排序方式: 共有392条查询结果,搜索用时 15 毫秒
31.
Single shot ablation of metallic materials of aluminium, titanium alloy (Ti6Al4V) and gold has been studied with 10 picoseconds (ps) laser pulses experimentally and theoretically. The ablation rate variation at high fluence was explained by a simplified predictive model based on critical-point phase separation (CPPS) theory. A comparison between experimental and numerical results inferred that CPPS may well be the dominant ablation mechanism for high fluence laser ablation at 10 ps laser duration. 相似文献
32.
V. M. Gordienko I. M. Lachko A. A. Rusanov A. B. Savel’ev D. S. Uryupina R. V. Volkov 《Applied physics. B, Lasers and optics》2005,80(6):733-739
We present atomic, energy, and charge spectra of ions accelerated at the front surface of a silicon target irradiated by a high-contrast femtosecond laser pulse with an intensity of 3×1016 W/cm2, which is delayed with respect to a cleaning nanosecond laser pulse of 3-J/cm2 energy density. A tremendous increase in the number of fast silicon ions and a significant growth of their maximum charge in the case of the cleaned target from 5+ to 12+ have been observed. The main specific features of the atomic, energy, and charge spectra have been analyzed by means of one-dimensional hydrodynamic transient-ionization modeling. It is shown that fast highly charged silicon ions emerge from the hot plasma layer with a density a few times less than the solid one, and their charge distribution is not deteriorated during plasma expansion.This revised version was published online in August 2005 with a corrected cover date. 相似文献
33.
H. Frahm C. Rödenbeck 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):409-414
We study the phase diagram of coupled spin-1/2 chains with bilinear and (chiral) three-spin exchange interactions in a magnetic
field. The model is soluble on a one-parametric line in the space of coupling constants connecting the limiting cases of a
single and two decoupled Heisenberg chains with nearest neighbour exchange only. We give a complete classification of the
low-energy properties of the integrable system and introduce a numerical method which allows to study the possible phases
of spin ladder systems away from the soluble line in a magnetic field.
Received 17 November 1998 and Received in final form 22
January 1999 相似文献
34.
We have investigated spin singlet Mott states of spin-one bosons with antiferromagnetic interactions. These spin singlet states do not break rotational symmetry and exhibit remarkably different macroscopic properties compared with nematic Mott states of spin-one bosons. We demonstrate that the dynamics of spin singlet Mott states is fully characterized by even- or odd-class quantum dimer models. The difference between spin singlet Mott states for even and odd numbers of atoms per site can be attributed to a selection rule in the low energy sectors of on-site Hilbert spaces; alternatively, it can also be attributed to an effect of Berry’s phases on bosonic Mott states. We also discuss evidence for spin singlet quantum condensate of spin-one atoms. Our main finding is that in a projected spin singlet Hilbert space, the low energy physics of spin-one bosons is equivalent to that of a Bose-Hubbard model for spinless bosons interacting via Ising gauge fields. The other major finding is spin-charge separation in some one-dimensional Mott states. We propose charge-e spin singlet superfluid for an odd number of atoms per lattice site and charge-2e spin singlet superfluid for an even number of atoms per lattice site in one-dimensional lattices. All discussions in this article are limited to integer numbers of bosons per site. 相似文献
35.
Microdroplets of 15-μm diameter are subjected to ultra-short laser pulses of intensities up to 1015Wcm−2 to produce hot dense plasma. The hot electrons produced in the microdroplet plasma result in efficient generation of hard X-rays in the range 50–150keV at an irradiance as low as 8×1014Wcm−2. The X-ray source efficiency is estimated to be about 2 ×10−7%. A prepulse that is about 11ns ahead of the main pulse strongly influences the droplet plasma and the resulting X-ray emission. For a similar laser prepulse and intensity, no measurable hard X-ray emission is observed when the laser is focused on a solid target of similar composition and this indicates that liquid droplet targets are best suited for hard X-ray generation in laser–plasma interactions. 相似文献
36.
R. Lü J.-L. Zhu X. Chen L. Chang 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):35-40
At low temperatures the Neel vector in a small antiferromagnetic particle can possess quantum coherence between the classically
degenerate minima. In some cases, the topological term in the magnetic action can lead to destructive interference between
the symmetry-related trajectories for the half-integer excess spin antiferromagnetic particle. By studying a macroscopic quantum
coherence problem of the Neel vector with biaxial crystal symmetry and a weak magnetic field applied along the hard axis,
we find that the quenching of tunnel splitting could take place in the system without Kramers' degeneracy. Both the Wentzel-Kramers-Brillouin
exponent and the pre-exponential factors are found exactly for the tunnel splitting. Results show that the tunnel splitting
oscillates with the weak applied magnetic field for both the integer and half-integer excess spin antiferromagnetic particles,
and vanishes at certain values of the field. All the calculations are performed based on the two sublattices model and the
instanton method in spin-coherent-state path integral.
Received: 24 July 1997 / Accepted: 30 September 1997 相似文献
37.
Semi-quantitative time resolved LIBS measurements 总被引:1,自引:0,他引:1
R. Barbini F. Colao R. Fantoni A. Palucci S. Ribezzo H.J.L. van der Steen M. Angelone 《Applied physics. B, Lasers and optics》1997,65(1):101-107
Received: 2 February 1996/Accepted: 20 January 1997 相似文献
38.
C. Boulmer-Leborgne J. Hermann B. Dubreuil 《Applied Physics A: Materials Science & Processing》1992,55(4):340-346
In many laser applications such as drilling, welding and cutting, the role of the plasma in the transfer of energy between the laser beam and the metal surface appears to be rather important. It depends on several parameters such as laser wavelength, irradiation time and deposited energy but especially on the buffer gas nature. In this work the plasma is initiated by a TEA-CO2 laser beam perpendicularly focussed onto a Ti target (100 MW/cm2), in a cell containing He, Ar or a He-Ar mixture as buffer gas. The plasma is studied by time and space resolved spectroscopic diagnostics. The results show that helium allows target erosion whereas a highly absorbing breakdown plasma develops in argon shielding the target from the subsequent laser heating. With only 20% Ar in He, a strong quenching of the He plasma by Ar occurs, and the Ar plasma effect is dominant. 相似文献
39.
Y.J. Kim M. Greven U.-J. Wiese R.J. Birgeneau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):291-297
Antiferromagnetic Heisenberg spin chains with various spin values (S=1/2,1,3/2,2,5/2) are studied numerically with the quantum Monte-Carlo method. Effective spin S chains are realized by ferromagnetically coupling n=2S antiferromagnetic spin chains with S=1/2. The temperature dependence of the uniform susceptibility, the staggered susceptibility, and the static structure factor
peak intensity are computed down to very low temperatures, . The correlation length at each temperature is deduced from numerical measurements of the instantaneous spin-spin correlation
function. At high temperatures, very good agreement with exact results for the classical spin chain is obtained independent
of the value of S. For the S=2 chain which has a gap , the correlation length and the uniform susceptibility in the temperature range are well predicted by the semi-classical theory of Damle and Sachdev.
Received: 23 December 1997 / Revised and Accepted: 11 March 1998 相似文献
40.
T. Verkholyak A. Honecker W. Brenig 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(3):283-287
The Jordan-Wigner transformation is applied to study the ground
state properties and dimerization transition in the J1-J2
XXZ chain. We consider different solutions of the mean-field
approximation for the transformed Hamiltonian. Ground state
energy and the static structure factor are compared with complementary
exact diagonalization and good agreement is found
near the limit of the Majumdar-Ghosh model.
Furthermore, the ground state phase diagram is discussed
within the mean-field theory. In particular, we show that an
incommensurate ground state is absent for large J2 in a fully
self-consistent mean-field analysis. 相似文献