Optimizations of the Thickness and the Operating Temperature of LiB3O5, BaB2O4, and KTiOPO4 Crystals for Second Harmonic Generation

박두재,Hong Chu,조원배,최수봉 한국물리학회 2015 새물리 Vol.65 No.12

We demonstrate a theoretical study for determining the optimal crystal thickness and operating temperature when generating a second harmonic of a pulse laser with pulsewidths ranging from a few tens of femtosecond to a few nanosecond by using commonly-used nonlinear crystals of lithium barium borate, beta barium borate, and potassium titanyl phosphate. The optimal thicknesses of those crystals to avoid any pump pulse depletion for a fundamental-mode laser pulse having a high intensity and a long pulsewidth was calculated as a function of the intensity and the pulsewidth of the fundamental mode. Also, for short-pulse operation, thickness limits are calculated for conditions under which no pulse dispersion due to group velocity mismatch is observed. Finally, the fluctuation of second-harmonic yield due to temperature variations which introduce a refractive-index change is calculated, and the effective temperature ranges are demonstrated for room-temperature operation.

한전의 전력분야 기후변화협약 대응 전략

박두재,Park, Du-Jae 대한전기협회 2008 전기저널 Vol.- No.375

Dielectric substrate effect on the metamaterial resonances in terahertz frequency range

박두재,S.J. Park,박익모,안영환 한국물리학회 2014 Current Applied Physics Vol.14 No.4

We report on the effect of dielectric substrate on the resonance shift of metallic metamaterials operating in the terahertz frequency region. The resonance frequencies for various metamaterials obtained by time-domain spectroscopy agree well with calculations based on the finite-difference time-domain method. The dependencies of the resonance frequency to substrate index are studied, and are systematically determined by introducing an effective substrate index. The relative contributions of the substrate index for various metamaterials are obtained by fitting the numerically obtained effective refractive indices as a function of substrate index, which is found to be w0.63 regardless of the metamaterial geometry.

Development of a Theoretical Model for Strong-Field Photoemission in a 2-Dimensional Conducting Sheet

박두재,Y. H. Ahn 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.75 No.11

We propose a theoretical model simulating ultrafast electron emission at the edge of a twodimensional conducting sheet due to a strong field tunneling process in the presence of a static electric field. Under the assumption of a charge distribution following the square root law associated with a Sommerfeld half plane, the electric field was found to exhibit square-root dependence. The electron emission yield was estimated based on a Fowler-Nordheim tunneling, from which the resultant current flow was calculated by using the quasi-classical model. Importantly, we considered the number of the recoil electrons that do not contribute to the net current. We found a large variation in the nonlinearity of the power-dependence of the net field-emission yield; this is due to the combined contributions of the laser field irradiation and a static electric field. The validity of our model was confirmed based on experimental results obtained using devices with a nanometer-sized gap fabricated on a single layer of graphene.

A Breaching of Electromagnetic Shielding by Narrow Aperture in Metal Film

박두재,홍철,경지수,최수봉 한국광학회 2016 Current Optics and Photonics Vol.20 No.5

We report a theoretical research for the condition of electromagnetic shield breaching when a narrowaperture is punctured in thin metal film. To calculate electromagnetic field transmission through a narrowslit, a Rayleigh wave expansion has been applied for free standing, thin metal film. We found that theDC electric field allows perfect transmission when the length of the slit is infinite, regardless of the othergeometrical factors such as slitwidth and thickness. Slitwidth dependent transmission spectra as a functionof frequency shows a cutoff frequency that decreases almost linearly to the slitwidth, giving that almostsuccessful shielding is only possible when the slitwidth is smaller than 1 micron.

Effect of a Dielectric Substrate with a Subwavelength Thickness on Light Diffraction by Rectangular Hole Arrays on Metallic Film

박두재,정문석,S. B. Choi 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.9

A theoretical study of the effect of ultrathin dielectric substrate in THz wave diffraction phenomenaon a subwavelength nanostructured system is conducted. The proposed system is composedof a dielectric substrate with a thickness of /1000 and a subwavelength-scaled rectangular holearray on a metal thin film in THz wavelength region. A modified Rayleigh diffraction theory hasbeen developed to take into account the contribution of reflection at the air-substrate interface. A calculation of the terahertz transmission while varying the thickness shows that the effect of athin dielectric substrate starts to vanish when the thickness becomes 1/100 of the incident light’swavelength. Theoretically, the results are well explained because most electric fields are confinednear the rectangular aperture, which results in the dominant existence of the field inside the thinsubstrate. Additionally, the effect of a thin dispersive substrate is discussed.

Control of Surface Plasmon Excitation in Metallic Slit Nanostructures in a Wet Environment

박두재,R. P. Smith,N. Kwon,최수봉 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.71 No.8

We report a modification of the electromagnetic field distribution associated with a surface plasmon polariton excited on a metal slit array in the vicinity of liquid. By successful operation of a Near-field Scanning Optical Microscope (NSOM) in both dry and wet environments, we found that near-field distribution showed a considerable change from a clear double-periodic distribution (spatial oscillation of electromagnetic field having the period half of that of slit array), which is a signature of surface plasmon excitation, to a single periodic distribution, which denotes that the surface plasmon polariton no longer exists. A simulation performed based on a partial wave expansion combined with a surface impedance boundary conditions show that such change of electromagnetic field distribution are explained by a change of surface plasmon resonance, associated with the change of dielectric constant of the surrounding media.

초고속 전자 현미경의 개발과 극복 과제

박두재,Park, Doo Jae 한국진공학회 2015 진공 이야기 Vol.2 No.1

In this article, a historical and scientific review on the development of an ultrafast electron microscope is supplied, and the challenges in further improvement of time resolution under sub-picosecond or even sub-femtosecond scale is reviewed. By combining conventional scanning electron microscope and femtosecond laser technique, an ultrafast electron microscope was invented. To overcome its temporal resolution limit which originates from chromatic aberration and Coulomb repulsion between individual electrons, a generation of electron pulse via strong-field photoemission has been investigated thoroughly. Recent studies reveal that the field enhancement and field accumulation associated with the near-field formation at sharply etched metal nanoprobe enabled such field emission by ordinary femtosecond laser irradiation. Moreover, a considerable acceleration reaching 20 eV with near-infrared laser and up to 300 eV acceleration with mid-infrared laser was observed, and the possibility to control the amount of acceleration by varying the incident laser pulse intensity and wavelength. Such findings are noteworthy because of the possibility of realizing a sub-femtosecond, few nanometer imaging of nanostructured sample.in silicon as thermoelectric materials.

Optimization of the Thickness and the Operating Temperature of LiB3O5, BaB2O4, and KTiOPO4 Crystals for Sum Frequency Generation

박두재,Hong Chu,Jisoo Kyoung,최수봉 한국물리학회 2017 New Physics: Sae Mulli Vol.67 No.1

We perform a theoretical study to determine an optimal crystal thickness and operating temperature in sum-frequency generation by using commonly-used nonlinear crystals such as lithium barium borate, beta barium borate, and potassium titanyl phosphate. The optimal thicknesses of those crystals to avoid any decrease in the yield due to interference originating from different path lengths between the two pump pulses are calculated as functions of the fundamental intensity and the pulse width. Additionally, the fluctuation of the sum-frequency generation yield with temperature, which introduces a refractive-index change, is calculated, and the temperature ranges giving low fluctuations in the yield are demonstrated in room-temperature operation.

A Carbon Contamination Cleaning of Gold Film by Electron Beam Irradiation with Minimum Structural Damages

박두재,T. H. Kang,D. S. Kim,김현태,최수봉 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.71 No.8

We demonstrate a successful removal of carbon contamination in gold surface simply by exposing relatively low energy electron emitted from field effect scanning electron microscope apparatus. An atomic force microscope image of gold film taken after a few tens of minute exposure of electron beam indicates small morphology change, however, a lateral force microscope image taken simultaneously shows a considerable increase of surface potential, which suggest an effective change of atomic composition between gold and other contaminant atoms as carbon. Energy-dispersive X-ray spectroscopy confirms that the carbon composition is substantially decreased due to electron beam exposure.