High-Sensitivity Sensor Based on Surface Plasmon Resonance Enhanced Lateral Optical Beam Displacements

We present a new optical sensor based on surface plasmon resonance （SPIt） enhanced lateral optical beam displacements. Compared with the traditional SPIt methods, the new method provides higher sensitivity to the sensor system. Theoretical simulations show that the refractive index （RI） detection sensitivity of the SPR sensor based on the displacement measurement has a strong dependence on the thickness of the metal film. When the optimal thickness of the metal film is selected, the RI resolutlon of the SPIt sensor is predicted to be 2.2 × 10^-7 refractive index units （RIU）. Furthermore, it is found that the incidence angle can be used as a parameter to adjust the operating range of the sensor to different refractive index ranges.     

FDTD Studies of Metallic Cylinder Arrays： Plasmon Waveguide and Y-Splitter

The plasmon waveguide based on double chain of gold cylinders is studied using the finite-difference time-domain method （FDTD）. The wavelength of the incident Gaussian beam ranges from 650 to 1200nm, and the corresponding attenuation factors are calculated. We also present a Y-splitter with 90° splitting angle, each branch in the form of double chains. The transmission efficiencies for different wavelengths are evaluated.     

Tunable Omnidirectional Surface Plasmon Resonance in Cylindrical Plasmonic Structure

The tunable omnidirectional surface plasmon resonance in the optical range is theoretically demonstrated in a cylindrical plasmonic crystal by using rigorous coupled-wave analysis. The cylindrical plasmonic crystal consists of an infinite chain of two-dimensional cylindrical metal--dielectric-dielectric-metal structures. The dispersion relation of the cylindrical plasmonic crystal is obtained by calculating the absorptance as a function of a TM-polarized incident plane wave and its in-plane wave vector. The omnidirectional surface plasmon resonance can be tuned from UV region to visible region by adjusting the thickness of the cylindrical dielectric layers. The absorption spectrum of the infinite chain of nanocylinders is also investigated for comparison.     

All-Optical Modulation with a Surface Plasmon Mach-Zehnder Interferometer

We use two parallel nano-slits in a silver film to form a surface plasmon Mach Zehnder interferometer （MZI）, based on the interference of two surface plasmon waves propagating along the two surfaces of the silver film. Coating the silver film with a photoinduced birefringence polymer film, we achieve optical modulation of the MZI output by changing the refractive index of the polymer film with a pump beam. An on/off ratio 0f 2. 7 is obtained for a probe wavelength of 865 nm.     

Analytical Investigation of Transmission Properties of Metallic Gratings

We re-examine the classical one-dimensional transmission grating to explain the enhanced transmission in the surface impedance approximation. The nearly zero transmission and extraordinary transmission phenomena related to the surface plasmon are presented by analysing the scattering amplitude of waveguide mode at the output surface of grating. It is revealed that the transmission peaks are related to the Fabry-Perot factor and the interaction of surface plasmon and other diffractive orders.     

Negative magnetic permeability of split ring resonators in the visible light region

Negative magnetic permeability of split ring resonator (SRR) is theoretically investigated in the visible light region. In our calculations, we considered the delay of the current inside the metal SRR in order to estimate the permeability of the SRR precisely. From the results, the silver SRR array with small capacitance exhibits negative permeability in all the visible range. The dependence of the permeability on the filling factor of the SRR elements is also discussed.     

Temperature Effects on Prism-Based Surface Plasmon Resonance Sensor

We theoretically analyse the temperature effects on a surface plasmon resonance （SPR） sensor in Kretschmann configuration. The temperature effects include the thermo-optic effect and the dispersion of thermal-optic coefficient in the dielectric along with the thermal expansion effect, phonon-electron scattering and electron-electron scattering in the metal layer. We simulate the temperature dependence of the resonance position and the sensitivity of the SPR sensor under wavelength-interrogation and angular-interrogation mode of operation and the differences are pointed out in the two modes.     

Surface Plasmon Resonance and Field Enhancement of Au/Ag Alloyed Hollow Nanoshells

We investigate the nanostructure, surface plasmon resonance （SPR） absorption and nonlinear enhancement of Au/Ag alloyed hollow nanoshells prepared by the replacement reaction of Ag nanoparticles in a HAuCI4 aqueous solution. As the volume of HAuCl4 increases from OmL to 0.S mL, the SPR band of the Au/Ag alloyed nanoshells is tuned from 430nm to 780nm, and the third-order nonlinear optical susceptibility is enhanced nearly by an order of magnitude, which indicates a large enhancement of local field in the Au/Ag alloyed hollow nanoshells with hole defects.     

Complex Modulation in Plasmon-Assisted Transmission Spectra of a Two-Slit Structure

We study the plasmon-assisted transmission of two kinds of slit structures in a 290-nm-thick silver film on a glass substrate. For the two-slit structure, the total transmission intensity spectra displays a complex modulation, which is attributed to different propagation constants of the surface plasmon polaritons （SPPs） on the silver-air and silver-glass interfaces. Replacing one of the two slits by a shallow corrugation results in a simple sinusoidal intensity modulation because of the only effective SPP excitation and propagation on the silver-air interface. These confirm the role of different SPP propagations and interference in the transmission properties of metal nanoslits.     

Resonance Absorption of Metallic Plate with Subwavelength Hole Array

The optical reflectance by a metallic plate arranged with array consisting of subwavelength periodic square hole is investigated by using the three-dimensional finite-difference time-domain method （3D-FDTD）. There are dips in the reflectivity spectra, which indicate the absorption peaks. The absorption peaks behave differently according to the ratio of hole width and the period of the hole array. Combined with the near fields of the absorption peaks, it is found that the surface plasmon （SP） resonance on the surface of plate and localized SP in the hole play a major role for the two absorptions.     

Plasmon mechanism of light transmission through a metal film or a plasma layer

It is shown that a smooth metal film (or a plasma layer) can be made transparent for an electromagnetic wave when two identical subwavelength diffraction gratings are placed on both sides of the film. The electromagnetic wave transmission through the metal film is caused by excitation of evanescent surface waves (plasmons) and their transformation into propagating waves at the gratings. A model which is developed analytically shows that the problem of the wave transmission is physically equivalent to the problem of excitation of two coupled resonators of evanescent waves which are formed at the two film surfaces.     

Development of high-throughput combinatorial terahertz time-domain spectrometer and its application to ternary composition-spread film

We have developed a high-throughput combinatorial terahertz (THz) time-domain spectrometer (CTTDS) and applied to a ternary composition-spread film. This technique has possibilities to reveal a variety of physical properties such as complex refractive index, complex dielectric constant, and complex electrical conductivity. Further, this method is a non-contact and non-destructive way to map those physical properties. The demonstration of THz transmittance mapping of ternary composition-spread film, with a spatial resolution of 1 mm, reveals metallic behavior in specific range of film compositions. This prospective technique may serve as a convenient tool for the high-throughput, non-contact, non-destructive, and spatially resolved characterization suited for combinatorial composition-spread films.     

Theoretical Design of a Wedged Output Coupler Coated by Capacitive Strip-Grating for Optically Pumped Terahertz Lasers

An output coupler for optically pumped terahertz laser consisting of capacitive strip-grating and wedged high- resistivity silicon substrate is designed theoretically and its transmittance performance is also discussed. The etalon effects frequently occurring in previous experiments are effectively suppressed, and thus a fiat and accurate transmittance spectrum is obtained in a narrow wavenumber interval of 2 cm^-1 near a particular center wavenumber. Furthermore the transmittance sensitivity to the slight shift of substrate thickness is also completely eliminated. The wedged output coupler is easy to fabricate and its substrate may be used repeatedly to meet various transmittance requirements.     

Coupled THz Waveguide Utilizing Surface Plasmon Polaritons on Thin Dielectric Slab Sandwiched between Two Corrugated Metallic Claddings

We present a comprehensive experimental study of terahertz （THz） wave propagation utilizing surface plasmon polaritons （SPPs） on the interfaces of a thin dielectric core layer sandwiched between two corrugated metallic claddings. THz wave impinges on the structured surfaces at normal incidence. Long-lasting oscillation propagation features are observed in the temporal waveform after traveling through the periodic arrays. The enhanced THz transmission can be achieved due to the coupling between incident waves to SPPs at the bottom and top interfaces. The finite element method is used to simulate the field distribution and the transmission mode in the waveguide. The hybrid waveguide with low absorption has great potential applications in THz integrated devices.     

Abnormal Cutoff Thickness of Long-Range Surface Plasmon Polariton Modes Guided by Thin Metal Films

Long-range surface plasmon polariton （LRSPP） modes guided by a thin metal film surrounded by semi-infinite dielectrics with different refractive indices are studied. Our calculation results show that the cutoff thickness of the metal film does not monotonically increase with refractive index difference An between the substrate and superstrate. Just because of this abnormal behaviour of cutoff thickness, the existence of LRSPP illustrates complicated situations in asymmetric configurations. For a certain metal film thickness, LRSPP may exist in one, two or three refractive index difference Δn regions.     

Influence of grooves in the electromagnetic transmission of a periodic metallic grating filter

The light transmittance of metal film with periodic slits and grooves structure has been investigated. It was demonstrated that the grooves significantly affect the transmittance of the metal film. The structure excavating two grooves symmetric to the central slit in a cell of a period grating displays a dent in the transmission spectrum comparing with the structure with only one slit in the cell. Deepening the grooves moves the dents to the longer wavelengths in the transmission spectrum. An analytical equation is also provided to approximately locate the dents. The grooves in the grating filter supply the advantage of removing the needless transmission of certain frequency.     

测量金属膜粗糙度的表面等离子激元光谱方法

介绍了确定金属膜表面粗糙度的表面等离子激元光谱方法。测量了二种银膜在表面等离子激元激发条件下的光散射强度分布。通过与理论计算的拟合，得到了描写这二种银膜／空气同粗糙界面的特征参数。     

Spectroscopic Ellipsometry Study on Surface Roughness and Optical Property of AZO Films Prepared by Direct-Current Magnetron Reactive Sputtering Method

All as-deposited AZO films by direct current magnetron reactive sputtering （DC-MS） exhibit ZnO characteristic （002） and （103） diffraction peaks. Especially, AZO films prepared at 200℃ show a strongest （002） c-axis pref- erential orientation due to the minimum stress along the （002） orientation. The results show that larger stress easily induces a rougher surface. The film real and imaginary parts of dielectric constants show a sharp changes near the optical absorption edge due to the interband direct transition. The film blue and red shifts of the optical absorption edge can be explained in terms of the change of Free-electron concentration in as-deposited AZO films.     

Effect of Aspect Ratio Distribution on Localized Surface Plasmon Resonance Extinction Spectrum of Gold Nanorods

Gold nanorods with different aspect ratios are prepared in micells using a seeded growth method. Their extinction spectra are observed with an UV-visible spectrophotometer and analysed theoretically. It is known that there are two plasmon resonance peaks for gold nanorod corresponding to transverse and longitudinal plasmon resonance respectively. Moreover, the longitudinal plasmon resonance peak shifts to long wavelength when we increase the aspect ratio determined from TEM. Especially, we model the extinction spectrum using Gans' theory and compare it with our experimental result. Considering the aspect radios distribution of gold nanorods, it is found that longitudinal plasmon resonance peak will be wider than the nanorods with single aspect ratio, which is consistent with our experimental result. In addition, the effect of dielectric constant of surrounding medium is considered.     

Thickness Dependence of Resistivity and Optical Reflectance of ITO Films

Indium-tin-oxide （ITO） films deposited on crystalline silicon wafer and Corning glass are prepared by directcurrent magnetron sputtering method at room temperature with various thicknesses. The thickness dependences of structure, resistance and optical refectance of ITO films are characterized. The results show that when the film thickness is less than 40 nm, the resistivity and optical reflectance of the ITO film changes remarkably with thickness. The optoelectrical properties trend to stabilize when the thickness is over 55 nm. The GXRD result implies that the ITO film begins to crystallize if only the thickness is large enough.