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Search Results: 1 - 10 of 291 matches for " Masanobu Iwanaga "
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First-Principle Analysis for Electromagnetic Eigen Modes in an Optical Metamaterial Slab
Masanobu Iwanaga
PIER , 2012, DOI: 10.2528/PIER12071202
Abstract: Electromagnetic (EM) eigen modes in a fishnet metamaterial (MM) slab have been comprehensively analyzed in an experimental configuration, based only on precise solutions of Maxwell equations. The EM eigen modes were directly detected from light-absorption peaks. Each mode was explicitly characterized by the dispersion diagram and EM field distributions. It was consequently found that the modes were classfied into either inner modes inside the slab or a mode at the interface with the surrounding media. The symmetric properties of the inner modes were clarified using group theory. The interface mode was found to come from surface plasmon polariton at flat metal/insulator interface. The present analysis procedure is generally applicable to MM slabs and enables to clarify the properties without models or assumptions, which have been usually used in MM studies.
Photonic metamaterials: a new class of materials for manipulating light waves
Masanobu Iwanaga
Science and Technology of Advanced Materials , 2012,
Abstract: A decade of research on metamaterials (MMs) has yielded great progress in artificial electromagnetic materials in a wide frequency range from microwave to optical frequencies. This review outlines the achievements in photonic MMs that can efficiently manipulate light waves from near-ultraviolet to near-infrared in subwavelength dimensions. One of the key concepts of MMs is effective refractive index, realizing values that have not been obtained in ordinary solid materials. In addition to the high and low refractive indices, negative refractive indices have been reported in some photonic MMs. In anisotropic photonic MMs of high-contrast refractive indices, the polarization and phase of plane light waves were efficiently transformed in a well-designed manner, enabling remarkable miniaturization of linear optical devices such as polarizers, wave plates and circular dichroic devices. Another feature of photonic MMs is the possibility of unusual light propagation, paving the way for a new subfield of transfer optics. MM lenses having super-resolution and cloaking effects were introduced by exploiting novel light-propagating modes. Here, we present a new approach to describing photonic MMs definitely by resolving the electromagnetic eigenmodes. Two representative photonic MMs are addressed: the so-called fishnet MM slabs, which are known to have effective negative refractive index, and a three-dimensional MM based on a multilayer of a metal and an insulator. In these photonic MMs, we elucidate the underlying eigenmodes that induce unusual light propagations. Based on the progress of photonic MMs, the future potential and direction are discussed.
Effective optical constants in stratified metal-dielectric metameterial
Masanobu Iwanaga
Physics , 2007, DOI: 10.1364/OL.32.001314
Abstract: We present effective optical constants of stratified metal-dielectric metameterial. The effective constants are determined by two complex reflectivity method (TCRM). TCRM reveals full components of effective permittivity and permeability tensors and indicates the remarkable anisotropy of metallic and dielectric components below effective plasma frequency. On the other hand, above the plasma frequency, one of the effective refractive indexes takes a positive value less than unity and is associated with small loss. The photonic states are confirmed by the distribution of electromagnetic fields.
Photoacoustic wave propagating from normal into superconductive phases in Pb single crystals
Masanobu Iwanaga
Physics , 2005, DOI: 10.1103/PhysRevB.72.012509
Abstract: Photoacoustic (PA) wave has been examined in a superconductor of the first kind, Pb single crystal. The PA wave is induced by optical excitation of electronic state and propagates from normal into superconductive phases below T$_{\rm C}$. It is clearly shown by wavelet analysis that the measured PA wave includes two different components. The high-frequency component is MHz-ultrasonic and the relative low-frequency one is induced by thermal wave. The latter is observed in a similar manner irrespective of T$_{\rm C}$. On the other hand, the MHz-frequency component is obviously enhanced below T$_{\rm C}$. The behavior is reproduced by the change of attenuation of longitudinal ultrasonic wave and is consistent with BCS theory.
Diamagnetic nature of stratified thin metals in visible range
Masanobu Iwanaga
Physics , 2007,
Abstract: It is numerically demonstrated that effectively strong diamagnetic resonance emerges at visible frequencies in stratified metal-dielectric metamaterials. The effective optical constants are extracted by two-complex reflectivity method. It is clarified that the effective diamagnetic response originates from local diamagnetism at stratified thin metals. The effective diamagnetism is crucially sensitive to the sturucture of unitcell. The effective diamagnetic response is always associated with effective plasma frequency and is therefore regarded as a magnetic component of the collective excitation.
Photoacoustic detection of phase transitions at low temperatures in CsPbCl$_3$ crystals
Masanobu Iwanaga
Physics , 2003, DOI: 10.1080/01411590500114732
Abstract: Phase transitions in CsPbCl$_3$ crystals have been explored by photoacoustic (PA) method in a wide temperature range of 150--300 K. The PA signals, induced by ns-pulsed laser excitation of electronic states and detected with a piezoelectric transducer, are thermoelastic ultrasonic waves lasting for hundreds of microseconds. The wavelet analysis of the PA wave has clarified that the thermoelastic wave includes several MHz components. The PA signals have been made use of in order to examine phase transitions at low temperatures in the crystal. Changes of PA signals indicate that two phase transitions take place at low temperatures around 200 K. The types of phase transitions are discussed taking into recent experimatal results.
Full optical responses of one-dimensional metallic photonic crystal slabs
Masanobu Iwanaga,Teruya Ishihara
Physics , 2005,
Abstract: We reveal all the linear optical responses, reflection, transmission, and, diffraction, of typical one-dimensional metallic photonic crystal slabs (MPhCS) with the periodicity of a half micrometer. Maxwell equations for the structure of deep grooves are solved numerically with good precision by using the formalism of scattering matrix, without assuming perfect conductivity. We verify characteristic optical properties such as nearly perfect transmission and reflection. Moreover, we present large reflective diffraction and show that, in the energy range where diffraction channels are open, the photonic states in the MPhCS originate from surface plasmon polaritons.
Exciton-relaxation dynamics in lead halides
Masanobu Iwanaga,Tetsusuke Hayashi
Physics , 2002, DOI: 10.1016/S0022-2313(02)00619-1
Abstract: We survey recent comprehensive studies of exciton relaxation in the crystals of lead halides. The luminescence and electron-spin-resonance studies have revealed that excitons in lead bromide spontaneously dissociate and both electrons and holes get self-trapped individually. Similar relaxation has been also clarified in lead chloride. The electron-hole separation is ascribed to repulsive correlation via acoustic phonons. Besides, on the basis of the temperature profiles of self-trapped states, we discuss the origin of luminescence components which are mainly induced under one-photon excitation into the exciton band in lead fluoride, lead chloride, and lead bromide.
Self-trapped electrons and holes in PbBr$_2$ crystals
Masanobu Iwanaga,Junpei Azuma,Masanobu Shirai,Koichiro Tanaka,Tetsusuke Hayashi
Physics , 2002, DOI: 10.1103/PhysRevB.65.214306
Abstract: We have directly observed self-trapped electrons and holes in PbBr$_{2}$ crystals with electron-spin-resonance (ESR) technique. The self-trapped states are induced below 8 K by two-photon interband excitation with pulsed 120-fs-width laser light at 3.10 eV. Spin-Hamiltonian analyses of the ESR signals have revealed that the self-trapping electron centers are the dimer molecules of Pb$_2$$^{3+}$ along the crystallographic a axis and the self-trapping hole centers are those of Br$_2$$^-$ with two possible configurations in the unit cell of the crystal. Thermal stability of the self-trapped electrons and holes suggests that both of them are related to the blue-green luminescence band at 2.55 eV coming from recombination of spatially separated electron-hole pairs.
Reciprocal transmittances and reflectances: An elementary proof
Masanobu Iwanaga,Takafumi Hatano,Teruya Ishihara,A. S. Vengurlekar
Physics , 2006, DOI: 10.1119/1.2752820
Abstract: We present an elementary proof concerning reciprocal transmittances and reflectances. The proof is direct, simple, and valid for the diverse objects that can be absorptive and induce diffraction and scattering, as long as the objects respond linearly and locally to electromagnetic waves. The proof enables students who understand the basics of classical electromagnetics to grasp the physical basis of reciprocal optical responses. In addition, we show an example to demonstrate reciprocal response numerically and experimentally.
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