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Frequency-Modulated Pulse-Amplification Method for Reducing Pulse Shape Distortion
Jihoon Jeong,Seryeyohan Cho,Seungjin Hwang,Tae Jun Yu 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.11
To reduce the laser pulse shape distortion accompanying the amplification process and achieve an intended output pulse shape in the Nd:YAG amplifier chain, we propose a frequency-modulated pulse-amplification method. Assuming carrier-frequency-modulated seed pulses, we numerically simulate the pulse amplification in an Nd:YAG amplifier chain where severe distortion occurs. For the calculation, we develop a modified Frantz-Nodvik equation, which enables two inputs with different carrier frequencies. The simulation results indicate that the temporal contrast of the seed pulse needed to obtain a at output pulse shape is reduced by 16 - 25 dB when frequency modulation is applied.
Numerical study of a thermally-compensated high-energy double-pass Nd:YAG amplifier design
Jeong, Jihoon,Cho, Seryeyohan,Kim, Taeshin,Yu, Tae Jun 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.
<P>We conducted a comparative study of double-pass Nd:YAG laser amplifiers by comparing the thermally-induced optical losses of various designs through numerical simulations. The simulation code was developed to estimate the total optical losses from three thermal effects: depolarization, thermal lensing, and bi-focusing. At first, we verified the code with the well-known single-rod amplifier configurations. After that, we extended the code for dual-rod designs, which are more appropriate for high-energy applications. Finally, the adoption of a diverging input beam is suggested to reduce thermal losses dramatically and to avoid stubborn design issues, such as damage, aberration, system complexity, etc., in dual-rod high-energy double-pass amplifiers.</P>
Development of an Impedance Matching Layer in an Ultrasound Transducer with Gradient Properties
( Jihoon Jeong ) 한국센서학회 2018 센서학회지 Vol.27 No.6
The piezocomposite transducer is widely used because it is highly efficient in transforming electric energy into mechanical energy, and its frequency range is broader than that of other types of ultrasound transducers. A general piezocomposite transducer is composed of an acoustic lens, impedance matching layers, piezoelectric materials, and backing layers. When an input voltage is applied to a piezoelectric material as an active material, it generates sound waves while vibrating. At that time, an impedance matching layer helps the sound waves to propagate forward while reducing the impedance mismatch that may occur at the interface between the active material and its front material. The impedance mismatch has a negative effect on the signal of an ultrasound transducer; thus, it is important to design a matching layer to overcome the issue. In this study, an optimized feature of a matching layer with gradient properties is studied. An objective function is defined to minimize both the average and the deviation of the reflection coefficients that are functions of the frequencies. As a result, an improvement in the signal characteristics with respect to the sensitivity and bandwidth is reported.
Numerical Study of a Thermally-compensated High-energy Double-pass Nd:YAG Amplifier Design
Jihoon Jeong,Seryeyohan Cho,Taeshin Kim,Tae Jun Yu 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.5
We conducted a comparative study of double-pass Nd:YAG laser amplifiers by comparing the thermally-induced optical losses of various designs through numerical simulations. The simulation code was developed to estimate the total optical losses from three thermal effects: depolarization, thermal lensing, and bi-focusing. At first, we verified the code with the well-known single-rod amplifier configurations. After that, we extended the code for dual-rod designs, which are more appropriate for high-energy applications. Finally, the adoption of a diverging input beam is suggested to reduce thermal losses dramatically and to avoid stubborn design issues, such as damage, aberration, system complexity, etc., in dual-rod high-energy double-pass amplifiers.
Jeong, Jun Hyeok,Choi, Sungwook,Lee, Seul-Lee,Jeong, Sun Jae,Christian, Nouaze Joseph,Kim, Jihoon,Kang, Hyun Wook,Nam, Seung Yun,Oh, Junghwan,Lee, Yong Wook American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.11
<P>In this paper, we demonstrated a polarimetric fiber vibration sensor based on a polarization-diversified loop (PDL) with short polarization-maintaining photonic crystal fiber (PM-PCF) as a sensor head and investigated the dependence of its frequency response on the sensing fiber length. The fabricated PM-PCF vibration sensor is composed of a polarization beam splitter for forming the PDL, PM-PCF as a sensor head, and two wave plates such as a quarter-wave plate and a half-wave plate. A laser diode and a photodetector were also utilized for intensity-based vibration measurement. In particular, two kinds of PM-PCF segments with fiber lengths of similar to 6 and similar to 10 cm were employed to explore the effect of the sensor head length on the sensor frequency response. The frequency response was examined over 1-3000 Hz using a piezoelectric transducer that can apply single-frequency vibration to the sensor head. Every measured frequency response showed a resonance peak at each sensor head length, and cut-off frequencies were measured as similar to 1240 and similar to 794 Hz for PM-PCF lengths of similar to 6 and similar to 10 cm, respectively. That is, a higher cut-off frequency was obtained in a shorter sensor head length. Moreover, it was observed that the sensor head length dependence of the frequency response was maximized in a frequency range from 1000 to 2400 Hz and faded away beyond 2400 Hz. From the measurement results, it is concluded that the short sensor head can provide higher normalized sensitivity, i.e., better signal to noise ratio, at frequencies higher than the resonance frequency, let alone convenience of installation and in sensitiveness to external perturbations in a PDL-based PM-PCF vibration sensor. The phase shift per unit strain and the minimum detectable strain perturbation, regarded as sensitivity and resolution, were measured as similar to 0.377 mrad/mu epsilon and similar to 0.16 n epsilon/Hz(1/2) at 2000 Hz for similar to 6-cm-long PM-PCF, respectively.</P>
Excitation Wavelength Dependence of Terahertz Radiation from InAs: UV versus IR
Hoonill Jeong,Jihoon Jeong,G. Hugh Song,조영달 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.1
Terahertz (THz) radiation measurements from p-doped InAs (carrier density:~7 × 1017 cm−3)surfaces were carried out encompassing both IR (770–830 nm) and UV (360–385 nm) excitations by employing two synchronized femtosecond lasers. Each laser was independently tunable, and the jitter was controlled below the pulse width (~150 fs). One laser was used for THz generation,and the other for detection via a photoconductive antenna. For the IR-pulse excitation, two frequency components were observed, between which the higher-side peak disappeared as we tuned the excitation wavelength toward the UV range.
폴리에스테르-폴리아민 분산제의 합성 및 카본 분산 특성
손정매(Jeong-Mae Son),육정숙(Jeong-Suk Yuk),이상준(Sangjun Lee),김주현(Juhyun Kim),김남균(Nam-Kyun Kim),신지훈(Jihoon Shin),김영운(Young-Wun Kim) 한국트라이볼로지학회 2014 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.30 No.4
We prepared polyester-polyamines to improve the effect of carbon black dispersibility for use in thermal transfer ink, and synthesized polymeric dispersing agents by two-step reactions. In the first step, we made polyester by polycondensing 1,6-hexanediol and adipic acid. The resulting polymers had carboxylic acid, which was linked with polyamine via an acid-base reaction. We then characterized the polyester-polyamine structure by NMR spectroscopy and Fourier transform infrared spectroscopy (FT-IR). We also determined the basic characterizations such as total acid numbers (TAN) (5.0?67.5 mgKOH/g), hydroxyl values (27.1?67.5 mgKOH/g), and molar masses (Mn = 1.6?8.4 kg mol<SUP>?1</SUP>) for the polyester and total base numbers (TBN) (15.3?57.1 mgKOH/g), hydroxyl values (33.0?79.8 mgKOH/g), and nitrogen contents (1.02?3.48%) for the polyesterpolyamine polymers. We thus prepared thermal transfer ink using carbon blacks and the polyester-polyamine dispersing agents, and evaluated the resulting mixtures for printability, adhesive force, storage stability, ink appearance, ink gloss, and processability. These mixtures showed significant dispersibility for carbon black in the ink. Thus, we concluded that the dispersibility of the polymeric materials depended on the polyamine structure and the hydrophilicity-hydrophobicity distribution of the polymeric dispersants.
Yang, Jihoon,Lee, Hyung Gon,Cho, Suyeong,Kim, Woong Mo,Jeong, Seongtae,Bae, Hong-Beom,Yoon, Myung Ha,Choi, Jeong Il Elsevier 2019 Neuroscience Letters Vol.690 No.-
<P><B>Abstract</B></P> <P>Macrophage-inducible C-type lectin (Mincle), a pattern recognition receptor, is a critical component of the innate immune system that is involved in the pathogenesis of chronic pain. Previous studies have reported the expression of Mincle in neuronal and glial cells of the brain, but its expression and role in pain processing at the spinal level remain to be determined. The current study was performed to identify Mincle in the spinal cord and to investigate the effect of Mincle activation on spinal sensitization.</P> <P>Most Mincle immunoreactivity was localized within the grey matter and the dorsal and ventral horns of the lumbar spinal cord in naïve rats. A single intrathecal (i.t.) injection of trehalose-6,6-dibehenate (TDB), a Mincle ligand, induced mechanical allodynia. Immunoreactivity to Mincle and Iba-1 in the spinal cord significantly increased after i.t. injection of TDB. Mechanical allodynia was attenuated by daily i.t. injection of minocycline. However, double immunofluorescence revealed that Mincle co-localizes with NeuN (neurons), but not with Iba-1 (microglia) or GFAP (astrocytes).</P> <P>In conclusion, we found that Mincle was present in spinal cord neurons, but not microglia or astrocytes, and may play a role in microglia-induced spinal sensitization.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mincle is expressed in the dorsal and ventral horns of the lumbar spinal cord in rat. </LI> <LI> Mincle is present in neuron, but not microglia or astrocyte in the lumbar spinal cord. </LI> <LI> Intrathecal injection of Mincle ligand, trehalose dibehenate induces mechanical allodynia. </LI> <LI> Microglia is activated by intrathecal injection of Mincle ligand. </LI> <LI> Intrathecal minocycline reduces the allodynic response induced by Mincle activation. </LI> </UL> </P>