Double nanohole apex-enhanced transmission in metal films

We first present experimental results of enhanced transmission through nanofabricated double-hole arrays in a gold film. An increase in the transmission is observed when the holes are overlapping to produce two apexes, with the transmission more than doubling when the apexes are nearly touching. When the holes are non-overlapping, the transmission maximum drops. The measured spectra through these arrays showed a red-shift in the peak transmission wavelength around 770 nm of nearly 30 nm. These experimental results agree well with our finite-difference time-domain simulations of the double-hole arrays. PACS 78.66.Bz; 42.79.Ag; 42.79.Dj     

Plasmonic sensors based on thick metal film perforated with rectangular nanohole arrays

The dependence of optical properties on the ambient medium, the period of nanohole arrays and the metal film thickness in a thick silver film perforated with rectangular nanohole arrays is investigated using the finite‐difference time‐domain technique. As a result of the coupling between top and down surface plasmon polaritons, mediated by localized surface plasmon resonances supported by the metallic rectangular nano‐ holes, interesting light phenomena are observed for varying thickness of the metal film and period of the rectangular nanohole arrays. Based on the dependence of the optical properties on the ambient medium, the possibility of exploiting thick metal rectangular nanohole arrays as plasmonic sensors is further discussed, the potential application as plasmonic sensors is revealed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polarization tomography of metallic nanohole arrays

We report polarization tomography experiments on metallic nanohole arrays with square and hexagonal symmetry. As a main result we find that a fully polarized input beam is partly depolarized after transmission through a nanohole array. This loss of polarization coherence is found to be anisotropic; i.e., it depends on the polarization state of the input beam. The depolarization is ascribed to a combination of two factors: (i) the nonlocal response of the array as a result of surface-plasmon propagation and (ii) the non-plane-wave nature of a practical input beam.     

Fano-type interference in the point-spread function of nanohole arrays

Measurement of the point-spread function of metal nanohole arrays by using microscopic imaging reveals two contributions. The first of these is due to propagating resonant surface plasmons and the second to nonresonant transmission through the holes. We observe a Fano-type interference between these contributions.     

Strong polarization in the optical transmission through elliptical nanohole arrays

Strong polarization dependence is observed in the optical transmission through nanohole arrays in metals. It is shown that the degree of polarization is determined by the ellipticity and orientation of the holes; the polarization axis lies perpendicular to the broad edge of the ellipse. Furthermore, the depolarization ratio shows a squared dependence on the aspect ratio of the holes, which is discussed in terms of coupling into and out of the surface plasmon modes. The observed results will be useful for tailoring the polarization behavior of metallic nanophotonic elements in many applications, including surface plasmon enhanced optical sensing and ultrafast optical switching.     

The surface plasmon resonance of metal-film nanohole arrays

In this paper we investigated the enhanced transmission and surface plasmon resonance through a thin gold film with a periodic array of subwavelength nanoholes. Both freestanding gold-film nanohole arrays and gold-film nanohole arrays deposited on a gallium arsenide (GaAs) substrate are considered. Periodic arrays of nanoholes exhibit two different surface plasmon resonance features: localized waveguide resonance and the well-recognized photonic crystal resonance. The tangential electric field component $Ey$ is nonzero only in the hole region for a freestanding gold-film nanohole array, but it can exist in the hole region and in the metallic region for a gold-film nanohole array deposited on a GaAs substrate.     

Strong optical transmission through the ellipsoid metal-film nanohole arrays

The transmission characteristics of a metallic film with subwavelength ellipsoid nanohole arrays are investigated by using the three-dimensional finite-difference time-domain (3D-FDTD) method. The extraordinary transmission is attributed to the collaboration of localized waveguide resonance and surface plasmon resonance. The influences of the lattice constant and the hole shape on the transmission are studied. By analyzing the picture of electric field and electromagnetic energy distribution, we show the mechanisms of the two different resonances: Localized waveguide resonance mode can be confined inside the ellipsoid holes region, while electric field and electromagnetic energy are localized separately at the two ends of ellipsoid holes for the surface plasma resonance mode. Supported by the National Natural Science Foundation of China (Grant No. 60708014), the Distinguished Youth Foundation of Hunan Province (Grant No. 03JJY1008), the Science Foundation for Post-doctorate of China (Grant No. 2004035083), and the Natural Science Foundation of Hunan Province (Grant No. 06JJ20034)     

基于金属孔阵列的聚酰亚胺薄膜太赫兹探测

优化设计了多种不同孔径和形状的太赫兹波段的亚波长金属孔阵列结构,结合超薄低折射率的聚酰亚胺（PI）薄膜,探索了太赫兹时域光谱技术对超薄低折射率的探测灵敏性。利用飞秒微加工技术制备了一系列亚波长金属孔阵列结构,利用太赫兹时域光谱技术测试了阵列结构的反射波谱,获得了强烈的反射共振现象。然后在亚波长金属孔阵列结构背面叠加PI薄膜,结果表明太赫兹反射峰出现了显著低频移动现象。利用这一现象,实现了低至10 m的PI薄膜的有效探测,说明亚波长金属孔阵列结构在太赫兹传感领域对检测超薄低折射率薄膜材料有极强敏感性。收稿日期:; 修订日期:     

基于金属孔阵列的聚酰亚胺薄膜太赫兹探测

优化设计了多种不同孔径和形状的太赫兹波段的亚波长金属孔阵列结构,结合超薄低折射率的聚酰亚胺（PI）薄膜,探索了太赫兹时域光谱技术对超薄低折射率的探测灵敏性。利用飞秒微加工技术制备了一系列亚波长金属孔阵列结构,利用太赫兹时域光谱技术测试了阵列结构的反射波谱,获得了强烈的反射共振现象。然后在亚波长金属孔阵列结构背面叠加PI薄膜,结果表明太赫兹反射峰出现了显著低频移动现象。利用这一现象,实现了低至10 m的PI薄膜的有效探测,说明亚波长金属孔阵列结构在太赫兹传感领域对检测超薄低折射率薄膜材料有极强敏感性。收稿日期:; 修订日期:     

Aluminium nanohole arrays enhanced resonance Raman scattering spectra in the near ultraviolet region

Aluminium nanohole arrays with fixed diameter were fabricated by focused ion beam and the periodicities were turned.Aluminium nanohole arrays enhanced resonance Raman scattering spectra in the near ultraviolet region were studied experimentally and theoretically,which revealed that the SERRS enhancement factor was as high as 6 orders.     

Conversion efficiency enhanced photovoltaic device with nanohole arrays in antireflection coating layer

In this paper, the authors introduce an enhanced photovoltaic device with nanohole arrays only in its antireflection coating. These nanoholes can improve light trapping efficiency as well as photoelectric conversion efficiency of the device. The authors analyze the light absorption of the devices with nanohole arrays by Finite-Difference Time Domain method and calculate the photoelectric conversion efficiency. The results show that the nanohole arrays can improve the light trapping more efficiently than the Si₃N₄ antireflection coating, especially, in 400-600 nm spectral range. Nanohole arrays with different characteristic parameters were fabricated in the antireflection coating layer of a Φ200 μm Si detector by using focused-ion beam system. With the optimized nanohole arrays, the enhancements factor of the experimental sample's photoelectric conversion efficiency is ~ 16% within the 400-600 nm spectral range and ~ 10% within the 400-1100 nm spectral range.     

Phase change associated with resonant surface plasmon polariton-assisted transmission in nanohole arrays

We report FDTD simulation results demonstrating that the optical phase change of surface plasmon polariton-assisted transmission through nanohole arrays in a metal film undergoes a sharp change under resonant conditions. The phenomenon can be explained by various resonant modes between the nanoholes. We further explore the possibility of using this effect for phase-sensitive surface plasmon resonance biosensing applications.     

Experimental study of unidirectional excitation of SPPs by binary area-coded nanohole arrays

We present an experimental study on a unidirectional surface plasmon polariton （SPP） launcher based on a compact binary area-coded nanohole array, where the symmetry breaking is realized via effective-index modulation in the binary pattern of the gold film, thus avoiding the challenge of modulating nanostructure in its depth. It is shown that SPPs can be unidirectionally and effectively excited at normal incidence. The SPP intensity and asymmetric excitation ratio, which are two key figure-of-merits of SPP launchers, can be improved by increasing the number of array rows. The proposed device is compatible with most mature top-town nanofabrieation techniques and thus is perspective for low-cost mass production.     

Light transmission through metal films perforated with arrays of asymmetric cross-shaped hole

The transmission characteristics of metallic film perforated with an array of asymmetric cross-shaped hole are studied by using the three-dimensional finite difference time-domain method. We find that the wavelengths and intensities of transmission peaks depend strongly on the asymmetric parameters of the cross-shaped hole. The transmission peaks in the structure of asymmetric cross-shaped hole array originate from the splitting of the transmission peak in the corresponding one of symmetric cross-shaped hole array. Moreover, it is also found that the transmission spectra can be adjusted by changing other geometrical parameters of asymmetric cross-shaped hole due to the their effect on the distribution of the oscillating charges on metal surfaces.     

Guided wave arrays for high resolution inspection

The paper describes a general approach for processing data from a guided wave transducer array on a plate-like structure. The raw data set from such an array contains time-domain signals from each transmitter-receiver combination. The technique is based on linear superposition of signals in the frequency domain with some amplitude and phase factors and can be applied to any array geometry and any types of array elements. The problem of finding optimal coefficients, which allow the best resolution to be achieved with the minimum number of array elements, is investigated. It is shown that improvements in resolution are obtained at the expense of sensitivity to noise. A method of quantifying this sensitivity is presented. Results are shown that illustrate the application of the technique to a linear array and an array of circular geometry (containing a single ring of elements). Experimental data obtained from a guided wave array containing electromagnetic acoustic transducer elements for exciting and detecting the S0 Lamb wave mode in a 5-mm-thick aluminum plate are processed with different algorithms and the results are discussed. Generalization of the technique for the case of multimode media is suggested.     

Laser heterodyne measurements of photo-induced refractive-index changes in amorphous As-S films

A differential-type heterodyne interferometer has been successfully utilized for studying the refractive-index changes in As-S films under illumination. The measuring system can detect phase changes down to 1° in angle in accuracy and sensitivity. It is confirmed that illumination of the films involves two distinct factors: a thermal and an optical one. The index changes are caused only by the optical effect. The time-dependent characteristics of the index changes are explained to be closely related to the photo-darkening effect.     

Enhanced light transmission through cascaded metal films perforated with periodic hole arrays

We report experimental results on enhanced light transmission through two periodically perforated metal films separated by a layer of dielectric. A perforated metal film (single metallic structure) exhibits extraordinary optical transmission, and when two such perforated metal films are spaced by a dielectric layer (cascaded metallic structure), the transmission is further increased. The maximum transmission of the cascaded metallic structure, which depends on the distance between the two metal films, can be more than 400% greater than that of a corresponding single metallic structure. It is proposed that the coupling of surface plasmon polaritons between the two metal films is involved in the process.     

Fabrication of self-ordered nanohole arrays on Si by localized anodization and subsequent chemical etching

Nanohole arrays with a 60 nm hole periodicity were fabricated on a Si substrate by the anodization of an aluminum film sputtered on a Si substrate in sulfuric acid and subsequent chemical etching. The transfer of the nanoporous pattern of anodic alumina into the Si substrate was achieved by the selective removal of silicon oxide, which was produced by the anodic oxidation of the underlying Si substrate through the anodic porous alumina used as a mask.     

Selective tungsten deposition into ordered nanohole arrays of anodic porous alumina by electron-beam-induced deposition

The selective deposition of a metal (tungsten) into ordered nanohole arrays of an anodic porous alumina membrane was performed using an electron-beam-induced deposition process. After deposition, the membrane was observed and analyzed using electron microscopy and energy-dispersive X-ray spectroscopy. It is shown that the deposition was preferentially conducted in the holes in the irradiated area of the electron beam. A calculation of the electron-beam intensity explains the reason for the preferential deposition in the holes. PACS 81.07.-b; 81.16.Rf; 61.46.+w