• 한국광학회지
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• 제21권1호
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• pp.33-37
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• 2010

본 연구에서는 전도성이 매우 높은 탄소나노튜브 박막을 제작하고 테라파 영역에서의 광학상수를 측정하였다. 탄소나노튜브박막은 스핀코팅법 또는 진공여과법을 이용하여 연성플라스틱 기판 위에 증착되었다. 테라파 영역의 전자파 투과율은 박막의 두께조절을 통해 가능하며, 산처리 등의 후속공정을 통해서도 조절이 가능하다. 시분해 테라파 투과파의 진폭과 위상 측정을 통해유전상수를 포함한 광학상수의 스펙트럼을 측정하였다. 이를 통해 탄소나노튜브 박막이 Drude 자유전자 모델에 잘 부합하며, 높은 플라즈마 진동수를 가지는 등, 우수한 금속의 특성을 가지고 있음이 밝혀졌다. 또한 산처리 전후 유전상수가 변화하는 것을 직접확인할 수 있었다. 마지막으로 셀룰로즈 멤브레인에 증착된 CNT 필름의 경우엔 기판의 효과가 제거된 광학계수 측정이 가능함을 보여준다.

• Current Optics and Photonics
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• 제7권2호
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• pp.119-126
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• 2023

The vibratory and rotational levels of many biological macromolecules lie in the terahertz (THz) band, which means that THz techniques can be used to identify and detect them. Moreover, since the biological activity of most biomolecules only becomes apparent in aqueous solution, we use microfluidic technology to study the biological properties of these biomolecules. THz time-domain spectroscopy was used to study the THz absorption characteristics of graphene oxide (GO) aqueous solution at different concentrations and different exposure times in fixed electric or magnetic fields. The results show that the spectral characteristics of the GO solution varied with the concentration: as the concentration increased, the THz absorption decreased. The results also show that after placing the solution in an external electric field, the absorption of THz first increased and then decreased. When the solution was placed in a magnetic field, the THz absorption increased with the increase in standing time. In this paper, these results are explained based on considerations of what is occurring at the molecular scale. The results of this study provide technical support for the further study of GO and will assist with its improved application in various fields.

• Composites Research
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• 제34권3호
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• pp.143-147
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• 2021

유리섬유 복합재료(GFRP) 내부 미세 박리에서 나타나는 테라헤르츠(THz) 중첩 신호의 FWHM 분석을 통한 미세 박리 검출 기술을 연구하였다. 테라헤르츠 시간영역 분광(THz-TDS) 시스템의 반사모드를 통해 유리섬유 복합재료 내부의 미세 박리 크기 별 THz 신호를 측정하였고, 미세 박리 위치에서 반사되어 검출되는 THz 중첩 신호의 Full Width Half Maximum (FWHM) 값을 추출하였다. 이후, 유리섬유 복합재료의 복소굴절률을 측정하여 미세 박리 크기에 따른 미세 박리 위치에서의 THz 중첩 신호 및 FWHM 값을 계산하여 비교하였다. 이론적으로 계산된 THz 중첩 신호로부터 미세 박리 크기와 중첩 신호에서의 FWHM 값의 상관관계를 도출하였으며, 미세 박리 위치에서의 THz 신호로부터 추출된 FWHM의 분석을 통해 미세 박리 크기를 예측할 수 있었다.

• Journal of the Optical Society of Korea
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• 제15권2호
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• pp.155-160
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• 2011

Lymph node metastasis is an important prognostic factor in cervical cancer patients. We report THz imaging for detecting micro-metastatic foci in the lymph nodes of early-stage uterine cervical cancer patients. Five paraffin-embedded metastatic lymph nodes from two cervical cancer patients were imaged using a THz time-domain spectroscopy system in the reflection mode. The size and shape of the tumor regions were compared with those from histopathologic examinations. The metastatic portions of lymph nodes as small as 3 mm were well delineated by THz imaging. The reflected peak amplitudes were lower in metastatic portions than in the normal portions of lymph nodes, and the difference in their peak-to-peak amplitudes was ~5%.

• Current Optics and Photonics
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• 제5권1호
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• pp.66-71
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• 2021

The resonance characteristics of H-shaped metamaterials, whose widths were varied while keeping the height constant, were investigated in the terahertz (THz) frequency range. The H-shaped metamaterials were numerically analyzed in two modes in which the polarization of the incident THz electric field was either parallel or perpendicular to the width of the H-shaped structure. The resonant frequency of the metamaterial changed stably in each mode, even if only the width of the H shape was changed. The resonant frequency of the metamaterial operating in the two modes increases without significant difference regardless of the polarization of the incident electromagnetic wave as the width of the H-shaped metamaterial increases. The electric field distribution and the surface current density induced in the metamaterial in the two modes were numerically analyzed by varying the structure ratio of the metamaterial. The numerical analysis clearly revealed the cause of the change in the resonance characteristics as the width of the H-shaped metamaterial changed. The efficacy of the numerical analysis was verified experimentally using the THz-TDS (time-domain spectroscopy) system. The experimental results are consistent with the simulations, clearly demonstrating the meaningfulness of the numerical analysis of the metamaterial. The analyzed resonance properties of the H-shaped metamaterial in the THz frequency range can be applied for designing THz-tunable metamaterials and improving the sensitivity of THz sensors.

• 한국광학회지
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• 제19권6호
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• pp.435-438
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• 2008

중수($D_2O$, 산화중수소)는 수소원자(H)보다 중성자 한 개가 더 많은 수소원자 동위원소(D)로 이루어진 물이다. 중수는 자연 상태의 물 가운데 5만분의 1정도 존재하며 경수($H_2O$)와 매우 비슷한 성질을 가지고 있으나 경수보다 11%정도 무겁고, 특이점은 235 K로 228 K인 경수와 약간의 차이를 가진다. 중수는 중성자를 흡수하여 원자로의 중성자 감속재로 쓰이고 최근 중수 농도에 따라 세포에 미치는 독성효과가 다르게 나타나는 현상이 발견 되어 암 치료에 사용하려는 연구가 진행되고 있다. 우리는 테라헤르츠 시간축 분광학을 이용하여 경수와 중수 혼합물의 농도별 굴절률과 흡수율 변화를 거대 분자간 결합에너지 영역을 포함하는 테라헤르츠 영역 ($0{\sim}2.5\;THz$)에서 측정하여 중수의 비율이 높을수록 굴절률은 감소하고 흡수율 또한 감소하는 결과를 얻었다.

• Current Optics and Photonics
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• 제3권6호
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• pp.566-570
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• 2019

To investigate dependence of the sensitivity of THz metamaterials on the position of target dielectric materials, we functionalized the metamaterial gap with an adhesive polymer. A shift in resonance frequency occurs when polystyrene microbeads are deposited in the gap of the metamaterial's metal resonator pattern, while little change is observed when they are deposited on other areas of the metasurface. A two-dimensional mapping of the sensitivity, with a grid size of 1 ㎛, is obtained from a finite-difference time-domain simulation: The frequency shift is displayed as a function of the position of a target dielectric cube. The resulting sensitivity distribution clearly reveals the crucial role of the gap in sensing with metamaterials, which is consistent with the electric field distribution near the gap.

• Current Optics and Photonics
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• 제1권6호
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• pp.637-641
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• 2017

We present dielectric constant measurements of thin films using THz metamaterials fabricated on a quartz substrate. The resonance shifts of the metamaterials exhibit saturation behavior with increasing film thickness. The saturation frequency shift varies with the real part of the dielectric constant, from which the numerical expression for the particular metamaterial design was extracted. We first performed finite-difference time-domain simulations to find an explicit relationship between the saturated frequency shift and the dielectric constant of a thin film, which was confirmed by the experimental results from conventional techniques. In particular, the quartz substrate enables us to determine their values more accurately, because of its low substrate index. As a result, we extracted the dielectric constants of various films whose values have not been addressed previously without precise control of the film thickness.

• Current Optics and Photonics
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• 제2권4호
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• pp.378-382
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• 2018

In most previous investigations of plasmonic and metamaterial applications, the metallic film has been regarded as a perfect electrical conductor. Here we demonstrate the resonance characteristics of THz metamaterials fabricated from metal film that has a finite dielectric constant, using finite-difference time-domain simulations. We found strong redshift and spectral broadening of the resonance as we decrease the metal's plasma frequency in the Drude free-electron model. The frequency shift can be attributed to the effective thinning of the metal film, originating from the increase in penetration depth as the plasma frequency decreases. On the contrary, only peak broadening occurs with an increase in the scattering rate. The metal-thickness dependence confirms that the redshift and spectral broadening occur when the effective metal thickness drops below the skin-depth limit. The electromagnetic field distribution illustrates the reduced field enhancement and reduced funneling effects near the gap area in the case of low plasma frequency, which is associated with reduced charge density in the metal film.

• 전기학회논문지
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• 제61권12호
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• pp.1939-1943
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• 2012

In this paper we presented the detection of the explosive material RDX using a parallel plate waveguide (PPWG) THz time domain spectroscopy (TDS). Normally the explosive materials have been characterized through identification of vibrational fingerprint spectra. Until now, most of all THz spectroscopic measurements have been made using pellet samples where disorder effects contribute to line broadening such that individual resonances merge into relatively broad absorption features. In order to avoid such disadvantages we used the technique of PPWG THz-TDS to achieve sensitive characterization of explosive material RDX. The PPWG THz-TDS used in this work well established ultrafast optoelectronic techniques to generate and detect sub-picosecond THz pulses. The explosive material was analyzed as powder layers in $112{\mu}m$ gap of metal PPWG. The thin later mass was estimated to be about $700{\mu}g$. Finally, we showed spectra of explosives from 0.2 to 2.4 THz measured using PPWG THz-TDS.