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Hiroaki Yasuda

Bio: Hiroaki Yasuda is an academic researcher from National Institute of Information and Communications Technology. The author has contributed to research in topics: Terahertz radiation & Quantum cascade laser. The author has an hindex of 8, co-authored 34 publications receiving 567 citations.

Papers
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Journal ArticleDOI
01 Oct 2007
TL;DR: The current status of developments in developments in terahertz quantum cascade lasers, quantum well photodetectors, and an example of a database for materials of fine art are reported, and results obtained from measuring atmospheric propagation are reported.
Abstract: The National Institute of Information and Communications Technology (NICT, Japan) started the Terahertz Project in April 2006. Its fundamental purpose in the next five years is to enable a nationwide technical infrastructure to be created for diverse applications of terahertz technology. The technical infrastructure includes the development of semiconductor devices such as terahertz quantum cascade lasers, terahertz-range quantum well photodetectors, and high-precision tunable continuous wave sources. It also includes pulsed terahertz measurement systems, modeling and measurement of atmospheric propagation, and the establishment of a framework to construct a materials database in the terahertz range including standardization of the measurement protocol. These are common technical infrastructure even in any terahertz systems. In this article, we report the current status of developments in these fields such as terahertz quantum cascade lasers (THz-QCLs) (with peak power of 30 mW, 3.1 THz), terahertz-range quantum well photodetectors (THz-QWPs) (tuned at 3 THz) an ultrawideband terahertz time domain spectroscopy (THz-TDS) system (with measurement range of from 0.1 to 15 THz), an example of a database for materials of fine art, and results obtained from measuring atmospheric propagation.

202 citations

Journal ArticleDOI
TL;DR: In this article, a dye-doped polystyrene microspheres with diameters ranging from 10 µm to 92 µm were examined under optical pumping with nanosecond pulses whose frequency was tuned to the absorption band of the dye.
Abstract: Lasing of dye-doped polystyrene microspheres with diameters ranging from 10 µm to 92 µm is observed. Emission from an individual sphere placed on a glass plate is examined under optical pumping with nanosecond pulses whose frequency is tuned to the absorption band of the dye. Spectral and temporal responses, and spatial profile show the characteristics of lasing with spherical cavity modes.

137 citations

Journal ArticleDOI
TL;DR: In this article, the performance of a four-level scheme terahertz quantum cascade laser (4L-QCL) with the nonequilibrium Green's function method was analyzed.
Abstract: We have calculated the performance of a recently proposed four-level scheme terahertz quantum cascade laser (4L terahertz-QCL) with the nonequilibrium Green’s function method. The calculation result for 40 K showed that the 4L QCL has a larger terahertz gain than the conventional resonant phonon QCL. This is because a large number of electrons accumulate in the upper lasing level and contribute to lasing in the new scheme. When the temperature is increased, the advantage of gain decreases due to thermally activated phonon scattering.

59 citations

Journal ArticleDOI
TL;DR: In this article, the complex refractive index of gold was measured in the terahertz frequency range using THz-TDS, which is relatively close to that obtained from Kramers-Kronig analysis of the surface resistance of gold.
Abstract: The complex refractive index of metal has significant effects on plasmon waveguide performance. We measured the complex refractive index of gold in the terahertz frequency range using terahertz time-domain spectroscopy (THz-TDS). The measured refractive index is relatively close to that obtained from Kramers–Kronig analysis of the surface resistance of gold.

58 citations

Journal ArticleDOI
TL;DR: In this paper, the authors theoretically investigated GaN-based resonant phonon terahertz-quantum cascade laser (QCL) structures for possible high-temperature operation by using the non-equilibrium Green's function method.
Abstract: We theoretically investigated GaN-based resonant phonon terahertz-quantum cascade laser (QCL) structures for possible high-temperature operation by using the non-equilibrium Green’s function method. It was found that the GaN-based THz-QCL structures do not necessarily have a gain sufficient for lasing, even though the thermal backfilling and the thermally activated phonon scattering are effectively suppressed. The main reason for this is the broadening of the subband levels caused by a very strong interaction between electrons and longitudinal optical (LO) phonons in GaN.

24 citations


Cited by
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Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Proceedings Article
01 Jan 2005
TL;DR: In quantum optical devices, microcavities can coax atoms or quantum dots to emit spontaneous photons in a desired direction or can provide an environment where dissipative mechanisms such as spontaneous emission are overcome so that quantum entanglement of radiation and matter is possible.
Abstract: Microcavity physics and design will be reviewed. Following an overview of applications in quantum optics, communications and biosensing, recent advances in ultra-high-Q research will be presented.

2,857 citations

Journal ArticleDOI
Haruma Kawaguchi1
TL;DR: In this paper, examples of the above-mentioned functional particles are reviewed and discussed, including absorbents, latex diagnostics, affinity bioseparators and drug and enzyme carriers.

891 citations

Journal ArticleDOI
TL;DR: This paper provides a comprehensive survey on VLC with an emphasis on challenges faced in indoor applications over the period 1979-2014.
Abstract: Visible Light Communication (VLC) is an emerging field in Optical Wireless Communication (OWC) which utilizes the superior modulation bandwidth of Light Emitting Diodes (LEDs) to transmit data. In modern day communication systems, the most popular frequency band is Radio Frequency (RF) mainly due to little interference and good coverage. However, the rapidly dwindling RF spectrum along with increasing wireless network traffic has substantiated the need for greater bandwidth and spectral relief. By combining illumination and communication, VLC provides ubiquitous communication while addressing the shortfalls and limitations of RF communication. This paper provides a comprehensive survey on VLC with an emphasis on challenges faced in indoor applications over the period 1979–2014. VLC is compared with infrared (IR) and RF systems and the necessity for using this beneficial technology in communication systems is justified. The advantages of LEDs compared to traditional lighting technologies are discussed and comparison is done between different types of LEDs currently available. Modulation schemes and dimming techniques for indoor VLC are discussed in detail. Methods needed to improve VLC system performance such as filtering, equalization, compensation, and beamforming are also presented. The recent progress made by various research groups in this field is discussed along with the possible applications of this technology. Finally, the limitations of VLC as well as the probable future directions are presented.

687 citations

Journal ArticleDOI
TL;DR: In this article, the progress in WGM microcavity lasers is summarized, and the laser performance considering resonator geometries and materials as well as lasing mechanisms is discussed.
Abstract: Whispering gallery mode (WGM) optical microresonators have attracted intense interests in the past decades. The combination of high quality factors (Q) and small mode volumes of modes in WGM resonators significantly enhances the light-matter interactions, making them excellent cavities for achieving low threshold and narrow linewidth lasers. In this Review, the progress in WGM microcavity lasers is summarized, and the laser performance considering resonator geometries and materials as well as lasing mechanisms is discussed. Label-free detection using WGM resonators has emerged as highly sensitive detection schemes. However, the resolution is mainly limited by the cavity Q factor which determines the mode linewidth. Microcavity lasers, due to their narrow laser spectral width, could greatly improve the detection resolution. Some recent developments in sensing using microcavity lasers are discussed.

482 citations