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Terahertz Electrodynamics and Superconducting Energy Gap of NbN
심경익,조영찬,한태우,김종현,김재훈,Hirotake Yamamori 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.71 No.9
We have measured the transmission spectra of the conventional Bardeen-Cooper-Schrieffer (BCS) superconductor niobium nitride (NbN) thin films (Tc = 11 K) using terahertz time-domain spectroscopy (THz-TDS) over the spectral range of 10 - 110 cm−1 and the temperature range of 3.9 - 295 K. We extracted both the real part, 1, and the imaginary part, 2, of the optical conductivity, ˜ = 1 + i2, independently and simultaneously, without a Kramers-Kronig analysis. The superconducting gap (T) was observed in the real part of the conductivity, 1, below Tc = 11 K with a maximum value of 2(0) = 30 cm−1 and the gap ratio 2(0)/kBTc = 3.92.
한태우,이호원,심경익,김종현,조영찬,김재훈,백나연,강대일,이한형 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.9
We have established optimal methods for terahertz time-domain spectroscopic analysis of highly absorbing pigments in powder form based on our investigation of representative traditional Chinese pigments, such as azurite [blue-based color pigment], Chinese vermilion [red-based color pigment], and arsenic yellow [yellow-based color pigment]. To accurately extract the optical constants in the terahertz region of 0.1 - 3 THz, we carried out transmission measurements in such a way that intense absorption peaks did not completely suppress the transmission level. This required preparation of pellet samples with optimized thicknesses and material densities. In some cases, mixing the pigments with polyethylene powder was required to minimize absorption due to certain peak features. The resulting distortion-free terahertz spectra of the investigated set of pigment species exhibited well-defined unique spectral fingerprints. Our study will be useful to future efforts to establish non-destructive analysis methods of traditional pigments, to construct their spectral databases, and to apply these tools to restoration of cultural heritage materials.
Terahertz Time-domain and Fourier-transform Infrared Spectroscopy of Traditional Korean Pigments
홍태윤,최규진,하태우,박병철,심경익,김종현,김재훈,권지은,이상현,강대일,이한형 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.5
indigo [jjok], azurite [seokcheong], malachite [seokrok], and red lead [yeondan]) have been studiedwith terahertz time-domain spectroscopy (THz-TDS) and Fourier-transform infrared spectroscopy(FTIRS) over the spectral region of 0.1 − 7.5 THz. Both the refractive index n and the extinctioncoefficient k were simultaneously and independently determined in the terahertz region withouta Kramers-Kronig analysis while the absoprtion coefficient spectra were acquired in the infraredregion. All pigments studied in the present work exhibited a set of characteristic absorption peaksunique to the pigment species in addition to a background that increased with increasing frequency. Our study demonstrates that terahertz and infrared techniques can be useful identification anddiagnostic tools for the traditional Korean pigments used in heritage buildings and artworks.
백나연,강대일,하태우,심경익,이호원,김재훈,이한형 한국문화재보존과학회 2016 보존과학회지 Vol.32 No.2
회화문화재의 손상상태를 진단하기 위하여 현재까지 국내에서는 육안관찰, 적외선 촬영, X선 촬영 등이 활용되고 있으나 표면에서 확인되지 않는 하부층의 손상상태에 대한 3차원적 정보획득에는 한계점이 있었다. 본 연구에서는 최근 우리나라에서 문화재 분야에 막 응용되기 시작한 테라헤르츠 분광분석기술을 회화문화재 상태진단에 적용하는 연구를 수행하였다. 먼저 우리나라 회화문화재의 손상양상을 고려한 의사시편을 제작하고 테라헤르츠 반사펄스 이미징기술을 적용하여 채색층 하부의 바탕층 및 배접층의 손상에 대한 정보 획득을 시도하였다. 그 결과 바탕층과 배접층의 균열, 층위 간 이격, 이격의 범위와 정도에 대한 정보획득이 가능함을 확인할 수 있었다. 또한 의사시편에서 얻어진 결과를 바탕으로 실제 회화문화재인 보물 제1792호 남양주 봉선사 비로자나삼신괘불도에 대하여 테라헤르츠 이미징기술을 적용한 결과, 유물의 3차원적 손상 형태와 손상 정도에 대한 정보를 획득할 수 있었다. 이는 비파괴, 비접촉식의 테라헤르츠 이미징기술이 우리나라 회화문화재의 3차원 손상상태 진단에 활용될 수 있음을 확인시켜 주는 결과이다. Conventional imaging techniques such as ultraviolet, infrared, and X-ray are used mainly to diagnose the damaged parts of the painted cultural assets in Korea. These techniques, however, have limits in diagnosing damages of interlayer parts. We have performed and extensive study on the applicability of Terahertz(THz) analysis technique, introduced recently to this field of study on cultural properties in Korea, to diagnose painted cultural assets. The specimens, produced to imitate the damage types of Korean painted properties, were analyzed over their painting, supporting, and backing layers by terahertz pulse imaging technique. The analyzed results provided information about the cracks, the separated areas, and the separated distances between layers on the specimens. Our research, then, was extended to real painted cultural remains, Birojana Sam-shin Gwebul-do at Bongseon Temple in Namyang-ju, Korea National Treasure Number 1792, through which we have obtained 3D information about the extent and pattern of damages to the asset. These results demonstrate that terahertz 3D imaging technique has the capability of noncontact 3D diagnosis on painted cultural properties.