Akihiko Shinya

Optical Modes in Two-dimensionally Ordered Dielectric Spheres

We have experimentally observed the optical modes of periodic two-dimensionally ordered polystyrene spheres with a diameter of 5.15 µm using the attenuated total reflection method. The dispersion relation of such optical modes clearly shows that there are two types of propagating modes in the ordered spheres. We point out that one of the two optical modes is related to the guided modes in optical fibers and the periodicity of the spheres plays an important role in its excitation mechanism. The other mode propagates along spherical surfaces.

Optical constants and growth mode of Ni films deposited on evaporated Al, Ag and Cu films

Abstract Information about the optical constants and structures of Ni films in Ni/Al(AlO x ·Al), Ni/Ag and Ni/Cu(CuO x ·Cu) bilayer systems are obtained through an attenuated total reflection (ATR) analysis, scanning electron spectroscopy (SEM) observation and the X-ray diffraction measurements. In particular, the optical constants of the Ni films are evaluated at various stages of growth. It is finally concluded that the Ni films show island growth for the Ni/Al(AlO x ·Al) and Ni/CuO x ·Cu bilayers, whereas layer-by-layer growth is found for the Ni films in the Ni/Cu system. It is confirmed from SEM images that the Ni film on the Ag film shows island growth, but the ATR experimental results indicate that it becomes continuous at a very early stage of growth.

Studies on optical constants of metal films evaporated at low temperatures

Abstract Using an attenuated total reflection (ATR) technique, we have investigated the optical constants of metal films evaporated at low temperatures. It has been found that the optical constants of metal films on a low-temperature substrate are very different from those on a room-temperature substrate. When such films evaporated on a low-temperature substrate are annealed up to room temperature, the optical constants approach the values for films evaporated on a room-temperature substrate. The temporal change and the annealing effect of the optical constants of metal films on a low-temperature substrate have been also investigated.

Lifetime of optical modes in two dimensionally ordered spheres

We have numerically calculated the lifetimes of optical modes, e.g., a propagating mode, in two-dimensionally (2D) ordered spheres on a glass substrate using a finite-difference time-domain method. The lifetimes of the optical modes excited by the evanescent light in an attenuated total reflection (ATR) geometry are much shorter than those excited by a light source embedded in the 2D ordered spheres on substrates. The spatial distributions of the light intensity associated with the optical modes excited in the ATR geometry are found to be different from those in the case of the embedded light source. The light energy of the optical modes excited in the ATR geometry flows extending over the entire the respective spheres and thus can be easily coupled out through the prism. On the other hand, the light energy associated with the optical modes excited by the embedded light source flows straight around the central axis of spheres, leading to a longer life time.

Interaction of Light with Ordered Dielectric Spheres: Finite-Difference Time-Domain Analysis

Using the finite-difference time-domain (FDTD) method, interaction between a gaussian wave and ordered dielectric spheres has been numerically calculated for the first time. Real-time images of the spatial distribution of the intensity of light coupling to the dielectric spheres have been presented for gaussian wave and plane-wave incidences. From the images for gaussian wave incidence, we have been able to clearly confirm a remarkable reduction in the light velocity for a flat photon band, i.e., a heavy photon band. It has been pointed out that the situation of the propagation of the gaussian wave is similar to that of the plane-wave. The transmittance T and reflectance R for the normal incidence of light to the ordered spheres have also been evaluated from the FDTD analyses. It has been found that T and R for the gaussian wave can be exactly estimated for the heavy photon band, differing from the plane-wave case.

Numerical Analysis of Optical Modes in Two-Dimensionally Ordered Polystyrene Spheres in Attenuated Total Reflection Geometry

We have numerically calculated attenuated total reflection (ATR) signals due to two-dimensionally ordered (2D) spheres on a glass substrate for both TE- and TM-polarized incident light beams using a finite difference time-domain method. The calculated ATR spectra are in good agreement with the experimental ones reported previously by us. From the ATR spectra and the spatial distribution of light intensity, it has been found that the ATR dips are due to the excitation of the optical modes in the 2D spheres. The propagation length of the optical modes is confirmed to be comparable to the diameter of the sphere. It indicates that the optical modes propagate in a variety of fashions and the light intensity in the 2D spheres takes a maximum value at the contact points between the spheres.