• Journal of the Optical Society of Korea
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• 제18권1호
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• pp.60-64
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• 2014

We report the generation of 3.3-mW single-cycle terahertz (THz) pulses at 1-kHz repetition rate via optical rectification in MgO-doped prism-cut stoichiometric LiNbO3. Efficient pulse-front tilting of 800-nm pulses was realized by an optimized single-lens focusing scheme for radially-symmetric propagation of THz beams. In this geometry, nearly-diffraction-limited THz Gaussian beams with electric field strength as high as 350 kV/cm were generated. The pump-to-THz energy conversion efficiency of $1.36{\times}10^{-3}$ and the extremely high signal-to-noise ratio of ~1:15000 achieved are among the best results for 1-kHz single-cycle terahertz pulse generation ever demonstrated in room temperature operation.

• 공학기술논문지
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• 제11권4호
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• pp.245-251
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• 2018

Terahertz waves (T-ray) was extensively studied for the NDE (nondestructive evaluation) of characterization of trailing edges for a use of turbines composed with composite materials. The used NDE system were consisted of both CW(Continuous wave) and TDS (Time domain spectroscopy). The FRP composites were utilized for two kinds of both trailing edges of wind energy (non-conducting polymeric composites) and carbon fiber composites with conducting properties. The signals of T-ray in the TDS (Time domain spectroscopy) mode resembles almost that of ultrasound waves; however, a terahertz pulse could not penetrate a material with conductivity unlike ultrasound. Also, a method was suggested to obtain the "n" in the materials, which is called the refractive index (n). The data of refractive index (n) could be solved for the trailing edges. The trailing edges were scanned for characterization and inspection. C-scan and B-scan images were obtained and best optimal NDE techniques were suggested for complicated geometry samples by terahertz radiation. Especially, it is found that the defect image of T-ray corresponded with defect locations for the trailing edges of wind mill.

• 식품기술
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• 제22권2호
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• pp.237-246
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• 2009

• 한국전자파학회논문지
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• 제21권6호
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• pp.617-626
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• 2010

본 논문에서는 광혼합 방식으로 서브 밀리미터 및 테라헤츠 대역 연속파 신호를 발생시키는 기법 중 가장 널리 사용되는 광반송파가 억제된 양측 대역 발생 방식(Double Sideband-Suppressed Carrier: DSB-SC)을 이용하여 발생된 연속파(Continuous Wave: CW) 신호의 위상 잡음 개선을 위하여 광신호의 편광과 위상 제어 기법을 제안하고 실험적으로 증명하였다. 광신호의 편광 및 위상 제어 기법은 일반적인 DSB-SC 신호와 DSB-SC 신호에 포함된 광반송파와 동일한 파장과 위상차를 가지며, 광반송파의 편광 성분 중 하나의 편광 성분만을 갖도록 편광제어된 광신호를 결합하여 광혼합하는 방법이다. 실험 및 측정 결과, 서브 밀리미터파 대역 CW 신호의 크기는 1.5 dB 증가하였으며, 위상 잡음 특성은 약 3 dB@10 kHz offset frequency 개선됨을 확인하였다. 따라서 본 논문의 결과는 광신호의 위상 및 편광 성분 제어만으로 광반송파를 효과적으로 억제하여 서브 밀리미터 및 테라헤르츠 대역 CW 신호의 특성을 개선함으로써 광혼합 방법을 이용한 밀리미터파 및 테라헤르츠파 대역 CW 신호 발생기의 저가화를 위한 기본적인 데이터로서 활용 가치가 높다.

• 센서학회지
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• 제27권5호
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• pp.328-334
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• 2018

The paper reviews an improved continuous-wave (CW) terahertz (THz) imaging system developed for nondestructive inspection, such as CW-THz quasi-time-domain spectroscopy (QTDS) and interferometry. First, a comparison between CW and pulsed THz imaging systems is reported. The CW-THz imaging system is a simple, fast, compact, and relatively low-cost system. However, it only provides intensity data, without depth and frequency- or time-domain information. The pulsed THz imaging system yields a broader range of information, but it is expensive because of the femtosecond laser. Recently, to overcome the drawbacks of CW-THz imaging systems, many studies have been conducted, including a study on the QTDS system. In this system, an optical delay line is added to the optical arm leading to the detector. Another system studied is a CW-THz interferometric imaging system, which combines the CW-THz imaging system and far-infrared interferometer system. These systems commonly obtain depth information despite the CW-THz system. Reportedly, these systems can be successfully applied to fields where pulsed THz is used. Lastly, the applicability of these systems for nondestructive inspection was confirmed.

• 한국광학회지
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• 제25권5호
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• pp.279-285
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• 2014

본 논문에서는 온도 변화에 따라 절연체-금속 상전이 특성을 보이는 이산화바나듐($VO_2$)과 메타물질을 이용하여 전기적으로 제어 가능한 테라헤르츠 변조기를 제시하였다. 변조기 기능을 하는 메타물질 구조가 $VO_2$의 도전율 변화에 영향을 주는 열을 전기적으로 조절할 수 있는 히터의 역할도 동시에 할 수 있는 정사각고리 구조의 메타물질을 설계하였다. 설계한 $VO_2$기반 메타물질 변조기의 전파 투과량은 정사각고리 메타물질에 직접 연결된 전압 인가용 도선을 통한 인가 전압 변화로 조절이 가능하다. $VO_2$의 도전율 변화에 따라 전파 투과계수는 470 GHz 에서 0.27에서 0.80으로 안정적으로 조절되었고, 13% 주파수 대역폭에서 투과계수 변화폭이 일정하게 유지되었다.

• Current Optics and Photonics
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• 제6권3호
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• pp.337-343
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• 2022

Microfluidic chips are new devices that can manipulate liquids at the micrometer level, and terahertz (THz) time-domain spectroscopy has good applicability in biochemical detection. The combination of these two technologies can shorten the distance between sample and THz wave, reduce THz wave absorption by water, and more effectively analyze the kinetics of biochemical reactions in aqueous solutions. This study investigates the effects of different external magnetic field intensities on the THz transmission characteristics of deionized water, CuSO₄, CuCl₂, (CH₃COO)₂Cu, Na₂SO₄, NaCl, and CH₃COONa; the THz spectral intensity of the sample solutions decrease with increasing intensity of the applied magnetic field. Analysis shows that the magnetic field leads to a change in the dipole moment of water molecules in water and electrolyte solutions, which enhances not only the hydrogen-bond networking ability of water but also the hydration around ions in electrolyte solutions, increasing the number of hydrogen bonds. Increasing the intensity of this magnetic field further promotes the hydrogen-bond association between water molecules, weakening the THz transmission intensity of the solution.

• Journal of electromagnetic engineering and science
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• 제17권4호
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• pp.202-207
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• 2017

This paper presents the performance of a planar, low-profile, and wide-gain-bandwidth leaky-wave slit antenna in different thickness values of high-permittivity gallium arsenide substrates at terahertz frequencies. The proposed antenna designs consisted of a periodic array of $5{\times}5$ metallic square patches and a planar feeding structure. The patch array was printed on the top side of the substrate, and the feeding structure, which is an open-ended leaky-wave slot line, was etched on the bottom side of the substrate. The antenna performed as a Fabry-Perot cavity antenna at high thickness levels ($H=160{\mu}m$ and $H=80{\mu}m$), thus exhibiting high gain but a narrow gain bandwidth. At low thickness levels ($H=40{\mu}m$ and $H=20{\mu}m$), it performed as a metasurface antenna and showed wide-gain-bandwidth characteristics with a low gain value. Aside from the advantage of achieving useful characteristics for different antennas by just changing the substrate thickness, the proposed antenna design exhibited a low profile, easy integration into circuit boards, and excellent low-cost mass production suitability.

• 전자통신동향분석
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• 제37권2호
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• pp.11-20
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• 2022

Terahertz electromagnetic waves are considered the waves for the next generation of security checking technology. They can penetrate opaque materials, such as plastics, fibers, papers, and leathers. In addition, they are harmless to humans they cannot penetrate human skins. Moreover, because their frequencies are higher than those of millimeter waves, higher resolution and more detailed information is expected than the millimeter wave-based technologies In this study, we describe the trends and prospectives of terahertz technology as security checking technology that can be directly applied to a human body.

• 한국광학회지
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• 제13권5호
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• pp.430-434
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• 2002

$12{\mu}{\textrm}{m}$ 길이, $5{\mu}{\textrm}{m}$ gap의 dipole 안테나에 입사되는 펨토초 레이저의 위치에 따른 테라헤르트 전자기 펄스의 크기를 관찰하였다. 비록 11volt의 작은 전압을 인가 시켰음에도 불구하고 테라헤르츠 전자기 펄스가 최대 4.7nA의 전류로 발생되었는데 이는 dipole 안테나 구조가 아닌 두 전송라인(transmission line)의 간격이 $300{\mu}{\textrm}{m}$ 떨어진 구조의 송신기(transmitter chip)에 비해 6배 작은 전압을 인가하여 3.4배 더 큰 전류가 발생됨을 알 수 있었다. 또한 팸토초 레이저로 여기 되는 dipole 안테나 구조의 송신기에 구형 교류전압을 최소 0.11volt에서 최대 10volt까지 변화시켜 테라헤르트 전자기 펄스의 최대값 크기에 따른 이진신호를 발생시켰다.