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Optical Bistability in Carbon Nanotube Suspensions
Jungho Mun,Sok Won Kim 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.II
The phenomenon of optical bistability in multi-walled carbon nanotube (MWNT) suspensions was investigated. Two suspensions of carbon nanotubes were prepared by sonicating MWNT bundles and dispersing them in distilled water and chloroform, respectively. The light source was a modulated diode-pumped-solid-state Nd:YVO4 laser with a wavelength of 532 nm. Through the study of the optical bistability in MWNT suspensions, we found that MWNT suspended in chloroform was more effective than that in water, which was explained by the nonlinear absorption coefficient related to the thermodynamic properties of the solvents and the heat exchange between the carbon nanotubes and the solvents.<?
Design and fabrication of side-coupled RF cavity for S-band 6/3 MeV dual-energy electron linac
Mun Jungho,Chae Moonsik,Lee Jaehyun,Yeon Yeong Henm,Park Jae Yeon,Lee Nam-Ho 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.80 No.7
We demonstrate the design and manufacture of RF (radio-frequency) electron linac (linear accelerator) cavity of 6/3 MeV dual-energy X-ray generator for air-cargo security inspections. When an accelerated electron beam collides with the metal target, an X-ray is generated by a bremsstrahlung process. We designed a dual-energy RF cavity using a three-dimensional electromagnetic field simulation code and an electron beam trajectory code. The designed RF cavity is a side-coupled standing-wave type, driven by the π/2 mode, and has a resonant frequency of 2856 MHz. The maximum dose rate of X-ray was calculated to be 7.07 and 0.91 Gy/min at 1 m for an X-ray energy of 6 and 3 MeV using a tungsten target, respectively. In the simulation results, the accelerating gradient was about 13.5 MV/m, the Q-factor was 15,900, and the total length of the RF cavity was 57 cm for 6 MeV of the maximum accelerated electron energy. The resonance frequency and the Q-factor of the fabricated RF cavity were measured by 2855.34 MHz and 14,000, respectively.
Importance of higher-order multipole transitions on chiral nearfield interactions
Mun, Jungho,Rho, Junsuk De Gruyter 2019 Nanophotonics Vol.8 No.5
<P><B>Abstract</B></P><P>Surface-enhanced circular dichroism (SECD) of chiral molecules adsorbed on plasmonic nanostructures can substantially enhance chiroptical molecular signals by several orders, which is otherwise very weak to be directly measured. Several mechanisms were proposed to explain this extreme enhancement, but the exact mechanism is still controversial. We investigate strong higher-order multipole contribution to SECD near plasmonic nanostructures using the superposition T-matrix method and discuss how 3-dimensional full-field simulations implementing a homogeneous chiral medium have succeeded in the reconstruction of the extreme enhancement. We also discuss how theoretical studies modeling chiral molecules based on dipole approximation have failed to reconstruct the extreme enhancement and show that SECD enhancement of such chiral dipoles is directly governed by optical chirality enhancement. In addition, strong multipolar transitions in subwavelength chiral plasmonic nanoparticles are discussed based on the T-matrix. This work reviews theoretical frameworks describing chiral molecules, demonstrates significant contribution of a multipolar transition on the extreme SECD enhancement near plasmonic nanostructures, and emphasizes the importance of a multipolar transition in chiral nearfield interaction.</P>
Jungho Mun,Young Uk Jeong,Byung Cheol Lee,Hyuk Jin Cha,Ji Young Lee,Kitae Lee,Kwon-hae Yea,Pil Dong Ahn,Seong Hee Park,Yong Ho Cha,Yong Woo Lee 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.I
Terahertz (THz) pulses from solid targets, such as an aluminum (Al) and a strong polyester film (Mylar), irradiated by ultra-intense laser pulses were measured by using a liquid-helium-cooled Ge:Ga detector. The irradiating intensity of the Ti:Sapphire laser was more than 10$^{18}$ W/cm$^2$. The typical pulse energy and pulse duration on the target were 200 mJ and 30 fs, respectively. To prevent ultraviolet (UV), visible, and near-infrared (NIR) radiation from being measured by the detector, we used polyethylene (PE) plates and indium-tin-oxide (ITO) films as selective windows and mirrors for the THz radiation. The reflectivity of the ITO film for THz radiation is 10 times higher than that for visible and NIR radiations. The THz wave radiated from a laser-induced plasma has a linear component of the polarization, which may be explained by linear mode conversion from a laser wakefield. This intense and wide-band radiation is expected to be a useful source for various THz applications, as well as for real-time diagnostics for a plasma in which particles are accelerating.
Surface-enhanced circular dichroism by multipolar radiative coupling
Mun, Jungho,Rho, Junsuk The Optical Society 2018 Optics letters Vol.43 No.12
<P>We present numerical investigation of the mechanism of surface-enhanced circular dichroism of a chiral medium near nanoantennas. Strong circular dichroism was observed from the chiral medium surrounding nanoantennas with multipolar resonant modes, and the strong circular dichroism was more correlated to the multipolar resonances than to nearfield enhancement or optical helicity enhancement. According to this observation, we suggest multipolar radiative coupling between the nanoantennas and chiral medium as a possible mechanism of the strong chiral response. This work clarifies a mechanism of surface-enhanced chiral responses and would be useful for designing an enantiomeric-sensing platform and realizing devices relying on strong chirality, such as topological metamaterials for scattering-immune propagation of light and negative index metamaterials. (C) 2018 Optical Society of America</P>
APPROXIMATION TO DERIVATIVES BASED RADIAL BASIS FUNCTION INTERPOLATION
Mun Bae Lee,Jungho Yoon 한국산업응용수학회 2007 한국산업응용수학회 학술대회 논문집 Vol.3 No.2
In this paper, we consider approximation of a function f and its derivatives by using radial basis function interpolation and its derivatives (respectively). This is called simultaneous approximation. The current theories of this approach provide optimal error bounds when the approximand f is in a certain reproducing kernel Hilbert space F?. However, the space F? is very small when the function ? is smooth. Thus, our major concern is to observe the spectral accuracy of simultaneous approximation on the Sobolev space. Specifically, we show that if f belongs to the L∞-Sobolev space of smoothness order k, ∥f<SUP>(μ)</SUP> - R<SUP>(μ)</SUP>f, X∥L∞(Ω)) = o(h<SUP>k-|μ|₁</SUP>) as h → 0, where h represents the fill-distance of a set of scattered centers X and Rf.X is an interpolant to f on X by a scaled basis function ?(ㆍ/ω) with h|log h|<SUP>1+ρ</SUP> ≤ω≤1 FOR A FIXED ρ>0.
MOVING LEAST SQUARE APPROXIMATION USING RADIAL BASIS FUNCTIONS
Mun Bae Lee,Jungho Yoon 한국산업응용수학회 2007 한국산업응용수학회 학술대회 논문집 Vol.2 No.1
In this study, we are concerend with the moving least square (MLS) methods which reproduce a finite set of shifts of a Gaussian function of the form exp(-λ|x|²) with λ > 0 and x ∈ ?d. We show that the Gaussian based MLS has the same approximation order as the polynomial based MLS method in some sense. However, for a suitable range of λ, the Gaussian based MLS method provides better accuracy.
알루미늄 맞대기 아크 용접부 형상이 피로강도에 미치는 영향
조정호(Jungho Cho),백성진(Sungjin Baek),신승철(Seungchul Shin),이건호(Gunho Lee),강문구(Mun-Gu Kang),조영래(Young-Rae Jo) 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.1
The use of aluminum in auto odies is increasing due to the requirement of mass reduction for gas mileage enhancement. However, few open studies have been conducted on the fatigue strength of arc welded aluminum butt joints. In this study, the fatigue strength of arc welded butt joints of aluminum sheets was investigated. The material was 6061-T6 with a thickness of 4 mm. Welding specimens were prepared to determine the effects of the top bead toe angle, penetration depth, top surface misalignment, and alternative double-butt joint formation. Results showed that the top surface misalignment and partial penetration were more critical than the top bead toe angle on fatigue strength. Partial and full penetration revealed the lowest and highest fatigue strength, respectively. Because of the low viscosity and surface tension, achieving full penetration in butt joint aluminum arc welding without a backing component while also controlling penetration depth are impossible. An alternative solution to this problem is to apply a double-butt joint design, with experimental results showing for the first time the validity of this solution in terms of fatigue strength.
So, Sunae,Mun, Jungho,Rho, Junsuk American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.27
<P>Recent introduction of data-driven approaches based on deep-learning technology has revolutionized the field of nanophotonics by allowing efficient inverse design methods. In this paper, a simultaneous inverse design of materials and structure parameters of core-shell nanoparticles is achieved for the first time using deep learning of a neural network. A neural network to learn the correlation between the extinction spectra of electric and magnetic dipoles and core-shell nanoparticle designs, which include material information and shell thicknesses, is developed and trained. We demonstrate deep-learning-assisted inverse design of core-shell nanoparticles for (1) spectral tuning electric dipole resonances, (2) finding spectrally isolated pure magnetic dipole resonances, and (3) finding spectrally overlapped electric dipole and magnetic dipole resonances. Our finding paves the way for the rapid development of nanophotonics by allowing a practical utilization of deep-learning technology for nanophotonic inverse design.</P> [FIG OMISSION]</BR>