Chau-Shioung Yeh

Beaming light from a subwavelength metal slit surrounded by dielectric surface gratings.

In this article, we demonstrate that a subwavelength metal slit surrounded by dielectric surface gratings possesses a directional beaming effect. We propose a surface plasmon diffraction scheme to explain the three kinds of beaming conditions. The numerical simulations of the illustrative structures undertaken used a Finite Difference Time Domain (FDTD) Method and a Rigorous Coupled Wave Analysis (RCWA) Method. Our simulations were found to be consistent and in agreement with the experimental results. In comparison with other metal structures, we find that dielectric metal structures offer better performance as well as the advantage of being able to be efficiently mass produced for large volume industrial applications.

The magnetoelastic problem of a crack in a soft ferromagnetic solid

The induced magnetoelastic stresses and Maxwell stresses generated by a uniform magnetic field in an infinite soft ferromagnetic medium containing a finite plane crack are analyzed in this paper. The soft ferromagnetic elastic solids with a finite crack are considered to be high magnetic susceptibility materials. By the use of complex variable theory, the exact solutions for magnetic field quantities and both magnetoelastic stresses and Maxwell stresses can be obtained in a closed form. The singularity of stress intensity in the vicinity of crack tip and crack opening condition can also be determined.

Directional light beaming control by a subwavelength asymmetric surface structure

We propose a direct experimental set-up to observe the directional beaming effect of surface plasmon. A single diffracted beam from an asymmetric-sided surface corrugation is demonstrated. A single subwavelength slit with an asymmetric structure was fabricated using a focused ion beam (FIB) onto a metal surface with a glass substrate. By means of surface plasmon (SP) diffraction, the directionality of the light can be changed by the period of the metallic gratings. We show corresponding numerical simulations achieved by a Rigorous Coupled-Wave Analysis (RCWA) method and a Finite-Difference Time-Domain (FDTD) method. The simulation results were in agreement with the experimental data.

Subwavelength nondiffraction beam generated by a plasmonic lens

We experimentally examined the near-field and far-field optical properties of a subwavelength annular aperture (SAA) made on silver film and undertook finite difference time domain simulations. In our near-field measurements, an interference pattern with a period very close to half of the surface plasmon (SP) wavelength (λSP∕2) was found on the surface of the silver film. Moreover, we observed that the transmitted light of the 442nm incident laser was focused at several micrometers behind the silver SAA structure at a tiny spot (354nm) and with a remarkable 31μm depth of focus. This implies that the silver SAA structure can generate a nondiffraction beam and can be used to fabricate high aspect ratio subwavelength structures.

Experimental analysis of surface plasmon behavior in metallic circular slits

Using a focused ion beam, the authors fabricated metallic circular slits onto a glass substrate coated with silver film. The influence of the number of slits and the focusing light phenomena was investigated by capturing the light transmitted through the circular slits. They demonstrate experimentally that the circular grating formed by a set of periodical slits can excite both stronger surface plasmon (SP) and localized surface plasmon as the number of slits increases. They found that the SP tended to congregate at the center of the circular grating, and that the reemitted light could be used to achieve a focusing phenomenon.

High-Precision Ultrasonic Ranging System Platform Based on Peak-Detected Self-Interference Technique

A high-precision ultrasonic ranging system platform is presented and evaluated in this work. By queuing peaks of the self-destructive interference, the proposed hardware platform can enhance the accuracy without complex algorithms. At the emitter, the developed technique generates two amplitude-modulated pulses with 180° phase shift. At the receiver, on the other hand, the two pulses create a self-destructive interference. This interference waveform can be used to directly determine the time of flight. By implementing the developed technique on a low-cost microcontroller platform, the experimental result shows the accuracy with 0.06 mm over a range of 50-1000 mm. Moreover, the system accuracy remains 0.15 mm within the range of 2000 mm. The developed system establishes an effective method for low-cost and high-performance ranging systems.

Similarities and differences for light-induced surface plasmons in one- and two-dimensional symmetrical metallic nanostructures

Two types of double-sided nanostructure, one possessing a slit aperture with parallel grooves and the other possessing a circular aperture with concentric grooves, were fabricated to examine the similarities and differences of their diffraction behavior in one-dimensional (1-D) and two-dimensional (2-D) nanostructures. Based on the projection-slice theory, we conjecture that the surface plasmons in these two different nano-scale grooves possess similar modes. A localized surface plasmon (LSP) was used to examine the transmission characteristics induced by the apertures. The transmission characteristics of the slitted nanostructure and the circular nanostructure aperture were then measured. We coupled the transmission spectra measured from these two apertures with a 1-D parallel groove transmission curve simulated by a 1-D rigorous coupled wave analysis. Measured spectra results show reasonable agreement with the simulated data. We propose that the apparent blueshift observed in the peak frequency of a 2-D nanostructure is due to the difference in the shape of the aperture and the spot transmission characteristics of 1-D and 2-D systems as induced by a LSP.

On Evaluation of Lamb's Integrals for Waves in a Two-Dimension Elastic Half-Space

In this paper, a modified version of the method of steepest descent is proposed for the evaluation of Lambs integrals which can be considered as basis functions dealing with the development of the transition matrix method which can be used to study the wave scattering in a two-dimensional elastic half-space. The formal solutions of the generalized Lambs problem are studied and evaluated on the basis of the proposed method. After defining a phase function which presents in wavenumber integral, an exact mapping and an inverse mapping can be obtained according to the phase function. Thus, the original integration path can be deformed into an equivalent admissible path, namely, steepest descent path which passed through the saddle point, and then mapped onto a real axis of mapping plane, finally, resulted in an integral of Hermite type. This integral can be efficiently evaluated numerically in spite of either near- to far-field or low to high frequency. At the same time, the asymptotic value can easily be obtained by applying the proposed method. The numerical results for generalized Lambs solutions are calculated and compared with analytic, asymptotic or other existing data, the excellent agreements are found. The properties of generalized Lambs solutions are studied and discussed in details. Their possible applications for wave scattering in elastic half-space are also pointed out.

Scattering of Elastic Waves by a Buried Tunnel Under Obliquely Incident Waves Using T Matrix

This paper first studies the transition matrix formulation for the analysis of responses of an elastic halfspace with a buried tunnel subjected to obliquely incident waves. The basis functions are constructed using the moving P-, SV-, and SH-wave source potentials and to represent the scattered and refracted wave fields in series forms. The associated T-matrix expression of elastic inclusion is derived using Bettis third identity. Second, this study proposes a technique for calculating the integral representation of basis functions in the wave-number domain using the method of steepest descent. Finally, typical numerical results obtained under incident plane waves are presented for verification.

Enhancing intensity of emitted light from a ring by incorporating a circular groove

We fabricated a ring containing a single circular groove (RCG) on silver film and which was supported on a glass substrate. We found that by changing the mean radius of the circular groove, the light intensity emitted from the RCG can be modulated by using the scattering light from the circular groove. In addition, we also fabricated circular grooves with the same depth but of different widths so that we could examine the scattering light behavior of the grooves. Herein, we propose a theoretical model which takes into account the amplitude modulation of the cylindrical waves. Our results showed that our proposed model agreed well with the experimental results.