23 results on '"Gae Hwang Lee"'
Search Results
2. Green-light-selective organic photodiodes for full-color imaging
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In-Sun Jung, Gae Hwang Lee, Yong Wan Jin, Kwang Hee Lee, Dong-Seok Leem, Xavier Bulliard, Seon-Jeong Lim, Chul-Joon Heo, Sungyoung Yun, Kyung-Bae Park, Jung-Hwa Kim, and Yeong Suk Choi
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Materials science ,Absorption spectroscopy ,Organic solar cell ,business.industry ,02 engineering and technology ,Green-light ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Polymer solar cell ,Photodiode ,law.invention ,010309 optics ,Optics ,law ,Attenuation coefficient ,0103 physical sciences ,Quantum efficiency ,0210 nano-technology ,Absorption (electromagnetic radiation) ,business - Abstract
In this work, organic photodiodes (OPDs) based on two newly synthesized p-type dipolar small molecules are reported for application to green-light-selective OPDs. In order to reduce the blue-color absorption induced by the use of C60 as the n-type material in a bulk heterojunction (BHJ), the electron donor:electron acceptor composition ratio is tuned in the BHJ. With this light manipulation approach, the blue-wavelength external quantum efficiency (EQE) is minimized to 18% after reducing the C60 concentration in the center part of the BHJ. The two p-type molecules get a cyanine-like character with intense and sharp absorption in the green color by adjusting the strength of their donating and accepting parts and by choosing a selenophene unit as a π-linker. When combined to C60, the green-wavelength EQE reaches 70% in a complete device composed of two transparent electrodes. Finally, the optical simulation shows the good color-balance performance of hybrid full-color image sensor without an additional filter by using the developed green OPD as the top-layer in stacked device architecture.
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- 2019
3. Highly durable organic photodetector for complementary metal oxide semiconductor image sensors
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Chul-Joon Heo, Sungjun Park, Takkyun Ro, Kyung-Bae Park, Takao Motoyama, Gae Hwang Lee, Yong-young Park, Sunghan Kim, Seon-Jeong Lim, Jae-Cheol Lee, Yeon-hee Kim, Kiyohiko Tsutsumi, Jong-Bong Park, Sungyoung Yun, Yong Wan Jin, Yeoung Suk Choi, and Younhee Lim
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Materials science ,Fabrication ,Semiconductor device fabrication ,Photodetector ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,law.invention ,Biomaterials ,law ,Materials Chemistry ,Electrical and Electronic Engineering ,Diode ,Organic electronics ,business.industry ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Photodiode ,Organic semiconductor ,Optoelectronics ,0210 nano-technology ,business ,Dark current - Abstract
Utilizing organic electronics compatible with conventional semiconductor fabrication processes is extremely difficult because of their low chemical resistivity and poor environmental durability. To preserve the intrinsic functionality of organic materials, only a few fabrication processes can be used. Moreover, it is essential to achieve process expandability and silicon-process compatibility to develop high-resolution electronics suitable for mass production. Therefore, we developed wet-process-compatible organic photodetectors by replacing the conventional shadow-mask process with photolithography. This suppresses particle deposition during the serial fabrication processes, providing high operational stability. The fabricated green organic photodiodes exhibit a low dark current (1.0 × 10−11 A/cm2) with high photon–electron conversion efficiency (EQE = 65%). The charge collection and charge separation efficiencies are stable (ηcc = 84.6% and ηcs = 97.7%, respectively). Moreover, the organic semiconductors are compatible with conventional wet- and dry-etching processes owing to thin-film encapsulation layers. Finally, the novel organic image sensor can withstand 500 h under 85 °C/85% relative humidity and 1000 thermal cycles (−55–125 °C). Because of its robustness and strong barrier properties, the novel process architecture reported herein can be extended to any organic electronic devices, including widely commercialized organic light-emitting diodes and organic photovoltaic devices.
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- 2021
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4. Bi-layered metal-oxide thin films processed at low-temperature for the encapsulation of highly stable organic photo-diode
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Gae Hwang Lee, Seon-Jeong Lim, Kyung-Bae Park, Ryuichi Satoh, Yong-young Park, Yeon-hee Kim, Sang Yoon Lee, Ki-deok Bae, Takkyun Ro, Wenxu Xianyu, Chul-Joon Heo, Yong Wan Jin, Dong-Seok Leem, Xavier Bulliard, Woo-Yong Yang, and Jong-Bong Park
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Silicon oxynitride ,Nanotechnology ,02 engineering and technology ,Chemical vapor deposition ,010402 general chemistry ,01 natural sciences ,law.invention ,Biomaterials ,Atomic layer deposition ,chemistry.chemical_compound ,Plasma-enhanced chemical vapor deposition ,law ,Materials Chemistry ,Electrical and Electronic Engineering ,Thin film ,Chemistry ,business.industry ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Active layer ,Optoelectronics ,Quantum efficiency ,Photolithography ,0210 nano-technology ,business - Abstract
A novel approach for the thin film encapsulation (TFE) of organic photo-diode (OPD) for the next generation of organic/inorganic hybrid complementary metal oxide semiconductor (CMOS) image sensor is reported. The TFE is composed of two different metal-oxides stacked in bi-layer thin film architecture. The first layer is composed of aluminum oxide (AlOx) deposited by atomic layer deposition (ALD) at a moderate temperature of 100 °C to avoid any damage to the organic active layer. The first layer acts as a water barrier layer and also as a first protective layer for the deposition of a second silicon oxynitride (SiON) layer that could be processed by plasma-enhanced chemical vapor deposition (PECVD) at higher temperatures. The second layer ensures a better mechanical and chemical stability of the whole structure and also serves as a second protective layer from damages induced during the additional processing stages, such as photolithography or microlensing. With the TFE architecture the overall device stability at 85 °C and 85% relative humidity exceeded 1000 h without observable device performance decrease. This was confirmed by fabricating a green-light sensitive OPD characterized by a stable external quantum efficiency of 60–70%.
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- 2017
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5. Energy Gap between Photoluminescence and Electroluminescence as Recombination Indicator in Organic Small-Molecule Photodiodes
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Kwang Hee Lee, Moon Gyu Han, Yong Wan Jin, Seon-Jeong Lim, Sungyoung Yun, Tadao Yagi, Kyung-Bae Park, Sang Yoon Lee, Dong-Seok Leem, Xavier Bulliard, Gae Hwang Lee, and Yeong Suk Choi
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Physics ,Chemical substance ,Quenching (fluorescence) ,Photoluminescence ,business.industry ,Band gap ,02 engineering and technology ,Electroluminescence ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Polymer solar cell ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Photodiode ,law.invention ,General Energy ,Optics ,law ,Optoelectronics ,Physical and Theoretical Chemistry ,0210 nano-technology ,business ,Recombination - Abstract
Charge transfer (CT) states at the donor–acceptor interfaces play an important role in organic optoelectronic devices, yielding photocarrier generation or recombination losses. In this study, we fabricate and characterize vacuum-deposited organic photodiodes (OPDs) composed of SubPc:C60 with various active-layer thicknesses and mixing ratios in terms of the charge separation efficiency (CSE) and charge collection efficiency (CCE). We demonstrate that the combined field-assisted quenching study using both photoluminescence (PL) and electroluminescence (EL) reveals detailed information on the device physics of bulk heterojunction photodiodes as related to the CT state. Our modified PL quenching efficiency approach allows us to reasonably evaluate the CSE. In addition, we find that the EL energy is closely related to the recombination loss factor, and the energy gap between PL and EL exhibits a strong linear relationship with the CCE. As a result, the energy gap is proved to be a meaningful indicator of the ...
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- 2016
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6. The role of defects in organic image sensors for green photodiode
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Seong Heon Kim, Chul-Joon Heo, Yongsung Kim, Kyung-Bae Park, Takkyun Ro, Sung Heo, Jun-Ho Lee, Dong-Jin Yun, Gae Hwang Lee, EunAe Cho, Sunghan Kim, Dongwook Lee, Jooho Lee, and Yong Wan Jin
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0301 basic medicine ,Materials science ,Deep-level transient spectroscopy ,Silicon oxynitride ,Photodetector ,lcsh:Medicine ,Article ,law.invention ,03 medical and health sciences ,chemistry.chemical_compound ,0302 clinical medicine ,law ,lcsh:Science ,Multidisciplinary ,Dopant ,business.industry ,Doping ,lcsh:R ,Acceptor ,Photodiode ,030104 developmental biology ,chemistry ,Optoelectronics ,Quantum efficiency ,lcsh:Q ,business ,030217 neurology & neurosurgery - Abstract
Controlling defect states in a buffer layer for organic photo devices is one of the vital factors which have great influence on the device performance. Defect states in silicon oxynitride (SiOxNy) buffer layer for organic photo devices can be controlled by introducing appropriate dopant materials. We performed ab initio simulations to identify the effect on doping SiOxNy with carbon (C), boron (B), and phosphorous (P) atoms. The results unveil that hole defects in the SiOxNy layer diminish with the phosphorous doping. Based on the simulation results, we fabricate the small molecule organic photodetector (OPD) including the phosphorous-doped SiOxNy buffer layer and the active film of blended naphthalene-based donor and C60 acceptor molecules, which shows excellent enhancement in the external quantum efficiency (EQE). The results of our charge-based deep level transient spectroscopy (Q-DLTS) measurements confirmed that the EQE enhancement originates from the decrease of the hole traps induced by the reduced hole defects. The method of controlling the defect states in SiOxNy buffer layers by the doping can be used to improve the performance in various organic photo devices.
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- 2018
7. Dipolar donor–acceptor molecules in the cyanine limit for high efficiency green-light-selective organic photodiodes
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Yeong Suk Choi, Dong-Seok Leem, Xavier Bulliard, Takkyun Ro, Seon-Jeong Lim, Yong Wan Jin, Kyung-Bae Park, Ryuichi Satoh, Chul-Joon Heo, Sungyoung Yun, Sang Yoon Lee, Tadao Yagi, and Gae Hwang Lee
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Materials science ,business.industry ,Aryl ,Photodetector ,02 engineering and technology ,General Chemistry ,Specific detectivity ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Polymer solar cell ,0104 chemical sciences ,Photodiode ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Materials Chemistry ,Optoelectronics ,Moiety ,Quantum efficiency ,Cyanine ,0210 nano-technology ,business - Abstract
We report on two novel p-type small molecules with a donor–acceptor molecular structure for application to green-light-selective organic photodiodes (OPDs). To achieve the requirement of high light selectivity and sensitivity, an electron-donating aryl amino moiety is combined with two respective electron-accepting heterocycles so that the molecules approach cyanine-like character, characterized by intense and sharp absorption. Molecular stacking is controlled by the addition of bulky aryl functional groups to the main backbone to further control the electrical charge transport properties. With this molecular design, a maximum external quantum efficiency close to 61% (λmax = 550 nm) and a dark-current density below 1.6 nA cm−2 (or specific detectivity D* = 1.19 × 1013 cm Hz1/2 W−1) at an applied reverse bias of 3 V are obtained when mixed with fullerene (C60) in an inverted-structure bulk heterojunction OPD composed of two transparent electrodes. The potential construction of a full-color photodetector or an image sensor is demonstrated by combining the green-light-selective OPD with a silicon photodiode containing solely blue and red color filters in a stacked architecture.
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- 2016
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8. Narrow-Band Organic Photodiodes for High-Resolution Imaging
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Yong Wan Jin, Kyoung-won Na, Takkyun Ro, Sungyoung Yun, Chul-Joon Heo, Moon Gyu Han, Tadao Yagi, Sakurai Rie, Sang Yoon Lee, Seon-Jeong Lim, Dong-Seok Leem, Xavier Bulliard, Jung-Chak Ahn, Sang-chul Sul, Kyung-Bae Park, and Gae Hwang Lee
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Materials science ,Pixel ,business.industry ,Color image ,Heterojunction ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Photodiode ,law.invention ,Optics ,CMOS ,law ,Color gel ,Optoelectronics ,General Materials Science ,Image sensor ,0210 nano-technology ,business ,Absorption (electromagnetic radiation) - Abstract
There are growing opportunities and demands for image sensors that produce higher-resolution images, even in low-light conditions. Increasing the light input areas through 3D architecture within the same pixel size can be an effective solution to address this issue. Organic photodiodes (OPDs) that possess wavelength selectivity can allow for advancements in this regard. Here, we report on novel push–pull D−π–A dyes specially designed for Gaussian-shaped, narrow-band absorption and the high photoelectric conversion. These p-type organic dyes work both as a color filter and as a source of photocurrents with linear and fast light responses, high sensitivity, and excellent stability, when combined with C60 to form bulk heterojunctions (BHJs). The effectiveness of the OPD composed of the active color filter was demonstrated by obtaining a full-color image using a camera that contained an organic/Si hybrid complementary metal-oxide-semiconductor (CMOS) color image sensor.
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- 2016
9. Applications of multidirectional reflective light-control films on reflective polymer-dispersed liquid crystal displays for enhancement in image quality at lower viewing angles
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Gae Hwang Lee, Jin Woo Lee, Young Jae Jeon, Jae Eun Jung, Muhammad Jamil, Jae Eun Jang, Farzana Ahmad, and Kyu Young Hwang
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Brightness ,Fabrication ,Materials science ,Liquid-crystal display ,business.industry ,Scattering ,General Chemistry ,Condensed Matter Physics ,Light scattering ,law.invention ,Optics ,Liquid crystal ,law ,General Materials Science ,Contrast ratio ,Prism ,business - Abstract
In this paper, multidirectional light-control reflective (LCR) films are developed in order to create an active reflective structure that will enhance the image brightness and contrast ratio of reflective dye-doped polymer-dispersed liquid crystal (D-PDLC) displays at lower viewing angles. Advantages of LCR films are that their production is low cost and they require a simple photolithographic fabrication method. The optimum design prism-type light-control reflective film succeeded in minimising the surface scattering effect; thus, the contrast ratio is much enhanced. The symmetric and asymmetric LCR films produced multidirectional scattering that enhances the reflectance at lower viewing angles, which has importance in future display applications. In particular, the prism LCR film has been found to be more influential on the reflectance of D-PDLC films due to multidirectional scattering of light by non-symmetric arrays. The improvement in contrast ratio has been confirmed by the enhancement of optical pr...
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- 2012
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10. Ablative microstructuring with plasma-based XUV lasers and efficient processing of materials by dual action of XUV/NIR–VIS ultrashort pulses
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Gae Hwang Lee, Bedřich Rus, SoonAe Park, Tomas Fort, Jaroslav Sobota, Chang Hee Nam, Taekeun Kim, Michaela Kozlova, Věra Hájková, Libor Juha, J. Hrebicek, Tomas Mocek, M. Sawicka, Krzysztof Jakubczak, Chul Min Kim, Jiri Polan, P. Homer, I. J. Kim, and Jaromir Chalupsky
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Nuclear and High Energy Physics ,Radiation ,Materials science ,business.industry ,Plasma ,Condensed Matter Physics ,Laser ,law.invention ,X-ray laser ,Optics ,law ,Extreme ultraviolet ,Optoelectronics ,High harmonic generation ,General Materials Science ,Charge carrier ,business ,Absorption (electromagnetic radiation) ,Lithography - Abstract
We report on a single-shot micropatterning of an organic polymer achieved by ablation with demagnifying projection using a plasma-based extreme ultraviolet (XUV) laser at 21 nm. A nickel mesh with a period of 100 μ m was 10×demagnified and imprinted on poly(methyl methacrylate) (PMMA) via direct ablation. This first demonstration of single-shot projection, single-step lithography illustrates the great potential of XUV lasers for the direct patterning of materials with a resolution scalable down to the submicrometer domain. In the second part, we present a novel experimental method for improving the efficiency of surface processing of various solids achieved by simultaneous action of XUV, obtained from high-order harmonic generation, and near-infrared (NIR)–VIS laser pulses. The NIR–VIS pulse interacts with free charge carriers produced by the energetic XUV photons, so that its absorption dramatically increases. Laser-induced periodic surface structures were effectively produced using this technique.
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- 2010
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11. Organic-on-silicon complementary metal–oxide–semiconductor colour image sensors
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Dong-Seok Leem, Xavier Bulliard, Chul-Joon Heo, Myung-Won Lee, Gae Hwang Lee, Tae-Yon Lee, Seon-Jeong Lim, Sang-chul Sul, Tadao Yagi, Takkyun Ro, Jung-kyu Jung, Kyung-Bae Park, Ryuichi Satoh, Moon Gyu Han, Yong Wan Jin, Im Dong-Mo, Kwang Hee Lee, Kyu-Sik Kim, Kyoung-won Na, and Sang Yoon Lee
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CMOS sensor ,Multidisciplinary ,Materials science ,Pixel ,Silicon ,business.industry ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,chemistry.chemical_element ,Bioinformatics ,Article ,Photodiode ,law.invention ,Organic semiconductor ,CMOS ,chemistry ,law ,Hardware_INTEGRATEDCIRCUITS ,Optoelectronics ,Image sensor ,business ,Absorption (electromagnetic radiation) - Abstract
Complementary metal–oxide–semiconductor (CMOS) colour image sensors are representative examples of light-detection devices. To achieve extremely high resolutions, the pixel sizes of the CMOS image sensors must be reduced to less than a micron, which in turn significantly limits the number of photons that can be captured by each pixel using silicon (Si)-based technology (i.e., this reduction in pixel size results in a loss of sensitivity). Here, we demonstrate a novel and efficient method of increasing the sensitivity and resolution of the CMOS image sensors by superposing an organic photodiode (OPD) onto a CMOS circuit with Si photodiodes, which consequently doubles the light-input surface area of each pixel. To realise this concept, we developed organic semiconductor materials with absorption properties selective to green light and successfully fabricated highly efficient green-light-sensitive OPDs without colour filters. We found that such a top light-receiving OPD, which is selective to specific green wavelengths, demonstrates great potential when combined with a newly designed Si-based CMOS circuit containing only blue and red colour filters. To demonstrate the effectiveness of this state-of-the-art hybrid colour image sensor, we acquired a real full-colour image using a camera that contained the organic-on-Si hybrid CMOS colour image sensor.
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- 2015
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12. Efficient surface processing by ultrafast XUV/NIR dual action
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Libor Juha, Tomas Mocek, Gae Hwang Lee, Taekeun Kim, Chang Hee Nam, Krzysztof Jakubczak, Laura Gemini, Bedřich Rus, Jaromir Chalupsky, M. Toufarová, Daniele Margarone, SoonAe Park, and Věra Hájková
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Laser ablation ,Materials science ,business.industry ,chemistry.chemical_element ,Laser ,law.invention ,Optics ,Amorphous carbon ,chemistry ,law ,Extreme ultraviolet ,Femtosecond ,Optoelectronics ,Thin film ,business ,Ultrashort pulse ,Carbon - Abstract
We have developed a novel method for efficient structuring of the surface of materials by applying femtosecond near infrared laser pulses simultaneously with a weak extreme ultraviolet beam, which leads to a very strong radiation-matter interaction and brings a dramatic increase of the surface processing speed. We present our recent experimental results on surface nanostructuring of thin films of amorphous carbon and polymethyl methacrylate deposited on bulk substrates and discuss the underlying physical mechanisms. In the case of amorphous carbon, large areas of laser-induced periodic surface structures with a spatial period of 550 nm were created, having their origin in laser-induced convective currents. Our method provides a powerful tool for fast modification of tribological properties of the irradiated sample.
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- 2011
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13. Characteristics of color optical shutter with dye-doped polymer network liquid crystal
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Jae Eun Jang, J.E. Jung, Suyoun Lee, Kyu-young Hwang, Gae Hwang Lee, and Y. W. Jin
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chemistry.chemical_classification ,Materials science ,business.industry ,Scattering ,Optical instrument ,Physics::Optics ,Polymer ,Atomic and Molecular Physics, and Optics ,Light scattering ,law.invention ,Condensed Matter::Soft Condensed Matter ,Optics ,chemistry ,Liquid crystal ,law ,Shutter ,Attenuation coefficient ,Optoelectronics ,business ,Absorption (electromagnetic radiation) - Abstract
The optical properties and the theoretical prediction of color optical shutter with dye-doped polymer network liquid crystal (PNLC) were investigated. The view-angle dependence of reflectance according to the bias conditions showed distinctive characteristics, which could be explained from the effects of dye absorption and path length. It was also shown that the thickness dependence of reflectance was strongly influenced by the light-scattering coefficient. Our experimental results matched up well with the theoretical prediction based on the light scattering of liquid crystals in polymer network and the absorption of dichroic dye. This work indicates potential to improve the optical device using dye-doped liquid crystal-polymer composite.
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- 2011
14. Highly Efficient Surface Modification of Solids by Dual Action of XUV/Vis-NIR Laser Pulses
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Gae Hwang Lee, Věra Hájková, Jaromír Chalupský, Jiri Polan, Krzysztof Jakubczak, P. Homer, I. J. Kim, Taekeun Kim, SoonAe Park, Chang Hee Nam, Chul Min Kim, Libor Juha, Tomas Mocek, and Bedřich Rus
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Materials science ,business.industry ,Radiation ,Laser ,Fluence ,law.invention ,Optics ,Amorphous carbon ,law ,Extreme ultraviolet ,Surface modification ,High harmonic generation ,Irradiation ,business - Abstract
We demonstrate a novel experimental method for unusual structural surface modification of various solids (PMMA, amorphous carbon) achieved by simultaneous action of XUV (21.6 nm), obtained from high-order harmonic generation, and Vis-NIR (410/820 nm) laser pulses. Although the fluence of each individual pulse was far below the surface ablation threshold, very efficient and specific material expansion was observed after irradiation by a few shots of mixed XUV/Vis-NIR radiation.
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- 2009
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15. Development of ultrafast soft x-ray beamline based on high-order harmonic generation at PALS
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Dong Hyuk Ko, Chang Hee Nam, I Jong Kim, Krzysztof Jakubczak, Gae Hwang Lee, Bedrich Rus, Tomas Mocek, and Deuk Su Kim
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Materials science ,business.industry ,Holography ,Nonlinear optics ,Laser ,law.invention ,Interferometry ,Optics ,Beamline ,law ,Sapphire ,High harmonic generation ,business ,Ultrashort pulse - Abstract
We report on the development of ultrafast coherent soft X-ray beamline at the Prague Asterix Laser System (PALS) Research Center intended for interdisciplinary applications such as ablation and controlled surface modification of solid materials for a micro/nano-patterning, soft X-ray interferometry and holography for surface probing with nanometric resolution, and improvement of focusing optics for soft X-ray beams. The beamline is based on 1 kHz, table-top, highorder harmonic generation (HHG) source capable of delivering fully coherent beam, tunable in the 13 - 40 nm spectral range. The Ti:sapphire (810 nm) laser pulses with a duration of 35 fs and energy 1.1 mJ are focused into a static gas cell containing conversion medium (Ar). To achieve highly efficient HHG at 30 nm we apply the technique of guided laser pulses. Experimental results on HHG source characterization, optimization, and spectral tunability are presented. Achievements on the implementation of so called two-color HHG using gas cell have been reported for the first time. The complete beamline will consist of a tandem of two vacuum chambers: one for the HHG source and its diagnostics, and second intended for the application experiments. The access to this new soft X-ray installation will be opened to external users since 2009.
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- 2008
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16. Measurement of the polarization of high-order harmonics from aligned N(2) molecules by spatial interferometry
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Tae Keun Kim, Chang Hee Nam, I Jong Kim, Seung Beom Park, and Gae Hwang Lee
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Physics ,business.industry ,Polarimetry ,Optical polarization ,Laser ,Polarization (waves) ,Diatomic molecule ,Atomic and Molecular Physics, and Optics ,law.invention ,Interferometry ,Optics ,law ,Harmonics ,High harmonic generation ,business - Abstract
The polarization of high-harmonics from aligned N(2) molecules was measured by observing the visibility of spatial interference between two high-harmonics generated separately. The minimum visibility was observed at an angle of 60 degrees between the polarization of the harmonic generation laser field and the molecular orientation. In this case, the angular shift of harmonic polarization is 15 degrees from the molecular orientation. Our measurement of the visibility variation matches the theoretical prediction based on the harmonic field calculation for aligned N(2) molecules.
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- 2008
17. Control of rotational wave packets in field-free molecular alignment by chirped laser pulses
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Chang Hee Nam, Yong Soo Lee, I Jong Kim, Seung Beom Park, and Gae Hwang Lee
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Physics ,Field (physics) ,business.industry ,Phase (waves) ,Physics::Optics ,Laser ,Signal ,law.invention ,Optics ,law ,Rotational wave ,Harmonics ,Physics::Atomic and Molecular Clusters ,Chirp ,Physics::Accelerator Physics ,Physics::Atomic Physics ,Molecular alignment ,business ,Nonlinear Sciences::Pattern Formation and Solitons - Abstract
We experimentally observed revival signals of high-order harmonics under field-free molecular alignment by applying chirp-free and chirped laser pulses. The revival signal obtained even with chirp-free laser pulses exhibited linearly dependant spectral phase with respect to frequency, and the slope of the spectral phase changed with the laser chirp condition.
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- 2007
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18. Generation of Exceptionally Strong Harmonics from He in an Orthogonally Polarized Two-color Laser Field
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Hyung Taek Kim, Chul Min Kim, I Jong Kim, Chang Hee Nam, and Gae Hwang Lee
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Physics ,Field (physics) ,business.industry ,Energy conversion efficiency ,Electron ,Laser ,law.invention ,Optics ,law ,Harmonics ,Harmonic ,High harmonic generation ,business ,Order of magnitude - Abstract
Highly efficient high-harmonic generation was achieved using a two-color laser field that consisted of the fundamental and its second harmonic. The harmonics generated in an orthogonally polarized two-color field were stronger than those obtained in the fundamental field by more than two orders of magnitude. Conversion efficiency as high as 5 × 10−5 was obtained for the 38th harmonic (21.6 nm) from helium driven by the two-color laser field with a proper relative phase. This enhancement is explained by analyzing the electron behavior in the two-color field. In addition, we confirmed the effects of mixed field by controlling the time delay between the two-color laser fields.
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- 2007
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19. Generation of efficient high harmonics in an orthogonally polarized two-color laser field
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Hyung Taek Kim, Yong Soo Lee, Ju Yun Park, Chang Hee Nam, Chul Min Kim, I Jong Kim, and Gae Hwang Lee
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Physics ,business.industry ,Energy conversion efficiency ,Laser ,Polarization (waves) ,law.invention ,Optics ,law ,Harmonics ,Femtosecond ,Sapphire ,Optoelectronics ,High harmonic generation ,business ,Order of magnitude - Abstract
Highly efficient high-harmonic generation was achieved in helium using an orthogonally polarized two-color laser field that consisted of the fundamental and second harmonic of a femtosecond Ti:sapphire laser. By applying a higher intensity second harmonic, the harmonics in the two-color field were stronger than those obtained in the fundamental field by more than two orders of magnitude. The conversion efficiency was as high as 5/spl times/10/sup -5/ for the 38/sup th/ harmonic at 21.6 nm.
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- 2005
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20. Highly Efficient High-Harmonic Generation in an Orthogonally Polarized Two-Color Laser Field
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Yong Soo Lee, Chang Hee Nam, Ju Yun Park, David Jaeyun Cho, Chul Min Kim, Gae Hwang Lee, Hyung Taek Kim, and I Jong Kim
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Physics ,business.industry ,Energy conversion efficiency ,General Physics and Astronomy ,Electron ,Laser ,Polarization (waves) ,law.invention ,Optics ,law ,Electric field ,Harmonics ,Femtosecond ,High harmonic generation ,Atomic physics ,business - Abstract
Highly efficient high-harmonic generation was achieved in helium using a two-color laser field that consisted of the fundamental and the second harmonic fields of a femtosecond Ti:sapphire laser. By applying a high intensity second harmonic, the harmonics generated in the orthogonally polarized two-color field were stronger than those obtained in the fundamental field by more than 2 orders of magnitude, and even stronger than those of the parallel polarization case. A conversion efficiency as high as $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ was obtained for the 38th harmonic at 21.6 nm. The physical origin of this enhancement was deduced by analyzing the electron behavior in the two-color field.
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- 2005
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21. Enhanced surface structuring by ultrafast XUV/NIR dual action
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Vera Hájková, Jaromir Chalupsky, Tomas Mocek, Libor Juha, M. Toufarová, Bedrich Rus, Krzysztof Jakubczak, Seung Beom Park, Tae Keun Kim, Chang Hee Nam, and Gae Hwang Lee
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Physics ,business.industry ,Energy conversion efficiency ,General Physics and Astronomy ,Laser ,Spectral line ,law.invention ,Optics ,Amorphous carbon ,law ,Extreme ultraviolet ,Femtosecond ,Optoelectronics ,Thin film ,business ,Ultrashort pulse - Abstract
Materials processing utilizing ultrashort near-infrared (NIR) laser pulses with duration in the range of tens to hundreds of femtoseconds (1fs = 10 15 s) has attracted a great deal of interest in the scientific and industrial world recently. Unfortunately, a number of materials that often exhibit great technological and scientific importance are transparent in NIR, making it very difficult to process them by laser radiation in this spectral range. Here, we present a new method for the efficient structuring of the surface of materials by applying femtosecond NIR laser pulses simultaneously with a weak extreme ultraviolet (XUV) beam, which leads to very strong radiation-matter interaction, bringing a dramatic increase in the surface processing speed. A laser system providing 5mJ, 820nm, 32fs, 10Hz pulses was used to generate high-order harmonics with the strongest spectral line at 21nm and with a conversion efficiency of 5%. The two beams were focused on the samples by using an off-axis paraboloidal multilayer mirror. As an example, we present the results of the surface nanostructuring of thin films of amorphous carbon and poly(methyl methacrylate) deposited on bulk substrates. We discuss the physical mechanisms that lead to the laser-induced periodic surface structures when our method is used.
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- 2011
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22. Surface modification of organic polymer by dual action of extreme ultraviolet/visible-near infrared ultrashort pulses
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Chang Hee Nam, Chul Min Kim, Bedřich Rus, Tomas Mocek, Věra Hájková, Jaromír Chalupský, Krzysztof Jakubczak, Jiri Polan, P. Homer, I. J. Kim, Libor Juha, and Gae Hwang Lee
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Materials science ,Infrared ,business.industry ,General Physics and Astronomy ,Laser ,Fluence ,law.invention ,law ,Extreme ultraviolet ,Optoelectronics ,Surface modification ,Optical radiation ,Irradiation ,Absorption (electromagnetic radiation) ,business - Abstract
We present the experimental evidence of structural surface modifications of poly(methyl methacrylate) (PMMA) caused by simultaneous action of extreme ultraviolet (XUV) (∼21 nm) and visible-near infrared (visible-NIR) (820/410 nm) ultrashort pulses. Although the fluence of each individual beam was far below the surface modification threshold, very efficient and specific material expansion was observed after irradiation of PMMA by more than ∼20 shots of mixed XUV/visible-NIR radiation. As the XUV photons generate free charge carriers, absorption of the optical radiation dramatically increases, which heats up the material and further enhances the XUV induced damage to the polymer chain.
- Published
- 2009
- Full Text
- View/download PDF
23. Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field
- Author
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Tomas Mocek, Gae Hwang Lee, I Jong Kim, Tae Keun Kim, Chang Hee Nam, Seung Beom Park, Krzysztof Jakubczak, and Yong Soo Lee
- Subjects
Physics ,Jet (fluid) ,Physics and Astronomy (miscellaneous) ,Field (physics) ,business.industry ,Energy conversion efficiency ,chemistry.chemical_element ,Laser ,law.invention ,Optics ,chemistry ,law ,Harmonics ,Harmonic ,High harmonic generation ,business ,Helium - Abstract
We have achieved very efficient high-harmonic generation in a two-color laser field using a long gas jet of He. With the optimization of laser parameters and target conditions, strong harmonics were produced at 2(2n+1)th orders in an orthogonally polarized two-color field. The strongest harmonic at the 38th order (21.6nm) reached an energy of 0.6μJ with a 6mm gas jet, giving a conversion efficiency as high as 2×10−4.
- Published
- 2008
- Full Text
- View/download PDF
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