Takanari Kashiwagi

Geometrical resonance conditions for THz radiation from the intrinsic Josephson junctions in Bi(2)Sr(2)CaCu(2)O(8+δ).

Subterahertz radiation emitted from a variety of short rectangular-, square-, and disk-shaped mesas of intrinsic Josephson junctions fabricated from a Bi(2)Sr(2)CaCu(2)O(8+δ) single crystal was studied from the observed I-V characteristics, far-infrared spectra, and spatial radiation patterns. In all cases, the radiation frequency satisfies the conditions both for the ac Josephson effect and for a mesa cavity resonance mode. The integer higher harmonics observed in all spectra imply that the ac Josephson effect plays the dominant role in the novel dual-source radiation mechanism.

Broadly tunable subterahertz emission from internal branches of the current-voltage characteristics of superconducting Bi2Sr2CaCu2O(8+δ) single crystals.

Continuous, coherent subterahertz radiation arises when a dc voltage is applied across a stack of the many intrinsic Josephson junctions in a Bi2Sr2CaCu2O(8+δ) single crystal. The active junctions produce an equal number of I-V characteristic branches. Each branch radiates at a slightly tunable frequency obeying the Josephson relation. The overall output is broadly tunable and nearly independent of heating effects and internal cavity frequencies. Amplification by a surrounding external cavity to allow for the development of a useful high-power source is proposed.

Evidence for a Dual-Source Mechanism of Terahertz Radiation from Rectangular Mesas of Single Crystalline Bi2Sr2CaCu2O8+δ Intrinsic Josephson Junctions

The THz radiation emitted from rectangular mesas of single-crystal Bi 2 Sr 2 CaCu 2 O 8+δ was studied using angular distribution measurements and Fourier transform infrared spectroscopy. Unlike the recent theoretical predictions, the results provide strong evidence for a dual-source mechanism in which the uniform and non-uniform parts of the ac-Josephson current act as electric and magnetic current sources, respectively. The latter synchronizes with cavity modes of the mesa with integral harmonics of the fundamental radiation.

High Temperature Superconductor Terahertz Emitters: Fundamental Physics and Its Applications

Coherent and continuous radiation sources of the electromagnetic (EM) waves at terahertz (1 THz = 1012 c/s) frequencies using a mesa structure fabricated from high temperature superconducting Bi2Sr2CaCu2O8+? single crystals are described with a special emphasis on the physics of the radiation mechanism and the applications. After the intensive studies of many mesas fabricated with different conditions, it is revealed that the ac-Josephson effect works as a primary driving mechanism of the radiation and the cavity resonance needed for stronger radiation plays an additional role to the mechanism, although both are working together while radiating. A prototype of the imaging machine for multipurpose uses has successfully been developed.

Continuous 30 μW terahertz source by a high-Tc superconductor mesa structure

Using a modified mesa structure of high-Tc superconducting Bi2Sr2CaCu2O8+δ with a thin underlaying base superconductor (∼3 μm), the effective working temperature of the continuous and monochromatic terahertz emitter is extended up to 70 K, and the maximum power of ∼30 μW at 0.44 THz is achieved at the relatively high temperature of Tb = 55 K in a low bias current retrapping region. The diverging behavior of the intensity occurring at 55 K in the low current regime without hot spot formation may provide us an important clue for the stronger THz radiation from intrinsic Josephson junction devices.

Terahertz imaging system using high-Tc superconducting oscillation devices

Microwatt power oscillation devices at sub-terahertz frequency region between 0.3 and 1.0 terahertz (THz) were fabricated from high-Tc superconducting single crystalline Bi2Sr2CaCu2O8+δ and used as a source of the transmission terahertz imaging system. As test examples, terahertz images of coins and a razor blade placed inside the brownish paper envelopes with the spatial resolution of 1 mm are presented. The signal-to-noise ratio exceeds 130 in these images. Using a simple wedge-shaped interferometer and analysing the interference fringe pattern, the wavelength of the terahertz wave is calibrated within 0.1% accuracy. This interferometer also provides a simple method to measure the absorption coefficient of the liquid sample. Two test measurements for distilled water and ethanol are demonstrated and their absorption coefficients are obtained with 99.2% accuracy. This suggests that our terahertz imaging system can be applied to many practical applications, such as biological and biomedical imaging, enviro...

Local SiC photoluminescence evidence of hot spot formation and sub-THz coherent emission from a rectangular Bi2Sr2CaCu2O8+δ mesa

From the photoluminescence of SiC microcrystals uniformly covering a rectangular mesa of the high transition temperature

High-power terahertz electromagnetic wave emission from high-Tc superconducting Bi2Sr2CaCu2O8+δ mesa structures

{T}_{c}

Generation of electromagnetic waves from 0.3 to 1.6 terahertz with a high- Tc superconducting Bi2Sr2CaCu2O8+δ intrinsic Josephson junction emitter

superconductor

Geometrical Full-Wavelength Resonance Mode Generating Terahertz Waves from a Single-Crystalline Bi2Sr2CaCu2O8+\delta Rectangular Mesa

{\text{Bi}}_{2}{\text{Sr}}_{2}{\text{CaCu}}_{2}{\text{O}}_{8+\ensuremath{\delta}}