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1.
The generating mechanism of the energy-stream loops (ESLs) for the evanescent waves around the interfaces of a left-handed material (LHM) slab has been investigated with a finite-difference time-domain (FDTD) method. The simulations have shown that these ESLs originate from standing waves, attributed to the intervention of counter-propagating evanescent waves. Large numbers of ESLs can appear because of the numerous values of wave vectors ky. The larger ESLs die out more quickly than the smaller ones in time after the source is switched off, the ESLs shrink continuously with increasing delay, and the oscillated distributions of the evanescent waves between the surfaces can also be validated. It is greatly helpful for the further comprehension on energy fluxes of evanescent waves in the LHM slab. 相似文献
2.
Left-handed materials do not make a perfect lens 总被引:1,自引:0,他引:1
By means of an analysis on evanescent waves in left-handed materials (LHM), we show that within a slab of such a medium, sandwiched between two positive refraction media, there is amplification of evanescent waves in ideal lossless, dispersiveless media; however, contrary to previous claims, this is limited to a finite width of the slab so that it prevents their restoration and perfect focusing. We illustrate this by considering their coupling to propagating waves through a tunnel barrier containing a slab of LHM. Further, we show that the effect of absorption, necessarily present in such materials, may drastically change any evanescent amplifying wave into a decaying one. 相似文献
3.
4.
关于左手性介质几何光学的研究(一) 总被引:2,自引:1,他引:1
根据几何光学中的费马原理和完善成像原理研究了光线经过正负折射率界面时的传播特性,推导了单负折射率完善成像的曲面方程,讨论了单块负折射率透镜成像特性的一些缺陷及改进方案,依此指出了最短时间原理的适用范围的局限性和利用左手性介质制作光学器件的优越性,为进一步研究左手性介质的光学特性和相关光学器件设计提供了理论基础. 相似文献
5.
A. A. Zharov N. A. Zharova R. E. Noskov 《Journal of Experimental and Theoretical Physics》2009,109(5):734-750
We develop a theory describing the dynamics and interaction of electromagnetic surface waves (ESWs) resonantly excited by
an external source in a slab of left-handed material (LHM) with identical negative (equal to −1) values of dielectric permittivity
and magnetic permeability that makes up a so-called perfect lens, or a superlens. We show that subwavelength imaging by a
superlens is associated with the degeneracy of the spectrum of eigen electromagnetic surface modes at the interfaces of the
metamaterial slab, whereas the dynamic response of the superlens is completely determined by the dynamics of these modes and
the dispersion properties of the metamaterial. We obtain conditions that enable one to find out when a superlens produces
subwavelength images of an external source. We consider the cases of a stationary and a pulse source, as well as of a source
that moves with constant velocity or oscillates in space. 相似文献
6.
The ratio of amplitudes of waves generated by different interfaces in stratified inhomogeneous liquid is analytically studied. The amplitudes of waves generated by the second interface depend on the initial conditions and can be greater or less than the amplitudes of waves generated by the third interface. The amplitude ratio of the external and internal waves significantly depends on the ratio of liquid densities and layer thicknesses. Substantial effect of the initial conditions is manifested as a variation in the ratio of the amplitudes of external and internal waves and the amplitude ratio of waves generated by different interfaces. 相似文献
7.
Lenses made of negative index materials have the ability to focus the propagating and evanescent components of electromagnetic
waves. Such a possibility enables super resolution, in turn resulting in sharper, subwavelength size images. In this present
work, we present subwavelength imaging that was obtained from a one-dimensional left-handed metamaterial (LHM) composed of
alternating layers of split-ring resonators and thin wires. We investigated the effect of the thickness of LHM lenses on image
size. The left-handed pass band within the negative permittivity and permeability region is shown experimentally and theoretically
for different thicknesses of LHM slabs. We also studied the transmission-phase of LHMs with a different number of unit cells
along the propagation direction. The phase decreases with the increasing thicknesses of LHM slabs, proving that the phase
velocity is negative in the left-handed transmission band.
PACS 42.25.-p; 41.20.Jb; 81.05.-t 相似文献
8.
Padilla F Poiree B Talmant M Quentin G 《The Journal of the Acoustical Society of America》2000,108(1):25-30
It is shown that the circumferential internal waves propagating around an elastic cylinder can be locally seen as plane evanescent waves, at any observation point inside the surrounding fluid. This is done by direct calculation of the associated complex bivector. The exact anatomy of the wave is detailed and the phase propagation paths are found to be curved, as expected. The transition to the plane interface is achieved. Polarization ellipses associated with the acoustic displacement vector are described. The additional low evanescence assumption leads to conventional ray interpretation with identification of the ray tube divergence coefficients, and the wavefront is found to be the involute of a circle. 相似文献
9.
The characteristics of an imaging system formed by a left-handed material (LHM) slab of finite length are studied, and the influence of the finite length of the slab on the image quality is analyzed. Unusual phenomena such as surface bright spots and negative energy stream at the image side are observed and explained as the cavity effects of surface plasmons excited by the evanescent components of the incident field. For a thin LHM slab, the cavity effects are found rather sensitive to the length of the slab; the bright spots on the bottom surface of the slab may stretch to the image plane and degrade the image quality. 相似文献
10.
A slab of left-handed material (LHM) with refractive index -1 forms a perfect lens that retains subwavelength information about a source or object. Such lenses are highly susceptible to perturbations affecting their performance. It is shown that illuminating a roughened interface between air and an LHM produces a regime for enhanced focusing of light close to the boundary. This generates caustics that are brighter, fluctuate more, and cause Gaussian speckle at distances closer to the interface than in right-handed matter. These effects present fresh challenges for perfecting the perfect lens. 相似文献
11.
We suggest a simple and high efficient method for trapping particles in the evanescent field. In this method, a single plane wave is normally incident on the cylindrical surface of a cylindrical lens and then incident on the plane surface of the lens at an angle larger than the critical angle. Multiple reflections of light within the cylindrical lens create two evanescent waves with different directions in the transmitted field. Interference of two evanescent waves comes into being a standing wave which can stably trap particles close to the top of the cylindrical lens. Based on the Rayleigh approximation, we obtain analytical expressions of optical force acting on a Rayleigh particle placed in the vicinity of the lens. We find that the trap stiffness and trap depth is dependent on the radius of the cylindrical lens, wavelength and polarization of light, and incident angle at the lens–liquid interface. 相似文献
12.
In a planar lens made of left-handed material (LHM), the rays converge to a focal point in the material and once again in
free space. The problems exhibited by the planar lens are its great thickness, the long optical path length, and energy concentration
in the LHM. We examine a bowl-shaped LHM lens with an index n = −1. In this lens, the back is a concave hemispherical surface and the rays never converge in the LHM, but in free space
only. We also designed a quantized bowl-shaped LHM lens composed of multiple layers of thin LHM plates of uniform thickness.
A bowl-shaped LHM lens quantized with more than 4 bits has a lens function similar to that of a smooth curved lens. The bowl-shaped
lens is characterized by its thinness, its short optical path length, and the absence of energy concentration in the LHM.
Furthermore, the quantized bowl-shaped LHM lens can be fabricated. Wave propagation through these lenses is numerically simulated
using the finite difference time domain (FDTD) method. 相似文献
13.
Linearly polarised three-colour lasing emission from an evanescent wave pumped and gain coupled fibre laser
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A novel Whispering--Gallery--Mode (WGM) fibre laser,
emitting linearly polarised three-colour light, is demonstrated by
pumping and gain coupling with evanescent waves. The pump light is
longitudinally coupled into a bare optical fibre immersed in a dye
solution of lower refractive index. The dye molecules around the
bare fibre are excited by the evanescent waves of pump light when
they propagate along the fibre in a total internal reflection. When
the pump beam within the fibre is a meridian beam, the WGM lasing
emission from the fibre laser is a linearly polarised transverse
electric wave, while it is a mixed wave of the linearly polarised
transverse electric and magnetic waves if the pump beam is a skew
beam within the fibre. Because the excited molecules are located
within the evanescent field of WGM, a good spatial overlap between
the dye gain and the evanescent field leads to a high pumping
efficiency and a longer gain distance along the fibre. Once the bare
fibre is inserted into three glass capillaries filled with Rhodamine
6G, 610 and 640 dye solutions, respectively, WGM laser oscillations
at the wavelengths of 567--575, 605--614 and 656--666~nm occur
simultaneously, and a linearly polarised three-colour lasing
emission is achieved in a single optical fibre. 相似文献
14.
Godin OA 《The Journal of the Acoustical Society of America》2011,129(2):EL45-EL51
Sound transmission through gas-solid interfaces is usually very weak because of the large contrast in wave impedances at the interface. Here, it is shown that diffraction effects can lead to a dramatic increase in the transparency of gas-solid interfaces at low frequencies, resulting in the bulk of energy emitted by compact sources within a solid being radiated into a gas. The anomalous transparency is made possible by power fluxes in evanescent body waves and by excitation of interface waves. Sound transmission into gas is found to be highly sensitive to absorption of elastic waves within a solid. 相似文献
15.
Negative refraction in two-dimensional photonic crystals 总被引:1,自引:0,他引:1
M. Qiu S. Xiao A. Berrier S. Anand L. Thylén M. Mulot M. Swillo Z. Ruan S. He 《Applied Physics A: Materials Science & Processing》2005,80(6):1231-1236
We present some of our recent results for negative refraction in photonic crystals. The concept of negative refraction in photonic crystals is firstly introduced. Then, the propagation of electromagnetic waves in photonic crystals is systematically studied. By the layer Korringa–Kohn–Rostoker method, the coupling efficiency between external plane waves and the Bloch waves in photonic crystals is investigated. It is found that the coupling coefficient is highly angular dependent even for an interface between air with n=1 and a photonic crystal with effective index neff=-1. It is also shown that, for point imaging by a photonic crystal slab, owing to the negative refraction, the influence of the surface termination on the transmission and the imaging quality is significant. Finally, we present results experimentally demonstrating negative refraction in a two-dimensional photonic crystal at optical communication wavelengths. PACS 42.70.Qs; 41.85.Ct; 42.30.Va 相似文献
16.
Yifeng Xiang Xi Tang Changjun Min Guanghao Rui Yan Kuai Fengya Lu Pei Wang Hai Ming Qiwen Zhan Xiaocong Yuan Joseph R. Lakowicz Douguo Zhang 《Annalen der Physik》2020,532(4):1900497
Near-field optical trapping can be realized with focused evanescent waves that are excited at the water–glass interface due to the total internal reflection, or with focused plasmonic waves excited on the water–gold interface. Herein, the performance of these two kinds of near-field optical trapping techniques is compared using the same optical microscope configuration. Experimental results show that only a single-micron polystyrene bead can be trapped by the focused evanescent waves, whereas many beads are simultaneously attracted to the center of the excited region by focused plasmonic waves. This difference in trapping behavior is analyzed from the electric field intensity distributions of these two kinds of focused surface waves and the difference in trapping behavior is attributed to photothermal effects due to the light absorption by the gold film. 相似文献
17.
In this paper we have investigated three external fields
interacting with the four-level Y-type atomic system described by
the density-matrix approach. The results show that
left-handedness with zero absorption is achieved. The zero
absorption property displays the possibility of manipulation by
varying the phase and the intensity of the coupling field. Also, the
zero absorption property may be used to amplify the evanescent waves
that have been lost in imaging by traditional lenses. We propose
an approach to obtain a negative refractive medium with zero
absorption and the possibility of enhanceingthe imaging resolution in
realizing `superlenses'. 相似文献
18.
Y.-C. Chuang R. Dudley M. A. Fiddy 《Applied Physics A: Materials Science & Processing》2013,112(3):575-582
Superresolution depends on near-field capture and transfer of high spatial frequencies from the scattering object. These evanescent waves are transferred to a near-field image domain using a negative index material. Measuring images with subwavelength scale resolution in the near field by scanning is not practical and ignores inevitable object–lens–image coupling phenomena as well as the need to employ inverse scattering algorithms. An alternative approach based on compressive sampling permits the use of a single fixed detector. Traditionally, in such a system, an image-bearing wavefront is projected onto a series of patterns (= basis functions) and the transmitted light integrated by a lens onto a single-point detector. Image reconstruction is possible by weighting each basis function with its measured coefficient and summing, including basis functions representing evanescent waves. We employ a single fixed detector in the back focal plane of a negative index concave lens and basis functions realized by structured illumination from combinations of a set of discrete sources. We have investigated this as an approach to recover subwavelength scale details about a scattering object and report our results. 相似文献
19.
T. I. Kuznetsova N. A. Raspopov 《Journal of Experimental and Theoretical Physics》2014,118(3):395-400
A one-dimensional photonic crystal and an incident light wave that is noncollinear with the permittivity gradient of the crystal are considered. On the basis of coupled-mode equations, eigensolutions for the fields are obtained; a special focus is placed on evanescent waves. Field transformation at the crystal-air and crystal-metal interfaces is analyzed. A condition for the resonance excitation of surface waves at the interface between a crystal and a metal is obtained, and an estimate is given for the efficiency of transformation of the original traveling wave into a surface wave. 相似文献
20.
Structure for localizing electromagnetic waves with a left-handed-medium slab and a conducting plane 总被引:1,自引:0,他引:1
A new structure is proposed for localizing electromagnetic waves and energies with a left-handed-medium (LHM) slab and a perfectly electrically conducting (PEC) plane. When a current source is placed in front of a perfectly matched LHM slab with negative permittivity -epsilon0 and negative permeability -mu0 and a PEC plane is placed at the image point, we show rigorously that all the electromagnetic waves are confined in a region between the source and the PEC plane, and the fields outside the region are completely zero. Such an energy-localization system would be useful in medical treatments that use concentrated optical and microwave energies. However, a perfectly matched LHM is unphysical and does not exist in nature. Hence we further study the loss and retardation effects of LHM on the energy localization. Numerical results are presented for the lossy LHM structure to demonstrate the energy localization. 相似文献