Masuo Fukui

Two-dimensionally localized modes of a nanoscale gap plasmon waveguide

We report numerical analysis and experimental observation of two dimensionally localized plasmonic modes guided by a nanogap in a thin metal film. Dispersion, dissipation, and field structure of these modes are analyzed using the finite-difference time-domain algorithm. The experimental observation is conducted by the end-fire excitation of the proposed gap plasmon waveguides and detection of the generated modes using their edge scattering and charge coupled device camera imaging. Physical interpretation of the obtained results is presented and origins of the described modes are discussed.

Theoretical and experimental investigation of strongly localized plasmons on triangular metal wedges for subwavelength waveguiding

We report numerical analysis and experimental observation of strongly localized plasmons guided by a triangular metal wedge. Dispersion and dissipation of such wedge plasmons are analyzed using the finite-difference time-domain algorithm. Experimental observation is conducted by the end-fire excitation and near-field detection of the predicted plasmons on a 40° silver nanowedge. Good agreement with the theoretically predicted propagation distances is demonstrated. Differences between the theoretical and experimental field distribution are explained by insufficient resolution of the near-field optical probe.

Characteristics of gap plasmon waveguide with stub structures

We found that metal-dielectric-metal plasmon waveguides with a stub structure, i.e. a branch of the waveguide with a finite length, can function as wavelength selective filters of a submicron size. It was found that the transmission characteristics of such structures depend on the phase relationship between the plasmon wave passing through the stub and the one returning to the waveguide from the stub. We also propose structures with a lossless 90 degrees bend in a plasmon waveguide, utilizing a stub structure. Furthermore, we present a functional stub structure, e.g., a 1:1 demultiplexer and a wavelength selective demultiplexer.

Experimental Observation of Long-Range Surface Plasmon Polaritons

ATR technique (glass prism-index matching oil-Ag-CaF 2 single crystal) has been used to observe long-range surface plasmon polaritons discussed recently by Sarid. At 632.8 nm, we have successfully ...

Numerical analysis of coupled wedge plasmons in a structure of two metal wedges separated by a gap

This paper presents the results of the numerical finite-difference time-domain analysis of a strongly localized antisymmetric plasmon, coupled across a nanogap between two identical metal wedges. Dispersion, dissipation, field structure, and existence conditions of such coupled wedge plasmons are determined and investigated on an example of the fundamental coupled mode. It is shown that in the general case there exist three critical wedge angles and a critical gap width (separation between the wedge tips). If the gap width is larger than the critical separation, then the antisymmetric wedge plasmons can exist only in the ranges between the first and the second critical angles, and between the third critical angle and 180°. If the gap width is smaller or equal to the critical separation, then the third and the second critical angles merge, leaving only one interval of wedge angles within which the antisymmetric coupled wedge plasmons can exist. The effect of rounded wedge tips is also investigated and is s...

In situ and real-time observation of optical constants of metal films during growth

Abstract Optical constants of metal films with an average thickness in the 0–50 nm range have been studied by using the attenuated total reflection technique. The measurements were performed in situ during the growth of evaporated films. The effective optical constants of ultrathin discontinuous metal films have been evaluated precisely.

Numerical and experimental investigation of wedge tip radius effect on wedge plasmons

We report numerical analysis and experimental observation of strongly localized plasmons guided by triangular metal wedges and pay special attention to the effect of smooth (nonzero radius) tips. Dispersion, dissipation, and field structure of such wedge plasmons are analyzed using the compact two-dimensional finite-difference time-domain algorithm. Experimental observation is conducted by the end-fire excitation and near-field scanning optical microscope detection of the predicted plasmons on 40° silver nanowedges with the wedge tip radii of 20, 85, and 125 nm that were fabricated by the focused-ion beam method. The effect of smoothing wedge tips is shown to be similar to that of increasing wedge angle. Increasing wedge angle or wedge tip radius results in increasing propagation distance at the same time as decreasing field localization (decreasing wave number). Quantitative differences between the theoretical and experimental propagation distances are suggested to be due to a contribution of scattered b...

New type of photothermal spectroscopic technique

We propose a new type of photothermal spectroscopic technique. The experimental setup is simple and the experiment can be readily carried out, even in the difficult environments that are often required for opticaland surface studies of materials. Features of the method proposed here are nondestructive and noncontact; in addition, the simplicity of our design enables us easily to make the system resistant to vibration and drift, which leads to a high signal-to-noise ratio of the photothermal signal. A few experiments have been conducted to demonstrate the utilization of the method, e.g., a quantum-radiative efficiency of surface polaritons in an air-Ag film-BK-7 prism geometry has been evaluated.

Instantaneous observation of angular scan-attenuated total reflection spectra

Abstract We have advised a new apparatus capable of observing a rapid variation of angular scan-attenuated total reflection spectra with time. Our method can be conveniently used to study dynamics of molecular adsorption and desorption at a surface.

Long-Range Surface Plasmon Polaritons in Metal Films Bounded by Similar-Refractive-Index Materials

We have numerically and experimentally investigated the propagation characteristics of surface plasmon polaritons (SPs) in metal films bounded by materials with very similar refractive indices. The calculation indicates that the SPs can propagate over macroscopic distances in the visible region. ATR experiments for angle scans (glass prism-index matching oil-Ag film-Pyrex glass) have shown that a propagation length of ∼200 µm can be readily gotten at 632.8 nm wavelength under an appropriate condition.