• Journal of Astronomy and Space Sciences
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• v.19 no.4
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• pp.319-326
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• 2002

Laboratory tests have been carried out for investigation of the spectroscopic characteristics at visible wavelength of 12 common satellite materials used in satellite bus and payload. The obtained spectral data show that the materials can be classified and identified since their spectral features and albedos distinctly differ among them. It is suggested that the result of the laboratory tests for the satellite materials can be used for the predictions of material types, material composition ratios, sizes, and masses in comparison with the spectral data obtained from observations of new satellites or space debris.

• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.277-282
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• 1997

The complex refractive index of Diamond-like Carbon (DLC) thin films, which can be applied to optical devices or electrical devices, have been determined using optical methods. DLC thin films are grown on Si(100) substrates and vitreous silica substrates respectively, using the technique of plasma enhanced chemical vapor deposition (PECVD). The spectroscopic ellipsometry data($\psi$, $\Delta$) and the transmission spectra of these DLC films are obtained. These optical spectra are analyzed with the help of the Sellmeier dipersion relation and a quantum mechanically derived dispersion relation. Using spectroscopic ellipsometry data at their transparent region, the refractive index and the effective thickness of DLC films on vitreous silica are model calculated, Then the transmission spectra are inverted to yield the extinction coefficient spectra k(λ) at absorbing region. These spectra are fit to the quantum mechanical dispersion relation and the best fit dispersion constants are determined. The complex refractive indices are easily calculated with these constants. The spectroscopic ellipsometry data at the absorbing region in model calculated to give the packing densities and the degrees of surface microroughness of DLC films. Discussions are made in correlation with the growth condition of DLC films.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11b
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• pp.188-195
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• 2000

This study was conducted to measure the moisture content of powdered food using RF impedance spectroscopic method. In frequency range of 1.0 to 30㎒, the impedance such as reactance and resistance of parallel plate type sample holder filled with wheat flour and red-pepper powder of which moisture content range were 5.93∼-17.07%w.b. and 10.87 ∼ 27.36%w.b., respectively, was characterized using by Q-meter (HP4342). The reactance was a better parameter than the resistance in estimating the moisture density defined as product of moisture content and bulk density which was used to eliminate the effect of bulk density on RF spectral data in this study. Multivariate data analyses such as principal component regression, partial least square regression and multiple linear regression were performed to develop one calibration model having moisture density and reactance spectral data as parameters for determination of moisture content of both wheat flour and red-pepper powder. The best regression model was one by the multiple linear regression model. Its performance for unknown data of powdered food was showed that the bias, standard error of prediction and determination coefficient are 0.179% moisture content, 1.679% moisture content and 0.8849, respectively.

• Vacuum Magazine
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• v.2 no.3
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• pp.4-10
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• 2015

We developed a real-time three-polarizer spectroscopic ellipsometer based on a new data acquisition algorithm and a general data reduction (the process of extracting the ellipsometric sample parameters from the Fourier coefficients). The data acquisition algorithm measures Fourier coefficients of radiant flux waveform accurately and precisely. The general data reduction is introduced to represent the analytic functions of the standard uncertainties of the ellipsometric sample parameters, and the extracted theoretical values closely agree with the corresponding experimental data. Our approach can be used for optimization of measurement conditions, instrumentation, simulation, standardization, laboratory accreditation, and metrology.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.62.1-62.1
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• 2014

Metallicity distribution of globular clusters (GCs) provides an important clue for star formation history of their host galaxy. With an assumption that GCs are generally old, GC colors have been used as a proxy of GC metallicities. Bimodal GC color distributions observed in most large galaxies have, for decades, been interpreted as bimodal metallicity distributions, indicating the presence of two populations within a galaxy. However, the conventional view has been challenged by a new theory that non-linear GC color-metallicity relations (CMRs) can cause a bimodal color distribution even from a single-peaked metallicity distribution. Using the photometric and spectroscopic data of NGC 5128 GCs in combination with stellar population simulation models, we examine the effect of non-linearity in GC CMRs on the transformation of GC color distributions into metallicity distributions. Although, in some colors, offsets are present between observations and models in the CMRs, their overall shape agrees well for various colors. After the offsets are corrected, the observed spectroscopic metallicity distribution is well reproduced via modeled CMRs from various color distributions having different morphologies. On the other hand, the linearly converted metallicity distributions from GC colors show a significant discrepancy with the observed spectroscopic metallicity distribution. We discuss the implications of our results.

• Korean Journal of Optics and Photonics
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• v.10 no.3
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• pp.208-213
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• 1999

We proposed a new technique to precisely calibrate the angle of incidence in spectroscopic ellipsometer. The proposed technique can be useful to the thickness measurement of semiconductor thin films and optical thin films. The usefulness has been confirmed experimentally. We cut a block of optical glass into two pieces and made a prism as well as a slab using each piece. The apex angle and the angle of the minimum deviation of prism were measured. From these angles, the refractive index of glass material was calculated. From the analysis of the spectro-ellipsometric data collected near Brewster's angle, we could not only determine the error in the angle of incidence in the spectroscopic ellipsometer, but also calibrated the angle of incidence to the accuracy of 0.01 degree.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.272-278
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• 2003

We studied patterned ITO layers of PDP thin films on glass substrates using spectroscopic ellipsometry. The optical property of ITO is expressed with the optical model based on two Lorentz oscillators. The effect of patterned ITO is calculated by taking the weighted average of reflectance in proportion to ITO coverage. The relative coverage of ITO is determined by using the model analysis of spectroellipsometric data. The difference of ITO coverage obtained by the best-fit model analysis of ellipsometric spectra to the expected one is critically examined and suggestions are made to minimize the observed discrepancy.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.56.3-56.3
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• 2019

We are currently living in the era of the wide field cosmological surveys, either spectroscopic such as Dark Energy Spectrograph Instrument or photometric such as the Dark Energy Survey or the Large Synoptic Survey Telescope. By analyzing the distribution of matter clustering, we can use the growth of structure, in combination with measurements of the expansion of the Universe, to understand dark energy or to test different models of gravity. But we also live in the era of multi-tracer or multi-messenger astrophysics. In particular, during the next decades radio surveys will map the matter distribution at higher redshifts. Like in optical surveys, there are radio imaging surveys such as continuum radio surveys such as the ongoing EMU or spectroscopic by measuring the hydrogen 21cm line. However, we can also use intensity mapping as a low resolution spectroscopic technique in which we use the intensity given by the emission from neutral hydrogen from patches of the sky, at different redshifts. By cross-correlating this maps with galaxy catalogues we can improve our constraints on cosmological parameters and to understand better how neutral hydrogen populates different types of galaxies and haloes. Creating realistic mock intensity mapping catalogues is necessary to optimize the future analysis of data. I will present the mock neutral hydrogen catalogues that we are developing, using the Horizon run 4 simulations, to cross-correlate with mock galaxy catalogues from low redshift surveys and I will show the preliminary results from the first mock catalogues.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.72.3-72.3
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• 2015

We present the mid-infrared (MIR) luminosity function (LF) of local (z < 0.3) star forming (SF) galaxies based on the AKARI's NEP-Wide Survey data. We utilized a combination of the NEP-Wide point source catalogue containing a large number (114,000) of infrared (IR) sources distributed over the wide (5.4 sq. deg) field and spectroscopic redshift (z) data for 1790 selected targets obtained by optical follow-up surveys with MMT/Hectospec and WIYN/Hydra. The AKARI's continuous $2{\sim}24{\mu}m$ wavelength coverage and the spectroscopic redshifts for sample galaxies enable us to derive accurate spectral energy distributions (SEDs) in the mid-infrared. We carried out SED-fit analysis and employed 1/Vmax method to derive the mid-IR (e.g., $8{\mu}m$, $12{\mu}m$, and $15{\mu}m$ rest-frame) luminosity functions. Our results for local galaxies from the NEP region generally consistent with various previous works for other fields over wide luminosity ranges. The comparison with the results of the NEP-Deep data implies the luminosity evolution from higher redshifts towards the present epoch. We attempted to fit our derived LFs to the double power-laws and present the resulting power indices. We also examined the correlation between mid-IR luminosity and total IR luminosity.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.78.2-78.2
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• 2021

We present high resolution spectroscopic observations of transverse magnetohydrodynamic (MHD) waves in mottles located near the solar disk center. Different from previous studies that used transversal displacements of the mottles in the imaging data, we investigated the line-of-sight (LOS) velocity oscillations of the mottles in the spectral data. The observations were carried out by using the Fast Imaging Solar Spectrograph of the 1.6 meter Goode Solar Telescope of Big Bear Solar Observatory. Utilizing the spectral data of the Hα and Ca II 8542 Å lines, we measure the LOS velocity of a quiet region including the mottles and rosettes that correspond to the footpoints of the mottles. Our major findings are as follows: (1) Alfvénic waves are pervasive in the mottles. (2) The dominant period of the waves is 2 to 4 minutes. (3) From the time-distance maps of the three-minute filtered LOS velocity constructed along the mottles, it is revealed that the transverse waves in the mottles are closely related to the longitudinal waves in the rosettes. Our findings support the notion that Alfvénic waves can be generated by mode conversion of the slow magnetoacoustic waves as was shown in sunspot regions by Chae et al. (2021).