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51.
52.
H. Pu T. Cai N.P. Bigelow 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(3):269-278
We present a semi-classical theory of the light pressure force for atoms interacting with a two-dimensional laser field. Unlike
previous 2D theory, ours is valid for general atomic level and laser field configurations. We show that striking new features
appear in the velocity-dependent force arising from the multi-dimensionality. Finally, we describe in detail the novel numerical
technique used in the calculation.
Received 4 December 1998 and Received in final form 13 February 1999 相似文献
53.
We have analyzed the optical properties of a-Ge30-xSbxS70 chalcogenide glass films (x=0,10,20 and 30 at%); the chalcogenide films were prepared by vacuum thermal evaporation. The optical-absorption data indicate that the absorption mechanism is non-direct transition. We found that the optical band gap, Eopt, decreases from 2.04±0.01 to 1.74±0.01 eV, whereas the refractive index increases with increasing Sb content. Data are analyzed by the Wemple equation, which is based on the single-oscillator model. 相似文献
54.
The increasing use of low power cw lasers in various applications calls for the design of optical limiters with low thresholds. To this end, the optical nonlinearity exhibited by zinc tetraphenyl porphyrin at low laser powers is utilized to design an optical limiter for low threshold operation. The basic parameter responsible for limiting action, the nonlinear refractive index of the medium, is measured using the Z-scan technique and found to have a value of at the helium–neon laser wavelength of 632.8 nm. The origin of nonlinearity is explained on the basis of the thermal lens model. It is shown that effective optical limiting at desired threshold values can be achieved by the optimal choice of aperture size and experimental geometry. 相似文献
55.
L. Besombes Y. Lger L. Maingault D. Ferrand J. Cibert H. Mariette 《Physica E: Low-dimensional Systems and Nanostructures》2006,35(2):300
The magnetic state of a single magnetic ion (Mn2+) embedded in an individual quantum dot is optically probed using micro-spectroscopy. The fine structure of a confined exciton in the exchange field of a single Mn2+ ion (S=) is analyzed in detail. The exciton–Mn2+ exchange interaction shifts the energy of the exciton depending on the Mn2+ spin component and six emission lines are observed at zero magnetic field. The emission spectra of individual quantum dots containing a single magnetic Mn atom differ strongly from dot to dot. The differences are explained by the influence of the system geometry, specifically the in-plane asymmetry of the quantum dot and the position of the Mn atom. Depending on both these parameters, one has different characteristic emission features which either reveal or hide the spin state of the magnetic atom. The observed behavior in both zero field and under magnetic field can be explained quantitatively by the interplay between the exciton–Mn2+ exchange interaction (dependent on the Mn position) and the anisotropic part of the electron–hole exchange interaction (related to the asymmetry of the quantum dot). 相似文献
56.
Filled and unfilled polyvinylalcohol (PVA) films were prepared by the casting technique. Films of equal amounts with various concentrations of two fillers (CoBr2 and MgCl2) were prepared. Spectroscopic, structural and some physical properties of these films were studied with different techniques. Fourier-transform infrared (FTIR) revealed that the syndiotacticity structure of the PVA samples causes dense molecular packing in the crystal and also stronger intermolecular hydrogen bonds, which are responsible for the disappearance of the molecular motion. X-ray diffraction (XRD) scans evidenced the presence of some semicrystalline structure of PVA films. The optical absorption spectra suggested the presence of an optical gap (Eg), which depends on filler concentration for all the filling levels. Differential thermal analysis (DTA) suggests that the segmental mobility of an amorphous pure PVA increases as a result of the addition of mixed fillers, becoming less-rigid segments. This indicates that the mixed fillers act as plasticizers. 相似文献
57.
R. Kheradmand M. Sahrai H. Tajalli G. Tissoni L. A. Lugiato 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(1):107-112
We present here a method for selecting optical patterns in a passive
semiconductor microresonator, by using a spatial perturbation. A pattern is
spontaneously generated in the system, and a switching beam causes this
pattern to rotate even if the power in the switching beam is much lower than
the power in the pattern. Thus, an all optical switch is realized, that
operates at low light levels. 相似文献
58.
Nonlinear wave propagation is studied theoretically in a one-dimensional photonic band gap structure containing single negative materials. It is found that Kerr nonlinearity is greatly enhanced near the lower edge of a recently explored angular gap for transverse magnetic polarized light. Consequently, optical bistability is achieved at very low values of input intensity in a periodic structure composed of only a few repeating units. The characteristics of optical bistability are affected only slightly with the variation of the incident angle and thickness ratio of the layers. The effect of losses is also found to be relatively insignificant in such a small structure. 相似文献
59.
Yu-jun Quan Pei-de Han Qi-jiang Ran Fan-ping Zeng Li-peng Gao Chun-hua Zhao 《Optics Communications》2008,281(11):3105-3110
A photonic wire-based directional coupler based on SOI was fabricated by e-beam lithography (EBL) and the inductively coupled plasma (ICP) etching method. The size of the sub-micron waveguide is 0.34 μm × 0.34 μm, and the length in the coupling region and the separation between the two parallel waveguides are 410 and 0.8 μm, respectively. The measurement results are in good agreement with the results simulated by 3D finite-difference time-domain method. The transmission power from two output ports changed reciprocally with about 23 nm wavelength spacing between the coupled and direct ports. The extinction ratio of the device was between 5 and 10 dB, and the insertion loss of the device in the wavelength range 1520-1610 nm was between 22 and 24 dB, which included an about 18.4 ± 0.4 dB coupling loss between the taper fibers and the polished sides of the device. 相似文献
60.
Summary The theory of the RPA optical response of a solid has been generalized in order to take into account also the possible presence
of spatially nonlocal potentials in the Hamiltonian. Explicit expressions for first- and second-order susceptibilities are
given in the new framework. The expressions obtained depend on the matrix elements of operators of the form of a commutator
of a component of the position operatorr and an operator that commutes with the lattice translations. The problem of the evaluation of these matrix elements is solved
in a simple manner by introducing an auxiliary, periodic position operator,XXXr. In such a way a general formulation is obtained that preserves the gauge invariance. As an application of the new theory,
the second harmonic generation (SHG) from a semiconductor in a simple two-band model has been studied. The differences between
our correct gauge-invariant results and those obtained in the usual local approximation is an indication of a slow convergence
of the expressions obtained in the local approximation. 相似文献