다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Over the past three decades a new spectroscopic technique with unique possibilities has emerged. Based on coherent and time-resolved detection of the electric field of ultrashort radiation bursts in the far-infrared, this technique has become known as terahertz time-domain spectroscopy (THz-TDS). In this review article the authors describe the technique in its various implementations for static and time-resolved spectroscopy, and illustrate the performance of the technique with recent examples from solid-state physics and physical chemistry as well as aqueous chemistry. Examples from other fields of research, where THz spectroscopic techniques have proven to be useful research tools, and the potential for industrial applications of THz spectroscopic and imaging techniques are discussed.

Terahertz spectroscopy and imaging – Modern techniques and applications

Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

https://iopscience.iop.org/article/10.1088/1361-6463/50/4/043001/pdf

The 2017 terahertz science and technology roadmap

This paper introduces a novel method that allows fast and reliable extraction of material parameters in terahertz time-domain spectroscopy. This method could be applied for most materials and requires neither simplifying assumptions nor samples of different thickness for the extraction. The presented extraction procedure operates either on truncated terahertz signals when temporal windowing is possible, or on full ones otherwise. Some experimental examples covering all practical cases are given. In particular, the extraction procedure treats the tedious case of samples for which internal reflections of the terahertz pulse slightly overlap.

A reliable method for extraction of material parameters in terahertz time-domain spectroscopy

Time-domain spectroscopy allows fast and broadband measurement of the optical constants of materials in the terahertz domain. We present a method that improves the determination of the optical constants through simultaneous determination of the sample thickness. This method could be applied to any material with moderate absorption and requires only two measurements of the temporal profile of the terahertz pulses: a reference one without the sample and one transmitted through the sample.

Highly precise determination of optical constants and sample thickness in terahertz time-domain spectroscopy

From classical charge transport equations and dipole radiation equations, we derive a simple analytical model for the signal detected in terahertz time-domain spectroscopy using photoconducting antennas. The validity of our model is checked by comparison to published calculated results and to experimental data we have measured. This expression depends mostly on the carrier lifetime in the antennas' semiconductor material and on the laser pulse duration. The analytical form of the detected terahertz (THz) signal allows us to separate the contribution of the different experimental parameters. Together with a detailed noise analysis in THz time-domain spectroscopy, we optimize the parameter values in order to achieve the largest dynamics of measurement.

Analytical modeling and optimization of terahertz time-domain spectroscopy experiments, using photoswitches as antennas

We analyze the contributions of various error sources to uncertainty in the far-infrared optical constants (refractive index and absorption coefficient) measured by terahertz (THz) time-domain spectroscopy We focus our study on the influence of noise This noise study is made with a thick slab of transparent material for which the THz transmitted signal exhibits temporal echoes owing to reflections in the sample Extracting data from each of these time-windowed echoes allows us to characterize the noise sources In THz time-domain spectroscopy experiments in which photoswitches are used as antennae, the transmitting antenna constitutes the principal noise source The uncertainty in the far-infrared optical constants can be strongly reduced when the extraction is performed with THz echoes that have encountered many reflections in the sample

Influence of noise on the characterization of materials by terahertz time-domain spectroscopy

A high-quality smart filter for terahertz range with relative tunability reaching 20% has been demonstrated. The filter is based on a narrow transmission band, which originates from a defect mode that appears due to insertion of a single crystal of KTaO3 into otherwise periodic one-dimensional photonic crystal. Frequencies of defect modes are controlled by the refractive index of the defect: their high tunability is achieved by the strong temperature dependence of the dielectric properties of KTaO3. The low losses of KTaO3 lead to a high peak transmission of the filter. Influence of the defect losses on the properties of the filter is also discussed.

Frédéric Garet

Papers

A reliable method for extraction of material parameters in terahertz time-domain spectroscopy

Highly precise determination of optical constants and sample thickness in terahertz time-domain spectroscopy

Analytical modeling and optimization of terahertz time-domain spectroscopy experiments, using photoswitches as antennas

Influence of noise on the characterization of materials by terahertz time-domain spectroscopy

Thermally tunable filter for terahertz range based on a one-dimensional photonic crystal with a defect