• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1B
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• pp.8-14
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• 2000

This paper analyzes and accesses the gain of optically pumped surface-normal MQW optical amplifiers. The proposed amplifiers have the advantage of polarization independence, high coupling efficiency to and from optical fibers, and flexibility of operating wavelength. We analyzed the gain characteristics of 100 - 200-period MQWs and verified the dependence of a strained lattice and selective doping. Theoretical analysis of such MQWs showsa single-pass gain of 3 dB with broad operation bandwidth. A single-pass gain of 2.6 dB is obtained experimentally in an InGaAs/InGaAlAs MQW amplifier, which is compared with calculations. The use of Fabry-Perot interferometer (FPI) structure in an optical amplifier is a useful way to increase the gain, but causes a problem of narrow operation bandwidth when the single-pass gain is low. Therefore, a single-pass gain above 2to 3 dB is a prerequisite to achieve both a high gain and moderate operation bandwidth in FPI-structured opticalamplifiers. We have designed an FPI-structured surface-normal optical amplifier both with a high gain of broad operation bandwidth of 4.6mm, when a single-pass gain is 3 dB.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.28 no.3
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• pp.234-238
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• 2002

Photodynamic therapy (PDT) is based on a photochemical reaction which is initiated by light activation of a photosensitizer. The photosensitizer accumulates more in tumor tissues than in normal tissues and is activated with specific wavelength of light, usually laser. The photochemical reaction produces highly reactive oxygen products causing cytotoxiciy and vascular shutdown to the tumor. The advantages of PDT are its relative selective tumor destruction and tissue healing by regeneration, which can maintain important structures with very good functional and esthetic results. Therefore, PDT is considered as an alternative modality for cancers of the head and neck. In this article, we will report three cases of photodynamic therapy for treatment of oral leukoplakia, squamous cell carcinoma, and basal cell carcinoma of head and neck. It was observed that premalignant and malignant lesions responded well to the photodynamic therapy with Aminolevulinic acid (ALA) and $Foscan^{(R)}$. Photodynamic therapy can be considered as a new treatment method for the premalignant and malignant tumors in Oral and Maxillofacial Surgery.

• Korean Journal of Optics and Photonics
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• v.14 no.2
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• pp.184-188
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• 2003

We fabricated a P-I-i-I-N $GaAs/Al_{0.35}Ga_{0.65}As$waveguide phase modulator with significant phase shift for the TE mode but negligible for the TM mode. We selected the P-I-i-I-N structure to cause a phase shift about the TM mode. The wavelength of $\lambda=1.55$\mu\textrm{m}$ was measured for both the TE and TM modes, respectively. As a result, the measured phase shift efficiency ($\Delta\phi$) by using the Fabry-Perot resonance method was $7.9^{\circ}/V.mm$ for TE-polarized light. Also, no modulation was observed for TM-polarized light.

• Journal of the Korean Graphic Arts Communication Society
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• v.18 no.2
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• pp.41-54
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• 2000

Photochemical modulation of Bragg-reflection wavelengths based on isomerization of an azobenzene (Azo) and subsequent change in reflectance was investigated in cholesteric liquid crystals (ChLCs) which reflect light in visible wavelength region. Irradiation at 366 nm, which causes an efficient transcis isomerization of Azo, led to change in reflected color of ChLCs toward shorter wavelengths with a concomitant lowering of phase transition. Reversible change in color was induced all-optically by alternate irradiation at effective wavelengths for reversible isomerization of Azo. A considerable variation in reflectance was also observed when the photoinduced change in color was measured by a probe light with the same handedness as the ChLCs. The spectral Position of selective light reflection in the initial states played an important role to produce a normal-mode and a reverse-mode switching in photoinduced modulation of reflectance of the ChLCs with respect to the probe light.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.281.2-281.2
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• 2013

Since heavy metal ions included in water or food resources have critical effects on human health, highly sensitive, rapid and selective analysis for heavy metal detection has been extensively explored by means of electrochemical, optical and colorimetric methods. For example, quantum dots (QDs), such as semiconductor QDs, have received enormous attention due to extraordinary optical properties including high fluorescence intensity and its narrow emission peaks, and have been utilized for heavy metal ion detection. However, the semiconductor QDs have a drawback of serious toxicity derived from cadmium, lead and other lethal elements, thereby limiting its application in the environmental screening system. On the other hand, Graphene oxide (GO) has proven its superlative properties of biocompatibility, unique photoluminescence (PL), good quenching efficiency and facile surface modification. Recently, the size of GO was controlled to a few nanometers, enhancing its optical properties to be applied for biological or chemical sensors. Interestingly, the presence of various oxygenous functional groups of GO contributes to opening the band gap of graphene, resulting in a unique PL emission pattern, and the control of the sp2 domain in the sp3 matrix of GO can tune the PL intensity as well as the PL emission wavelength. Herein, we reported a photoluminescent GO array on which heavy metal ion-specific DNA aptamers were immobilized, and sensitive and multiplex heavy metal ion detection was performed utilizing fluorescence resonance energy transfer (FRET) between the photoluminescent monolayered GO and the captured metal ion.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.11
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• pp.191-198
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• 2000

Laser direct patterning of the coated photoresist (PMER-NSG31B) layer was studied to make halftone dots on gravure printing roll. The selective laser hardening of photoresist by Ar-ion laser(wavelength: 333.6~363.8nm) was controlled by the A/O modulator. The coating thickness in the range of 5~11$\mu m$ could be obtained by using the up-down directional moving device along the vertically located roll. The width, thickness and hardness of the hardened lines formed under the laser power of 200~260㎽ and irradiation time of 4.4~6.6 $\mu$sec/point were investigated after developing. The hardened width increased as the coating thickness increased. Though the hardened thickness was changed due to the effect of the developing solution, the hardened layer showed good resistance to the scratching of 2H pencil. Also, the hardened minimum line widths of 10$\mu m$ could be obtained. The change of line width was also found after etching, and the minimum line widths of 6$\mu m$ could be obtained. The hardened lines showed the good resistance to the etching solution. Finally, the experimental data could be applied to make gravure halftone dots using the developed imaging process, successfully.

• Journal of the Korea Institute of Military Science and Technology
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• v.26 no.3
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• pp.246-251
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• 2023

RADAR(Radio Detection and Ranging) is an important system for surveillance and reconnaissance by detecting a reflected signal which obtains the range from the radar to the target, and the velocity of the target. The magnitude of the reflected signal varies due to the radar cross section of the target, characteristic of the transmission and reception antenna, distance between the radar and the target, and power and wavelength of the transmitted signal. Thus, the RCS is the important characteristic of the target to determine if the target can be observed by the RADAR system. It is based on the material and shape of the target. We have measured the reflection signal of a simple square-shaped (20 × 20 cm) target made of a new material, a gallium-based liquid metal alloy and compared that of well-known metals including copper, aluminum. The magnitude of reflected signal of the aluminum target was the largest and it was 2.4 times larger than that of the liquid metal target. We also investigated the effect of the shape by measuring reflectance of the F-22 3D model(~1/95 ratio) target covered with/without copper, aluminium, and liquid metal. The largest magnitude of the reflected signal measured from side-view with the copper-covered F-22 model was 2.6 times greater than that of liquid metal. The reflectance study of the liquid metal would be helpful for liquid metal-based frequency selective surface or metamaterials.

• Journal of Pharmaceutical Investigation
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• v.35 no.3
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• pp.137-142
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• 2005

A rapid, selective and sensitive reversed-phase HPLC method for the determination of glipizide in human serum was validated and applied to the pharmacokinetic study of glipizide. Glipizide and internal standard, tolbutamide, were extracted from human serum by liquid-liquid extraction with benzene and analyzed on a Nova Pak $C_{18}\;60{\AA}$ column with the mobile phase of acetonitrile-potassium dihydrogen phosphate (10 mM, pH 3.5) (4:6, v/v). Detection wavelength of 275 nm and flow rate of 0.7 ml/min were fixed for the study. The assay robustness for the changes of mobile phase pH, organic solvent content, and flow rate was confirmed by $3^3$ factorial design using a fixed glipizide concentration (500 ng/ ml) with respect to its peak area and retention time. And also, the ruggedness of this method was investigated at three different laboratories using same quality control (QC) samples. This method showed linear response over the concentration range of 10-1000 ng/ml with correlation coefficient greater than 0.999. The lower limit of quantitation using 0.5 ml of serum was 10.0 ng/ml, which was sensitive enough for pharmacokinetic studies. The overall accuracy of the quality control samples ranged from 82.6 to 105.0% for glipizide with overall precision (% C.V.) being 1.13-13.20%. The percent recovery for human serum was in the range of 85.2 93.5%. Stability studies showed that glipizide was stable during storage, or during the assay procedure in human serum. The peak area and retention time of glipizide were not significantly affected by the changes of mobile phase pH, organic solvent content, and flow rate under the conditions studied. This method showed good ruggedness (within 15% C.V.) and was successfully used for the analysis of glipizide in human serum samples for the pharmacokinetic studies at three different laboratories, demonstrating the suitability of the method.

• Journal of Pharmaceutical Investigation
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• v.35 no.6
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• pp.437-443
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• 2005

A rapid, selective and sensitive reversed-phase HPLC method for the determination of a major metabolite of terfenadine, fexofenadine, in human serum was developed, validated, and applied to the pharmacokinetic study of terfenadine. Fexofenadine and internal standard, haloperidol were extracted from human serum by liquid-liquid extraction with acetonitrile and analyzed on a $Symmetry^{TM}$ C8 column with the mobile phase of 1% triethylamine phosphate (pH 3.7)-acetonitrile (67:33, v/v, adjusted to pH 5.6 with triethylamine). Detection wavelength of 230 nm for excitation, 280 nm for emission and flow rate of 1.0 mL/min were fixed for the study. The assay robustness for the changes of mobile phase pH, organic solvent content, and flow rate was confirmed by $3^{3}$ factorial design using a fixed fexofenadine concentration (50 ng/mL) with respect to its peak area and retention time. In addition, the ruggedness of this method was investigated at three different laboratories using same quality control (QC) samples. This method showed linear response over the concentration range of 10-500 ng/mL with correlation coefficients greater than 0.999. The lower limit of quantification using 0.5 mL of serum was 10 ng/mL, which was sensitive enough for the pharmacokinetic studies of terfenadine. The overall accuracy of the quality control samples ranged from 95.70 to 114.58% for fexofenadine with overall precision (% C.V.) being 3.53-14.39%. The relative mean recovery of fexofenadine for human serum was 90.17%. Stability studies (freeze-thaw, short-term, extracted serum sample and stock solution) showed that fexofenadine was stable during storage, or during the assay procedure in human serum. However, the storage at $-70^{\circ}C$ for 4 weeks showed that fexofenadine was not stable. The peak area and retention time of fexofenadine were not significantly affected by the changes of mobile phase pH, organic solvent content, and flow rate under the conditions studied. This method showed good ruggedness (within 15% C.V.) and was successfully used for the analysis of fexofenadine in human serum samples for the pharmacokinetic studies of orally administered Tafedine tablet (60 mg as terfenadine) at three different laboratories, demonstrating the suitability of the method.

• Journal of Pharmaceutical Investigation
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• v.35 no.4
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• pp.265-271
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• 2005

A rapid, selective and sensitive reversed-phase HPLC method for the determination of etodolac in human serum was developed, validated, and applied to the pharmacokinetic study of etodolac. Etodolac and internal standard, ibuprofen were extracted from human serum by liquid-liquid extraction with hexane/isopropanol (95:5, v/v) and analyzed on a Luna C18(2) column with the mobile phase of 1% aqueous acetic acid-acetonitrile (4:6, v/v). Detection wavelength of 227 nm and flow rate of 1.0 mL/min were fixed for the study. The assay robustness for the changes of mobile phase pH, organic solvent content, and flow rate was confirmed by $3^3$ factorial design using a fixed etodolac concentration $(1\;{\mu}g/mL)$ with respect to its peak area and retention time. And also, the ruggedness of this method was investigated at three different laboratories using same quality control (QC) samples. This method showed linear response over the concentration range of $0.05-40\;{\mu}g/mL$ with correlation coefficients greater than 0.999. The lower limit of quantification using 0.5 mL of serum was 0.05 ${\mu}g/mL$, which was sensitive enough for pharmacokinetic studies. The overall accuracy of the quality control samples ranged from 92.00 to 110.00% for etodolac with overall precision (% C.V.) being 1.08-10.11%. The percent recovery for human serum was in the range of 76.73-115.30%. Stability studies showed that etodolac was stable during storage, or during the assay procedure in human serum. The peak area and retention time of etodolac were not significantly affected by the changes of mobile phase pH, organic solvent content, and flow rate under the conditions studied. This method showed good ruggedness (within 15% C.V.) and was successfully used for the analysis of etodolac in human serum samples for the pharmacokinetic studies of orally administered Lodin XL tablet (400 mg as etodolac) at three different laboratories, demonstrating the suitability of the method.