太赫兹波段下金属狭缝的透射增强特性研究

用太赫兹时域光谱技术研究了具有不同宽度的金属狭缝透射光谱特征. 实验结果显示在实验测量有效光谱范围(02 THz—26 THz)内,当狭缝宽度小到一定程度,在频谱中出现了共振增强,具有明显的带通带阻现象,并在理论上分析了这种共振透射现象的原因. 关键词： 表面等离子体 太赫兹脉冲 时域光谱技术 金属狭缝     

Light transmission through metallic slit with a bar

The transmission characteristics of a metallic slit with a bar are investigated by using the two-dimensional finite difference time-domain method. It is found that the introduction of a bar enriches the transmission spectrum. As the bar locates at the center of the electric (magnetic) field antinodes, the transmission peaks have longer (shorter) wavelengths in comparison with the corresponding resonant peaks of the single slit. It is true for both the fundamental mode and second order mode. The proposed mode in a previous paper [Y. Wang, Y. Wang, Y. Zhang, S. Liu, Opt. Express 17 (2009) 5014] can well explain the above phenomenon. The increase in ability to accumulate charge or decrease in the length of current flow dominates when the bar lies at different positions, which results in a redshift or blueshift of transmission peaks. Moreover, it is also found that the transmission spectrum of the studied structure can be tuned by adjusting the length and width of the bar. It is expected that our results may be utilized to control the electromagnetic wave in subwavelength optics.     

Remarkable zeroth-order resonant transmission of microwaves through a single subwavelength metal slit

A slit in a thick metal plate that is extremely subwavelength will not transmit microwaves polarized parallel to it. It is shown here that cuts perpendicular to the slit allow parallel polarized radiation to resonantly transmit. Furthermore, a zero-order mode may be excited within the slit, the frequency of which, to first order, is independent of the plate depth. Remarkably, for this novel type of resonance, the field in the slit oscillates with a constant phase and little amplitude variation throughout the plate depth, while the resonant wavelength tends to infinity as the slit width approaches zero.     

Optical transmission through double-layer metallic subwavelength slit arrays

We present measurements of transmission of infrared radiation through double-layer metallic grating structures. Each metal layer contains an array of subwavelength slits and supports transmission resonance in the absence of the other layer. The two metal layers are fabricated in close proximity to allow coupling of the evanescent field on individual layers. The transmission of the double layer is found to be surprisingly large at particular wavelengths, even when no direct line of sight exists through the structure as a result of the lateral shifts between the two layers. We perform numerical simulations using rigorous coupled wave analysis to explain the strong dependence of the peak transmission on the lateral shift between the metal layers.     

Role of propagating slit mode in enhanced transmission through slit arrays in a metallic films

The mechanisms responsible for enhanced transmission of electromagnetic wave through an array of subwavelength slits in a metallic film are analyzed. Theoretical model of the enhanced transmission which takes into account the penetration of electromagnetic field into real metal is developed. Semi-analytical model based on Fabry–Perot formula is considered. Comparison of theoretical model, semi-analytical model and results of numerical simulation of Maxwell equations in time-dependent form (FDTD method) for silver with various geometric parameters is presented. The roles of surface plasmons and plasmon localized along slits are studied.     

Optical transmission through subwavelength slit apertures in metallic films

Transmission of polarized light through subwavelength slit apertures is studied in visible and near infrared range wavelengths. We examine the roles played by the slit apertures, such as length, depth, period and number of slits. The experiment results, including dispersion curves, demonstrate among other things that the surface plasmon polariton and Fabry-Perot waveguide modes collectively dictate the transmission properties of subwavelength slit arrays and that as they approach each other, not only large gaps are formed but also mode interconversion occurs. These findings are discussed and compared to theoretical predictions.     

Effects of a bar on optical transmission through Z-shaped metallic slit arrays

We investigate the effects of a bar on optical transmission through Z-shaped metallic slit arrays by using the finite-difference time domain (FDTD) method. A new hybrid Fabry-Perot (FP) surface plasmon polariton (SPP) mode emerges when changing the geometric parameters of the bar, and this mode can be viewed as a coupling between FP mode and SPP mode. In addition, an obvious dip appears in a featured area when the bar deviates from the central line, and a small displacement of the bar leads to tremendous change of the dip. These behaviors can be attributed to the phase resonance. In short, the structure is very sensitive to the metal bar. Furthermore, it combines photonic device miniaturization with sensitivity, which is useful for making optical switches.     

微型腔单一亚波长金属狭缝的光波透射

利用时域有限差分法模拟了厚金属层上单一亚波长狭缝内壁刻有一微型腔结构光波传输,结果发现在特定波长发生异常的增强透射。结合透射峰值对应波长近场分布,利用麦克斯韦方程组和波导理论对增强透射进行解释,认为光波在微型腔和狭缝中形成共振腔模起了重要作用:在狭缝内形成纵模,可以形成透射峰;在腔内形成不同的腔模也可以形成透射模。     

Surface plasmon resonance transmission filters at 1053nm based on metallic grating with narrow slit

Metallic gratings with narrow slits can lead to special optical properties such as strongly enhancing the transmission and considerably strengthening the polarized effect. A narrow-band filter suitable for application in optical communication is designed by sandwiching a metallic grating between two identical dielectric films. The maximum transmission can reach 96% after optimizing the parameters of films and grating at a central wavelength of 1053 nm. It is the first time, to our knowledge, that such high transmission has been reported since the discovery of the extraordinarily high transmission through periodic holes or slits; moreover, the extremely polarized effect is also found in P mode of this symmetric grating.     

Optical resonance in a narrow slit in a thick metallic screen.

Interaction of TM-polarized waves with a subwavelength thick metallic slit has been analyzed. A Fabry-Pérot-like behavior is reported. The resonance peaks, however, have very low magnitude and a systematic shift towards longer wavelengths is observed. The slit being narrow, this shift can be interpreted as the result of an aperture effect. Spectral transmission from a periodic array of such slits features the same peaks with a high increase in their magnitude, confirming that a grating acts as an amplifier of those resonances. Such a mechanism might explain the enhancement of the transmission observed in recent experiments [T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, Nature (London) 391, 667 (1998)].     

Resonant transmission of light through finite chains of subwavelength holes in a metallic film

In this Letter we show that the extraordinary optical transmission phenomenon found before in 2D hole arrays is already present in a linear chain of subwavelength holes, which can be considered as the basic geometrical unit showing this property. In order to study this problem, we have developed a new theoretical framework, able to analyze the optical properties of finite collections of subwavelength apertures and/or dimples (of any shape and placed in arbitrary positions) drilled in a metallic film.     

Resonant transmission of terahertz waves through metallic slot antennas on various dielectric substrates

We report on terahertz electromagnetic field transmission through metallic slot antennas supported on various dielectric substrates. The substrate effect strongly modifies the transmission resonance compared to the free-standing case, while the resonance can be determined systematically by introducing an effective refractive index. The relative contribution of the substrate index to the effective index has been measured for various substrates, and shows a good agreement with theoretical calculations based on a coupled mode method. In addition, the slot antenna arrays embedded in a flexible substrate show a transmission resonance governed by a substrate refractive index.     

Resonant freak microwaves

The Helmholtz equation describing transverse magnetic modes in a closed flat microwave resonator with 60 randomly distributed discs is numerically solved. At lower frequencies, the calculated wave intensity spatially distributed obeys the universal Porter-Thomas form if localized modes are excluded. A superposition of resonant modes is shown to lead to rare events of extreme intensities (freak waves) at localized “hot spots”. The temporally distributed intensity of such a superposition at the center of a hot spot also follows the Porter-Thomas form. Branched modes are found at higher frequencies. The results bear resemblance to recent experiments reported in an open cavity.     

1D Bessel-like beam generation by highly directive transmission through a sub-wavelength slit embedded in periodic metallic grooves

A new method to generate a quasi-one dimensional (1D) Bessel-like beam whose non-diffracting length extends to macroscopic scale is proposed by utilizing highly directive transmission through a sub-wavelength single slit embedded in periodic metallic grooves. We employed finite-difference time-domain methods for full-vectorial diffraction and spectral analysis. In optimal conditions, unique quasi-1D Bessel-like beams were generated in transmission for the incident p-polarized plane wave such that highly asymmetric far-field distribution was achieved; Bessel-like beam along the slit axis and a flat-top super-Gaussian beam along the other perpendicular axis. Detailed parametric studies for the proposed structure are reported in terms of the operating spectral range and a general window of optimal conditions.     

金属亚波长狭缝中凹槽对其透过特性的影响

利用时域有限差分方法,研究了单个二维金属亚波长狭缝中空气凹槽的结构、位置等参数变化对其透过特性的影响. 整个缝槽结构可以类比为LC振荡环路,凹槽结构变化时,不同程度地改变振荡电路的电感和电容,从而使共振透射峰出现移动. 凹槽位置变化时,电路的驱动源改变,从而改变缝槽结构中的电磁场分布,使得共振透射峰出现分裂. 利用LC共振原理分析了凹槽各个参数变化时共振透射峰的变化情况. 关键词： 表面等离子体 透射率 LC振荡')" href="#">LC振荡     

Influence of slit width on the electromagnetic transmission of a periodic metallic grating

The light transmittance of a periodic metallic grating with varied slit widths has been investigated. The transmission peaks move to the shorter wavelength direction with an increase in the width of slits while keeping the other parameters unchanged. It was demonstrated that the slit width affects the spectral transmittance of the metal grating significantly. It was also found that the effective refractive index and cavity modes in slits are responsible for this phenomenon. Cavity modes play an important role in extraordinary transmission of the sub-wavelength aperture grating. When a complete resonant mode forms in the slits, a high transmission will appear. A wider slit results in a smaller efficient refractive index and thus affects the cavity mode in the slits. These two elements cause the transmission peaks to move to the shorter wavelength direction with widening of slits. The results obtained here may provide a useful guide to design metallic slit grating devices.     

Transmission of light through metallic Z-shaped slit array with inner metallic bar

The transmission of a normally incident wave through a Z-shaped channel metallic slit array with metallic bar inside has been investigated by using finite-difference time-domain method. It is obtained that transmission spectra are nearly the same of the slit array with straight channel as that with Z-shaped channel in the condition the material of the slit array the same as that of the inner bar. If the Au bar is replaced by Al of the Au slit array, both resonance modes red shift obviously, especially for the structure with bent channel. Along with the width of the inner bar increasing, the localized waveguide resonance mode red shifts regularly with a tiny decrease of the peak value of all the kinds of composed structure introduced here, and the surface plasmon resonance mode red shifts regularly accompanied by peak value changing uniformly for the structures with only one type of metal. However, the surface plasmon resonance behaves different obviously, its center peak first moves to a larger wavelength fast, then red shifts slowly, for the Au-film Al-bar structure, but that moves in a very small wavelength range for the Al-film Au-bar one. The results obtained here are helpful to design subwavelength optical devices.     

Optical control over surface-plasmon-polariton-assisted THz transmission through a slit aperture

We demonstrate optical control over the transmission of terahertz (THz) radiation through a single subwavelength slit in an otherwise opaque silicon wafer. The addition of periodic corrugation on each side of the wafer allows coupling to surface plasmon polaritons, so that light not impinging directly on the slit can contribute to the transmission. A significant enhancement of the THz transmission can be achieved through control of the surface wave propagation length by excitation at optical wavelengths. The observed transmission increase is in distinct contrast to the reduction reported for photoexcitation of arrays of holes in semiconductors.     

Enhanced optical transmission through a silver plate with a slit array

The near- and far-field properties of a large-scale silver plate with a slit array are studied by applying the FDTD method. The far region scattering properties with different incident angles are also discussed. We find out that the silver plate with a suitable placed narrow slit array can excite the enhanced optical transmission (EOT) by the excitation of the surface plasmon polarition (SPP) and the Fabry-Perot resonance, and the cutoff angle is much larger than the ordinary LEDs. These unique properties suggest possible applications to the light-transparent metal contact.     

Buildup of a narrow plasma channel by microwaves

The paper deals with the effect of the buildup of a narrow plasma channel by a hf right-hand circularly polarized (RHCP) wave propagating through radially inhomogeneous plasma in the direction of the static magnetic field. The plasma channel occurs under conditions when the linear transformation of the RHCP wave takes place. The experiments were carried out in a homogeneous static magnetic field _ce /2.3;, _ce are the frequency of the RHCP wave and the electron cyclotron frequency, respectively.Nademlýnská 600, Praha 9, Czechoslovakia.