Faculty Profiles - KIWA Toshihiko

Optical response of amorphous Ge photoconductive switches with YBCO transmission lines

I. Kawayama, T. Miyadera, Y. Doda, T. Kiwa, H. Murakami, M. Tonouchi

Superconductor Science and Technology 16 ( 12 ) 1475 - 1478 2003.12

Language：English Publisher：IOP PUBLISHING LTD

Amorphous germanium (a-Ge) photoconductive switches coupled with YBCO transmission lines are fabricated on MgO (100) substrates. The optical responses of the photoconductive switches at lower temperatures are examined using the terahertz beam generation technique. The results have revealed that the a-Ge photoconductive switch can stably work at low temperatures and operation frequencies around 100 GHz. We also discuss the effects of YBCO transmission lines and the deterioration of the interface between a-Ge and YBCO.

DOI： 10.1088/0953-2048/16/12/034

Laser terahertz-emission microscope for inspecting electrical faults in integrated circuits. International journal

Toshihiko Kiwa, Masayoshi Tonouchi, Masatsugu Yamashita, Kodo Kawase

Optics letters 28 ( 21 ) 2058 - 60 2003.11

Language：English Publisher：OPTICAL SOC AMER

A laser terahertz-emission microscope (LTEM) system is proposed and developed for inspecting electrical faults in integrated circuits (IC). We test a commercial operational amplifier while the system is operating. Two-dimensional terahertz-emission images of the IC chip are clearly observed while the chip is scanned with a femtosecond laser. When one of the interconnection lines is cut, the damaged chip has a LTEM image different from that of normal chips. The results indicate that the LTEM system is a potential tool for IC inspection.

DOI： 10.1364/OL.28.002058

Characteristics of superconducting flux flow transistors under irradiation of femtosecond laser pulses

Y. Doda, T. Kiwa, I. Kawayama, H. Murakami, M. Tonouchi

Physica C: Superconductivity and its Applications 392-396 ( PART 2 ) 1504 - 1508 2003.10

Language：English Publisher：ELSEVIER SCIENCE BV

We have fabricated superconducting flux flow transistors with YBCO thin films and investigated the vortex flow characteristics under the irradiation of femtosecond laser pulses. The vortex flow velocity was calculated by the magnetic field dependence of the flow voltage. The obtained velocity without laser irradiation is 0.08-1.37 × 104 m/s for the bias current IB = 0.4-0.8 mA. The flow voltage increased gradually when the irradiated laser power was up to 10 mW, however, it increased drastically when the laser power was more than 10 mW. The maximum velocity of 6.3 × 10 4 m/s was obtained at the laser power of 15 mW. The result indicates that the laser pulses excite the vortices and accelerate the vortex velocity. © 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0921-4534(03)00779-2

Terahertz Radiation from InAs/AlGaSb heterostructures

Suzuki M., Kiwa T., Tonouchi M., Nakajima Y., Sasa S., Inoue M.

Meeting abstracts of the Physical Society of Japan 58 ( 2 ) 657 - 657 2003.8

THz radiation properties of Tl<inf>2</inf>Ba<inf>2</inf>CaCu<inf>2</inf>O<inf>8+δ</inf> thin films excited by femtosecond laser pulses

Yukihiro Tominari, Toshihiko Kiwa, Hironaru Murakami, Masayoshi Tonouchi, Henrik Schneidewind, Hagen Wald, Paul Seidel

IEEE Transactions on Applied Superconductivity 13 ( 2 III ) 3730 - 3732 2003.6

Language：English Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

Previously, we found the resonant THz wave radiation from c-axis oriented underdoped Tl2Ba2CaCu2O8+δ (Tl-2212) thin films by femtosecond laser pulse illumination under magnetic field. The properties of the resonant THz wave were well explained by the Josephson plasma resonance phenomenon. In the present study, the THz radiation properties were investigated for an overdoped Tl-2212 thin films. The amplitudes of THz waveform radiated under a bias current condition is much smaller than those of previous sample, while any trace of resonant THz signals could not be observed under magnetic field. These experimental results indicate the possibility that the initial THz wave radiated by ultrafast modulation in eddy-current around the vortices has an important role to excite the collective mode oscillation.

DOI： 10.1109/TASC.2003.812529

Backscattered terahertz radiation imaging system to visualize supercurrent distributions

T. Kiwa, Y. Kamata, M. Misra, H. Murakami, M. Tonouchi

IEEE Transactions on Applied Superconductivity 13 ( 2 III ) 3675 - 3678 2003.6

Language：English Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

A new type of terahertz (THz) radiation imaging has been proposed and demonstrated. The supercurrent distributions were visualized by detecting the backscattered THz radiation from optically excited high-temperature superconductors. The supercurrent distributions were clearly observed in 100- and 500-nmthick YBa2Cu3O7-δ films in the remanent state. Our system has performance similar to the system with transmission configuration.

DOI： 10.1109/TASC.2003.812428

Coherent terahertz radiation from Tl<inf>2</inf>Ba<inf>2</inf>CaCu<inf>2</inf>O<inf>8+δ</inf> thin films excited by optical laser pulse under magnetic field

Yukihiro Tominari, Toshihiko Kiwa, Hironaru Murakami, Masayoshi Tonouchi, Hagen Wald, Paul Seidel, Henrik Schneidewind

Physica C: Superconductivity and its Applications 388-389 481 - 482 2003.5

Language：English Publisher：ELSEVIER SCIENCE BV

We observed terahertz (THz) pulse radiation from Tl2Ba2CaCu2O8+δ thin films by femtosecond optical pulse excitation under a bias-current condition and a radial magnetic field of ∼100 Oe nearly parallel to the c-axis of the film. The observed waveform under magnetic field showed clear oscillations below 80 K, and the Fourier spectrum showed an additional peak other than the frequency components observed in the bias-current condition. The additional peak (630 GHz at 24 K) shifted towards lower frequency region with increasing temperature. The observed resonant THz wave behavior is quantitatively explained by Josephson plasma phenomenon. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)02589-3

THz imaging of supercurrent distribution in Meissner state of LPE-BSCCO film

H. Murakami, T. Kiwa, M. Tonouchi, T. Yasuda

Physica C: Superconductivity and its Applications 388-389 479 - 480 2003.5

Language：English Publisher：ELSEVIER SCIENCE BV

The terahertz (THz) imaging system applicable to bulk or thick superconductors was developed. The supercurrent distribution in Bi2Sr2CaCu2O8+δ (BSCCO) thick film in Meissner state was observed. The experimental technique and the results obtained on a liquid phase epitaxy grown (LPE-)BSCCO thick film were presented. The resistive measurement showed the critical temperature of about 75 K.

DOI： 10.1016/S0921-4534(02)02588-1