Tunable optical transmission through gold slit arrays with Z-shaped channels

The transmission of a normally incident wave through an array of subwavelength gold film with Z-shaped slits has been explored by using the finite-difference time-domain method. The results show that the transmission of a thinner metal film perforated with a Z-shaped slit array behaves nearly the same as that of a thicker metal film perforated with straight slit array with the same central slit length, which is useful for the miniaturization of the optical device. It is also presented that the transmission of a Z-shaped slit array sensitively depends on the slit geometrical parameters. By adjusting the width and length of each section of the Z-shaped slit, noticeable magnitude modification of the transmission, redshift, and blueshift of the resonance modes is found, which is useful for the design of frequency-selective and sensor optical devices.     

填充粘弹性材料剪力墙结构非线性有限元分析

基于被动控制的设计概念,该文在开缝剪力墙的基础上,在缝槽中填入粘弹性材料,并将这种构件应用到一幢八层钢筋混凝土剪力墙结构中。基于通用有限元软件ABAQUS,建立了该结构的弹塑性有限元模型,并对其在地震下的性能进行了数值模拟,重点研究了墙体开缝对结构地震反应的影响,以及缝槽中填充粘弹性材料对结构的控制作用。研究结果表明,墙体开缝降低了结构的刚度,增大了结构的位移反应,但开缝对减小结构底部反应及改变结构损伤分布有利。而缝中填充粘弹性材料后,可有效的控制结构的地震反应,减小结构的损伤,具有良好的实际应用意义。     

Excess Adsorption of Helium in Extremely Narrow Slit Pores

Wave functions of quantum helium in narrow slit pores are strongly restricted; as such, quantum helium condensed in narrow slit pores displays different behaviors from that in bulk. Herein, we report the densities of helium adsorbed on carbon surfaces and in carbon slit pores with average pore widths of 0.7, 0.9, and 1.1 nm at 2–5 K. The density of adsorbed quantum helium in the 0.7-nm slit pores was significantly higher than those in the larger slit pores and bulk. The average layer density of helium in the 0.7-nm pores was also significantly higher than those in the larger slit pores, suggesting solid-like structure formation even under helium vapor condition. The highly dense state of helium in narrow slit pores is due to strong attractive potential effects in such slit pores.     

Measurement of Optical Transfer Function with Polarization Interferometer

A method is described to determine the Fourier analysis of the image of a slit of finite width using polarization interferometers. Sinusoidal fringes of variable spatial frequency and of contrast one are projected on the slit image and the output flux is recorded. The modulation of the flux when the fringe system is displaced with respect to the slit image yields the spatial spectrum of the slit image. The spatial spectrum of the slit object being known, the transfer function (both amplitude and phase) of the optical system can be determined.     

Approximate model for surface-plasmon generation at slit apertures

We present a semianalytical model that quantitatively predicts the scattering of light by a single subwavelength slit in a thick metal screen. In contrast to previous theoretical works related to the transmission properties of the slit, the analysis emphasizes the generation of surface plasmons at the slit apertures. The model relies on a two-stage scattering mechanism, a purely geometric diffraction problem in the immediate vicinity of the slit aperture followed by the launching of a bounded surface-plasmon wave on the flat interfaces surrounding the aperture. By comparison with a full electromagnetic treatment, the model is shown to provide accurate formulas for the plasmonic generation strength coefficients, even for metals with a low conductivity. Limitations are outlined for large slit widths (>lambda) or oblique incidence (>30 degrees ) when the slit is illuminated by a plane wave.     

Anatomical analysis of the light transmission through a single subwavelength metal slit by the FDTD method

Transverse-magnetic (TM) polarized light transmission through a single subwavelength metal slit is re-examined with finite-difference time-domain (FDTD) simulations. In contrast to previous studies, we derive an anatomical view of the electromagnetic field distribution in different cross-sections and emphasize the generation of a field coupling mode in the slit. Numerical modeling reveals that both peak and dip transmissions are features of the field interference in the slit. The slit width and depth are mainly responsible for establishing the amplitude and phase, respectively, of the coupled mode. Moreover, it is found that the output energy dispensation between the radiative and surface components is actually determined by the slit width. Analysis of the physical properties of the slit, including the coupled mode structure in the transverse plane, the effective refractive index and Ohmic absorption losses, provides new insights into the light transmission processes.     

Effect of quadratic radial variation of phase on single slit diffraction of Laguerre–Gauss vortex beams

Effect of quadratic radial phase variation in the plane of the aperture on Fraunhofer diffraction of Laguerre–Gauss vortex beams by a slit is studied experimentally. For slit positions near the incident beam waist, its effect is to shear the diffraction pattern relative to that at the waist. The magnitude and sense of shear depend on the topological charge and slit location relative to the incident beam waist. For slit positions far from the waist, the diffraction pattern evolves to be significantly different and is dominated by two strong peaks. A closed form analytical expression for the diffraction pattern is presented, which reproduces experimental results quite well for all slit positions.     

Multiple plate problem in potential two-dimensional flow

Summary Presented is an elementary solution which is a particular solution of a thin slit in the potential two-dimensional flow. The solution satisfies the following conditions: 1) the remote velocities are equal to zero, 2) the normal velocity of fluid to the thin slit is a Dirac function, in other words, a flow with unit magnitude is passing through some point at the slit surface, 3) Joukowski hypothesis is used. The velocity at leading edge of the slit is infinite, and at trailing edge is finite. After using the obtained elementary solution, the multiple plate problem in potential two-dimensional flow can be reduced to a system of Fredholm integral equations. Numerical examples are given to demonstrate the use of proposed approach.     

Improvement of resolution for phase retrieval by use of a scanning slit

An improved method for resolution of object reconstruction using phase retrieval by use of a scanning slit aperture is proposed. The reconstruction is based on measurements of the Fraunhofer diffraction intensities of wave fields transmitted through a scanning slit in the Fresnel-zone plane of an object. In the improved method, the measurement coordinates of the intensities depend not only on the slit's position used in a previous method but also on the slit's position scaled by the ratio between two distances among the object, Fresnel-zone, and detector planes. The spatial-frequency band for the object reconstruction, which is limited in a previous method by the extent of the Fourier transform of the slit function, can be extended to the bandwidth dependent on the scanning area with the slit. In addition, even in the measurement of the Fresnel diffraction intensities of wave fields transmitted through the slit, the improved resolution can be retained by compensation for a transverse shift of the intensities.     

Image curvature correction and cosmic removal for high-throughput dispersive Raman spectroscopy

A key factor determining the sensitivity of a Raman spectrometer is the usable detection area, which is the product of the usable slit width and the height. For the majority of process Raman samples, the larger the sampling area is, the more the scattered Raman signal can be gathered. On a multi-channel-detector-based dispersive spectrometer, a given spectral resolution limits the slit width. Extending the slit height using a straight slit usually causes the image to be curved on the detector due to optical effects. If left untreated, the curved slit image will degrade the peak shape and spectral resolution; therefore, the slit height must also be kept small if this negative effect is to be avoided. The mechanism of the curvature formation was analyzed for an on-axis-lens-based spectrograph, and a correction technique was developed to generate a straight slit image on the charge-coupled device (CCD). This allowed a large portion of the CCD height to be used without degrading the spectral resolution. A large fiber bundle was usable instead of a single small core fiber, generating significant increase in collected signal strength in clear or translucent samples. The straight image also enabled a new cosmic spike removal method, wherein the CCD image was divided into multiple strips, and a comparison among them allowed the identification and removal of cosmic spikes in a single CCD integration. On the contrary, many existing cosmic removal methods rely on comparison of multiple sequentially acquired spectra, potentially introducing artifacts, particularly when the spectral features are changing.     

Near-field scattered by a single nanoslit in a metal film

Using a scanning near-field optical microscope, we visualize, in three dimensions, the electromagnetic field distribution near an isolated slit aperture in a thin gold film. At the metal-air interface and for a TM incident polarization, we confirm some recently observed results and show that the slit generates two kinds of surface waves: a slowly decaying surface plasmon polariton and a quasi-cylindrical wave that decreases more rapidly when moving away from the slit. These waves are not generated for a TE incident polarization. In a noncontact mode, we also observe how the transmitted light diverges in free space. At a small distance from the slit (< 2 microm), we find that the emerging light spreads in all directions for TM, forming an electromagnetic cloud, whereas it is concentrated above the slit for TE, forming a more directive light jet. The experimental images are in good agreement with the numerical simulations.     

Rainbow holography with a synthesized double slit

Rainbow holography with a synthesized double slit is proposed. Diffuse three-dimensional objects are translated uniformly in the x(0)-y(0) plane. The propagation direction of the coherent plane wave illuminating the objects is situated in the x(0)-z(0) plane. As a result of this process, a sinc function that modulates the complex-amplitude distribution of the objects is presented on the back focal plane of the lens, and the synthesized slit is formed. The central position of the synthesized slit depends on both the direction of motion of the object and the spatial frequency of the illuminating wave in the x(0) direction. Therefore the synthesized double slit is generated with a two-exposure method that has two illuminating waves of different spatial frequencies. The theoretical analysis and some experimental results are presented.     

T‐stress corrected notch stress intensity factors with application to welded lap joints

The definition, content and application of the notch stress intensity factors (NSIFs) characterizing the stress field at rounded slit tips (keyholes) is discussed. The same is done in respect of the T‐stress transferred from the corresponding pointed slit tips. A T‐stress based correction of the NSIF K_1,ρ is found to be necessary. The applicability of the T‐stress term supplemented by higher‐order terms in Williams’ solution to the slit tip stresses in tensile‐shear loaded lap joints is discussed in more detail. The role of the T‐stress in constituting the near‐field stresses of rounded slit tips is shown to cause a difference between internal and external slit tip notches. The notch stress equations for lap joints proposed by Radaj based on structural stress and by Lazzarin based on a finite element model of the rounded notch are reconsidered and amended based on the derivations above.     

Pseudocolour encoding by lensless one-step rainbow holography with a synthesized slit

Abstract

Pseudocolour encoding of holographic images by lensless one-step rainbow holography with a synthesized slit is proposed. When a different portion of the object is recorded the reference wave is incident at a different angle θ and during each exposure the incident angle changes continuously around this angle θ. The pseudocolour holographic image is obtained by white-light reconstruction of the lensless one-step rainbow hologram with synthesized slit. The basic advantage of this technique is the elimination of a narrow slit and a lens in the encoding process. The theoretical analysis and experimental result are presented.     

Fixed slit geometry passive phase separator for superfluid helium

A fixed slit geometry passive separator for superfluid helium (He II) was developed and tested. Six different phase separator test models were designed and built, three of them with 10 μm slit width and three with 8 μm width. The slit flow length was 8 mm for all test phase separators. The slit forming materials were stainless steel, copper and Zerodur. The phase separator flow behaviour was tested with He II in the temperature range 1.6–2.0 K. The flow characteristic was found to depend on the slit width, the channel geometry and the channel forming material, with copper yielding a much higher flow rate than stainless steel and Zerodur. This behaviour is attributed to the much higher thermal conductivity of copper. One phase separator was also tested for its dynamic behaviour with transient temperature change of the He II bath.     

Modeling of a slit-scan-type aerial image measurement sensor used for optical lithography

Theoretical modeling of a slit-scan-type aerial image measurement sensor used for optical lithography is presented. Slit transmission properties are fully represented by the slit transfer function in terms of incident and scattering angles of light, which is then incorporated into the scheme of a partially coherent imaging formula to obtain an expression for image profiles measured by slit scanning. As an exemplary case, we analyze the influence of a 100 nm width slit used in an ArF lithography system. To understand the mechanism of image profile changes by slit transmission, we focus on frequency transfer characteristics of sinusoidal patterns.     

Spot distribution measurement using a scanning nanoslit

A scanning and rotating nanoslit is used to measure submicrometer features in focused spot distributions. Using a filtered backprojection technique, a highly accurate reconstruction is demonstrated. Experimental results are confirmed by simulating the scanning slit technique using a physical optics simulation program. Analysis of various error mechanisms is reported, and the reconstruction algorithm is determined to be very resilient. The slit is 125 nm wide and 50 μm long and is fabricated on a 120 nm thick layer of aluminum. The size of the image field is 15 μm, and simulations indicate that 200 nm Rayleigh resolution is possible with an infinitely narrow slit.     

Effects of symmetrical and asymmetrical bumps on plasmonic behavior in a metallic grating

The influence was investigated of symmetrical and asymmetrical bumps on plasmonic behavior in a metallic grating. Compared with the resonant peaks of a smooth-slit grating, the peaks of odd (even) modes exhibit a blue-shift (red-shift) and the transmission properties are tunable by the size of bumps when the bumps are laid symmetrically. However, the peaks of all modes only exhibit a red-shift when the grating is engraved with a bump and a cut in the same slit (namely bend slit), and the bend slit can achieve the properties of a straight slit. Additionally, it is found that the dips in transmission spectrum can be adjusted by altering the size of the bumps if the bumps are set asymmetrically. Fabry–Pérot-like resonance, field interference and phase resonance mechanisms have been suggested for the physical origins of these observations.     

Experimental demonstration of tomographic slit technique for measurement of arbitrary intensity profiles of light beams

We demonstrate experimentally an optical imaging method that makes use of a slit to collect tomographic projection data of arbitrarily shaped light beams; a tomographic backprojection algorithm is then used to reconstruct the intensity profiles of these beams. Two different implementations of the method are presented. In one, a single slit is scanned and rotated in front of the laser beam. In the other, the sides of a polygonal slit, which is linearly displaced in a x-y plane perpendicular to the beam, are used to collect the data. This latter version is more suitable than the other for adaptation at micrometer-size scale. A mathematical justification is given here for the superior performance against laser-power fluctuations of the tomographic slit technique compared with the better-known tomographic knife-edge technique.     

Some properties of the optical resonances in a single subwavelength slit

Diffraction of TM-polarized waves by a slit in a thick screen of infinite conductivity is treated. The case of an arbitrary incident beam wave is considered. We study the resonances that appear when the wavelength of the incident beam wave is larger than the slit width, i.e., the subwavelength regime where a one-mode model for the slit can be considered. High anomalous values (resonances) of the transmission coefficient, the angular diffracted energy, and the magnetic field within the slit are analyzed. A simple linear relationship to determine the resonant wavelengths is proposed. We show that the transmission coefficient, the normal diffracted energy, and the magnetic field within the cavity are linear functions of the resonant wavelength and the thickness of the screen. Additionally and surprisingly, we reveal that under certain conditions the incident beam wave via the diffraction can give a suppressed light transmission; i.e., a minimum in the transmission is obtained where a maximum is expected.