Miyu Ozaki

Surface-Plasmon Holography with White-Light Illumination

A technique based on light-induced electronic excitations on a metal-film surface is used for three-dimensional color displays. The recently emerging three-dimensional (3D) displays in the electronic shops imitate depth illusion by overlapping two parallax 2D images through either polarized glasses that viewers are required to wear or lenticular lenses fixed directly on the display. Holography, on the other hand, provides real 3D imaging, although usually limiting colors to monochrome. The so-called rainbow holograms—mounted, for example, on credit cards—are also produced from parallax images that change color with viewing angle. We report on a holographic technique based on surface plasmons that can reconstruct true 3D color images, where the colors are reconstructed by satisfying resonance conditions of surface plasmon polaritons for individual wavelengths. Such real 3D color images can be viewed from any angle, just like the original object.

Calibration of Articulated Arm Coordinate Measuring Machine Considering Measuring Posture

A three-dimensional coordinate measuring machine (CMM) is widely used for measurement accuracy and wide measurement range. It is necessary to calibrate the parameters which describe the mechanism to use it as CMM. The geometric calibration is to find the parameters related with the straightness, rotational and scale errors and so on. Non-geometric calibration is to find the parameters except geometric parameters. The method to calibrate CMM is that the artifact is measured by the target CMM. However the most studies of the calibration of CMM are focused on the orthogonal CMM. The only some studies are focused on nonorthogonal CMM. This paper describes the calibration method and the result of the articulated arm CMM (ACMM) which is one of nonorthogonal CMM. It has more measuring freedom than orthogonal CMM. However, the measuring error of ACMM is larger than that of the orthogonal CMM. The kinematic parameters of ACMM are calibrated using the center coordinates of the spheres as the artifact. As in this method, a part of measuring volume is calibrated, ACMM is not sufficiently calibrated. Moreover, as it has more freedom of mechanism, the identical coordinates can be measured in a various posture of it. Therefore the deformations of the arms are different in each measurement. In this paper, to calibrate the deformations of the arms in different measuring posture in addition to the kinematic parameters, a new artifact is produced, a calibration method is proposed and the experiment is reported.

Color selectivity of surface-plasmon holograms illuminated with white light

By using the optical frequency dependence of surface-plasmon polaritons, color images can be reconstructed from holograms illuminated with white light. We report details on the color selectivity of the color holograms. The selectivity is tuned by the thickness of a dielectric film covering a plasmonic metal film. When the dielectric is SiO(2) and the metal is silver, the appropriate thicknesses are 25 and 55 nm, respectively. In terms of spatial color uniformity, holograms made of silver-film corrugations are better than holograms recorded on photographic film on a flat silver surface.

Identification of Fluids by the Color of Surface Plasmon Polaritons

When optical waves make the free electrons on a metal surface resonate, optical energy propagates along the surface as density waves of the free electrons. The longitudinal waves and electrical fields of the electrons are called surface plasmon polaritons (SPPs), which are widely applied in high sensitivity sensors because the excitation of SPPs sensitively depends on the refractive index of the surrounding dielectric sample. Here, we report the identification of fluids by using the color dispersion of SPPs. Silver film on a prism surface is illuminated with white light to excite SPPs. A color component in the white light is thereby selectively coupled with SPPs due to the color dispersion that depends on the refractive index of the fluid on the film. Thus, theoretically, when the refractive index is changed, the color of SPPs changes as well. Our application uses a medium consisting of fluid samples to be identified. The proposed identification method can be applied to fluid analysis for label-free visualization of or as a simple analysis method, since the refractive indices or concentrations of the sample fluids directly affect the color of the SPPs, and this color can be visually identified. We theoretically confirmed that the color of SPPs excited with white light illumination can help to differentiate between water and ethanol. Experimentally, SPPs belonging to the frequency region of the color green were detected when the sample was water, and the color changed to red when ethanol was used instead. In the future, we plan to develop simple, small, sensitive, and low-cost sensors that can determine the concentration and refractive index of fluids on the basis of the color of the SPPs.

Evaluation of Straightness of Two-Axes Stage

Two-axes stages (XY stage) are used for precise machining and precise positioning. The XY stage should have the resolution of nanometer in the nanotechonology. In order to determine that the XY stage has enough small resolution, it is necessary to evaluate the positioning accuracy. The shape of stage axes affects measurement result. Therefore, it is necessary to know the shape of the axes. This paper describes the method how to evaluate the straightness of the stage to measure the behavior of the stage. The behavior of the stage is measured by laser interferometer, which measures the displacement. The reflection mirrors are set up on the stage, which reflects the laser. The result of measurement by the laser interferometer includes both of the shape of the reflection mirrors and the shape of the axes. In the case of nanometer positioning, the shape of the reflection mirrors affects measurement result, as the profile error of reflection mirrors are as small as motion error. We theoretically and experimentally inspect whether both errors can be separated from the displacement. In this simulation, the shape of axes and the shape of the reflection mirrors are generated randomly. The shape of axes and the shape of reflection mirrors are estimated by non-linear least-squares method. The estimated shape of axes and shape of reflection mirrors are compared with the ideal shape of them. After simulation, similar method is applied to the actual stage and laser interferometer. The result of simulation and measurement are shown.

Self-Calibration of XY-Stage with Parallel Mechanism

It is important to calibrate the straightness and the squareness of the XY-stage for precision manufacturing and measurement. Normally it is calibrated using much higher precise and accurate measuring instruments and/or artifacts. The high precision and accurate instruments and artifacts are expensive. So, in this paper, Self-calibration method is applied to XY-stage. This method does not require any much high precision and accurate instruments and artifacts. The normal XY-stage moves to the location at the unique coordinates. In this case, it is difficult to apply self-calibration method. Therefore, XY-stage is expanded to XYθ-stage with parallel mechanism. As this stage moves to the location at a lot of coordinates, self-calibration method is applied. This method is confirmed in simulation and experiment. In simulation, the extension lengths of mechanism are estimated from known kinematic parameters and the target coordinates. After that, estimated kinematic parameters are calculated by least-squares method from the extension lengths and the target coordinates. Finally, the positioning coordinates are calculated from the estimated kinematic parameters and the extension lengths. It is proved that the calibration method is effective by comparing the target coordinates and the positioning coordinates. In experiment, the experimental process is similar to the simulation without the estimation of extension lengths. The results of simulation and experiment are shown in this paper.

Surface-plasmon holography with white light illumination

In various metamaterials, surface plasmon polaritons (SPPs) play important roles to produce novel electromagnetic functions through the field enhancement, the dispersion modification, and the frequency tunability. Here, we apply the function of the SPP to a color 3D image display with white-light back-illumination. We reconstructed the color image from a hologram with white-light by using SPP. The hologram is recorded as corrugations of a silver film, which is covered by a SiO2 film to modify the color dispersion of the SPP. A single-color light in the white-light is separated as the SPP owing to the color dispersion. The SPP is diffracted by the hologram to reconstruct the three dimensional wavefront with the selected color. To obtain a multi-color image, RGB-color holograms are recorded with azimuthal-angle multiplex and are reconstructed simultaneously. The silver is used as the metal film so that the SPP of whole visible region can be excited. The silver film is 55-nm thickness, in which the SPP is excited efficiency. The SiO2 film enhances color selectivity, but if its thickness overs 25-nm, SPP in high optical frequency such as blue vanishes. Corrugation depth is up to 25-nm, within which brightness of the image monotonically increases with the depth. If the depth overs the 25-nm, the brightness is decreased. The SPP on the corrugated silver surface and SiO2 film have made color selectivity to a thin hologram. The SPP color holography gives a new white-light reconstruction technique using back-lighting.

Observation of Scattered Evanescent Waves

Spatial resolution in the conventional optical microscopy depends on diffraction limit. Photon scanning tunneling microscopy is one of the microscopic methods that surpass the diffraction limit. It scans an object with detecting evanescent wave on object surface. Evanescent wave is scattered by the tip of a fiber probe and guided to a detector by the fiber probe. Not all of the scattered ray can be detected. Only the scattered ray from the aperture of a fiber probe can be detected. We propose to improve an image by detecting the state of scattered ray and a new method to maintain the probe sample distance constant by keeping the quantity of scattered ray constant.