Faculty Profiles - KIWA Toshihiko

Terahertz emission from YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7-δ</inf> Josephson junctions excited by femtosecond laser

Takahiro Yoshimura, Toshihiko Kiwa, Masayoshi Tonouchi

Physica C: Superconductivity and its Applications 362 ( 1-4 ) 329 - 332 2001.9

Language：English Publisher：ELSEVIER SCIENCE BV

We examine both power and bias current dependence of terahertz (THz) emission properties from YBa2Cu3O7-δ (YBCO) Josephson junctions. The junctions coupled to bow-tie antennas are fabricated by Ar ion milling from YBCO thin films grown on MgO bicrystals. We observe the radiation at bias currents from 0 to 50 mA, laser powers from 0 to 250 mW. The radiation amplitude increases with increasing laser power, and the frequency at which the radiation has a maximum amplitude decreases with increasing laser power. These trends are observed regardless of junction voltage. The results suggest that the voltage of the Josephson junction plays a less important role in the THz radiation excited by a femtosecond laser. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(01)00698-0

Terahertz emission properties from YBCO thin film log-periodic antennas

Hitoshi Saijo, Masahiko Morimoto, Toshihiko Kiwa, Masayoshi Tonouchi

Physica C: Superconductivity and its Applications 362 ( 1-4 ) 319 - 323 2001.9

Language：English Publisher：ELSEVIER SCIENCE BV

We study terahertz (THz) radiation properties from high-Tc superconductor thin film log-periodic antennas. Three sets of wire grid polarizers are employed to characterize the frequency-dependent polarization of the THz beam. The polarized radiation has clear resonance at frequencies corresponding to the antenna structures. The polarization patterns are thus well explained by the antenna structures. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(01)00696-7

Time-domain terahertz spectroscopy of (100)(LaAlO<inf>3</inf>)<inf>0.3</inf>-(Sr<inf>2</inf> AlTaO<inf>6</inf>)<inf>0.7</inf> substrate

Toshihiko Kiwa, Masayoshi Tonouchi

Japanese Journal of Applied Physics, Part 2: Letters 40 ( 1 A/B ) L38 - L40 2001.1

Language：English Publisher：INST PURE APPLIED PHYSICS

We measured terahertz (THz) properties of high-Tc superconductor's (HTS's) substrates, (100) MgO and (100) (LaAlO3)0.3-(Sr2 AlTaO6)0.7 (LSAT), at frequencies between 0.5 THz and 2 THz using time-domain terahertz spectroscopy (TDTS). The complex refractive index ñ and dielectric function ε̃ of the MgO substrate were independent of frequencies; those of LSAT slightly increased with increasing frequency. It was determined that ñ = 3.17 + i0.004 and ε̃ = 10.1 + i0.06 for the MgO substrate and ñ = 4.8 + i0.02 and ε̃ = 24 + i0.2 for the LSAT substrate at 1 THz. The LSAT values were almost independent of the temperature at these frequencies. The dielectric loss tan δ's of the LSAT and the MgO substrates were less than 0.01. The tan δ's of LSAT were several times larger than those of MgO, and increased with an increase of frequency.

DOI： 10.1143/jjap.40.l38

Tl₂Ba₂CaCu₂O_8+δからの光励起ジョセフソンプラズマ放射

富成征弘, 紀和利彦, 村上博成, 斗内政吉, WALD H, SEIDEL P, SCHNEIDEWIND H

光物性研究会論文集 12th 2001

Femtosecond optical response of Y dopping Bi2212 single crystal.

富成征弘, 紀和利彦, 村上博成, 斗内政吉, 荒井毅, 青峰隆文

電子情報通信学会技術研究報告 101 ( 183(SCE2001 16-23) ) 2001

ポンププローブテラヘルツ電磁波励起による光励起電荷ダイナミックスの評価(II)LT-GaAsの場合

河崎尚寛, 吉村尚洋, 紀和利彦, 村上博成, 斗内政吉

応用物理学関係連合講演会講演予稿集 48th ( 3 ) 2001

非晶質半導体薄膜のフェムト秒光応答とテラヘルツ電磁波放射

紀和利彦, 河崎尚寛, 吉村尚洋, 村上博成, 斗内政吉

応用物理学関係連合講演会講演予稿集 48th ( 2 ) 2001

BSCCO薄膜の時間領域テラヘルツ分光

村上博成, 紀和利彦, 斗内政吉, 斗内政吉, 内山哲治, 内山哲治, 井口家成, 井口家成

応用物理学関係連合講演会講演予稿集 48th ( 1 ) 2001

La_0.7Sr_0.3MnO_3-δ薄膜の作製とフェムト秒時間領域反射率変化

小谷研太, 紀和利彦, 貴田徳明, 村上博成, 斗内政吉

応用物理学関係連合講演会講演予稿集 48th ( 1 ) 2001

Bi₂Sr₂Ca_0.8Y_0.2CuO_8+δ単結晶の作製とフェムト秒光パルス応答

富成征弘, 荒井毅, 青峰隆文, 紀和利彦, 村上博成, 斗内政吉

応用物理学関係連合講演会講演予稿集 48th ( 1 ) 2001

Optical response in amorphous GaAs thin films prepared by pulsed laser deposition

Toshihiko Kiwa, Ichiro Kawashima, Shigeki Nashima, Masanori Hangyo, Masayoshi Tonouchi

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers 39 ( 11 ) 6304 - 6308 2000.11

Language：English Publisher：INST PURE APPLIED PHYSICS

Femtosecond optical response in GaAs thin films has been studied. We prepared GaAs thin films on MgO substrates and on YBa2Cu3O7-δ (YBCO) thin films using pulsed laser deposition (PLD) at temperatures below 250 °C. A photocarrier lifetime of less than 1 ps is measured for the prepared GaAs thin films using femtosecond time-domain reflectivity change measurements. Pulsed electromagnetic wave [terahertz (THz) radiation] containing a frequency component of up to 1 THz is emitted from fabricated photoconductive switches using the prepared thin films. We also evaluated the THz radiation properties emitted from the photoswitches on the YBCO thin films.

DOI： 10.1143/jjap.39.6304