Yukitoshi Otani

Quasi-Moseley's law for strong narrow bandwidth soft x-ray sources containing higher charge-state ions

Bright narrow band emission observed in optically thin plasmas of high-Z elements in the extreme ultraviolet spectral region follows a quasi-Moseleys law. The peak wavelength can be expressed as λ=(21.86±12.09)×R∞−1×(Z−(23.23±2.87))−(1.52±0.12), where R∞ is the Rydberg constant. The wavelength varies from 13.5 nm to 4.0 nm as the atomic number, Z, increases from Z = 50 to Z = 83. The range of emission wavelengths available from hot optically thin plasmas permits the development of bright laboratory-scale sources for applications including x-ray microscopy and x-ray absorption fine structure determination.

Generation of achromatic, uniform-phase, radially polarized beams.

Axially symmetric half-wave plates have been used to generate radially polarized beams that have constant phase in the plane transverse to propagation. However, since the retardance introduced by these waveplates depends on the wavelength, it is difficult to generate radially polarized beams achromatically. This paper describes a technique suitable for the generation of achromatic, radially polarized beams with uniform phase. The generation system contains, among other optical components, an achromatic, axially symmetric quarter-wave plate based on total internal reflection. For an incident beam with a constant phase distribution, the system generates a beam with an extra geometrical phase term. To generate a beam with the correct phase distribution, it is therefore necessary to have an incident optical vortex with an azimuthally varying phase distribution of the form exp( + iθ). We show theoretically that the phase component of radially polarized beam is canceled out by the phase component of the incident optical vortex, resulting in a radially polarized beam with uniform phase. Additionally, we present an experimental setup able to generate the achromatic, uniform-phase, radially polarized beam and experimental results that confirm that the generated beam has the correct phase distribution.

Manipulation of metal nanoparticles using fiber-optic laser tweezers with a microspherical focusing lens

This paper describes the laser manipulation of metal nanoparticles and dielectric particles by fiber-optic laser tweezers with a microspherical focusing lens. In this manner, a small ball lens attached to the end of the core focuses light guided through a single-mode optical fiber. Numerical electromagnetic analysis of the microfocusing structure showed the possibility of metal nanoparticle trapping with this method. An effective focus allows metallic particles located in the path of the focused light to be attracted to the center of the beam path and to be two-dimensionally trapped on a substrate. In the experiment, manipulation of Au nanoparticles with diameters of 40, 100, and 200 nm was demonstrated. In addition to metallic samples, manipulation of dielectric particles with 1 and 3 µm diameters was also demonstrated using the same configuration, showing the extended capability of the fiber-optic laser manipulator.

Dynamic temperature field measurements using a polarization phase-shifting technique

Abstract. In this study, an optical system capable of simultaneously grabbing three phase-shifted interferometric images was developed for dynamic temperature field measurements of a thin flame. The polarization phase-shifting technique and a Michelson interferometer that is coupled to a 4-f system with a Ronchi grating placed at the frequency plane are used. This configuration permits the phase-shifted interferograms to be grabbed simultaneously by one CCD. The temperature field measurement is based on measuring the refraction index difference by solving the inverse Abel transform, which requires information obtained by the fringe order localization. The phase map is retrieved by a three-step algorithm. Experimental results of a dynamic thin flame are presented.

Achromatic axially symmetric wave plate.

An achromatic axially symmetric wave plate (AAS-WP) is proposed that is based on Fresnel reflections. The wave plate does not introduce spatial dispersion. It provides retardation in the wavelength domain with an axially symmetric azimuthal angle. The optical configuration, a numerical simulation, and the optical properties of the AAS-WP are described. It is composed of PMMA. A pair of them is manufactured on a lathe. In the numerical simulation, the achromatic angle is estimated and is used to design the devices. They generate an axially symmetric polarized beam. The birefringence distribution is measured in order to evaluate the AAS-WPs.

Uni-axial measurement of three-dimensional surface profile by liquid crystal digital shifter

A uni-axial measurement of three dimensional surface profiles by a liquid crystal digital shifter is proposed using a telecentric optical system. Height information is captured by measuring the contrast in the projected pattern. A shadow less measurement of the objects area is archived by using a uni-axial system. The magnification of the object image captured by a CCD camera is made constant by changing the focus distance. The liquid crystal digital shifter is a powerful tool to make arbitrary intensity and frequency distribution. Surface profiles of mechanical parts were measured to demonstrate this method.

Optical Dew Sensor Using Surface Plasmon Resonance of Periodic Ag Nanostructure

The sensitivity of an optical dew sensor is enhanced by the use of the surface plasmon resonance (SPR) of a periodic Ag nanostructure. As the temperature of an SPR-excited Ag nanostructure decreases, vaporous water molecules condense and adsorb onto hydroxyl groups formed on the Ag surface. A redshift of 40 nm in absorption peak wavelength was observed owing to the amount of adsorbed water molecules due to the temperature. An SPR signal occurs at temperatures higher than the theoretical dew point and shows the sensitivity improvement of the optical dew sensor by the proposed SPR technique.

Determination of the polarization states of an arbitrary polarized terahertz beam: Vectorial vortex analysis

Vectorial vortex analysis is used to determine the polarization states of an arbitrarily polarized terahertz (0.1–1.6 THz) beam using THz achromatic axially symmetric wave (TAS) plates, which have a phase retardance of Δ = 163° and are made of polytetrafluorethylene. Polarized THz beams are converted into THz vectorial vortex beams with no spatial or wavelength dispersion, and the unknown polarization states of the incident THz beams are reconstructed. The polarization determination is also demonstrated at frequencies of 0.16 and 0.36 THz. The results obtained by solving the inverse source problem agree with the values used in the experiments. This vectorial vortex analysis enables a determination of the polarization states of the incident THz beam from the THz image. The polarization states of the beams are estimated after they pass through the TAS plates. The results validate this new approach to polarization detection for intense THz sources. It could find application in such cutting edge areas of physics as nonlinear THz photonics and plasmon excitation, because TAS plates not only instantaneously elucidate the polarization of an enclosed THz beam but can also passively control THz vectorial vortex beams.

Optically Three-Dimensional Control of Magnetic Levitation Using Temperature-Sensitive Ferrite

Optically driven actuators have a feature of a noncontact for applying moving energy remotely. In this paper, we propose a new method for optically driving a magnetic levitation system, which consists of a neodymium magnet as a movement object, a ferrite magnet, two blocks of graphite and a temperature-sensitive ferrite. The neodymium magnet is levitated by the diamagnetism of the graphite and the magnetic force between the neodymium and the ferrite. When a laser beam is irradiated on one of the temperature-sensitive ferrites, its magnetic susceptibility easily decreases owing to the photothermal effect. A levitated condition is derived from a numerical approach. As a result, the movement is successfully controlled in a three-dimensional area.

Developmental and morphological studies in Japanese medaka with ultra-high resolution optical coherence tomography

We propose ultra-high resolution optical coherence tomography to study the morphological development of internal organs in medaka fish in the post-embryonic stages at micrometer resolution. Different stages of Japanese medaka were imaged after hatching in vivo with an axial resolution of 2.8 µm in tissue. Various morphological structures and organs identified in the OCT images were then compared with the histology. Due to the medakas close resemblance to vertebrates, including humans, these morphological features play an important role in morphogenesis and can be used to study diseases that also occur in humans.