• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.1
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• pp.19-24
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• 1995

Large size potassium lithium niobate (KLN) crystals with dimensions of $8{\times}6{\times}2 mm^3$ were grown by the top - seeded solution growth (TSSG) method. The extraordinary refractive index $n_e$at the second harmonic frequency for KLN crystal depends on the composition and decreases in this crystal due to the large Li content. KLN crystal was characterized by observation in UV - VIS spectrometry. It is transparent from the ultraviolet to infrared spectral regions that the transmission limit and cut- off wavelength are about 350 and 380 nm.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1986.10a
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• pp.23-27
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• 1986

In this paper, The loss spectra between 1.1um and 1.7um were measured by cut-back method using tungsten-halogen lamp, a grating monochramator and an InGaAs detector. Typical fiber lengths measured were 30 meter. This result represent a further contribution to monomode fiber design and has been applied to come common profimes that are under study to optimize the fiber performance. It is very important that the parameter a. were designed more exactly and transmission of LPol mode in 1.55um. Therefore, Fiber designer have to be aware of the fact that this coupling loss and bending loss.

• Journal of the Korean Vacuum Society
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• v.20 no.5
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• pp.361-366
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• 2011

An in-situ, real-time monitoring of GaN epilayers grown by low pressure metalorganic chemical vapor deposition system modified for spectral reflectance was performed. Reflectance spectrums from 190~861 nm were observed using p-polarized light with incident angle of $75^{\circ}$. All reflectance spectrums showed interference oscillation caused by multiple reflection within GaN epilayers, and the spectrum from GaN with low crystalline quality showed weak reflectance intensity and much low amplitude of the oscillation because many defects in GaN resulted in light scattering and absorption. Signal variation of reflected light which was selected around strong constructive wavelength range was also observed during $NH_3$ supplying and $NH_3$ cut-off. There was no significant change in signal intensity when $NH_3$ cut-off for 10 sec, but it showed higher intensity when $NH_3$ was cut off for over 30 sec and its intensity kept unchanged. This result indicates that GaN surface was N-terminated during $NH_3$ supplying but Ga-terminated during $NH_3$ cut-off because of high nitrogen equilibrium vapor pressure of GaN, and metallic Ga-terminated surface caused slightly higher reflectance intensity.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.5
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• pp.230-234
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• 2013

IR cut-off thin films consisted of ATO nanoparticles were successfully fabricated by sol-gel method. The coating solution was synthesized with organic/inorganic hybrid binder and ATO colloidal solution and ATO thin films were coated on a slide glass with the withdrawal speed of 5~40 mm/s. As the withdrawal speed increased from 5 mm/s to 40 mm/s, the thickness of coating thin films also increased from $1.05{\mu}m$ to $4.25{\mu}m$ and the IR cut-off in wavelength of 780~2500 nm increased from 49.5 % to 66.7 %. In addition, the pencil hardness of ATO thin films dried at $80^{\circ}C$ was ca. 5H and the coating films were not removed after a cross cutter tape test because of the hybrid binder synthesized with tetraethylorthosilicate and methyltrimethoxysilane. The surface morphologies, optical properties and film thickness of prepared thin films with a different withdrawal speed were measured by field emission scanning electron microscope (FE-SEM), UV-Vis spectrophotometer, and Dektak.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.10 no.5
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• pp.43-51
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• 1996

An appropriate lighting standard for the museum is needed to minimize the deterioration of the exhibits by the light. To obtain the basic data for the standard, a system to measure the color change of the artifacts as a function of the radiation energy frequency was constructed. Xenon lamp is used as a light source, and the light is irradiated to the samples through serveral cut-off filters. Measuring the colors of the samples under each filters, color change of the samples is estimated for each frequency ranges of radiation energy. As a result, natural dyes show severe color change in a short time, but traditional papers shows relatively small color change. Using measured results, color change due to other light sources can be calculated and this will be the base of the standard.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.1
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• pp.63-69
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• 2015

In this paper, infrared reflector design targeting infrared stealth effect is presented using structural optimization based on the phase field method. The analysis model was determined to accomplish the design that an incident infrared wave was reflected to a desired direction. The design process was to maximize the objective value at the measuring domain located in a target region and the design objective was set to the Poynting vector value which represents the energy flux. Optimization results were obtained according to the variation of some parameter values related to the phase field method. The model with a maximum objective value was selected as the final optimal model. The optimal model was modified to eliminate the gray scale using the cut-off method and it confirmed improved performance. In addition, to check the desired effect in the middle wave infrared range(MWIR), the analysis was performed by changing the input wavelength. The finite element analysis and optimization process were performed by using the commercial package COMSOL combined with the Matlab programming.

• Korean Journal of Optics and Photonics
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• v.16 no.6
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• pp.494-499
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• 2005

We have demonstrated a fiber short-wavelength filter with a good cut-off property using dissimilar dispersive properties between? a thermally expanded cored fiber and an external medium. Side-polishing is applied to coupling between the fiber and the external medium. The experimental results revealed that the bend edge wavelength can be adjusted by controlling the degree of core expansion. Futhermore, the sharpness of wavelength response? was significantly? improved by employing expanded core fiber instead of a conventional single mode fiber. Tuning range of the band edge wavelength exceeded 400 m based on thermo-optic effect of the external medium.

• Korean Journal of Optics and Photonics
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• v.26 no.3
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• pp.162-167
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• 2015

In this paper, we developed a MTF (Modulation Transfer Function) measurement system using a knife-edge scanning method for infrared optics. It consists of an objective part to generate the target image, a collimator to make the beam parallel, and a detector to analyze the image. We used a tungsten filament as the light source and MCT (Mercury Cadmium Telluride) to detect the mid-infrared(wavelength $3-5{\mu}m$) image. We measured the MTF of a standard lens (f=5, material ZnSe) to test this instrument and compared the result to the theoretical value calculated using the ZEMAX commercial software. It was found that the difference was within ${\pm}0.035$ at the cut-off frequency (50 1/mm). Also, we calculated the A-type measurement uncertainty to check the reliability of the measurement. The result showed only 0.002 at 20 1/mm in spatial frequency, which means very little variation in the MTF measurement under the same conditions.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.250-254
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• 2023

In this study, Li₂O-BaO-Ga₂O₃-TeO₂-TiO₂-GeO₂ glasses with high transmittance in mid-infrared region and high refractive indices were successfully synthesized. The relationship between glass properties and glass composition was analyzed. In Li₂O-BaO-Ga₂O₃-TeO₂-TiO₂-GeO₂ glass system, as increasing TeO₂ concentration, the refractive index increases and the glass transition temperature decreases. In addition, as increasing BaO concentration, the refractive index increases without decrease of Abbe number. The IR-cut off wavelength shifted to the longer wavelength with increasing TeO₂ and BaO contents due to their large molecular weight. The glass transition temperature significantly decreases when BaO was replaced with Li₂O.

• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.183-188
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• 1997

Cut-off filters would reject all the radiation below and transmit all that above a certain wavelength or vice versa. In this paper, we study design and farbrication of dichroic mirror and broadband high reflective mirror for color separation of white laser beam source to R.G.B color beam source. In laser display system, color separation is very important. We fabricated below specific component for finite color separation of the Kr-Ar laser source. At 45$^{\circ}$ incidence s-polarized light , it is required that - H/R in blue region R>99%, H/T in green and red region T>90% - H/R in green and red region R>99%, H/T in blue region T>90% - H/R in green region R>99%, H/T in red region T>90% We composed the optical system and realize the full color image.