排序方式: 共有54条查询结果,搜索用时 15 毫秒
1.
When surfaces are structured on the scale of the wavelength, we can expect incident light to be strongly modified by the surface. This is especially the case when the surface is metallic. We have developed a formalism for computing these modifications, closely analogous to electron scattering theory, which we briefly review and present some results for optical properties of, and electron energy loss in, colloids. Our main theme is another effect associate with rough or structured metallic surfaces: Surface Enhanced Raman Scattering, or SERS. We model the rough surface by a periodic array of spheres and obtain the correct magnitude for the enhancement and for the frequency shifts observed. 相似文献
2.
3.
4.
5.
Marco Rahm David Schurig Daniel A. Roberts Steven A. Cummer David R. Smith John B. Pendry 《Photonics and Nanostructures》2008,6(1):87-VII
The technique of applying form-invariant, spatial coordinate transformations of Maxwell’s equations can facilitate the design of structures with unique electromagnetic or optical functionality. Here, we illustrate the transformation-optical approach in the designs of a square electromagnetic cloak and an omni-directional electromagnetic field concentrator. The transformation equations are described and the functionality of the devices is numerically confirmed by two-dimensional finite element simulations. The two devices presented demonstrate that the transformation optic approach leads to the specification of complex, anisotropic and inhomogeneous materials with well directed and distinct electromagnetic behavior. 相似文献
6.
Zhou J Koschny T Kafesaki M Economou EN Pendry JB Soukoulis CM 《Physical review letters》2005,95(22):223902
We investigate numerically the limits of the resonant magnetic response with a negative effective permeability mu(eff) for single-ring multicut split-ring resonator (SRR) designs up to optical frequencies. We find the breakdown of linear scaling due to the free electron kinetic energy for frequencies above approximately 100 THz. Above the linear scaling regime, the resonance frequency saturates, while the amplitude of the resonant permeability decreases, ultimately ceasing to reach negative value. The highest resonance frequency at which mu(eff) < 0 increases with the number of cuts in the SRR. A LC circuit model provides explanation of the numerical data. 相似文献
7.
We show that short pulses propagating in zero-gap periodic systems can be reversed with 100% efficiency by using weak nonadiabatic tuning of the wave velocity at time scales that can be much slower than the period. Unlike previous schemes, we demonstrate reversal of broadband (few cycle) pulses with simple structures. Our scheme may thus open the way to time reversal in a variety of systems for which it was not accessible before. 相似文献
8.
Wijnands F. Pendry J. B. Garcia-Vidal F. J. Bell P. M. Roberts P. J. Moreno L. Marti´n 《Optical and Quantum Electronics》1997,29(2):199-216
We present a new formalism for calculating the Green's function for Maxwell's equations. As our aim is to apply our formalism
to light scattering at surfaces of arbitrary materials, we derive the Green's function in a surface representation. The only
requirement on the material is that it should have periodicity parallel to the surface. We calculate this Green's function
for light of a specific frequency and a specific incident direction and distance with respect to the surface. The material
properties entering the Green's function are the reflection coefficients for plane waves at the surface. Using the close relationship
between the Green's function and the density of states (DOS), we apply our method to calculate the spontaneous emission rate
as a function of the distance to a material surface. The spontaneous emission rate can be calculated using Fermi's Golden
Rule, which can be expressed in terms of the DOS of the optical modes available to the emitted photon. We present calculations
for a finite slab of cylindrical rods, embedded in air on a square lattice. It is shown that the enhancement or suppression
of spontaneous emission strongly depends on the frequency of the light.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
9.
We consider a random medium in which scattering is exclusively in the forward direction. Waves are emitted by an object in the medium and Fourier components of the intensity are shown to propagate independently. At small wavevectors the intensity propagates very simply through increasing thickness, z, of medium, as λz, and Fourier components of the object can easily be reconstructed. For wavevectors greater than a critical value, qc, the intensity changes with z in a more complex fashion making it very difficult to reconstruct the object. They develop a simple model for the singularity and apply it to the reconstruction of an object degraded by passage through a random medium. 相似文献
10.
The c(2 × 2) configuration of CO chemisorbed on Ni(100) has been examined by the dynamical LEED method of surface structure analysis. Experimental LEED intensity spectra of the (00), () (10) and (11) LEED beams measured at 175 K are compared with the corresponding calculated spectra for two different CO potential constructions and a number of trial structures. The best agreement was found for a structure where the CO molecules sit directly above the Ni atoms with vertical spacings between the Ni and C and the C and O layers of 1.80 ± 0.10 A and 0.95 ± 0.10 Å respectively. It is proposed that the CO molecule is tipped over at an angle of 34° ± 10° with respect to the surface normal so that the actual carbon-oxygen bond length is close to the figure 1.15 Å found in Ni(CO)4. 相似文献