共查询到20条相似文献,搜索用时 328 毫秒
1.
B. Ketzer T. von Egidy F.J. Hartmann C. Maierl R. Pohl J. Eades E. Widmann T. Yamazaki M. Kumakura N. Morita R.S. Hayano M. Hori T. Ishikawa H.A. Torii I. Sugai D. Horváth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(3):305-316
The quenching of metastable states of antiprotonic helium by collisions with hydrogen and deuterium molecules was studied.
A systematic investigation of the delayed annihilation time spectra at various H2 and D2 admixture ratios at the ppm level revealed characteristic changes of their shape, which indicated a strong principal and
orbital quantum number dependent quenching of levels in both cases. Applying a laser spectroscopy technique to measure the
lifetimes of individual states and cascades we deduced H2 and D2 quenching cross-sections for the states (n, l )= (39, 35) and (37, 34). These cross-sections establish for D2 molecules the strong increase of the quenching efficiency with increasing principal quantum number n of the state under investigation previously reported for the case of H2 admixtures. Our experiments indicate that the low-n state (37, 34) is somewhat less affected by D2 than by H2, while the high-n state (39, 35) is equally quenched by both isotopes.
Received 2 October 2000 相似文献
2.
A. Andreoni M. Bondani G.M. D'Ariano M.G.A. Paris 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(3):415-421
We propose a novel scheme for the joint generation of two squeezed beams at arbitrary frequencies ω
1 and ω
2. The scheme consists of two successive steps, both involving nonlinear interactions in χ(2) crystals. The dynamics of the setup is analyzed both quantum mechanically and classically within the parametric approximation.
An experimental implementation involving the fundamental and the harmonics of a Nd:YAG laser pulse, and β-BaB
2
O
4 nonlinear crystals is suggested.
Received 17 May 2000 and Received in final form 9 October 2000 相似文献
3.
L.M. Blinov M.I. Barnik H. Ohoka M. Ozaki N.M. Shtykov K. Yoshino 《The European physical journal. E, Soft matter》2001,4(2):183-192
The temperature dependence of the surface polarization has been measured for both the planar and homeotropic orientation of
a nematic liquid crystal at a solid substrate. A conventional liquid crystal 5CB, pure and doped with an azo-dye, was used
in cells with controlled asymmetry for light absorption. The measurements have been made by a pyroelectric technique using
short pulses of a YAG laser to create a temperature increment. The latter, in turn, was measured independently by a novel
time-resolved “optical thermometer” technique monitoring temperature-dependent birefringence by a He- Ne laser beam. In accordance
with the symmetry of the order parameter, the surface polarization has different sign for the two orientations, its magnitude
ranges from -4 to +2pC/m. The same technique has been used for the measurement of the flexoelectric polarization in hybrid
cells. The sum of the flexoelectric coefficients is e
1 + e
3 = - 13pC/m at 25°C.
Received 28 February 2000 and Received in final form 5 September 2000 相似文献
4.
A. Bartelt S. Minemoto C. Lupulescu Š. Vajda L. Wöste 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):127-131
We have performed adaptive feedback optimization of phase-shaped femtosecond laser pulses to control the wavepacket dynamics
of small mixed alkali-metal clusters. An optimization algorithm based on Evolutionary Strategies was used to maximize the
ion intensities. The optimized pulses for NaK and Na2K converged to pulse trains consisting of numerous peaks. The timing of the elements of the pulse trains corresponds to integer
and half integer numbers of the vibrational periods of the molecules, reflecting the wavepacket dynamics in their excited
states.
Received 4 December 2001 相似文献
5.
C. Bobbert C.P. Schulz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):95-97
Nam(H2O)n Clusters ( n = 1...200, m = 1...50) are formed in a recently build pick-up arrangement. Preformed water clusters traverse a sodium oven, where sodium
atoms are picked up. At low sodium vapour pressure ( < 1×10-4 mbar) pure Na(H2O)n clusters are observed in the mass spectra. At high sodium vapour pressure ( > 1×10-3 mbar) the water cluster pick up more than 50 Na atoms and reaction products Na(NaOH)n ( n = 2, 4...50) dominate the mass spectra. The even number of NaOH units in the products indicate that also in a finite cluster
the reaction occurs in pairs as in the macroscopic reaction.
Received 4 December 2000 相似文献
6.
Determination of the helium-4 mass in a Penning trap 总被引:2,自引:0,他引:2
S. Brunner T. Engel A. Schmitt G. Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(2):181-188
The determination of the rotational quadrupole alignment of diatomic molecules via REMPI detection is investigated. In this process a high focal intensity usually increases the detection probability. At high
intensities the AC Stark effect may cause a splitting of the normally degenerate mJ sublevels of a rotational state J beyond the spectral width of the exciting radiation. This leads to a selective detection of only certain mJ states with the consequence that deduced alignment factors can be misleading. From the theoretical considerations line profiles
are explicitly calculated for dynamic polarizabilities which represent the B
1Σ+
u←X
1Σ+
g transition of H2, in order to fit an experimental (3+1) REMPI spectrum and to predict (1+1') line shapes as a function of laser intensity.
It is further shown that the deduced quadrupole alignment factor
A
0
(2) is significantly changed by the second order AC Stark effect when the intensities are chosen high enough to observe asymmetric
broadened line profiles. Different combinations of relative linear polarizations of the exciting and ionizing laser beams
are discussed.
Received 1st August 2000 and Received in final form 2 May 2001 相似文献
7.
V.S. Malinovsky J.L. Krause 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):147-155
We present a general theory of adiabatic rapid passage (ARP) with intense, linearly chirped laser pulses. For pulses with
a Gaussian profile and a fixed bandwidth, we derive a rigorous formula for the maximum temporal chirp rate that can be sustained
by the pulse. A modified Landau-Zener formula displays clearly the relationships among the pulse parameters. This formula
is used to derive the optimal conditions for efficient, robust population transfer. As illustrations of the theory, we present
results for two- and four-level systems, and selective vibronic excitation in the I2 molecule. We demonstrate that population transfer with chirped pulses is more robust and more selective than population transfer
with transform-limited pulses.
Received 6 September 2000 and Received in final form 25 September 2000 相似文献
8.
Ş. Erkoç H. Kökten Z. Güvenç 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(3):361-365
The fragmentation of water clusters, [(H
2
O)n;n = 2-8], have been investigated by using molecular-dynamics simulation method. In the simulations a polarizable-dissociable
potential energy function for water has been used. Particular attention has bee paid to investigate the effect of structural
properties and cluster size on the fragmentation.
Received 27 April 2000 and Received in final form 6 October 2000 相似文献
9.
P. Minutolo C. Corsi F. D'Amato M. De Rosa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):175-179
In this article we present experimental data for line parameters measurements of several transition lines of overtone bands
of C2H2 at 1540 nm. The measurements were done with a spectrometer based on a semiconductor diode laser and a direct absorption spectroscopy
scheme. Broadening and shift coefficients have been measured for the pure gas or in mixtures with N2, O2 and CO2 as perturbing gas.
Received 6 November 2000 and Received in final form 13 March 2001 相似文献
10.
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
11.
G. Bour A. Reinholdt A. Stepanov C. Keutgen U. Kreibig 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):219-223
We studied the effect of hydrogen in yttrium nanoparticles on a quartz substrate, using optical spectroscopy and electrical
resistance measurements. Pulsed laser deposition is used to obtain the Y clusters in an UHV environment. We show, that these
clusters are highly sensitive to monoatomic H1 produced from ambient hydrogen gas pressures, ranging from 10-5 to 50 mbar with our experimental arrangement. The changes of optical and electrical properties due to the chemical reaction
within the particles are sufficient to consider this material as a possible sensor for low concentrations of hydrogen.
Received 29 November 2000 相似文献
12.
C. Yannouleas U. Landman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):373-380
We show that the spin-and-space unrestricted Hartree-Fock method, in conjunction with the companion step of the restoration
of spin and space symmetries via Projection Techniques (when such symmetries are broken), is able to describe the full range of couplings in two-dimensional
double quantum dots, from the strong-coupling regime exhibiting delocalized molecular orbitals to the weak-coupling and dissociation
regimes associated with a Generalized Valence Bond combination of atomic-type orbitals localized on the individual dots. The
weak-coupling regime is always accompanied by an antiferromagnetic ordering of the spins of the individual dots. The cases
of dihydrogen (H2, 2e) and dilithium (Li2, 6e) quantum dot molecules are discussed in detail.
Received 19 December 2000 相似文献
13.
N.V. Brilliantov V.V. Malinin R.R. Netz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):339-345
A continuous liquid flow in a vacuum (a liquid beam) of an aqueous solution of adenine salt containing hydrochloric acid or
sodium hydroxide was irradiated with an intense pulsed IR laser at 3 μm, which is resonant to a vibrational mode related to
the OH stretch vibration of H2O. Neutral species isolated into the vacuum were ionized by a pulsed UV laser at 270 nm, and the product ions were mass-analyzed
by a time-of-flight mass spectrometer. It is found that AH 2
2 + . 2Cl- and [A-iH] i - .
iNa+ (i = 1-3) are isolated in the vacuum from the aqueous acidic and alkaline solutions, respectively, under irradiation of the
IR laser, and undergo four-photon ionization involving decomposition and proton transfer of the intermediate species under
irradiation of the UV laser.
Received 1st May 2002 Published online 13 September 2002 相似文献
14.
S. Tomita J.S. Forster P. Hvelplund A.S. Jensen S.B. Nielsen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):119-122
We have measured attenuation cross sections and fragmentation cross sections for protonated water clusters H(H2O)n
+ (n = 1 to 100) colliding with noble gas atoms (He and Xe) at a laboratory energy of 50 keV. In collisions with He, a transparency
effect in the attenuation cross section was observed. For the case of fragmentation in collisions with Xe, a strong enhancement
of small clusters was observed which we attribute to multifragmentation.
Received 30 November 2000 相似文献
15.
E. Hasmonay E. Dubois S. Neveu J.-C. Bacri R. Perzynski 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(1):19-29
A dynamic probing of magnetic liquids is performed experimentally, using a static magnetic field modulated by another smaller
field, normal and alternating. The optical magneto-birefringence under these crossed magnetic fields is recorded as a function
of the frequency for different field intensities and different sizes of the magnetic nanoparticles. A general reduced behavior
is found for the in-phase and the out-of-phase optical response which is well-described by a simple mechanical model. Depending
on the value H
ani of the anisotropy field of the nanoparticles, we can distinguish two different high magnetic field regimes: - a rigid dipole
regime (large anisotropy energy with respect to k
B
T) for cobalt ferrite nanoparticles with a relaxation time inversely proportional to the field intensity H
C(H
C < H
ani), - a soft dipole regime (anisotropy energy of the order of k
B
T) for maghemite nanoparticles with a relaxation time independent of the field intensity H
C(H
C > H
ani).
Received 5 June 2000 and Received in final form 8 January 2001 相似文献
16.
H. Lippert V. Stert L. Hesse C.P. Schulz W. Radloff I.V. Hertel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):445-448
The H atom transfer reaction in electronically excited indole(NH
3
)
n
clusters is studied in pump-probe experiments with femtosecond laser pulses. By applying different probe photon energies
we are able to detect the dissociation products (NH
3
)
n - 1
NH
4
for n
= 1-6. Furthermore we show that the analysis of the corresponding ion signals is not distorted by contributions from larger cluster
ions due to evaporation of NH
3
molecules. The formation times of the products are ca. 140ps for n
= 2-4 and about 80ps for n
= 5, 6.
Received 30 April 2002 / Received in final form 29 May 2002 Published online 13 September 2002 相似文献
17.
A.M. Malvezzi M. Patrini A. Stella P. Tognini P. Cheyssac R. Kofman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):321-324
Ga nanoparticle monolayers formed by evaporation-condensation in ultrahigh vacuum and embedded in a transparent SiOx matrix generate second harmonic (SH) signals in transmission and reflection when illuminated by a 150 fs, 800 nm laser pulses.
The observed SH light exhibits a critical dependence on input and output polarizations, angle of incidence and azimuthal orientation
of the samples. The results lead to a consistent picture of shape and orientation of the nanoparticles. Linear transmittance
spectra in the visible range support these findings and the observed size dependence of the SH signal.
Received 29 November 2000 相似文献
18.
M.A. Itskovsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):283-296
Theory of magnetoquantum oscillations with spin-split structure in strongly anisotropic (two-dimensional (2D)) metal is developed
in the formalism of level approach. Parametric method for exact calculation of oscillations wave forms and amplitudes, developed
earlier for spin degenerate levels is generalized on a 2D electron system with spin-split levels. General results are proved:
1) proportionality relation between magnetization and chemical potential oscillations accounting for spin-split energy levels
and magnetic field unperturbed levels (states of reservoir), 2) basic equation for chemical potential oscillations invariant
to various models of 2D and 1D energy bands (intersecting or overlapping) and localized states. Equilibrium transfer of carriers
between overlapping 2D and 1D bands, characterizing the band structure of organic quasi 2D metals, is considered. Transfer
parameter, calculated in this model to be of the order of unity, confirms the fact that the wave form of oscillations in organic metals should be quasisymmetric up to ultralow temperature. Presented theory accounts for spin-split magnetization oscillations at magnetic field directions tilted relative to the anisotropic
axis of a metal. Theoretical results are compared with available experimental data on organic quasi-2D metal α-(BEDT-TTF)2KHg(SNC)4 explaining the appearance of clear split structure under the kink magnetic field and absence above by the corresponding change
in the electron g-factor rather than cyclotron mass.
Received 20 December 2000 and Received in final form 13 July 2001 相似文献
19.
M. Schnürer S. Ter-Avetisyan H. Stiel U. Vogt W. Radloff M. Kalashnikov W. Sandner P.V. Nickles 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):331-335
Using 50 fs ( ∼ 2×1018 W/cm2) and 2 ps ( ∼ 5×1016 W/cm2) pulses from a Ti:Sa multi-TW laser at 800 nm wavelength large Xe-clusters ( 105...106 atoms per cluster) have been excited. Absolute yield measurements of EUV-emission in a wavelength range between 10 nm and
15 nm in combination with cluster target variation were carried out. The ps-laser pulse has resulted in about 30% enhanced
and spatially more uniform EUV-emission compared to fs-laser excitation. Circularly polarized laser light instead of linear
polarization results in enhanced emission which is probably caused by electrons gaining higher energies by the polarization
dependent optical field ionization process. An absolute emission efficiency at 13.4 nm of up to 0.8% in 2π sr and 2.2% bandwidth
has been obtained.
Received 11 January 2001 and Received in final form 27 March 2001 相似文献
20.
G.K. Paramonov H. Naundorf O. Kühn 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):205-215
The laser driven dynamics of the OH(D) stretching vibration in phthalic acid monomethylester is investigated. The combination
of a 55-dimensional all-Cartesian reaction surface Hamiltonian and the time-dependent self-consistent field approach is shown
to provide a microscopic picture of intramolecular vibrational energy redistribution taking place upon interaction with an
external laser field. Choosing suitable zeroth-order vibrational states and combinations thereof a quasi-periodic in-phase and out-of-phase oscillatory behavior is observed manifesting energy flow on different time scales. The fingerprints of this behavior in transient
absorption spectroscopy are also discussed.
Received 24 August 2000 and Received in final form 11 October 2000 相似文献