• Title/Summary/Keyword: Femtosecond laser

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Laser-based THz Time-Domain Spectroscopy and Imaging Technology (레이저 기반 테라헤르츠 시간영역 분광 및 영상 기술)

  • Kang, Kwang-Yong;Kwon, Bong-Joon;Paek, Mun Cheol;Kang, Kyeong Kon;Cho, Suyoung;Kim, Jangsun;Lee, Senung-Churl;Lee, Dae-sung
    • Journal of Sensor Science and Technology
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    • v.27 no.5
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    • pp.317-327
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    • 2018
  • Terahertz (THz) time-domain spectroscopy(TDS), imaging techniques, and related systems have become mature technologies, widely used in many universities and research laboratories. However, the development of creative technologies still requires improved THz application systems. A few key points are discussed, including the innovative advances of mode-locking energy-emitting semiconductor lasers and better photoconductive semiconductor quantum structures. To realize a compact, low cost, and high performance THz system, it is essential that THz spectroscopy and imaging technologies are better characterized by semiconductor and nano-devices, both static and time-resolved. We introduce the THz spectroscopy and imaging systems, the OSCAT(Optical Sampling by laser CAvity Tuning) system and the ASOPS(ASynchronous Optical Sampling) system, are constructed by our research team. We report on the THz images obtained from their use.

Terahertz Time Domain Spectroscopy, T-Ray Imaging and Wireless Data Transfer Technologies

  • Paek, Mun-Cheol;Kwak, Min-Hwan;Kang, Seung-Beom;Kim, Sung-Il;Ryu, Han-Cheol;Choi, Sang-Kuk;Jeong, Se-Young;Kang, Dae-Won;Jun, Dong-Suk;Kang, Kwang-Yong
    • Journal of electromagnetic engineering and science
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    • v.10 no.3
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    • pp.158-165
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    • 2010
  • This study reviewed terahertz technologies of time domain spectroscopy, T-ray imaging, and high rate wireless data transfer. The main topics of the terahertz research area were investigation of materials and package modules for terahertz wave generation and detection, and setup of the terahertz system for time domain spectroscopy(TDS), T-ray imaging and sub-THz wireless communication. In addition to Poly-GaAs film as a photoconductive switching antenna material, a table-top scale for the THz-TDS/imaging system and terahertz continuous wave(CW) generation systems for sub-THz data transfer and narrow band T-ray imaging were designed. Dielectric properties of ferroelectric BSTO($Ba_xSr_{1-x}TiO_3$) films and chalcogenide glass systems were characterized with the THz-TDS system at the THz frequency range. Package modules for terahertz wave transmitter/receiver(Tx/Rx) photoconductive antenna were developed.

Terahertz Detection Characteristics of Low-Temperature Grown InGaAs/InAlAs Multi Quantum Well

  • Park, Dong-U;Han, Im-Sik;Kim, Chang-Su;No, Sam-Gyu;Ji, Yeong-Bin;Tae, In;Lee, Gi-Ju;Kim, Jin-Su;Kim, Jong-Su
    • Proceedings of the Korean Vacuum Society Conference
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    • 2013.02a
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    • pp.317-318
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    • 2013
  • Terahertz (THz) wave는 광학 영역과 방송파 영역 사이에 광대역 주파수 스펙트럼을 차지하고 있다. X선과는 달리 비이온화 광원으로 직진성, 투과성, 낮은 에너지 (meV)를 가지고 있어 비파괴적이고 무해한 장점을 지니고 있다. 본 연구에서는 In0.53Ga0.47As:Be/In0.52Al0.48As의 multi quantum well (MQW)을 Semi-insulting InP:Fe substrate 위에 active layer의 두께와 적층을 변화주어서 성장하였고Au (200 nm)/Ti (30 nm)의 금속전극으로 공정을 하였다. Ti:Sapphire femtosecond pulse laser를 조사하여 THz time-domain spectrometer 시스템을 이용하여 광전도검출법으로 THz 검출 특성을 연구하였다. THz 검출은 짧은 전하수명과 높은 저항을 요구한다. LTInGaAs의 경우 AsGa antisite로 인하여 짧은 전하수명을 얻게 되면 n-type의 높은 전하밀도를 가지게 되어서 저항이 낮아지게 된다. 높은 저항을 만들기 위하여 Be doping을 이용하여 과잉의 전자들을 보상하고 InAlAs layer를 삽입시켜 보다 높은 저항을 얻었다. LT-InGaAs:Be는 LT-GaAs보다 1/70 정도의 amplitude를 보이는데 LT-InGaAs/InAlAs MQW의 경우 LT-GaAs 대비 약 3/4 정도의 큰 amplitude를 얻었다. 또 active layer의 두께가 얇고 적층이 많을수록 신호가 커지는 것을 알 수 있었다. 이는 상대적으로 band gap이 큰 InAlAs층이 더 높은 저항을 만든 것으로 사료된다.

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Supercontinuum Generation with Femtosecond Pulses and Photonic Crystal Fibers (펨토초 펄스와 광결정 광섬유를 이용한 초 연속스펙트럼의 발생)

  • Choi, Hyoung-Gye;Kim, So-An;Kee, Chul-Sik;Sung, Jae-Hee;Yu, Tae-Jun;Ko, Do-Kyeong;Lee, Jong-Min
    • Korean Journal of Optics and Photonics
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    • v.18 no.5
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    • pp.345-350
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    • 2007
  • The characteristics of the supercontinuum generated in photonic crystal fibers were investigated by using the generalized nonlinear $Schr\"{o}dinger$ equation and the split-step Fourier method. Based on the simulated results, we generated the supercontinuum spectrum with the flatness of ${\pm}4dB$ in the wavelength range of 650 to 900 nm by employing a 200-fs pulse of Ti:sapphire laser and a commercial photonic crystal fiber.

Fabrication of Microstructures Using Double Contour Scanning (DCS) Method by Two-Photon Polymerization (이광자 광중합의 윤곽선 스캐닝법에 의한 마이크로 입체형상 제작)

  • Park Sang Hu;Lim Tae Woo;Lee Sang Ho;Yang Dong-Yol;Kong Hong Jin;Lee Kwang-Sup
    • Polymer(Korea)
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    • v.29 no.2
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    • pp.146-150
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    • 2005
  • A nano-stereolithouaphy (NSL) apparatus has been developed for fabrication of microstructures with the resolution of 150 nanometers. In the NSL process, a complicated 3D structure can be fabricated by building layer by layer, so it does not require any sacrificial layer or any supporting structure. A laminated layer was fabricated by means of solidifying liquid-state monomers using two-photon absorption (TPA) which was induced by a femtosecond laser. When the fabrication of a 3D laminated structure was finished, unsolidified liquid-stage resins were removed to develop the fabricated structure by dropping several droplets of solvent, then the polymerized structure was only left on the glass substrate. A microstructure is fabricated by vector scanning method to save the fabrication time. The shell thickness of a structure is very thin within 200 nm, when it is fabricated by a single contour scanning (SCS) path. So, a fabricated structure can be deformed easily in the developing process. In this work, a double contour scanning (DCS) method was proposed to reinforce the strength of a shell typed structure, and a microcup was fabricated to show the usefulness of the developed NSL system and the DCS method.

Revealing the Spatial Distribution of Inorganic Elements in Rice Grains

  • Jeon, Ji Suk;Choi, Sung Hwa;Lee, Ji Yeon;Kim, Ji A;Yang, Young Mi;Song, Eun Ji;Kim, Jae Sung;Yang, Jung Seok;Kim, Kyong Su;Yoo, Jong Hyun;Kim, Hai Dong;Park, Kyung Su
    • Bulletin of the Korean Chemical Society
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    • v.35 no.11
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    • pp.3289-3293
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    • 2014
  • Femtosecond laser ablation (fs LA) was used in this study to identify pollution by heavy metals and the distribution of elemental nutrients at different rice milling ratios. Polished rice (degrees of milling of 3, 5, 7, 9, and 11) was collected from major Korean supermarkets and one sample thereof was selected. An internal quality control experiment was conducted using a rice flour certified reference material from the Korea Research Institute of Standards and Science (KRISS CRM) for the evaluation of the efficacy. To assess the effectiveness of the analysis method, the reliability was validated using a food analysis performance assessment scheme (FAPAS), with chili powder serving as an external quality control. The results of the analysis of the inorganic elements Ti, Ca, Al, Fe and Mn in white and brown rice with degrees of milling of 3, 5, 7, 9 and 11 using ICP-MS, ICP-OES and AAS revealed contents of 0.40, 49.2, 2.43, 5.36 and 10.3 mg/kg in white rice and 0.59, 78.0, 7.52, 11.0 and 18.5 mg/kg in brown rice, respectively. Among the elements, there were remarkable differences in the measured contents. By comparing the contents of the elements at different degrees of milling, Ti, Co, As, Ca, Al, Cu, Fe, and Mn were determined to be distributed on the surface of the rice grains, whereas the contents of Cd and Pb increased toward the center of the rice grains, and Si was evenly distributed. After the quantitative analysis of rice samples polished to different degrees of milling, Ca and Al, which were contained in large amounts, and Si were analyzed with specificity by fs LA. The results show that Ca and Al were distributed in the rice husk (protective covering of rice) and Si was distributed in all parts of the rice.

Molecular Dynamics Simulation on the Thermal Boundary Resistance of a Thin-film and Experimental Validation (분자동역학을 이용한 박막의 열경계저항 예측 및 실험적 검증)

  • Suk, Myung Eun;Kim, Yun Young
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.32 no.2
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    • pp.103-108
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    • 2019
  • Non-equilibrium molecular dynamics simulation on the thermal boundary resistance(TBR) of an aluminum(Al)/silicon(Si) interface was performed in the present study. The constant heat flux across the Si/Al interface was simulated by adding the kinetic energy in hot Si region and removing the same amount of the energy from the cold Al region. The TBR estimated from the sharp temperature drop at the interface was independent of heat flux and equal to $5.13{\pm}0.17K{\cdot}m^2/GW$ at 300K. The simulation result was experimentally confirmed by the time-domain thermoreflectance technique. A 90nm thick Al film was deposited on a Si(100) wafer using an e-beam evaporator and the TBR on the film/substrate interface was measured using the time-domain thermoreflectance technique based on a femtosecond laser system. A numerical solution of the transient heat conduction equation was obtained using the finite difference method to estimate the TBR value. Experimental results were compared to the prediction and discussions on the nanoscale thermal transport phenomena were made.