Hiroe Kitajima

Use of a total absorption ATR method to measure complex refractive indices of metal-foils

In this paper, the use of a total absorption attenuated total reflection (ATR) method to measure complex refractive indices and thicknesses of thin foils is discussed. Our studies show that in a prism metal-foil coupling system, the gap thickness between the prism and the metal-foil modifies the state of the coupled surface plasmons on the metal-foil interface, and yields total absorption at three different incident angles, under optimum conditions, respectively. The dependence of the conditions for total absorption on the complex refractive index and on the foil thickness is discussed. By preparing three prism coupling systems with different refractive indices, and by measuring the incident angle at minimum reflectance in each system, complex refractive indices and foil thicknesses of thin gold-foils have been measured.

Thickness measurement of ultrathin films on metal substrates using ATR

By modifying the surface plasma mode on a bare metal surface with an ultrathin film deposited on the metal, we measured the film thickness by attenuated total reflection (ATR). Various factors causing measurement errors are estimated with numerical examples. As a result, for example, it is shown that for some thicknesses, the errors due to the real part of the complex refractive index of a metal substrate become extremely small. Thicknesses of SiO(2) films sputtered onto Au foil and A1(2)O(3) films produced on Al foil by oxidation are measured.

Optimum conditions in the attenuated total reflection technique

In this paper the optimum condition for using the attenuated total reflection (ATR) technique is studied. In optimum conditions, the energy of an incident plane wave can be totally absorbed. The optimum condition can be realized by fabricating a localized thickness variation in the gap between a prism and a sample substrate with a point contact pressure. In the ATR technique, for example, the complex refractive index and the foil thickness of a thin metal foil, and the gap thickness are unknown parameters. To determine these unknown parameters, we prepared three prism coupling systems with different refractive indices. By this technique, we measured the complex refractive indices and the foil thicknesses of thin gold foils sputtered onto glass substrates, and the refractive index and the film thickness of a silica film sputtered onto a metal substrate.

Zero reflection from a dielectric film on metal substrate at oblique angles of incidence

This paper aims to clarify the conditions in which zero reflection from a dielectric film on metal substrate at oblique angles of incidence takes place. The numerical examples with experimental data show that the light absorption characteristics strongly depend on the film thickness. Therefore, it is useful to observe the oblique-incidence reflectance during the film deposition process for rapid and precise calibration of a thickness monitor.

Anomalies of electromagnetic waves in multilayered structures containing anisotropy

This paper is intended to show that in planar multilayered structures containing anisotropy, anomalies take place in which the reflected waves with the same polarization as that of the incident wave become zero due to the polarization conversion phenomenon. There exist conditions under which there can be no reflection. Not only when the waveguiding system supports hybrid polarization guided modes, but also when one of the polarizations is a guided mode and the other is a leaky mode, does no reflection occur. Formulas for such widths of the film and gap as would satisfy the no-reflection conditions are given. New schemes for various applications are proposed.

Multiple resonance FTR filters for nonpolarizing bandpass filters

A design procedure is given for multiple resonance FTR filters which are required to be nonpolarizing for a specific wavelength and angle of incidence. The optimum thickness of the buffer layer is derived to make the phase velocities of TE and TM modes coincide in a twin-waveguide system. With numerical examples and discussion, it is shown that the condition for zero dispersion of coupled modes of a polarization wave can extend to nonpolarizing coupled modes.

Resonant Coupling of the Guided Mode with Surface Plasma Mode in a Stratified Structure Containing a Metal-Clad Dielectric-Film Waveguide Having Low-Refractive-Index Buffer Layer

When the guided mode in a dielectric film waveguide couples with the surface plasma mode, the dispersion of the coupled guided mode, which depends on the thickness of buffer layer between the film waveguide and metal substrate, exhibits anomalous characteristics, and therefore the film waveguide supports even and odd guided modes. However, owing to the collision loss of the free electrons, the phase velocities of these modes degenerate and the dispersion becomes zero in the vicinity of the surface plasma mode, with an optimum buffer layer thickness. When the degenerate modes are optically excited through a prism region, this stratified structure exhibits double tuned absorption characteristics with a flat absorption peak. These resonant coupling phenomena were studied.

Zero dispersion of coupled modes in twin waveguides and reflection characteristics at prism–twin-waveguide-coupling boundaries

The zero-dispersion characteristics are shown of coupled modes in twin waveguides when the medium of the substrate is lossy or active or when leakage exists. When the coupling strength of coupled modes composed of even and odd modes is critical, the phase velocities of these modes degenerate to make dispersion zero. The condition for zero dispersion is analytically obtained. The characteristics of reflection coefficients at various boundaries in the twin-waveguiding structure are studied in terms of the dual relation in the case in which the medium of the substrate is lossy or is active. The effect of the degenerate modes caused by leakage on the phase-shift characteristics of reflected waves at the prism–twin-waveguide boundaries is also studied.

Various Light Resonance Mechanisms in Dielectric and Metallic Layers, and a Measurement Procedure for Optical Constants

In this paper, various light resonance mechanisms in dielectric and metallic film layers have been studied. In a prism metal film coupling structure for surface plasma wave excitations, under optimum conditions, which are related to the thickness of the metal film and the gap between the prism and the metal film, the reflectance at the prism gap boundary becomes zero at three different angles of incidence. Furthermore, anomalous light absorption occurs due to the excitation of longitudinal plasma waves; even when the collison loss of the free electrons is assumed to be zero, the reflectance becomes zero. A measurement procedure is also shown with experimental data for determining the complex refractive index and the film thickness of metal films at the same time.