• Proceedings of the Korean Nuclear Society Conference
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• 2003.10a
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• pp.246.1-246.1
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• 2003

• Proceedings of the Optical Society of Korea Conference
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• 2006.07a
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• pp.487-487
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• 2006

• The Journal of the Korean dental association
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• v.49 no.11
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• pp.660-669
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• 2011

Er: YAG laser irradiation utilizing the newly developed RCLase side-firing spiral tip was used for the cleansing of root canals following their bio-mechanical preparation with ProTaper Ni-Ti files. The distal and palatal roots of 20 freshly extracted molar teeth were instrumented to size F3 with ProTaper files. In the experimental group (10 teeth) the pulp chamber and the root canals were filled with EDTA 17% and the root canals were lased for 30 s using the Er: YAG laser irradiation at 600 mJ per pulse and a frequency of 12 Hz. In the control group (10 teeth) the root canals were not lased. Scanning electron microscope analysis showed clean wall surfaces of the lased root canals with open dentinal tubules, free of smear layer and debris. In the scanning electron microscope photographs of the walls of the non-lased root canals a considerable amount of debris could be detected. It appears that an efficient cleansing of the root canal system can be achieved by using the Er: YAG laser irradiation with the RCLase Side-firing Spiral Tip following bio-mechanical preparation of the root canal with Ni-Ti Taper files.

• Journal of Oral Medicine and Pain
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• v.24 no.4
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• pp.397-410
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• 1999

In order to obtain the basic data concerning the optimal parameters in using Nd:YAG laser as a therapeutic modality to dentinal hypersensitivity, the author prepared 3 sections of sound dentin and 10 sections of sclerotic dentin with thickness of $0.5mm{\pm}0.1mm$ from human extracted teeth of anteriors and premolars, and applied the laser energy from a fiberoptic delivered, free running, pulsed Nd:YAG laser (wavelength 1064nm, pulse duration $120{\mu}sec$, fiber diameter $320{\mu}m$) to surfaces of sound and sclerotic dentin sections for 1 second with contact/unidirectional moving mode of the fiber under speed of 3mm~4mm/sec and parameters of 0.5W/10Hz, 1.0W/10Hz, 1.5W/10Hz, 2.0W/10Hz: $62J/cm^2$, $124J/cm^2$, $187J/cm^2$, $249J/cm^2$. The author comparatively evaluated the characteristics of ultrastructural changes on surfaces of sound and sclerotic dentin sections irradiated by the pulsed Nd:YAG laser using the scanning electron microscopy. A fairly ill-defined bordered surface of partially closed and melted dentinal tubules can be seen on the scanning electron microscopic feature of the sound dentin surface irradiated by the pulsed Nd:YAG laser with energy density of $62J/cm^2$. The physical modification of sound dentin surface extensively occurred depended on the increase of energy density from $62J/cm^2$ to $124J/cm^2$, $187J/cm^2$, $249J/cm^2$. While, a fairly well-defined bordered surface of partially closed and melted dentinal tubules with thickened peritubular dentin can be seen on the scanning electron microscopic feature of the sclerotic dentin surface irradiated by the pulsed Nd:YAG laser with energy density of $62J/cm^2$. The physical modification of sclerotic dentin surface of a fairly rough, shallow depression with many cracks, thickened peritubular dentin and structureless dentinal tubules extensively occurred depended on the increase of energy density from $62J/cm^2$ to $124J/cm^2$, $187J/cm^2$, $249J/cm^2$ compared to those of sound dentin surface irradiated by the pulsed Nd:YAG laser under the same parameters. Therefore, it is recommended that the pulsed Nd:YAG laser as a therapeutic modality to dentinal hypersensitivity should be applied with the less energy density than $62J/cm^2$ on the sound dentin surface, and its energy density on the partially sclerotic dentin surface should be lower than that on the sound dentin surface to preserve tooth from unnecessary excessive structural destruction.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.285-287
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• 1997

We have deposited hydrogen-free diamond-like carbon (DLC) films by pulsed laser deposition of graphite. Pulsed laser deposition (PLD) can be utilized to generate films with desired properties quite different from those of the starting material. Since DLC films grown by PLD using turbo pump are perpared without hydrogen, they have a higher density and a higher index of refraction than the hydrogenated DLC films. In this study, effects of the substrate temperature and laser energy density on the properties of DLC films were systematically investigated. The structure and properties of the films have been studied by scanning electron microscopy (SEM), Fourier Transform Infrared (FT-IR), X-ray diffraction (XRD), and Raman spectroscopy.

• Korean Journal of Metals and Materials
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• v.48 no.2
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• pp.163-168
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• 2010

We here describe the laser-direct patterning of nanostructured metal thin films. This method involves light-matter interaction in which a pulsed laser beam impinging on the film generates a thermoelastic force that plays a role to detach the film from the substrate or underlying layers. A moderate cohesion of the nanostructured film enables localized desorption of the material upon irradiation by a spatiallymodulated laser beam, giving good fidelity with the transfered pattern. This photoresist-free process provides a simple high-resolution scheme for patterning metal thin films.

• Journal of the Optical Society of Korea
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• v.12 no.4
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• pp.303-308
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• 2008

Directly modulated fiber-optic links generally suffer higher link loss and larger signal distortion than externally modulated links. These result from the electron-photon conversion loss and laser modulation dynamics. As a method to overcome the drawbacks, we have experimentally demonstrated the RF performance of directly modulated, ultra-strong injection-locked gain-lever distributed Bragg reflector (DBR) lasers. The free-running DBR lasers exhibit an improved amplitude modulation efficiency of 12.4 dB under gain-lever modulation at the expense of linearity. By combining gain-lever modulation with ultra-strong optical injection locking, we can gain the benefits of both improved modulation efficiency from the gain-lever effect, plus improved linearity from injection locking. Using an injection ratio of R=11 dB, a 23.4-dB improvement in amplitude response and an 18-dB improvement in spurious-free dynamic range have been achieved.

• 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.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.942-944
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• 1992

The free electron laser (FEL) is driven by electron beams with energies ranging from hundreds of kilovolt to hundreds of megavolt. Therefore the efficiency of FEL strongly depends on the beam quality. In this paper we examined the relation between applied voltage and magnetic field at the magnetically insulated cylindrical cold cathode for the high quality electron beam by the numerical analysis. As a result, we knew that the beam widening strongly depended on applied magnetic field and voltage.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.5
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• pp.871-876
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• 2019

We fabricated concave optical fiber tips using hydrofluoric acid solution and photothermal effect induced by $1.55{\mu}m$ wavelength laser applied to an optical fiber. The radius of curvature of the concave optical fiber tips fabricated with different applied laser power, etching time, and concentration of hydrofluoric acid was measured with an optical microscope. Then, we analyzed how the radius of curvature changes for those three variables. In addition, the reliability of the measurement method using a microscope was verified through a free spectral range(FSR) and a scanning electron microscope(SEM). Through this paper, the radius of curvature can be adjusted by the variables of the fabrication process of concave optical fiber tips; thus, it is overcoming the limitations of conventional optical fiber etching methods using hydrofluoric acid solutions.