Highly enhanced broadband infrared absorption of germanium by multi-layer plasmonic nano-antenna

High-sensitivity and broad bandwidth photo-detector devices are important for both fundamental studies and high-technology applications. Here, by using three-dimensional （3D） finite-difference time-domain simulation, we design an optimized 3D multi-layer gold nano-antenna to enhance the near-infrared （NIR） absorption of germanium nanoparticles. The key ingredient is the simultaneous presence of multiple plasmonic resonance modes with strong light-harvesting effect that encompass a broad bandwidth of germanium absorption band. The simulation results show more than two orders of magnitude enhanced absorption efficiency of gernanium around 1550 nm. The design opens up a promising way to build high-sensitivity and broad bandwidth NIR photo-detectors.     

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.     

Ultrasmall focusing spot with a long depth of focus based on polarization and phase modulation

A design for focusing an incoming light into an ultrasmall spot with a long depth of focus is proposed. We use a phase plate with three concentric regions to modulate the incoming light from radial polarization into outward-inward-outward polarization. The analysis shows that the design is more suitable for a lens with a high numerical aperture because much energy is concentrated in the main lobe of the focus spot.     

线偏振器对偏振法折射率测量的影响

在一阶近似下，本文着重分析了偏振法折射率测量中线偏振器漏光误差和转角误差的影响，并导出了有关公式。数据计算表明，当线偏振器位于反射光路中时，转角误差影响最大，若转角误差小于５′时，由此产生的折射率误差约为５．５×１０（－７），此时漏光误差不影响折射率测量精度。当线偏振器位于人射光路中时，若利用中高精度线偏振器（消光比１０（－５）），则由此产生的折射率测量误差约为２．３×１０（－７）。相对该方法的随机误差１０（－５），无论线偏振器位于反射光路或入射光路中，由它产生的折射率测量误差均可忽略不计。     

Investigation of the impulse response of an image inversion interferometer

Based on the proposal of Wicker and Heintzmann “Interferometric resolution improvement for confocal microscopes” [1] we demonstrate in principle the functionality of an image inversion interferometer (III) experimentally, which can be described by an appropriate frequency transfer function. Thereby, the FWHM of the impulse response narrows around 30% compared to the PSF of a classical system. The experimental data yield a FWHM of the impulse response of 0.83 μm as compared to the theoretical value of 1.21 μm at by a wide field detection (NA=0.25) without an interferometer.     

利用偏振度研究混合目标的混合比

提出一种利用偏振度研究混合目标混合比的新方法。通过建立混合目标模型将混合目标散射光的偏振度与混合目标的混合比建立直接的关系,在理论上得到了混合目标混合比分别与混合目标偏振度和归一化偏振度之间的数值关系,并且进一步给出了混合目标混合比由归一化偏振度的反演结果,为研究混合目标提供了新的思路与方法,对偏振度探测混合目标的实验以及工程应用都有重要的理论意义。     

Demagnifying far field focusing spot to deep subwavelength scale by truncated hyperlens for nanolithography

A truncated hyperlens composed of pairs of metal-dielectric cylindrical multilayers is proposed to demagnify the diffraction limited spot to achieve deep subwavelength imaging. The diffraction limited spot is focused by far field converging cylindrical wave. Numerical simulations demonstrate that full width at half maximum (FWHM) of the image down to 32 nm (∼λ/11) can be achieved from object (∼λ/3) by 365 nm light illumination. It is discussed that the influence of size and focusing shift of the spot on those of the demagnification image on photoresist. It is also demonstrated that multi-objects can be demagnified and projected on the photoresist.     

Comparison of subwavelength focusing properties of diffraction and Fresnel zone plate plasmonic planar lenses

The subwavelength focusing properties of diffractive plasmonic planar lenses (DPLs) and Fresnel zone plate plasmonic planar lenses (FZPs) have been compared in this paper. To that end, we use the same lens material, incident wavelength, thickness and focal length for comparison. Both DPLs and FZPs consist of central circular slits surrounded by transparent and opaque zones and can get clear focusing performances. By using the rigorous electromagnetic numerical method, the fields in the focal region are analyzed in detail, and our results demonstrate that FZP can generate higher transmission efficiency, and higher peak field intensity at the focal plane. Focusing polarization properties of the lens illuminated by linearly polarized state, are calculated and analyzed also. The numerical results show that both the DPL and the FZP produce asymmetrical focal spot distributions with a low f-number. To the FZP, the full-width at half-maximum (FWHM) varies from 256 nm (along y-axis) to 516 nm(along x-axis) and to the DPL, the FWHM varies from 256 nm(along y-axis) to 580 nm(along x-axis), respectively. But for a high f-number, the asymmetrical performance of the focal spot will be reduced due to complicated electromagnetical field interferences and micro waveguide effect. Otherwise, the DPL can get a higher depolarization effect than the FZP does.     

Nanometer linear focusing of hard x rays by a multilayer Laue lens

We report on a type of linear zone plate for nanometer-scale focusing of hard x rays, a multilayer Laue lens (MLL), produced by sectioning a multilayer and illuminating it in Laue diffraction geometry. Because of its large optical depth, a MLL spans the diffraction regimes applicable to a thin Fresnel zone plate and a crystal. Coupled wave theory calculations indicate that focusing to 5 nm or smaller with high efficiency should be possible. Partial MLL structures with outermost zone widths as small as 10 nm have been fabricated and tested with 19.5 keV synchrotron radiation. Focal sizes as small as 30 nm with efficiencies up to 44% are measured.     

Determination of the orbital polarization in YTiO3 by using soft X-ray linear dichroism

We report measurements of linear dichroism in x-ray absorption at Ti L(2,3) edges of a Mott-insulating ferromagnet YTiO3, where orbital ordering occurs in the triply degenerate Ti 3d t(2g) states. Dichroic spectra and their integrated intensities are obtained for the incident electric field with polarizations parallel to a, b, and c axes. The comparison of the spectra with atomic multiplet calculations removes the ambiguity about the orbital polarization, i.e., the relative weights of |xy>, |yz>, and |zx> orbits, which are crucial for the origin of ferromagnetism. The result is consistent with the previous analysis of nuclear magnetic resonance in the Mizokawa-Fujimori scheme.     

Surface plasmon band tailoring of plasmonic nanostructure under the effect of water radiolysis by synchrotron radiation

Plasmonic metal nanostructures have a significant impact on a diverse domain of fields, including photocatalysis, antibacterial, drug vector, biosensors, photovoltaic cell, optical and electronic devices. Metal nanoparticles (MNps) are the simplest nanostructure promising ultrahigh stability, ease of manufacturing and tunable optical response. Silver nanoparticles (AgNp) dominate in the class of MNps because of their relatively high abundance, chemical activity and unique physical properties. Although MNps offer the desired physical properties, most of the synthesis and fabrication methods lag at the electronic grade due to an unbidden secondary product as a result of the direct chemical reduction process. In this paper, a facile protocol is presented for fabricating high‐yield in situ plasmonic AgNps under monochromatic X‐rays irradiation, without the use of any chemical reducing agent which prevents the formation of secondary products. The ascendancy of this protocol is to produce high quantitative yield with control over the reaction rate, particle size and localized surface plasmon resonance response, and also to provide the feasibility for in situ characterization. The role of X‐ray energy, beam flux and integrated dose towards the fabrication of plasmonic nanostructures has been studied. This experiment extends plasmonic research and provides avenues for upgrading production technologies of MNps.     

Generation of a hollow dark spherical spot by 4pi focusing of a radially polarized Laguerre-Gaussian beam

The properties of the focal spot for 4pi focusing with radially polarized first-order Laguerre-Gaussian beams are calculated. It is shown that a focal spot that has an extremely sharp dark region at the center and an almost-perfect spherical symmetry can be achieved. When such a hollow dark spherical spot is used in 4pi fluorescence depletion microscopy, an axial FWHM spot size of approximately 39 nm and a transverse FWHM spot size of approximately 64 nm can be achieved simultaneously in a practical system.     

On the linear dependence of 13C spin polarization parameters

The Jahn-Teller (J-T) effect in systems of four-fold symmetry is well known to differ from that in all other point groups with respect to the nature of the J-T active normal modes of vibration. The present report addresses some previously unnoticed features which are of intrinsic importance in recognizing and understanding the unique manifestations of quadrate symmetry in both the static and dynamic Jahn-Teller effects. We first consider the nature of the static J-T potential surfaces when coupling to and strains in two modes, b ₁ and b ₂, are included in the hamiltonian.

The second part of this paper is devoted to an examination of the dynamic J-T effect in four-fold systems. Utilizing both perturbation theory and numerical solution to the Schrödinger equation, we examine the spin-hamiltonian parameters for a metalloporphyrin ³ E_u triplet state and discuss some dynamical processes, including reorientation of the system between minima, spin-lattice relaxation, and the dependences of these phenomena on the nature and magnitude of the off-diagonal terms in the hamiltonian. There emerge from this analysis several signal differences between the Jahn-Teller effect for a doubly degenerate state in four-fold systems and in the more usual cubic or tetrahedral situation.     

Measurement of the photon linear polarization in the elementary bremsstrahlung process

In an electron-photon coincidence experiment the linear polarization of atomic-field bremsstrahlung was measured for a fixed direction of outgoing electrons. A polarization of P = -0.96 ± 0.32 was found which is in agreement with theoretical calculation. Electrons of 300 keV are used, incident on a carbon target.     

Relationship between the flexural properties and specimen aspect ratio in unidirectional composites

It is well known that the bending test provides a simple and convenient way of measuring the strength of unidirectional composite materials and gives very repeatable results. The aim of this research work was to study and analyze the flexural properties of unidirectional reinforced carbon fiber/epoxy (UD) specimens subjected to three-point loading. The effect of span-to-thickness ratio (L/h) and width-to-thickness ratio (b/h) on the three-point bending of UD composites has been investigated. Results have shown that unidirectional composites exhibit a transition in the failure mode from shear delamination to fiber yield with the span-tothickness ratio (L/h) is increased. The observed experimental data are confirmed by theoretical considerations presented here. Using the classical beam theory the conclusions of the tests could be extended by applying some reasonable requirements and simple rational fractional functions identified. This made it possible to express the asymptotic values of the flexural strength, the flexural modulus and apparent shear stress in a form that is independent from the values of the span-to-thickness ratio applied, and characterize the bending behavior of the composite materials at a more exact level.     

Determination of the parity of the 305 keV state of 48V by linear polarization correlation measurements

The linear polarization correlation of the (116–305) keV γγ cascade in the decay of ⁴⁸Cr has been investigated by means of a multidetector apparatus. In two different runs, we measured the polarization of the 305 keV radiation as well as that of the 116 keV radiation. Positive parity was derived for the 305 keV state, and the measured coefficients confirm this result. The measurements also give multipolarity assignments of the if γ-rays involved.