• Journal of the Optical Society of Korea
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• v.3 no.1
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• pp.10-14
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• 1999

Via THz Time domain spectroscopy, the characterization of high conductive n-type, 1.31Ω cm silicon can be measured by directly analyzing the multiple reflections using Fabry-Perot theory. The magnitude and phase difference of total transmission show good agreement between theoretical and experimental values over a 2.5 THz frequency range with complex index of refraction and power absorption. The measured absorption and dispersion are strongly frequency-dependent, and all of the results are well fit by a Cole-Davidson type distribution.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.75.3-75.3
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• 2015

Large area infrared surveys are often accompanied with follow-up optical spectroscopic surveys that has a significant legacy value even for other areas of research. Using these spectral database, we have performed a search for MgII absorption lines in the optical spectrum of background quasar. Over the ~4deg2 of AKARI North Ecliptic Pole survey field and Spitzer First Look Survey field, 18 and 16 MgII absorber systems are identified respectively. The redshift range for the background quasars was 1.0<$z_{qso}$<3.4, while the redshift range for the absorber was 0.6<$z_{abs}$<1.6. Galaxies responsible for MgII absorptions are identified in the deep optical images (CFHT r-band), yet the identification still remains ambiguous for 60% of the systems due to the limited image depth and the source crowdedness. The impact parameter ranges 20-60kpc, and the rest-frame equivalent width of MgII absorption ranges $0.7-4{\AA}$. The most critical part in the identification of MgII absorber galaxies is the existence of deep optical images in addition to the high S/N quasar spectrum with R>3000.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.746-748
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• 1998

Thin films of vanadium pentoxide ($V_{2}O_{5}$) have been deposited by r.f. magnetron sputtering from $V_{2}O_{5}$ target in gas mixture of argon and oxygen. Crystal structure, surface morphology, surface composition and optical properties of films prepared under different substrates are characterized through XRD, SEM, AES, XPS and optical absorption measurements. The films prepared below $100^{\circ}C$ are amorphous, and those prepared above $200^{\circ}C$ are polycrystalline. Thermally Induced oxidation of films into higher oxide has been observed with increasing substrate temperature. Vanadium oxide films show two optical absorption bands indicating the presence of direct and indirect transitions.

• Journal of the Optical Society of Korea
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• v.16 no.1
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• pp.80-84
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• 2012

A high reflectance mirror, which has very low absorption and scattering loss, was coated onto a crystalline substrate by ion beam sputtering and then annealed at $450^{\circ}C$. We carefully selected the mirror coating material, and designed the high reflectance mirror, in order to avoid UV degradation which comes from the He-Ne plasma. We measured the surface roughness of the Zerodur substrate using phase shift interferometry and atomic force microscopy, and compared it with the TIS scattering of the mirror. The cavity ring-down method was used to measure the absorption of the mirror, and the thin film structure was correlated to its results. We also compared the optical properties of coated mirrors before and after annealing.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.149-149
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• 2011

CdS films were deposited on glass substrates by R.F. magnetron sputtering method and the films were annealed at various substrate temperatures ranging from room temperature to $300^{\circ}C$. Structural properties of the films were studied by X-ray diffraction analysis. The structural parameters as crystallite size have been evaluated. The crystallite sizes were found to increase, and the X-ray diffraction patterns were seen to sharpen by increasing substrate temperatures. X-ray diffraction patterns of these films indicated that they contain both cubic (zincblende) and hexagonal (wurtzite) structures as a mixture. Optical properties of the films were measured at room temperature by using UV/VIS spectrometer in the wavelength range of 190 to 1100nm and optical absorption coefficients were calculated using these data. The energy gap of the films was found to decrease, and the band edge sharpness of the optical absorption was seen to oscillate by annealing. The results show that heat treatments under optimal annealing condition can provide significant improvements in the properties of CdS thin films.

• Current Optics and Photonics
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• v.7 no.2
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• pp.200-206
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• 2023

Near-infrared (NIR) sensing technology using CMOS image sensors is used in many applications, including automobiles, biological inspection, surveillance, and mobile devices. An intuitive way to improve NIR sensitivity is to thicken the light absorption layer (silicon). However, thickened silicon lacks NIR sensitivity and has other disadvantages, such as diminished optical performance (e.g. crosstalk) and difficulty in processing. In this paper, a pixel structure for NIR sensing using a stacked CMOS image sensor is introduced. There are two photodetection layers, a conventional layer and a bottom photodiode, in the stacked CMOS image sensor. The bottom photodiode is used as the NIR absorption layer. Therefore, the suggested pixel structure does not change the thickness of the conventional photodiode. To verify the suggested pixel structure, sensitivity was simulated using an optical simulator. As a result, the sensitivity was improved by a maximum of 130% and 160% at wavelengths of 850 nm and 940 nm, respectively, with a pixel size of 1.2 ㎛. Therefore, the proposed pixel structure is useful for NIR sensing without thickening the silicon.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.13-14
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• 2006

The use of soft-lithography instead of standard photolithography and dry etching technologies is attractive because inexpensive optical device can be realized. Polymerization using multi-photon absorption of materials is also a good method for optical waveguide fabrication. Laser induced self-writing technology of optical waveguide is also very simple and attractive. Using these processes, we can fabricate and interconnect optical circuits at once. In this presentation, several simple fabrication methods will be introduced. New optical loss evaluation method for polymer optical waveguides will also be presented

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.160-161
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• 2000

The 3rd order nonlinear properties show Optical bleaching (Saturation) and Reverse saturation in absorption aspect, whereas Self-focusing[3][4] and Self-defocusing in refraction aspect. Optical bleaching and Self-focusing phenomena of those properties in particular can be useful to make the optical beam spot size smaller for application on the higher optical storage density. (omitted)

• Korean Journal of Materials Research
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• v.12 no.11
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• pp.875-879
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• 2002

$Pb_{1-x}$ $Cd_{x}$ $I_2$ (x=0.0, 0.2, 0.5, 0.7, 0.9, 1.0) single crystals were grown by using Bridgman method and their structural and optical properties were investigated from the measurement of X-ray diffraction, optical absorption and photoluminescence. As-grown single crystals have hexagonal closed packed layered structure. The values of lattice constant c decrease with increasing composition x. Direct and indirect transition optical energy band gaps are calculated from optical absorption spectra measured at room temperature. They increase exponentially from 2.3eV to 3.2 eV with increasing composition x. The energies of photoluminescence peak due to donor bound exciton measured at 6K increase with increasing composition . However, the peak energies of donor-acceptor pair (DAP) are independent of the optical energy band gaps of $Pb_{1-x}$/$Cd_{x}$ $I_2$ single crystals.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.783-786
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• 2003

Thin films of vanadium oxide(VOx) have been deposited by r.f. magnetron sputtering from $V_2O_5$ target in gas mixture of argon and oxygen. The oxygen/(oxygen+argon) partial pressure ratio of 0% and 8% is adopted. Crystal structure and optical properties of films sputter-deposited under different oxygen gas pressures and in situ annealed in vacuum at $400^{\circ}C$ for 1h and 4h are characterized through XRD and optical absorption measurements. The films as-deposited are amorphous, but $0%O_2$ films annealed for time longer than 4h and $8%O_2$ films annealed for time longer than 1h are polycrystalline. The optical transmission of the films annealed in vacuum decreases considerably than the as-deposited films and the optical absorption of all the films increases rapidly at wavelength shorter than about 550nm. Indirect and direct optical band gaps were decreased with increasing the annealing time.