• Journal of the Korean Vacuum Society
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• v.7 no.4
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• pp.403-409
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• 1998

In this study, the effects of multi-dipole type of magnets on the characteristics of the inductively coupled plasmas and $SiO_2$ etch properties were investigated. As the magnets, 4 pairs of permanent magnets were used and, to etch $SiO_2, C_2F_6, CHF_3, C_4F_8, H_2$, and their combinations were used. The characteristics of the magnetized inductively coupled plasmas were investigated using a Langmuir probe and an optical emission spectrometer, and $SiO_2$ etch rates and the etch selectivity over photoresist were measured using a stylus profilometer. The use of multi-dipole magnets increased the uniformity of the ion density over the substrate location even though no significant increase of ion density was observed with the magnets. The use of the magnets also increased the electron temperature and radical densities while reducing the plasma potential. When $SiO_2$ was etched using the fluorocarbon gases, the significant increase of $SiO_2$ etch rates and also the increase of etch uniformity over the substrate were obtained using the magnets. In case of gas combinations with hydrogen, $C_4F_8/H_2$ showed the highest etch rates and etch selectivities over photoresist among the gas combinations with hydrogen used in the experiment. By optimizing process parameters at 1000 Watts of inductive power with the magnets, the highest $SiO_2$ etch rate of 8000 $\AA$/min could be obtained for 50% $C_4F_8/50% H_2$.

• Korean Journal of Optics and Photonics
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• v.29 no.6
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• pp.241-246
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• 2018

In this paper, a low-cost optical temperature sensor is implemented, using a fiber Bragg grating (FBG) as the temperature probe and a low-cost VCSEL with temperature-dependent output wavelength as the light source. To analyze the wavelength of the reflected light from the FBG, an interrogation was applied using a method of referring to the internal temperature according to the output wavelength of the VCSEL. When the temperature of the VCSEL was adjusted from 14 to $52.2^{\circ}C$, the output wavelength varied from 1519.90 to 1524.25 nm. The degree of wavelength tuning according to temperature was $0.114nm/^{\circ}C$. The variable wavelength repeatability error according to temperature was ${\pm}0.003nm$, and the temperature measurement error was ${\pm}0.18^{\circ}C$. As a result of measuring the temperatures from 22.3 to $194.2^{\circ}C$, the value of the internal temperature change of the light source according to the applied temperature ${\Delta}T$ was $0.146^{\circ}C/{\Delta}T$, the change in reflected wavelength of the temperature probe according to applied temperature ${\Delta}T$ was measured at $16.64pm/^{\circ}C$. and the temperature measurement error of the sensor was ${\pm}1^{\circ}C$.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.1
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• pp.53-60
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• 2012

Purpose: The purpose of this study was to compare Ni-Cr alloy property of gas-oxygen torch soldering and infrared welding using optical microscope and Electron Probe Micro Analyzer (EPMA). Materials and methods: Ni-Cr alloys were casted for specimens. Specimens had 3.0 mm diameter, 30.0 mm length and were divided into two groups. Each group had 4 specimens. One group was for gas-oxygen torch soldering and the other was infrared welding. Specimens were cut with low-speed disc and soldered each other with gas-oxygen torch and infrared machine. After soldering and polishing, specimens were observed at 3 points (soldering point, 5 mm distance point, 10 mm distance point) with optical microscope and analyzed 3 points (soldering point, 5 mm distance point, 10 mm distance point with EPMA. Results: The results of this study were as follows: 1. The observation of gas-oxygen torch soldering at 10 mm distance point under the optical microscope was not founded any specific surface properties, but some crack lines were observed at 5 mm distance and soldering point. 2. There were no crack lines were founded at the observation of infrared welding at 10 mm distance and 5 mm distance points under the optical microscope. However, at the 5 mm distance, the surface was not smooth enough compared with at 10 mm distance point. Some crack lines were observed at the welding point as well. 3. In the EPMA analysis of the gas-oxygen torch soldering, the component of Ni was increased by 4.5%, Cr was increased by 7.5% than that of the Ni-Cr alloy at the 10.0 mm distance. At the 5 mm distance, the component of Ni was decreased by 6.1%, Mo was increased by 9.0% than that of the Ni-Cr alloy but Cr was equally shown at the 5.0 mm distance. Only Ni was shown at the soldering point. 4. In the EPMA analysis of the infrared welding, the component of Ni was increased by 9.1%, Cr was increased by 0.4% than that of the Ni-Cr alloy but Al was equal at the 10.0 mm distance. At the 5 mm distance, the component of Ni was increased by 4.7%, Cr was increased by 4.7% and Al was increased by 0.1% than that of the Ni-Cr alloy. At the welding point, the component of Ni was increased by 8.8%, Cr was increased by 8.2% than that of the Ni-Cr alloy. Conclusion: From these results, at the 5 mm distance from the soldering point, the surface of the infrared welding was more smoother than that of the gas-oxygen torch soldering. On the EPMA analysis, the component of the specimens with infrared welding was more similar than that of the gas-oxygen torch soldering compared with the component of the Ni-Cr alloy.

• Korean Journal of Optics and Photonics
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• v.21 no.3
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• pp.123-128
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• 2010

Sum frequency generation was utilized to obtain a yellow laser with the wavelength of 578.4 nm for a probe laser of an Yb lattice clock. The output of an Nd:YAG laser with wavelength of 1319 nm and that of an Yb-fiber laser with wavelength of 1030 nm were passed through a waveguided periodically-poled lithium niobate (WG-PPLN) for sum frequency generation. It is required that the probe laser has a linewidth of the order of 1 Hz to fully resolve the Yb lattice clock transition. Thus, the linewidth of the probe laser was reduced by stabilizing the frequency to a super-cavity. This was made of ULE with a low thermal expansion coefficient, and was mounted on an active vibration-isolation table at the optimal point for the reduced sensitivity to vibration. Also, this was installed in a vacuum chamber, and the temperature was stabilized to 1 mK level. This system was installed in an acoustic enclosure to block acoustic noise. The finesse of the super-cavity was measured to be 380 000 from the photon life time of the cavity.

• Korean Journal of Optics and Photonics
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• v.11 no.6
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• pp.452-456
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• 2000

A measurement unit and signal processing algorithm have been developed for predicting arterial oxygen saturation noninvasively. The measurement set-up was composed of a probe including light source and photodetector, optical signal processing section, LED driving circuit, PC interface software for data acquisition and data processing software. Light from the LED's was irradiated onto the finger nail bed and transmitted light was measured at different wavelengths. An effective baseline correction method was developed and measured data were analyzed by using various data processing methods and prediction algOlithms. For performance evaluation, a pulse oximeter simulator (Bio- Tek Instrument Inc.) was used as reference. The best performance in terms of the correlation coefficient and the standard deviation was obtained under the following conditions; when the arterial signals were computed in terms of area rather than peak-valley difference, and when the algorithm calculating by $In(I_p/I_v)/I_{avr}$ value for pulsation waveform was used. In in vivo test, prediction was improved when the developed baseline correction method was used. In addition, wavelengths of 660 nm and 940 nm provided better linearity and precision than wavelengths of 660 nm and 805 nm. 05 nm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.1
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• pp.25-30
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• 2020

Oxide (SiO₂)/Metal(Ag)/Oxide(SiO₂, ITO, ZnO) multilayer films were fabricated using a magnetron sputtering technique at room temperature on Si (p-type, 100) and a glass substrate. The electrical and optical properties of the asymmetric multilayer films depended on the thickness of the mid-layer film and the type of oxide in the bottom layer. As the metal layer becomes thicker, the sheet resistance decreases. However, the transmittance decreases when the metal layer exceeds a threshold thickness of approximately 10~12 nm. In addition, the sheet resistance and transmittance change according to the type of oxide in the bottom layer. If the oxide has a large resistivity, the overall sheet resistance increases. In addition, the anti-reflection effect changes according to the refractive index of the oxide material. The optical and electrical properties of multilayer films were investigated using an ultraviolet visible (UV-Vis) spectrophotometer and a 4-point probe, respectively. The optimum structure is SiO₂ (30 nm)/Ag (10 nm)/ZnO (30 nm) multilayer, with the highest FOM value of 7.7×10^-3 Ω^-1.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.136.1-136.1
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• 2015

In the present study, UHF (320 MHz) in combination with RF (13.56 MHz) plasmas was used for the synthesis of hydrogenated silicon nitride (SiNx:H) films by PECVD process at low temperature. RF/UHF hybrid plasmas were maintained at a fixed pressure of 410 mTorr in the N2/SiH4 and N2/SiH4/NH3 atmospheres. To investigate the radical generation and plasma formation and their control for the growth of the film, plasma diagnostic tools like vacuum ultraviolet absorption spectroscopy (VUVAS), optical emission spectroscopy (OES), and RF compensated Langmuir probe (LP) were utilized. Utilization of RF/UHF hybrid plasmas enables very high plasma densities ~ 1011 cm-3 with low electron temperature. Measurements using VUVAS reveal the UHF source is quite effective in the dissociation of the N2 gas to generate more active atomic N. It results in the enhancement of the Si-N bond concentration in the film. Consequently, the deposition rate has been significantly improved up to 2nm/s for the high rate synthesis of highly transparent (up to 90 %) SiNx:H film. The films properties such as optical transmittance and chemical composition are investigated using different analysis tools.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.134-134
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• 2009

In this work, we report that crystallization speed as well as the electrical and optical properties about the N-doped $Ge_2Sb_2Te_5$ thin films. The 200-nm-thick N-doped $Ge_2Sb_2Te_5$ thin film was deposited on p-type (100) Si and glass substrate by RF reactive sputtering at room temperature. The amorphous-to-crystalline phase transformation of N-doped $Ge_2Sb_2Te_5$ thin films investigated by X-ray diffraction (XRD). Changes in the optical transmittance of as-deposited and annealed films were measured using a UV-VIS-IR spectrophotometer and four-point probe was used to measure the sheet resistance of N-doped $Ge_2Sb_2Te_5$ thin films annealed at different temperature. In addition, the surface morphology and roughness of the films were observed by Atomic Force Microscope (AFM). The crystalline speed of amorphous N-doped $Ge_2Sb_2Te_5$ films were measured by using nano-pulse scanner with 658 nm laser diode (power : 1~17 mW, pulse duration: 10~460 ns). It was found that the crystalline speed of thin films are decreased by adding N and the crystalline temperature is higher. This means that N-dopant in $Ge_2Sb_2Te_5$ thin film plays a role to suppress amorphous-to-crystalline phase transformation.

• Korean Journal of Optics and Photonics
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• v.17 no.4
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• pp.305-311
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• 2006

We propose a 7-level atom model, which takes into account two-photon coherence effects in saturation absorption spectroscopy. Using this model we explained spectral change with laser intensity and some of crossover resonance lines, which cannot be explained with Nakayama theory. The 7-level model consists of two upper levels and five lower levels, which account for $\pi-\pi$ polarization of both pump and probe beams in Zeeman sub levels. We compared our 7-level model with 4-level Nakayama theory for 5S$_{1/2}$ - 5P$_{1/2}$ transition line in $^{85}$Rb atoms. The results of the 7-level model calculation agree well the saturation absorption spectra data according to laser intensities.

• Korean Journal of Optics and Photonics
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• v.13 no.1
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• pp.15-20
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• 2002

We demonstrate a widely-tunable wavelength converter based on four-wave mixing in a semiconductor-fiber ring laser with no external pump light. Applying 10 GHz short pulses at -8 dBm as a probe signal, we achieve continuous wavelength tuning over the semiconductor optical amplifier gain-bandwidth reaching 30 nm down- and 17 m up-wavelength conversion. In addition to the wide tuning capability, the converter shows high-speed conversion and low saturation power capabilities.