Interaction of polarized light with comb-shaped metal-coated nanostructures

We have studied metal-coated (20-nm-thick gold) periodic grating structures (period T = 350 nm) with a rectangular profile formed on the surface of a GaAs substrate. The spectra of reflection of a linearly polarized light from these gratings have been measured in a wavelength range of 600–1200 nm. A sharp (more than 20-fold) maximum in the polarization contrast has been observed at 720–760 nm. The dependence of this peak on the angle of sample rotation is approximately described by a cos⁶θ function. The formation of contrast and its features are related to the excitation of surface plasmons at the metal-air interface on vertical walls of the grating structure.     

Tuning color by pore depth of metal-coated porous alumina

A simple and effective color tuning method has been developed by controlling the pore depth of the metal-coated porous alumina (PA) template. The mechanism for color tuning in this method was uncovered, which can be used to design a colorful complex pattern. A colorful 'world map' was produced and exhibited on a PA template by this method. Such vivid color tuning is predominantly due to the interference enhancement of the nanostructure. This method has the potential for tuning colors and being widely applied in the fields of nanotechnology, physics and photonics.     

Wavelength-dependent absolute reflectivities and effective mosaic widths of single crystal neutron monochromators

The wavelength-dependent reflecting properties of single crystal neutron monochromators as well as the principles of their experimental determination are analysed in detail. Experimental results obtained for pyrolitic graphite (002), Zn (002), Cu (111) and Pb (111) are reported.     

Resizing metal-coated nanopores using a scanning electron microscope

Electron beam-induced shrinkage provides a convenient way of resizing solid-state nanopores in Si(3) N(4) membranes. Here, a scanning electron microscope (SEM) has been used to resize a range of different focussed ion beam-milled nanopores in Al-coated Si(3) N(4) membranes. Energy-dispersive X-ray spectra and SEM images acquired during resizing highlight that a time-variant carbon deposition process is the dominant mechanism of pore shrinkage, although granular structures on the membrane surface in the vicinity of the pores suggest that competing processes may occur. Shrinkage is observed on the Al side of the pore as well as on the Si(3) N(4) side, while the shrinkage rate is observed to be dependent on a variety of factors.     

Modeling and simulation of macrobending losses in metal-coated single-mode fibers

A formula for calculating macrobending losses in single-mode fibers with metal coating is derived. The macrobending losses in a standard single-mode fiber coated with different metal coatings are simulated using this formula. Simulation results indicate that metal coating will induce strong bend loss oscillations as a function of bend radius and the stronger bend loss oscillations of the metal-coated fiber occur with the decrease of bend radius; the wavelength and coating refractive index also have significant impact on the fiber bend losses.     

Robust chirped mirrors

Optimized chirped mirrors may perform suboptimally, or completely fail to satisfy specifications, when manufacturing errors are encountered. We present a robust optimization method for designing these dispersion-compensating mirror systems that are used in ultrashort pulse lasers. Possible implementation errors in layer thickness are taken into account within an uncertainty set. The algorithm identifies worst-case scenarios with respect to reflectivity as well as group delay. An iterative update improves the robustness and warrants a high manufacturing yield, even when the encountered errors are larger than anticipated.     

Ferrofluidic adaptive mirrors

A magnetic liquid mirror based on ferrofluids was demonstrated. Magnetic liquid mirrors represent a major departure from solid mirror technology. They present both advantages and disadvantages with respect to established technologies. Stroke (from a fraction of a wave to several hundreds of micrometers), cost (a few dollars per actuator), and scalability (hundreds of thousands of actuators) are the main advantages. Very large mirrors having diameters of the order of a meter should be feasible. There are a few disadvantages. The most important disadvantage is the time response, which is of the order of a few milliseconds. Although this time response could be further decreased with additional technical developments, it is unlikely to match the speed of solid mirrors. The technology is still in its infancy, and considerable work must still be done. However, the advantages are such that the technology is worth pursuing.     

镀金属炭毡/树脂复合材料的电磁屏蔽性能

采用镀金属炭毡与环氧树脂、聚丙烯（PP）、ABS、聚苯乙烯（PS）、聚乙烯（PE）复合制备电磁屏蔽（EMS）复合材料,镀金属炭毡复合材料在1－1000MHz范围内的屏蔽效率可达40dB以上,不同的树脂体系对复合材料的屏蔽效率无显著影响,在炭毡纤维表面镀不同的金属对复合材料的屏蔽效率有较大的影响。     

Optimization of chirped mirrors

We demonstrate that a highly efficient global optimization of chirped mirrors can be performed with the memetic algorithm. The inherently high sensitivity of chirped-mirror characteristics to manufacturing errors can be reduced significantly by means of the stochastic quasi-gradient algorithm. The applicability of these algorithms is not limited to chirped mirrors.     

Experimental investigation of the current-induced breakage of metal-coated polymer films

We have experimentally studied the phenomenon of current-induced breakage of thin (∼20-to 30-nm-thick) metal films deposited onto poly(ethylene terephthalate) (PETP) and poly(propylene) (PP) substrates. Two mechanisms leading to the current-induced breakage of the metal film are established, which are characterized by different average threshold current densities: j _H ∼ 1.5 × 10¹⁰ A/m² and j _L ∼ 0.7 × 10¹⁰ A/m². The possible nature of these mechanisms is discussed.     

Electronic structure tailoring and selective adsorption mechanism of metal-coated nanotubes

Effects of various metal coating (Co, Ti, Pd, W, and Ru) on electronic structures of carbon nanotubes are systematically studied by both ab initio calculations and field-emission experiments. The theoretical results indicate that the adsorption of metal atoms leads to substantial changes in the band structures and work functions of nanotubes. In particular, titanium is found to be the most effective coating material for the application of nanotubes to the field emission display, by lowering the work function and increasing the local density of states near the Fermi level. This is confirmed by the field-emission experiments using Ti-coated nanotubes, which shows enhanced emission performances. In addition, it is found that the Ti coating extends the lifetime of the nanotube substantially. Through the thermogravimetric analysis and theoretical modeling, we propose that this is related to the role of metal coating as a protection layer against residual gases such as oxygen, which cause the degradation of nanotubes. The applications of metal-coated nanotubes to other types of electronic devices are also discussed.     

镀金属膨胀石墨的制备及性能研究

研究了在可膨胀石墨表面非电沉积金属,对镀金属膨胀石墨进行了FT-IR及热重分析,利用烟火药爆炸对其进行了膨化及分散试验,测试了其对8mm波的衰减率.结果表明600.0℃时,其热失重为4.96%;烟火药爆炸放出的热量能使其膨化,即使烟火药中含有黑索金、黑药,且配方为零氧平衡时,镀金属膨胀石墨也不会被高温所点燃,其耐热性及抗氧化性能均得以提高;小粒径样品及干扰剂中金属含量大的对8mm波的衰减率较大,最大衰减率可达5.68dB.     

Development of low-loss sapphire mirrors

We report on the successful development of low-loss sapphire mirrors for use at a 1-mum wavelength. Methods for polishing and coating are described. The analysis of each process shows a roughness of better than 0.1 nm, a coating scattering of 1 ppm, and a surface scattering of 13 ppm. The mirrors have been characterized in a Fabry-Perot cavity, having a finesse of 100, 000. Mode doublets result from the birefringence of the coatings.     

Terahertz graphene optics

The magnitude of the optical sheet conductance of single-layer graphene is universal, and equal to e ²/4? (where 2??? = h (the Planck constant)). As the optical frequency decreases, the conductivity decreases. However, at some frequency in the THz range, the conductivity increases again, eventually reaching the DC value, where the magnitude of the DC sheet conductance generally displays a sample- and doping-dependent value between ??e ²/h and 100 e ²/h. Thus, the THz range is predicted to be a non-trivial region of the spectrum for electron transport in graphene, and may have interesting technological applications. In this paper, we present the first frequency domain measurements of the absolute value of multilayer graphene (MLG) and single-layer graphene (SLG) sheet conductivity and transparency from DC to 1 THz, and establish a firm foundation for future THz applications of graphene.      

Terahertz gas photonics

The underlying physics of the generation and detection of terahertz (THz) waves in gases are described. The THz wave generation process takes place in two steps: asymmetric gas ionization by two-frequency laser fields, followed by interaction of the ionized electron wave packets with the surrounding medium, producing an intense ‘echo’ with tunable spectral content. In order to clarify the physical picture at the moment of ionization, the laser–atom interaction is treated through solution of the time-dependent Schrödinger equation, yielding an ab initio understanding of the release of the electron wave packets. The second step, where the electrons interact with the surrounding plasma is treated analytically. The resulting pressure dependence of the THz radiation is explored in detail. The THz wave detection process is shown to be the result of four-wave mixing, leading to analytical expressions of the signal obtained which allow for improved optimization of systems that exploit these effects.