Directional and hemispherical mid-infrared transmittance through microscale slit arrays on a semi-transparent substrate at normal incidence

The directional and hemispherical transmittance through four microscale slit arrays on a semitransparent substrate were investigated at normal incidence. Materials and vertical dimensions of all arrays were the same, but lateral dimensions varied among the three simple slit arrays. The complex slit array had three identical slits and three lamellae of dissimilar widths in a profile period. The incidence covered a broad-band mid-infrared region (2.5–25 μm) in which two linear polarizations were considered. Impacts of the structure profile, incidence polarization and wavelength, and optical constants of involved materials on spectra were studied numerically with programs based on the algorithm termed rigorous coupled-wave analysis (RCWA). Near-field patterns of electromagnetic fields that correlated with unique transmittance were also plotted to identify responsible physical mechanisms. In addition, the directional transmittance spectra of fabricated samples were measured with FT-IR spectrometry. Reasonable agreement between numerical and experimental results was obtained. Unique features in spectra were consistently found, regardless of the finite substrate thickness.     

Transmission properties of periodically patterned triangular prisms

Transmission properties of plasmonic structure arrays are simulated by finite element method. The array unit is composed of two combined triangular prisms. Results reveal that several resonant modes are found in the transmission spectra, which are due to the resonance of the surface plasmon polariton in the metal slit or to the localized surface plasmon resonance of the combined prisms. The resonant wavelengths can be tuned by changing the structural parameters of the combined prisms. In addition, the resonant modes are sensitive to small refractive index changes of the surrounding media, revealing potential detection applications in nanophotonic systems.     

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.     

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.     

Experimental and calculated research on a large band gap constituting of tubes with periodic narrow slits

A new band gap structure composed of a square array of parallel steel tubes with narrow slits is presented. The propagation of acoustic waves in a two-dimensional composite medium constituted of slit tubes in air is investigated both theoretically and experimentally. The band gap is calculated with the finite element method in which the acoustic-solid coupling is taken into account. The transmissions of the band system with both different single-width narrow slits and multi-width narrow slits are analyzed. Experimental measurements show that the transmission through an array of slit tubes with periodic narrow slits drops to noise level throughout frequency interval in good agreement with the calculated forbidden band. The large band gap and low starting frequency is obtained by arranging different width of slits embedded in the tubes. The experiments and theoretical results show that this new band gap structure has an especial character based on the resonant cavity playing an important role on the band gap besides the traditional Bragg interference.     

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     

Transmission through array of subwavelength metallic slits curved with a single step or mutli-step

The transmission of normally incident plane wave through an array of subwavelength metallic slits curved with a sin- gle step or mutli-step has been explored theoretically. The transmission spectrum is simulated by using the finite-difference time-domain method. The influences of surface plasmon polaritons make the end of finite long sub-wavelength metallic slit behaves as magnetic-reflecting barrier. The electromagnetic fields in the subwavelength metallic slits are the superpo- sition of standing wave and traveling wave. The standing electromagnetic oscillation behaves like LC oscillating circuit to decide the resonance wavelength. Therefore, the parameters of adding step may change the LC circuit and influence the transmission wavelength. A new explanation model is proposed in which the resonant wavelength is decided by four factors： the changed length for electric field, the changed length for magnetic field, the effective coefficient of capacitance, and the effective coefficient of inductance. The effect of adding step is presented to analyze the interaction of two steps in slit with mutli-step. This explanation model has been proved by the transmission through arrayed subwavelength metallic slits curved with two steps and fractal steps. All calculated results are well explained by our proposed model.     

Enhanced optical transmission through double-layer gold slit arrays

We investigate the relationship between the transmission and the layer distance of double-layer gold slit arrays by using the finite-difference time-domain method.The results show that the transmission properties can be influenced strongly by layer distance.We attribute the two types of resonant modes to surface plasmon resonance and the localised waveguide resonance.We find that the localised waveguide transmission peak redshifts and becomes broader with increasing layer distance D.We also describe and explain the splitting,shift,and degeneration of the surface plasmon resonant transmission peak theoretically.In addition,to clarify the physical mechanism of the transmission behaviours,we analyse the distributions of electric field and total energy for the three transmission peaks with distance D=45 nm for the double-layer system.Light transporting behaviours are mostly concentrated in the region of the slits as well as the interspaces of the two layers,and for different resonant wavelengths the electric field and energy distributions are different.It is expected that the results obtained here will be helpful for designing subwavelength metallic grating devices.     

阿达玛光谱仪的入射狭缝选择方法研究

为了确定光谱仪的入射多狭缝结构设计的可靠依据,研究了4种阿达玛S型狭缝阵列发生衍射后的光强分布.采用MEMS加工技术制作出最小狭缝单元为6 μm×6 μm的一体式微硅片阿达玛狭缝阵列,对3种S7型狭缝和一种S15型狭缝进行比较.首先利用阿达玛矩阵构造狭缝阵列的孔径函数,得到了衍射后的光强分布函数;然后运用Matlab软件对光强分布函数仿真,获得了符种狭缝衍射后的光强分布图及光通镀对比.搭建了试验装置进行验证,试验表明实际衍射光强分布及光通量间的比值都与仿真结果相符.最后分析了狭缝结构参数对光强分布的影响,总结了S型狭缝阵列衍射规律.所提出的衍射光强分布方法,为光谱仪中入射狭缝的选择与设计提供了理论依据,为实际应用提供了有价值的参考.     

Rapid dendritic growth and solute trapping within undercooled ternary Ni-5%Cu-5%Mo alloy

In this report, we present experimental results of transmittance through nanohole arrays created onto Au films on glass substrates. 110-nm-thick Au films with arrays of nanoholes were fabricated by using self-assembled polystyrene spheres, of which the diameters were reduced to designed values on site by dry etching, as a template. Transmission spectra of the nanostructured Au films show strong enhancement (more than 45%) in a wide range from 300 nm to 1600 nm, the measurement wavelength range. Besides a peak observed at around 500 nm in all spectra, a wider peak on the longer wavelength side was observed, which shifted to longer wavelength when periodicities of the hole arrays were increased.     

Near-field distribution of optical transmission of periodic subwavelength holes in a metal film

Optical transmission of a two-dimensional array of subwavelength holes in a metal film has been numerically studied using a differential method. Transmission spectra have been calculated showing a significant increase of the transmission in certain spectral ranges corresponding to the excitation of the surface polariton Bloch waves on a metal surface with a periodic hole structure. Under the enhanced transmission conditions, the near-field distribution of the transmitted light reveals an intensity enhancement greater than 2 orders of magnitude in localized ( approximately 40 nm) spots resulting from the interference of the surface polaritons Bragg scattered by the holes in an array.     

Microwave transmission of a compound metal grating

An array of subwavelength slits in a metallic substrate supports a series of Fabry-Perot-like resonances, where each harmonic results in a transmission peak. Addition of extra slits per period yields a compound grating with a structure factor associated with the basis. In this study each repeat period is comprised of a central slit flanked by a pair of narrower slits. It supports three resonances for every Fabry-Perot-like solution. New and useful insight into this phenomenon is gained by describing each of the modes in terms of the band structure of diffractively coupled surface waves.     

Plasmonic enhancement of the vanadium dioxide phase transition induced by low-power laser irradiation

Nanocomposites consisting of gold nanoparticle (NP) arrays and vanadium dioxide (VO₂) thin films are noteworthy for the tunability of both their thermal and optical properties. The localized surface plasmon resonance (LSPR) of the Au can be tuned when its dielectric environment is modulated by the semiconducting-to-metal phase transition (SMT) of the VO₂; the LSPR itself can be altered by changing the shape of the NPs and the pitch of the NP array. In principle, then it should be possible to choose a combination of VO₂ film and Au LSPR properties that maximizes the overall optical response of the nanocomposite. To demonstrate this effect, transient transmission measurements were conducted on lithographically fabricated arrays of Au NPs of diameter 140?nm, array spacing 350 nm, and covered with a 60?nm thick films of VO₂ via pulsed laser deposition. Both Au::VO₂ nanocomposites and bare VO₂ film were irradiated with a shuttered 785?nm pump laser, and their optical response was probed at 1550?nm by a fixed-frequency diode laser. The Au::VO₂ nanocomposite exhibited an increased effective absorption coefficient 1.5 times that of the plain film and required 37?% less laser power to induce the SMT. The time-dependent temperature rise in the film as a function of laser intensity was calculated from these measurements and compared with both analytic and finite-element models. Our results suggest that Au::VO₂ nanocomposites may be useful in applications such as thermal-management coatings for energy efficient ??smart?? windows.     

基于厚金属狭缝阵列的表面等离子激元光刻

提出一种利用厚金属狭缝阵列耦合激发表面等离子激元制作非周期图形的纳米光刻模型.采用时域有限差分电磁场模拟仿真软件研究了厚金属狭缝阵列中表面等离子激元的激发、模式选择以及光刻胶中的光场分布.结果表明,通过优化厚金属狭缝阵列结构参量和匹配介质参量可有效抑制表面等离子激元在光栅狭缝出口处的发散,增加表面等离子激元的穿透深度,...     

Metal grating on a substrate nanostructure for sensor applications

Extraordinary optical transmission via periodic array of sub-wavelength slits in a metal layer on a dielectric substrate is revisited for sensing applications. Numerical case studies using an in-house software tool showed two peaks of enhanced transmission, one being very sensitive to the ambient index and another to the substrate index. Based on this, we designed and realized an optical sensor with sensitivity of the order of 400 nm/RIU.     

狭缝宽度与取样间隔对镶嵌铜多孔铝膜透射光谱的影响

用阳极氧化的方法制备了阳极氧化铝膜，向其孔中镀入了铜，制备了镶嵌铜多孔铝膜。为了研究狭缝宽度与取样间隔对其透射光谱的影响，利用岛津UV－3101型分光光度计，测得了相同取样间隔不同狭缝宽度和相同狭缝宽度不同取样间隔情况下镶嵌铜多孔铝膜的透射光谱，并分析了狭缝宽度和取样间隔对透射曲线的影响，得到了测试镶嵌铜多孔铝膜所需合适的狭缝宽度和取样间隔。测试结果表明：对镶嵌铜多孔铝膜而言，在可见光波段选择3nm的狭缝宽度和0.5nm或1nm的取样间隔为宜；在近红外波段选择5nm或8nm的狭缝宽度和2 nm的取样间隔为宜。     

High refractive index sensitivity sensing in gold nanoslit arrays

The extraordinary optical transmission(EOT) phenomenon of nano-periodic aperture array in metallic film has been widely investigated and used in biosensors. The surface plasmon resonance and cavity mode in some periodic nanostructures, such as nanohole and nanoslit, cause EOTs at certain wavelengths. This resonance wavelength is sensitive to the refractive index on the surface of periodic nanostructures. Therefore, the metallic nanostructures are expected to be good sensing elements. The sensing performances of gold nanoslit arrays are experimentally and theoretically investigated.Three-dimensional finite difference time domain(FDTD) simulations are utilized to explore their transmission spectra and steady-state field intensity distributions. The electron beam evaporation, electron beam lithography, and ion milling are applied to the gold nanoslit arrays with different widths and periods. The sensing performances of the gold nanoslit array are characterized via transmission spectra in four kinds of refractive index samples. The highest sensitivity reaches726 nm/RIU when the width of the gold nanoslit array is 38.5 nm.     

Whispering gallery mode propagation in photonic crystals in front of subwavelength slit arrays: Interplay with extraordinary transmission

We numerically study the propagation of light in 2D photonic crystals (PC) made of infinite cylinders of high refractive index, via the excitation of their morphological dependent resonances, in the presence of metallic arrays of subwavelength slits, either corrugated or not, that may produce extraordinary transmission. In this way, we confirm and illustrate previous theoretical findings on PCs and show new effects when combined with slits. Among them, we show that the whispering gallery mode excitation in the PC couples dominates the transmission of the slit arrays alone. Appropriate design of the system parameters and the illumination conditions, selects the transport and confinement of energy.     

Extraordinary THz transmission through subwavelength semiconductor slits under antiparallel external magnetic fields

We theoretically study the resonant transmission of electromagnetic waves at the THz frequencies through subwavelength semiconductor slits under external static magnetic fields. The dispersion relations of the surface plasmon polaritons (SPPs) inside a subwavelength slit are analytically derived. It is found that the SPPs propagating along one direction and its reverse are symmetric when parallel external magnetic fields are applied, but are asymmetric when antiparallel external magnetic fields are applied. The transmission properties of periodic subwavelength semiconductor slit arrays with the antiparallel magnetic fields in each unit cell are investigated by the mode expansion technique. The two significant transmission characteristics are observed: (i) The resonant peaks are redshifted with increasing external magnetic fields; (ii) The transmissions in the two opposite directions through the slit arrays are asymmetric. The origin of the transmission asymmetry is reasonably explained by the magnetic-field induced asymmetric SPP propagation losses.     

二维阵列狭缝阿达玛光谱仪波长准确度研究

二维阵列狭缝模板是阿达玛编码模板的一种新的设计思想,分析了模板上同列狭缝的加工误差对仪器波长准确度的不利影响,在此基础上,给出了减少同列狭缝高度、垂直光谱维方向上位置不一致性误差对仪器波长准确度影响的方法,以及同列狭缝在光谱维方向上位置不一致导致解码所得谱线产生的光谱偏移量的粗略估计方法,并建立模型进行仿真,计算了当模板上某列狭缝存在宽度、光谱维方向上位置不一致性误差时,解码所得其他各列狭缝谱线分布上测量误差的大小,根据仿真结果可以初步确定模板的加工精度。通过该研究有助于合理设计MEMS(微机电系统)二维阵列狭缝模板,获得对系统误差的有效补偿,提高仪器的波长准确度。