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RISS 인기검색어
- 검색키워드
- 저자 : Keunwoo Lee (검색결과 47 건)
- 무료
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Absolute distance measurement by dual-comb interferometry with adjustable synthetic wavelength
Lee, Joohyung,Han, Seongheum,Lee, Keunwoo,Bae, Eundeok,Kim, Seungman,Lee, Sanghyun,Kim, Seung-Woo,Kim, Young-Jin IOP Pub 2013 Measurement Science and Technology Vol.24 No.4
<P>Absolute distances were measured using two femtosecond lasers of different pulse repetition rates by revisiting the dual-comb interferometric method proposed by Coddington <I>et al</I> (2009 <I>Nature Photon.</I> <B>3</B> 351–6). The apparatus built for experiments was designed to eliminate the dead zones in the measurement range by separating the measurement pulses from the reference pulses using orthogonal polarization. In addition, the pulse repetition rate of the signal laser was made tunable in order to extend the non-ambiguity range (NAR) by adaptively adjusting the synthetic wavelength in consideration of the <I>de facto</I> measurement stability in the air. Actual tests performed in the open air proved that a target distance of 69.3 m is measured without interruptions at a 200 µs update rate in the presence of a ∼170 µm drift of the optical path length caused by the fluctuation of the refractive index of air. The proposed hardware system design for effective NAR extension will facilitate the use of dual-comb interferometry for various terrestrial applications.</P>
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High precision laser ranging by time-of-flight measurement of femtosecond pulses
Lee, Joohyung,Lee, Keunwoo,Lee, Sanghyun,Kim, Seung-Woo,Kim, Young-Jin IOP Pub 2012 Measurement Science and Technology Vol.23 No.6
<P>Time-of-flight (TOF) measurement of femtosecond light pulses was investigated for laser ranging of long distances with sub-micrometer precision in the air. The bandwidth limitation of the photo-detection electronics used in timing femtosecond pulses was overcome by adopting a type-II nonlinear second-harmonic crystal that permits the production of a balanced optical cross-correlation signal between two overlapping light pulses. This method offered a sub-femtosecond timing resolution in determining the temporal offset between two pulses through lock-in control of the pulse repetition rate with reference to the atomic clock. The exceptional ranging capability was verified by measuring various distances of 1.5, 60 and 700 m. This method is found well suited for future space missions based on formation-flying satellites as well as large-scale industrial applications for land surveying, aircraft manufacturing and shipbuilding.</P>
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Keunwoo Lee,전형탁,Jeongtae Kim,Keunjun Kim,Seungjin Yeom,Youngjin Lee 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.4
Co films deposited by using a remote plasma atomic layer deposition (RPALD) method with cyclopentadienyl cobalt dicarbonyl (CpCo(CO)2) as a precursor were investigated. The process parameters, such as the deposition temperature, the plasma power, the process pressure, and the plasma gas, were varied, and the resulting Co films were characterized. The growth rate of the Co film was about 1.1 °A/cycle for a process window between 125 and 175 C. The impurity content of the Co films was minimized using a H2 plasma in the process pressure range between 0.1 and 2 Torr at a plasma power of 300 W. The carbon and the oxygen contents of the Co films were about 7 at.% and below 1 at.%, the detection limit, respectively. The Co films showed a very uniform surface with a root-mean-square (RMS) roughness of 1.51 °A, as determined by using an atomic force microscopy (AFM) analysis. The Co films deposited on contact holes, about 0.12 μm wide and 1.8 μm deep, showed excellent conformal coverage. The compositions of the Co films on the tops and the sidewalls of the contact holes were examined with Auger electron spectroscopy (AES), and the results showed nearly identical compositions.
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Epitaxial CoSi<sub>2</sub> formation using an oxynitride buffer layer
Lee, Jaesang,Lee, Keunwoo,Kim, Dongock,Park, Taeyong,Kim, Honggyu,Jeon, Hyeongtag Cambridge University Press (Materials Research Soc 2009 Journal of materials research Vol.24 No.8
<P>We investigated the epitaxial growth of CoSi2 (100) on an Si (100) substrate using a modified oxide mediated epitaxy (OME) method to overcome the disadvantages of the OME method. These disadvantages are sensitivity of Co films to contamination by oxygen and the need for reiterating the film growth process to obtain thicker films. To solve these problems, nitrogen atoms were incorporated into chemically grown oxide (SiO<I>x</I>) by NH3 plasma treatment prior to the deposition of a Co film on the oxynitride buffer layer using the metal organic chemical vapor deposition (MOCVD) method. Subsequently, ex situ rapid thermal annealing was performed to grow Co-silicide at a temperature between 400 °C and 700 °C for 1 min. The results show that the diffusion of Co was effectively controlled by the oxynitride buffer layer without the formation of additional SiO<I>x</I> in between Co and Si. Our findings indicate that by using an oxynitride buffer layer, CoSi2 films can be grown epitaxially despite the fact that the initial Co film was exposed to oxygen.</P>
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Active compensation of large dispersion of femtosecond pulses for precision laser ranging.
Lee, Sang-Hyun,Lee, Joohyung,Kim, Young-Jin,Lee, Keunwoo,Kim, Seung-Woo Optical Society of America 2011 Optics express Vol.19 No.5
<P>We describe an active way of compensation for large dispersion induced in the femtosecond light pulses travelling in air for laser ranging. The pulse duration is consistently regulated at 250 fs by dispersion control, allowing sub-micrometer resolution in measuring long distances by means of time-of-flight measurement. This method could facilitate more reliable applications of femtosecond pulses for satellite laser ranging, laser altimetry and active LIDAR applications.</P>
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