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11.
Yaling Yin 《Optics Communications》2008,281(22):5511-5514
We propose a simple optical device to convert a Gaussian laser beam into a neat semi-Gaussian laser beam without any diffraction fringe by using a spatial light modulator and a thin, sharp blade, and numerically calculate the diffracted, relative intensity distributions of both the semi-Gaussian laser field and the semi-Gaussian, pseudo-thermal light. We also study the dependence of the border width of the semi-Gaussian beam on the waist of the Gaussian beam. Our study shows that the proposed scheme can be used to cancel all diffraction fringes from both the straight edge of the blade and a finite lens aperture in all the planes vertical to the z axis and obtain a neat semi-Gaussian beam without any diffraction fringe, and find that the border width wB of the generated semi-Gaussian beam is not dependent on the waist of the incident Gaussian beam. 相似文献
12.
The kinetic process of Sr atom metastable-metastable transition lasers in He-St longitudinal pulsed discharge is analysed and a concise self-consistent physical model is developed. The temporal evolutions of discharge parameters, main paxticle densities, the electron temperature, and the lasing pulses are numerically calculated. The results provided by the model agree well with the experiment, and the temporal behaviour of each laser pulse is explained successfully by the simulation results. 相似文献
13.
A.S. Alexandrov 《Journal of Physics and Chemistry of Solids》2008,69(12):2971-2974
The electron-phonon interaction in cuprates with c-axis polarised optical phonons, which is roughly one order of magnitude stronger than superexchange, bounds holes into mobile bipolarons. Bipolarons pin the chemical potential within the charge-transfer gap of doped Mott insulators, accounting for unusual kinetics and thermodynamics of doped cuprates such as the Nernst and giant proximity effects, pseudo-gaps, and normal-state diamagnetism. We propose that “quasi-particle” peaks, “Fermi-arcs”, and high-energy “waterfalls” in the photoemission spectra of cuprates originate from the photo-ionization matrix elements of disorder-localised band-tails in the charge-transfer gap. 相似文献
14.
Development of a tunable mid-IR difference frequency laser source for highly sensitive airborne trace gas detection 总被引:4,自引:0,他引:4
Richter D Fried A Wert BP Walega JG Tittel FK 《Applied physics. B, Lasers and optics》2002,75(2-3):281-288
The development of a compact tunable mid-IR laser system at 3.5 μm for quantitative airborne spectroscopic trace gas absorption
measurements is reported. The mid-IR laser system is based on difference frequency generation (DFG) in periodically poled
LiNbO3 and utilizes optical fiber amplified near-IR diode and fiber lasers as pump sources operating at 1083 nm and 1562 nm, respectively.
This paper describes the optical sensor architecture, performance characteristics of individual pump lasers and DFG, as well
as its application to wavelength modulation spectroscopy employing an astigmatic Herriott multi-pass gas absorption cell.
This compact system permits detection of formaldehyde with a minimal detectable concentration (1σ replicate precision) of
74 parts-per-trillion by volume (pptv) for 1 min of averaging time and was achieved using calibrated gas standards, zero air
background and rapid dual-beam subtraction. This corresponds to a pathlength-normalized replicate fractional absorption sensitivity
of 2.5×10-10 cm-1.
Received: 29 April 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +1-303/497-1492, E-mail: dr@ucar.edu 相似文献
15.
Following our experimental observations of disclination lines in freely suspended droplets and free-standing films (Yu.A.
Nastishin et al., Eur. Phys. J. E 5 353 (2001)), topological defects of the twist grain boundary (TGBA) phase are considered according to two aspects: topological
and energetical. There are two classes of line defects, disclinations (as in the cholesteric (N*) phase and the liquid vortices phase (NL*), relating to the directors tripod symmetries) and dispirations (relating to the translation-rotation symmetries); there are no topological point defects. Differences between N*, NL* and
TGBA disclinations are physical, not topological. The absence of focal conic domains in the TGBA phase is an immediate consequence of the materialization of the helical axis
(along the χ-director); the same feature, coupled to the trend to parallelism of the smectic layers, accounts for the predominance
of λ-lines. Finally, the presence of defects akin to developable domains is explained in the frame of the leastcurvaturemodel, that requires the introduction of a third type of defects: the densitiesofedgedislocations of the smectic layers.
Received 20 February 2002 相似文献
16.
A novel scheme for all-optical image processing is suggested, which is based on spontaneous pattern-formation processes. The
spatiotemporal instabilities, connected with these self-organization effects, appear in many nonlinear optical systems and
mostly obstruct the intended application. We propose to utilize the particular features of pattern formation for parallel
image processing, namely the sensitivity to external influences, the selection of well-defined final states, and the rotational
and translational invariance. We report here on a single-feedback experiment with a liquid crystal light valve as the optical
nonlinearity. In this experiment, the recognition of hexagonal structures is realized. We characterize the response dynamics
and study associative properties of this scheme. The extension to square patterns is discussed, and first steps towards a
practical implementation are undertaken in providing a simple post-processing scheme and testing the concept on realistic
input images.
Received: 26 November 2002 / Revised version: 7 February 2003 / Published online: 9 April 2003
RID="*"
ID="*"Corresponding author. Fax: +49-6151/16-4123, E-mail: ralph.neubecker@physik.tu-darmstadt.de 相似文献
17.
Electrical resistivity and Seebeck coefficients of Y BaCo4−xZnxO7 (x=0.0,0.5,1.0,2.0) were investigated in the temperature range 350-1000 K. It was found that the electrical resistivity and activation energy increase with increasing Zn concentration, while Seebeck coefficients do not increase but decrease when electrical resistivity increases. We explained the increase of electrical resistivity and the drop of Seebeck coefficients for Zn-substituted samples by the decrease of carrier mobility, rather than of carrier concentration. The effect of oxygen absorption and desorption on the electrical resistivity and Seebeck coefficients was also investigated. An abrupt change of transport properties happens at about 650 K for x=0.0 and 0.5 samples measured in oxygen. For x=1.0 and 2.0 samples, however, such change disappears and the transport behavior in oxygen is almost same as that in nitrogen due to the significant suppression of oxygen diffusion caused by the higher Zn concentration in these samples. 相似文献
18.
Resonance Energies,Absorption Oscillator Strengths and Ionization Potentials for the Element Hassium (Z = 108) 下载免费PDF全文
On the basis of successfully predicting low-lying energy levels for the element fermium (Z = 100), we calculate the resonance energies, absorption oscillator strengths and the first ionization potential of the element hassium (Z = 108) by taking important relativistic and improved electron correlation effects into account using the multiconfiguration Dirac Fock method. These calculations are carried out with the aim of assisting experimental investigations of hassium. 相似文献
19.
O. Mondain-Monval J.C. Dedieu T. Gulik-Krzywicki P. Poulin 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):167-170
The role of surface energy in the behavior of colloidal particles in liquid crystalline phases is investigated. When the surface
energy dominates, a hedgehog defect is formed and, according to an electrostatic analogy, the distortions around the particles
exhibit a dipolar character. By contrast, for weaker anchoring, the configuration becomes quadrupolar as evidenced by the
structure of latex clusters in lyotropic systems and the observation of defects reminiscent of Saturn rings in thermotropic
systems.
Received 21 June 1999 相似文献
20.
A. Surzhykov U. D. Jentschura T. Stöhlker S. Fritzsche 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):27-36
We apply the density matrix theory to re-investigate the radiative
electron capture into heavy ions with one valence electron. Attention
has been paid particularly to the magnetic sublevel population of the
residual ions, as described in terms of alignment parameters. Simple
method, based on an independent particle model, which takes
into account the Pauli principle, is proposed for evaluating the
alignment of the excited ionic states. By making use of this method,
detailed calculations are performed for electron capture into (initially) hydrogen-like and lithium-like europium, gold and
uranium ions, and are compared with the results of the multiconfiguration Dirac-Fock approach.As seen from the calculations
and from the comparison with available experimental results, the independent particle model provides a good estimate for the
alignment parameters of few-electron heavy ions. Therefore, our simple model may help to understand the basic properties of
the X-ray emission from heavy, few-electron ions without the need for invoking sophisticated MCDF calculations. 相似文献