• Korean Journal of Materials Research
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• v.17 no.9
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• pp.475-479
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• 2007

Pulsed laser deposition was utilized to grow MnS thin films on c-sapphire substrate using a KrF excimer laser at growth temperatures that ranged from room temperature to $700^{\circ}C$. The results of X-ray diffraction (XRD) and UV-visible spectroscopy were employed to investigate the structural and optical properties of the MnS films. While the growth rate decreased as $T_s$ increased, the overall quality of the film improved. The highest quality MnS film was obtained at $700^{\circ}C$. Variations in the $T_s$ resulted in the MnS films exhibiting different growth mechanisms. The oriented (200) rocksalt MnS film was grown at room temperature. In the case of higher $T_s,\;200{\sim}500^{\circ}C$, the films consisted of mixed phases of rocksalt and wurtzite. The main structure of the films was altered to (111) rocksalt when the temperature was increased to in excess of $600^{\circ}C$. This behavior may very well be the result of elements such as surface energy and atomic arrangement during the growth process. The optical band gap of the obtained ${\alpha}-MnS$ film was estimated to be 3.32 eV.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2692-2695
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• 2008

Polydiacetylene (PDA) is chemosensor materials that exhibit non-fluorescent-to-fluorescent transition as well as blue-to-red visible color change upon chemical or thermal stress. They have been studied in forms of film or microarray chip, so far. In this paper, we provide a novel technique to fabricate continuous micro-fiber PDA sensor using in-situ laser-polymerization technique and 3-D hydrodynamic focusing on a microfluidic chip. The flow of a monomer solution with diacetylene (DA) monomer is focused by a sheath flow on a 3-D microfluidic chip. The focused flow is exposed to 365 nm UV laser beam for in-situ polymerization which generates a continuous fiber containing DA monomers. Then, the fiber is exposed to 254 nm UV light to polymerize DA monomers to PDA. Preliminary results indicate that the fiber size can be controlled by the flow rates of the monomer solution and sheath flows and that a PDA sensor fiber successively responds to chemical and thermal stress.

• Journal of Photoscience
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• v.5 no.2
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• pp.63-67
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• 1998

New photoinitiator systems of dimethylphenacylsulfonium butyltnphenylborate (DMPSB) as a donor-acceptor initiator and styryl dyes have been investigated for free radical polymerization of an acrylate with visible lasers (488, 514 and 647 nm). DMPSB was able to be sensitized by many styryl dyes. When polymerized with pentaerythrithol triacrylate, the sensitivity value of the photosensitive layer containing DMPSB was higher than that of an tetrabutylammonium butyltnphenylborate (TBAB) as an electron donating initiator or a dimethylphenacylsulfonium tetrafiuoroborate (DMPS) as an electron accepting initiator. The sensitivity values of the photosensitive layer containing the photoinitiator systems had a close relation to the free energy changes between the excited singlet styryl dyes and DMPSB.

• Information and Communications Magazine
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• v.28 no.12
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• pp.50-60
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• 2011

Visible light communication(VLC) is one type of short-range, optical, and wireless communication system utilizing light emitting diode(LED) and laser diode(LD) as optical source. In a VLC system, visible light is used as a transmission medium and used to illuminate. Using VLC has a lot of advantages: it is harmless to human body; it transmits with high power, and it has excellent security, a high data rate, and a license free frequency band. With such a unique blend of communication and illumination in one system, the most common application would be an indoor environment. We aim at reviewing key issues in VLC network such as : FOV(field of view), priority MAC, cooperative MAC, link switching, LED-ID technique, cell site diversity, and link recovery.

• Journal of the Optical Society of Korea
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• v.3 no.1
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• pp.27-31
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• 1999

The two-photon absorption of a SiC photodiode was utilized to obtain autocorrelation signals of the pulses from a mode-locked Rh6G dye laser. The autocorrelation signals were in good agreement with those obtained by a conventional autocorrelator using a second harmonic crystal and photomultiplier tube. The sensitivity of the autocorrelator with the SiC photodiode was about $4{\times}10^3 {(mW)}^2$ . From these results it was demonstrated that the SiC photodiode is suitable as a nonlinear device for an autocorrelation measurement in the visible range.

• Journal of Oral Medicine and Pain
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• v.18 no.2
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• pp.97-106
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• 1993

This study was performed to investigate the effects of infrared and visible light laser irradiation on cell viability of human gingival fibroblast. For the present study, the author used cultured fibroblast originated from sound gingiva which were fifth of sixth passage. Laser machine utilized here were stomalaser which irradiate infrared (GaAs diode) and red (HeNe) laser in turn with pulse wave pattern or continuous wave pattern, and the machine had several frequency mode presented by regeneration, relaxation and analgesic modalities. Cultured fibroblast samples were divided by this modalities of cell counts and laser exposure time which were 7-seconds of 150 seconds, respectively. 1 day after laser irradiation, each cell-well was treated with MTT and measured optical density with ELISA. The obtained results were as follows : 1. There was a tendency of increasing optical density in proportion to irradiation time in groups of $1\times10^4$ cell per well but in groups of $5\times10^3$ cell per well, reverse phenomena were observed. 2. The difference of optical density according to frequency modalities were not showed significantly except several cases in groups of $5\times10^3$ cell per well. 3. In general, cell viability of cultured human gingival fibroblast wer not showed consistent feature by low level laser irradiation.

• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.78-87
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• 2016

Red blood cells (RBCs) are customarily adhered to a bio-functionalised substrate to make them stationary in interferometric phase-imaging modalities. This can make them susceptible to receive alterations in innate morphology due to their own weight. Optical tweezers (OTs) often driven by Gaussian profile of a laser beam is an alternative modality to overcome contact-induced perturbation but at the same time a steeply focused laser beam might cause photo-damage. In order to address both the photo-damage and substrate adherence induced perturbations, we were motivated to stabilize the RBC in OTs by utilizing a laser beam of ‘arbitrary intensity profile’ generated by a source having cavity imperfections per se. Thus the immobilized RBC was investigated for phase-imaging with sinusoidal interferograms generated by a compact and robust Michelson interferometer which was designed from a cubic beam splitter having one surface coated with reflective material and another adjacent coplanar surface aligned against a mirror. Reflected interferograms from bilayers membrane of a trapped RBC were recorded and analyzed. Our phase-imaging set-up is limited to work in reflection configuration only because of the availability of an upright microscope. Due to RBC’s membrane being poorly reflective for visible wavelengths, quantitative information in the signal is weak and therefore, the quality of experimental results is limited in comparison to results obtained in transmission mode by various holographic techniques reported elsewhere.

• Laser Solutions
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• v.17 no.1
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• pp.1-6
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• 2014

Indium tin oxide (ITO) is an important transparent conducting oxide (TCO). ITO films have been widely used as transparent electrodes in optoelectronic devices such as organic light-emitting devices (OLED) because of their high electrical conductivity and high transmission in the visible wavelength. Finding ways to control ITO micromachining depth is important role in the fabrication and assembly of display field. This study presented the depth control of ITO patterns on glass substrate using a femtosecond laser and slit. In the proposed approach, a gaussian beam was transformed into a quasi-flat top beam by slit. In addition, pattern of square type shaped by slit were fabricated on the surfaces of ITO films using femtosecond laser pulse irradiation, under 1030nm, single pulse. Using femtosecond laser and slit, we selectively controlled forming depth and removed the ITO thin films with thickness 145nm on glass substrates. In particular, we studied the effect of pulse number on the ablation of ITO. Clean removal of the ITO layer was observed when the 6 pulse number at $2.8TW/cm^2$. Furthermore, the morphologies and fabricated depth were characterized using a optical microscope, atomic force microscope (AFM), and energy dispersive X-ray spectroscopy (EDS).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.867-872
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• 2020

Oil storage tanks are a major structure in chemical industrial complexes. Damage to the structure due to natural disasters or poor management can cause additional damage, such as leakage of chemicals, fire, and explosion, so it is essential to understand the deformation. In this study, data on oil storage tanks were acquired using a 3D laser scanner, and various analyzes were performed for storage tank management by comparing them with design data. Modeling of the oil storage tank was performed using the data and design drawings acquired by a 3D laser scanner. An inspection of the oil storage tank was effectively performed by overlapping. In addition, cross-sectional and exploded views of the deformation were produced to generate visible data on the deformation of the facility, and it was suggested that the oil storage tank had a maximum deformation of -7.16mm through quantitative analysis. Data that can be used for additional work was obtained by producing drawings to be precisely inspected for areas with large deformation. In the future, an inspection of oil storage tanks using 3D laser scanners is quantitative and visible data on oil storage tank deformation. This will greatly improve the efficiency of facility management by rebuilding it.

• Journal of the Optical Society of Korea
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• v.13 no.1
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• pp.65-74
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• 2009

Device quality indium tin oxide (ITO) films are deposited on glass substrates and ultra-thin diamond-like carbon films are deposited as a buffer layer on ITO by a pulsed Nd:YAG laser at 355 nm and 532 nm wavelength. ITO films deposited at room temperature are largely amorphous although their optical transmittances in the visible range are > 90%. The resistivity of their amorphous ITO films is too high to enable an efficient organic light-emitting device (OLED), in contrast to that deposited by a KrF laser. Substrate heating at $200^{\circ}C$ with laser wavelength of 355 nm, the ITO film resistivity decreases by almost an order of magnitude to $2{\times}10^{-4}\;{\Omega}\;cm$ while its optical transmittance is maintained at > 90%. The thermally induced crystallization of ITO has a preferred <111> directional orientation texture which largely accounts for the lowering of film resistivity. The background gas and deposition distance, that between the ITO target and the glass substrate, influence the thin-film microstructures. The optical and electrical properties are compared to published results using other nanosecond lasers and other fluence, as well as the use of ultra fast lasers. Molecularly doped, single-layer OLEDs of ITO/(PVK+TPD+$Alq_3$)/Al which are fabricated using pulsed-laser deposited ITO samples are compared to those fabricated using the commercial ITO. Effects such as surface texture and roughness of ITO and the insertion of DLC as a buffer layer into ITO/DLC/(PVK+TPD+$Alq_3$)/Al devices are investigated. The effects of DLC-on-ITO on OLED improvement such as better turn-on voltage and brightness are explained by a possible reduction of energy barrier to the hole injection from ITO into the light-emitting layer.