seen
for the third moment and the flow certainly is neither isotropic nor homogeneous, perfect ESS scaling based on the absolute
third moment is observed up to the twelfth moment, extending into a time domain regime where the Taylor hypothesis of frozen
turbulence is obviously violated. Reversing the argument this indicates that the correction scheme needed can be experimentally
decided on using the criterion stated above and especially so if ESS is to be expected. Finally we have used the corrected
data to quantify the deviations from Gaussian behavior of the velocity difference probability density function for a weakly
turbulent flow. Through comparison with results on the Gaussian-Lorentzian distribution we find that the even part of the
experimental distribution can be reproduced quite well by a single-parameter family of distributions with second moment equal
unity.
Received 5 August 1998 and Received in final form 21 December 1998 相似文献
18.
A. Martin P. Odier J.-F. Pinton S. Fauve 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):337-341
Magnetohydrodynamics studies in laboratory experiments have long been restricted to low magnetic Reynolds number flows, mainly
as a result of the very high magnetic diffusivity λ = 1/μσ of common conducting fluids (μ is the fluid's magnetic permeability
and σ its electrical conductivity). The best conductivities are found in liquid metals which have a unit magnetic permeability,
relative to vacuum. We show experimentally that a suspension of solid particles with a high magnetic permeability in a liquid
metal yields an effective medium that has a high electrical conductivity and an enhanced magnetic permeability. The dispersion
of the beads results from the turbulent fluid motion. The range of accessible magnetic Reynolds number can be increased by
a factor of as much as 4 in our experimental setup.
Received 6 March 2000 and Received in final form 13 July 2000 相似文献
19.
M. Ozer L. J. Graham 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):499-503
In a Hodgkin-Huxley neuron model driven just above threshold, external noise can increase both jitter and latency of the first
spike, an effect called “noise delayed decay” (NDD). This phenomenon is important when considering how neuronal information
is represented, thus by the precise timing of spikes or by their rate. We examine how NDD can be affected by network activity
by varying the model's membrane time constant, τm. We show that NDD is significant for small τm or high network activity, and decreases for large τm, or low network activity. Our results suggest that for inputs just above threshold, the activity of the network constrains
the neuronal coding strategy due to, at least in part, the NDD effect. 相似文献
20.
E. Kogan M. Auslender M. Kaveh 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):373-376
Localization and dephasing of conduction electrons in a low carrier density ferromagnet due to scattering on magnetic fluctuations
is considered. We claim the existence of the “mobility edge”, which separates the states with fast diffusion and the states
with slow diffusion; the latter is determined by the dephasing time. When the “mobility edge” crosses the Fermi energy a large
and sharp change of conductivity is observed. The theory provides an explanation for the observed temperature dependence of
conductivity in ferromagnetic semiconductors and manganite pyrochlores.
Received 17 January 1999 and Received in final form 12 March 1999 相似文献