Thick Metallic Screen Research Articles

Simulation and experimental observations of axial position control of a photonic nanojet by a dielectric cube with a metal screen.

In this Letter, we report on a numerical study, fabrication, and experimental observations of photonic nanojet (PNJ) shaping by control of a tangential electric field component. Here the PNJs are generated by a single mesoscale micro-cube that is fabricated from polydimethylsiloxane, deposited on a silicon substrate and placed on thick metal screen at illuminating wavelengths of 405, 532, and 671 nm. It is shown that the length, focal length, and width of the PNJ can be significantly reduced in the presence of the metal masks along the side faces of the micro-cube. Experimental measurements of the PNJ imaging are performed by a scanning optical microscope with laser sources. Our experimental results are in reasonable agreement with simulation predictions of the finite-difference time-domain method. Due to the appearance of the metal masks, the PNJ focal length decreases 1.5 times, the PNJ decay length decreases 1.7 times, and the PNJ resolution increases 1.2 times. Such PNJs possess great potential in complex manipulation, including integrated plasmonic circuits, biosensing, and optical tweezers.

Distant Behind-screen Action of Undamped Temperature Waves (Long-distance Propagation, X-ray Generation, LENR Stimulation)

The physical mechanism of the generation, features of propagation and the possible use of undamped temperature waves are con- sidered. The process of generation of these waves is related to the possibility of reversibility of local relaxation thermodynamic processes of heat transfer. In the course of experiments, it was shown that such waves can exist only at certain frequencies, de- pending on the relaxation time. The possibility of energy transfer using these waves over a long distance has been investigated. It is shown that using of these waves X-ray generation is possible, and effective stimulation of nuclear fusion in a TiD target located behind a thick metal screen which is remote from the wave source. In this work is also considered a possible physical mechanism for the realization of LENR reactions connected with the formation of coherent correlated states of interacting particles under the action of these temperature waves.

A Novel Theory for the Scattering of P-Polarized Hermite-Gaussian Electromagnetic Beams by a Double Metallic Nano-Slit

We present a rigorous theory for oblique incident Hermite-Gaussian beams, diffracted by two optical nano-slits of width l and separation d, in a thick metallic screen for the case of polarization TM (P). The far field spectra as a function of several opto-geometrical parameters, wavelength λ , slit width l, separation d , incidence angle θi  and Hermite order m  is analyzed. In the vectorial diffraction region given when λ /l >0.2, where l is the incident wavelength and as a function of the separation between slits d; we have numerically analyzed: the far field spectra, the energy diffracted along the incident beam direction Ei , and the validity of an approximate diffraction (scalar) property, namely Ei= Ntao/lambda .
  

Oblique incidence of a plane wave on an inhomogeneously loaded grating of slots in a screen

In this paper, we demonstrate a new method to control the enhanced transmission due to Fabry–Perot resonances through an array of dielectric-loaded slots in a thick metallic screen. We obtain approximate analytical formulas for each polarization (TM and TE) using a mode-matching technique based on the assumption that the slots are small compared to a free-space wavelength and that the metallic screen is a perfect electric conductor as is appropriate for microwave frequency applications. We show that the bandwidth and locations of enhanced transmission can be controlled by the angle of incidence or by making the material filling the slots inhomogeneous. Computational results are given that demonstrate the influence of the angle of incidence on the enhanced transmission bandwidth. We show that the separation between enhanced transmission frequencies can be controlled by introducing a gap within the slot with a different dielectric constant. Also, we illustrate how the total transmission bandwidth can be increased by adjusting the angle of incidence and the gap size.

Excitation of SPPs in graphene by a waveguide mode

We present a semi-analytical model that predicts the excitation of surface-plasmon polaritons (SPPs) on a graphene sheet located in front of a sub-wavelength slit drilled in a thick metal screen. We identify the signature of the SPP in the transmission, reflection, and absorption curves. Following the previous literature on noble-metal plasmonics, we characterize the efficiency of excitation of SPPs in graphene computing a spatial probability density. This quantity shows the presence of plasmonics resonances dispersing with the Fermi energy, EF, as an unambiguous signature of graphene plasmons.

A micropump based on water potential difference in plants

In land plants, water vapor diffuses into the air through the stomata. The loss of water vapor creates a water potential difference between the leaf and the soil, which draws the water upward. Quantitatively, the water potential difference is 1–2 MPa which can support a water column of 100–200 m. Here we present the design and operation of a biomimetic micropump. The micropump is mainly composed of a 48-μm thick metal screen plate with a group of 102-μm diameter micropores and an agarose gel sheet with nanopores of 100 nm diameter. The micropores in the screen plate imitate the stomata to regulate the flow rate of the micropump. The agarose gel sheet is used to imitate the mesophyll cells around the stomata. The lost of water from the nanopores in the gel sheet can generate a water potential difference (more than 30 kPa) which can drive solution flow in a microfluidic chip. Results have shown that a precise flow rate of 4–8 nl/min can be obtained by using this micropump, and its ultra-high flow rate is 113–126 nl/min. The advantages of this biomimetic micropump include adjustable flow rate, simple structure and low fabrication cost. It can be used as a “plug and play” fluid-driven unit in microfluidic chips without any external power sources or equipments.

Near-, mesoscopic and far-field regimes of a subwavelength Young's double-slit

The coupling distance between two narrow resonating slits made in a thick metal screen strongly modulates the optical spectral features of their scattering resonances. We show that these non-trivial modulations result from dipolar-type interactions between the slits. The radiation damping, frequency shift and local light enhancement of these modes vary with the coupling distance, and we derive analytical expressions for these physical quantities. We also explain how transmission and antenna-like radiation pattern can be tuned with specific incidence angles.

Analytical model for the transmission of electromagnetic waves through arrays of slits in perfect conductors and lossy metal screens

This paper presents a very simple analytical model for the analysis of the resonant transmission of microwaves or millimeter waves through periodically distributed slits in a thick metal screen. The model is based on equivalent circuits consisting of transmission line elements of known characteristic admittances and propagation constants loaded by capacitors. Closed-form analytical expressions are provided for all the circuit parameters. Alternatively, the circuit parameters can be quickly computed from numerical simulations carried out at a few frequency points. The proposed analytical model accounts for all the details of the observed transmission spectrum, including conventional Fabry-Pérot (FP) resonances, which are controlled by the thickness of the screen, as well as extraordinary transmission peaks, which are related to the periodicity. The range of validity of the model as a function of dimensional parameters is discussed. The experimentally observed and numerically predicted redshift of the Fabry-Pérot transmission peaks with respect to the ideal Fabry-Pérot resonance condition is accurately accounted for by the capacitors of the model. For narrow slits, the extraordinary transmission peak is linked to the singular behavior of the capacitances at the Rayleigh-Wood anomaly frequency point. Finally, the effect of the lossy nature of the metal screens is included in the model, providing accurate predictions of the transmission losses. Additionally, for lossy screens the model adequately predicts the anomalous behavior of the above mentioned redshift when the slit width becomes comparable to the skin depth in the metal, which is in good agreement with experimental and theoretical data previously reported for a single slit.

MULTI-SCALE APPROACH FOR THE ELECTROMAGNETIC SIMULATION OF FINITE SIZE AND THICK FREQUENCY SELECTIVE SURFACES

The scattering analysis from metallic Grid FSS consisting of rectangular perforations on a thick metallic screen illuminated by an oblique incident plane wave is presented. The grid structure is analyzed using Scale Changing Technique (SCT) which is based on the partition of the grid-plane into planar sub-domains deflned at various scale-levels. Electromagnetic interaction between subsequent scales is modeled by mutually independent Scale-Changing Networks and flnally the complete structure is simply represented by a cascade of these networks. Very good agreement is obtained between simulation results from SCT and the Finite Element Method (FEM) when computing the re∞ection/transmission coe-cients and electromagnetic fleld backscattered by thick and flnite size frequency selective surfaces. The computation time is signiflcantly reduced when using SCT-based software compared with the FEM simulation tool. The accurate prediction of the electromagnetic scattering by flnite size arrays is of great practical interest in the design and optimization of modern frequency selective surfaces (FSSs), re∞ect-arrays and transmit-arrays. A complete full-wave analysis of these structures requires generally enormous computational resources due to their large electrical dimensions which would require prohibitively large number of unknowns to be solved. The unavailability of e-cient and accurate design tools for these applications limits the engineers with the choice of low performance simplistic designs that do

Square-shaped metal screens in the infrared to terahertz spectral region: Resonance frequency, band gap, and bandpass filter characteristics

Resonance frequency of freestanding, square-shaped thick metal screens have been studied here in the wavelength range of infrared (IR) to mm (20 to 0.2 THz). It was found that their peak transmission has a linear relationship to the screen’s pitch. An experimental spectral feature, unaccounted for in typical simulations with plane parallel incident beams, was observed in the transmittance envelope for measurements in focused beams. In the past, this spectral feature was assigned to Wood’s anomaly. Yet, unlike the latter, the observed spectral feature appears here in the long wavelength regime as well. We investigated this phenomenon for a large frequency range and assigned the spectral feature to the formation of a photonic band gap at oblique incidence. Many IR Fourier transform spectrometers use a noncollimated incident beam and such spectral features will appear whenever the local state of polarization includes components which are parallel to the plane of incidence.

Analysis of inductive frequency selective surfaces by the method of moments with entire‐domain basis functions

AbstractThis study presents an efficient method for the analysis of thick metal screens perforated periodically with apertures (inductive frequency selective surfaces). The analysis is based on the Method of Moments with entire‐domain basis functions. The peculiarity of the proposed approach is the particular calculation of the basis functions in the case of arbitrarily shaped apertures. The method is validated through the comparison with published data and is applied to the design of a new dual‐band filter. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2929–2932, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22923

Band pass filters in the 1 μm spectral region: Thick metal screens

Free standing metal screens have long been used as band pass filters in the infrared (IR) wavelength region. One adjusts the screens’ periodicity constant, its opening-to-periodicity aspect ratio and its thickness to achieve desired infrared transmission properties. Here we concentrate on thick screens in the near IR wavelength region (1–2 μm). In addition to experiments and simulations we have considered the role of screen imperfection on its transmission characteristics. Uneven surfaces, inclined and sometimes rough walls of the screen and waveguide channels may be the result of thick-film lithography which is used in the process for screen manufacturing. Understanding these effects is crucial to applications of these filters in the entire IR region.

Angle-dependent optical transmission through a narrow slit in a thick metal film

The theory of optical transmission through a narrow slit in a thick metal screen was formulated previously for normal incidence [Y. Takakura, Phys. Rev. Lett. 86, 5601 (2001)]. In this work, the theory is generalized to include the parallel angle dependence of the optical transmission for angles in the plane of the slit. A fully analytic formulation of the parallel angle-dependent reflection coefficient and transmission is provided. It is shown that the slit width has a strong influence on the angle tuning of the Fabry-P\'erot resonances, which is caused by the angle dependence of the reflection coefficient. The theory agrees quantitatively with recent experiments and predicts angle-dependent variations that may readily be observed in future experiments over a wider angle and wavelength range.

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.

Creation of strongly localized and strongly enhanced optical near-field on metallic probe-tip with surface plasmon polaritons

A practical technique by which a strongly confined and strongly enhanced optical near-field can be created on a metallic probe-tip is investigated. The technique uses an I-shaped aperture in a pyramidal structure formed on a thick metallic screen. The pyramidal structure divided into two sections by the I-shaped aperture and one of them is used as a tapered metallic probe. A surface plasmon polariton (SPP), which is excited and enhanced in the I-shaped aperture, propagates along the side surface of the aperture and pyramidal structure and illuminate the probe-tip. Scattering of optical waves by this structure is solved numerically using a volume integral equation by a generalized minimum residual method and fast Fourier transformation. It is shown that a strongly localized and strongly enhanced optical field is created at the tip of this metallic probe by SPPs. The fundamental characteristics of the localized and enhanced optical near-field on the probe-tip are investigated.

Metallic tip probe providing high intensity and small spot size with a small background light in near-field optics

A metallic tip probe that gives high optical intensity and small spot size with a small background light is proposed and simulated. The proposed tip probe provides advantages of both the aperture probe and the apertureless probe currently used in the scanning near-field optical microscope. The tip probe is illuminated by surface plasmon polaritons transmitted through the I-shaped aperture in a pyramidal structure on a thick metallic screen. Scattering of optical waves by this structure is solved numerically using a volume integral equation by generalized conjugate residual iteration and fast Fourier transformation. The proposed tip probe is shown to simultaneously provide both high near-field intensity and small spot size with a small background light.

Simulation of confined and enhanced optical near fields for a long narrow aperture in a pyramidal structure on a thick metallic screen

A new type of long narrow aperture in a pyramidal structure on a thick metallic screen is proposed, and optical wave scattering by this structure is simulated. This aperture structure provides high emission intensity and small spot size simultaneously through excitation of the surface plasmon polaritons on the sidewalls of the pyramidal structure. Scattering of optical waves by this structure in the thick metallic screen is solved numerically with a volume integral equation by generalized conjugate residual iteration and fast Fourier transformation. The basic characteristics of the near-field intensities of the aperture are investigated in detail.

Simulation of confined and enhanced optical near-fields for an I-shaped aperture in a pyramidal structure on a thick metallic screen

A modification of the I-shaped aperture proposed previously by the authors—that is, an I-shaped aperture in a pyramidal structure on a thick metallic screen—is proposed and simulated. This structure is useful in the application of the I-shaped aperture to practical near-field optical systems. Scattering of optical waves by this structure in a thick metallic screen is solved numerically using a volume integral equation by generalized conjugate residual iteration and fast Fourier transformation. It is shown that this aperture structure simultaneously provides high emission intensity and small spot size through excitation of the surface plasmon polariton on the sidewalls of the aperture in the pyramid structure.

Analysis and numerical computation of diffraction of an optical field by a subwavelength-size aperture in a thick metallic screen by use of a volume integral equation.

Diffraction of an optical field by an aperture in a thick metallic screen is analyzed numerically by use of a three-dimensional volume integral equation together with a generalized conjugate residual method and fast Fourier transformation. Numerical results were validated by reciprocity and the independence of the results of the truncated discretized volume size used in numerical calculations. Near and far fields of square, circular, and triangular apertures in a thick screen are obtained numerically. Some of the numerical results obtained in the present study agree with previously reported experimental results. The surface plasmon polaritons excited on the sidewalls of the aperture can explain the basic characteristics of near-field distribution of apertures. The Bethe-Bouwkamp theory was found to be insufficient to explain the basic characteristics of the near field around the subwavelength aperture in a practical metallic screen.

Optimized computer-aided design of I-shaped subwavelength aperture for high intensity and small spot size

The design parameters of an I-shaped aperture in a thick metallic screen are optimized through computer simulation to obtain high near-field intensity and small spot size. The dependence of the near-field intensity on the complex relative permittivity of the screen, screen thickness and shape of the aperture is investigated in detail, and the characteristics of the optimized design are presented. The proposed aperture provides significantly higher near-field intensity than conventional simple rectangular apertures, while simultaneously providing a smaller spot size.