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Lu Yuehui,Wu Xuemei,Liu Xianghuai,Zhuge Lanjian 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
It is problematic that electrons are emitted from the Mo grid of pulsed-controlled grid traveling wave tubes, caused by the contamination of cathode evaporation material, i.e. BaO. Some studies show that a Mo grid coated with carbon can greatly suppress grid electron emission. However, the reason for the electron emission suppression is not completely clear. To understand the mechanism of electron emission suppression of a BaO/C/Mo system, carbon lms were prepared on Mo substrates at room temperature by means of DIBSD (dual ion beam sputtering deposition), and BaO layers were coated by using a chemical method. Post-annealing was conducted under a owing nitrogen ambient at 700 C for 1.5 hours. The structure of the as-deposited carbon lms was evaluated by TEM, AES and Raman spectroscopy. The annealed samples, the BaO/ Mo and BaO/C/Mo systems, were analyzed by XPS. The results suggest that the chemical reaction between BaO and C at high temperature eliminates the concentrations of Ba or BaO on the surface of the C/Mo system. It can be believed that the high work function material used as the grid surface coating and elimination of BaO on its surface have a critical eect on grid electron emission suppression. Moreover, the carbon lm was characterized by density, homogeneity and high adhesion, owing to the features of DIBSD.
Plasmonic electromagnetically-induced transparency in symmetric structures
Lu, Yuehui,Jin, Xingri,Zheng, Haiyu,Lee, YoungPak,Rhee, Joo Yull,Jang, Won Ho The Optical Society 2010 Optics express Vol.18 No.13
<P>A broken symmetry is generally believed to be a prerequisite for plasmonic electromagnetically-induced transparency (EIT), since the asymmetry allows the excitation of the otherwise forbidden dark mode. Nevertheless, according to the picture of magnetic plasmon resonance (MPR)-mediated plasmonic EIT, we show that plasmonic EIT can be achieved even in symmetric structures based on the second-order MPR. This not only sharpens our understanding of the existing concept, but also provides a profound insight into the plasmonic coherent interference in the near-field zone.</P>
Lu, Yuehui,Rhee, Joo Yull,Jang, Won Ho,Lee, Young Pak The Optical Society 2010 Optics express Vol.18 No.20
<P>Plasmonic electromagnetically-induced transparency (EIT) can be excited by a single optical field unlike EIT in atom system, since the coupling between the bright and the dark modes is inherently induced through the near-field interaction in metamaterials. As a result, the complexity of the experimental realization can be reduced significantly, while the tunability is lost inevitably.We suggest a scheme that the plasmonic EIT is possible to be actively manipulated even by the single optical field. The bright and the dark modes are selective to be either coupled or uncoupled, depending on the angle of incidence. Even though the mechanical control has the disadvantage for high-speed applications, it paves the way for active manipulation of plasmonic EIT and benefits the clarification of its origin.</P>
Studies of electromagnetically induced transparency in metamaterials
Xu, Hua,Lu, Yuehui,Lee, YoungPak,Ham, Byoung Seung The Optical Society 2010 Optics express Vol.18 No.17
<P>We have studied electromagnetically induced transparency (EIT) in metamaterials for various schemes corresponding to those in an atomic medium. We numerically calculate a symmetric dolmen scheme of metamaterials corresponding to a tripod model of EIT-based optical switching and illustrate plasmonic double dark resonances. Our study provides a fundamental understanding and useful guidelines in using metamaterials for plasmonic-based all-optical information processing.</P>
Magneto-optic Study on a Transverse Gyrotropic Grating
Min Hyung Cho,Yuehui Lu,Joo Yull Rhee,이영백 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.3
A two-dimensional scalar Helmholtz equation is derived for a transverse electric mode transverse gyrotropic grating. In the frame of a rigorous coupled-wave analysis, a Bloch-type wave solution and a Fourier expansion of the dielectric tensors are substituted into the Helmholtz equation to obtain a system of ordinary differential equations, and an Airy-like internal-reflection series is applied for better convergence. In the derivation, no approximation or estimate has been employed, and it is easy to implement. Finally, the numerical method is tested with various parameters. A two-dimensional scalar Helmholtz equation is derived for a transverse electric mode transverse gyrotropic grating. In the frame of a rigorous coupled-wave analysis, a Bloch-type wave solution and a Fourier expansion of the dielectric tensors are substituted into the Helmholtz equation to obtain a system of ordinary differential equations, and an Airy-like internal-reflection series is applied for better convergence. In the derivation, no approximation or estimate has been employed, and it is easy to implement. Finally, the numerical method is tested with various parameters.
Maxwell's Equation for Non-diagonal Tensors and its Application to the Polar Gyrotropic Gratings
Min Hyung Cho,Yuehui Lu,Jooyull Rhee,YoungPak Lee 한국산업응용수학회 2008 한국산업응용수학회 학술대회 논문집 Vol.4 No.3
The Maxwell's equation with non-diagonal dielectric tensors are solved with rigorous coupled-wave analysis (RCWA) [1] for magnetic gratings. In order to enhance the convergence of the method, Airy-like multiple reflection series are used [2]. Numerical results are compared with experimental results and magneto-optical (MO) Kerr effects are calculated as a function of grating depth. At last, a large MO enhancement is observed for the thin gratings.
Cho, Min Hyung,Lu, Yuehui,Rhee, Joo Yull,Lee, Young Pak The Optical Society 2008 Optics express Vol.16 No.21
<P>The rigorous coupled-wave analysis with Airy-like internal-reflection series and Fourier-factorization for the calculation of the diffracted magneto-optical (MO) effects from polar and longitudinally magnetized gyrotropic gratings are fully described. For both gratings the numerical and experimental results are in good agreement, and the enhancement of Kerr rotation in higher orders compared to that of the 0th order diffraction is calculated as a function of grating depth. At last, this numerical method can be applied to many other applications such as extraordinary optical transmission from metallic gratings either through surface plasmon or cavity mode, and MO hysteresis loops.</P>
Multifunctional Antireflection Coatings Based on Novel Hollow Silica–Silica Nanocomposites
Zhang, Xianpeng,Lan, Pinjun,Lu, Yuehui,Li, Jia,Xu, Hua,Zhang, Jing,Lee, YoungPak,Rhee, Joo Yull,Choy, Kwang-Leong,Song, Weijie American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.3
<P>Antireflection (AR) coatings that exhibit multifunctional characteristics, including high transparency, robust resistance to moisture, high hardness, and antifogging properties, were developed based on hollow silica–silica nanocomposites. These novel nanocomposite coatings with a closed-pore structure, consisting of hollow silica nanospheres (HSNs) infiltrated with an acid-catalyzed silica sol (ACSS), were fabricated using a low-cost sol–gel dip-coating method. The refractive index of the nanocomposite coatings was tailored by controlling the amount of ACSS infiltrated into the HSNs during synthesis. Photovoltaic transmittance (<I>T</I><SUB>PV</SUB>) values of 96.86–97.34% were obtained over a broad range of wavelengths, from 300 to 1200 nm; these values were close to the theoretical limit for a lossy single-layered AR coating (97.72%). The nanocomposite coatings displayed a stable <I>T</I><SUB>PV</SUB>, with degradation values of less than 4% and 0.1% after highly accelerated temperature and humidity stress tests, and abrasion tests, respectively. In addition, the nanocomposite coatings had a hardness of approximately 1.6 GPa, while the porous silica coatings with an open-pore structure showed more severe degradation and had a lower hardness. The void fraction and surface roughness of the nanocomposite coatings could be controlled, which gave rise to near-superhydrophilic and antifogging characteristics. The promising results obtained in this study suggest that the nanocomposite coatings have the potential to be of benefit for the design, fabrication, and development of multifunctional AR coatings with both omnidirectional broadband transmission and long-term durability that are required for demanding outdoor applications in energy harvesting and optical instrumentation in extreme climates or humid conditions.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-3/am405258d/production/images/medium/am-2013-05258d_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am405258d'>ACS Electronic Supporting Info</A></P>