• Korean Journal of Optics and Photonics
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• v.19 no.4
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• pp.294-301
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• 2008

We have performed modeling and simulations of optical characteristics for a cholesteric liquid crystal (CLC) color filter. Berreman's $4{\times}4$ matrix method was used for the calculation of reflectance spectra of the CLC color filter with respect to the incident angle. The results were employed as input parameters for a user-defined coating property of an illumination design software based on the ray-tracing method, LightTools. Color shift characteristics of a planar transmission-type CLC color filter were simulated using LightTools. The results were compared with the results obtained with Berreman's $4{\times}4$ matrix method. It was found that color shift characteristics of the CLC color filter could be simulated to a reasonable accuracy when the reflectance spectra with less than 5 degrees of incremental incidence-angle were used as the input data for the user-defined coating property of LightTools. We have simulated color shift characteristics of a reflection-type CLC color filter having hemi-spherical patterns. The simulation method reported in this paper has been found to be also used for a non-planar CLC color filter structure.

• Journal of Sensor Science and Technology
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• v.12 no.6
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• pp.273-281
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• 2003

A stoichiometric mixture for $CdIn_2Te_4$ single crystal was prepared from horizontal electric furnace. The $CdIn_2Te_4$ single crystal was grown in the three-stage vertical electric furnace by using Bridgeman method. The quality of the grown crystal has been investigated by the x-ray diffraction and the photoluminescence measurements. The (001) growth plane of oriented $CdIn_2Te_4$ single crystal was confirmed from back-reflection Laue patterns. The carrier density and mobility of $CdIn_2Te_4$ single crystal measured with Hall effect by van der Pauw method are $8.61{\times}10^{16}\;cm^{-3}$ and $242\;cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the $CdIn_2Te_4$ single crystal obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)=1.4750\;eV-(7.69{\times}10^{-3}\;eV)T^2/(T+2147)$. After the as-grown $CdIn_2Te_4$ single crystal was annealed in Cd-, In-, and Te-atmospheres, the origin of point defects of $CdIn_2Te_4$ single crystal has been investigated by the photoluminescence(PL) at 10 K. The native defects of $V_{Te}$, $Cd_{int}$, and $V_{Cd}$, $Te_{int}$ obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the Cd-atmosphere converted $CdIn_2Te_4$ single crystal to an optical n-type. Also, we confirmed that In in $CdIn_2Te_4$ did not form the native defects because In in $CdIn_2Te_4$ single crystal existed in the form of stable bonds.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1622-1622
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• 2001

The purpose of this research was to develop a the reflection technique with near infrared (NIR) radiation for estimating physico-chemical properties in compost. The composts (cattle, pig, chicken and waste composts) were air dried and then ground to pass through a 0.5 or 2mm sieve for the physico-chemical properties and spectroscopic determinations. The physico-chemical properties of compost were shown high values ; moisture(30-60%), T-N(0.8-2.9%), organic matter(29-89%), pH(5.89-9.60) K$_2$O(0.27-5.66%), P2O$\sub$5/(0.07-2.62%), CaO(0.03-4.80%), MgO(0.09-1.56%), NaCl(0.01-1.13%), EC(1.41-13.76dS/m). Generally, we should select a simple calibration and prediction method for determining physico-chemical properties in compost under similar accuracy and precision of prediction. It should be remembered that the NIRS approach will never replace the traditional methods. However, NIRS technique may be an effective method for rapid and nondestructive measurements of a large number of compost samples. Near infrared reflectance spectra of composts was obtained by Infra Alyzer 500 scanning spectrophotometer at 2-nm intervals from 1100 to 2500nm. Multiple linear regression(MLR) or partial least square regression (PLSR) was used to evaluate a NIRS method for the rapid and nondestructive determination of physico-chemical properties and humic acid contents in composts. The standard error of prediction(SEP) for finely sized sample(<0.5mm) and coarsely sized sample(<2mm) did not show much difference. The NIR instrument of filter type showed the same accuracy of the monochromator scanning type to estimate the compost properties. The results summarized that NIR spectroscopy can be used as a routine testing method to determine quantitatively the OM, moisture, T-N, color, pH, cation content in the compost samples nondestructively.

• Korean Journal of Soil Science and Fertilizer
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• v.34 no.4
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• pp.273-277
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• 2001

Traditional methods of chemical analysis for the soil properties take time and produce harmful waste. The purpose of this research was to evaluate an NIR technique for measuring some soil properties that are rapid and accurate in soil fertility assessments. The NIR instrument (InfraAlyzer 500, Bran & Luebbe Co.) was used for obtaining spectral data from 140 finely ground soil for calibrations and validation estimating pH, CEC, extractable Ca, Mg, K, $SiO_2$, humic acid and EC. Partial least square regression analysis was used to develop a calibration of NIR spectroscopy method. The results indicated that NIR spectroscopy could be used as a routine nondestructive method quantitatively determining soil chemical properties quickly. However the NIR technique may require sample preparation to obtain even diffuse reflection spectra from the soil and data manipulations to obtain optimal predictions.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.669-669
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• 2013

Hierarchical N doped TiO2 nanostructured catalyst with micro, meso and macro porosity have been synthesized by a facile self-formation route using ammonia and titanium isopropoxide precursor. The samples were calcined in different calcination temperature ranging from $300^{\circ}C$ to $800^{\circ}C$ at slow heating rate ($5^{\circ}C$/min) and designated as NHPT-300 to NHPT-800. $TiO_2$ nanostructured catalyst have been characterized by physico-chemical and spectroscopy methods to explore the structural, electronic and optical properties. UV-Vis diffuse reflectance spectra confirmed the red shift and band gap narrowing due to the doping of N species in TiO2 nanoporous catalyst. Hierarchical macro porosity with fibrous channel patterning was observed (confirmed from FESEM) and well preserved even after calcination at $800^{\circ}C$, indicating the thermal stability. BET results showed that micro and mesoporosity was lost after $500^{\circ}C$ calcination. The photocatalytic activity has been evaluated for methanol oxidation to formaldehyde in visible light. The enhanced photocatalytic activity is attributed to combined synergetic effect of N doping for visible light absorption, micro and mesoporosity for increase of effective surface area and light harvestation, and hierarchical macroporous fibrous structure for multiple reflection and effective charge transfer.

• Journal of the Korean Vacuum Society
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• v.15 no.3
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• pp.280-286
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• 2006

A distributed Bragg reflector (DBR) for the application of $1.3{\mu}m$ vertical cavity surface emitting laser (VCSEL) has grown by digital-alloy AlGaAs layer using the molecular beam epitaxy (MBE) method. The measured reflection spectra of the digital-alloy AlGaAs/GaAs DBR have uniformity in 0.35% over the 1/4 of 3-inch wafer. Furthermore, the TEM image showed that the composition and the thickness of the digital-alloy AlGaAs layer in AlGaAs/GaAs DBR was not affected by the temperature distribution over the wafer whole surface. Therefore, the digital-alloy AlGaAs/GaAs DBR can be used to get higher yield of VCSEL with the active medium of InAs quantum dots whose gain is inhomogeneously broadened.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.6
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• pp.297-303
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• 2003

Mn-Ni-Co type thin films were prepared at various conditions by a rf magnetron sputtering system. At the condition. or substrate temperature of $300^{\circ}C$ and $Ar/O_2$= 10/0, a cubic spinel phase was obtained. When oxygen was included in process gas, a cubic spinel phase was not formed even after the thermal annealing at $900^{\circ}C$. The thermistor thin film had no other elements except Mn, Ni and Co. The infrared reflection spectra of the thermistor thin films showed that the films had somewhat high reflectance for incoming infrared ray with some angle. The etch rate of the thermistor thin films was about 63nm/min at a condition of DI water : $HNO_3$: HCl = 60 : 30 : 10 vol%. The B constant and temperature coefficient of resistance of the thermistor thin films were 3500 K and -3.95 %/K, respectively. The voltage responsivity of the thermistor thin film infrared sensor was 108.5 V/W and its noise equivalent power and specific detectivity were $5.1\times 10^{-7}$ W/$Hz^{-1/2}$ and $0.2\times 10^6$cm $Hz^{1/2}$/W, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.4
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• pp.133-140
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• 2006

The growth characteristics and properties of large size $SrAlF_5$ single crystals are described and compared with those of $BaMgF_4$. Transmission spectra in the vacuum ultraviolet wavelength region indicate a high transparency of $SrAlF_5$ (about 90% without considering surface reflection loses) down to 150 nm, on contrast to the optical loses observed for $BaMgF_4$. The ferroelectric character of $SrAlF_5$ is evidenced by the reversal of the spontaneous polarization in a hysteresis loop. The higher potential of $SrAlF_5$ in comparison with $BaMgF_4$ for the realization of all-solid-state lasers in the ultraviolet wavelength region by the quasi-phase matching (QPM) technique is pointed out. $SrAlF_5$, besides a higher grade of transparency, shows a nonlinear effective coefficient similar to that of quartz and uniaxial nature, on contrast to the one order smaller nonlinear coefficient and biaxial character of $BaMgF_4$. The refractive index of $SrAlF_5$ from the ultraviolet to the near-infrared wavelength region is measured by the minimum deviation method. The Sellmeier and Cauchy coefficients are obtained from the fits to the curves of the ordinary and extraordinary refractive indices, and the grating period for the first order QPM is estimated as a function of the wavelength. The poling periodicity for 193 nm SHG from 386 nm is $4{\mu}m$.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.6
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• pp.52-60
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• 1999

Fabricability of phase shifted grating filters has been theoretically studied by an effective index transfer matrix method. In the optical band-pass filter with multiple ${\lambda}/4$ phase-shifts, the phase-shift error and random variation of the grating period should be suppressed such that corresponding resonance frequency lies within, the filter pass-band. The tolerance for the relative error is less than $10^3$, and is quite stringent in typical filters for WDM application. End facet reflection produces ripple in the transmission spectra and the reflectivity should be less than 1% in order to keep the ripple less than 0.25dB. Also, the effect of waveguide absorption loss is enhanced by the resonance in the filter, and the absorption should be limited to 1dB/cm for the signal loss of less than 0.2dB.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.225-225
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• 2011

The dielectric and optical properties of GaInZnO (GIZO), HfInZnO (HIZO) and InZnO (IZO) thin films on glass by RF magnetron sputtering method were investiged using reflection electron energy loss spectroscopy (REELS). The band gap was estimated from the onset values of REELS spectra. The band gaps of GIZO, HIZO and IZO thin films are 3.1 eV, 3.5 eV and 3.0 eV, respectively, Hf and Ga incorporated into IZO results in an increase in the energy band gap of IZO by 0.5 eV and 0.1 eV. The dielectric functions were determined by comparing the effective cross section determined from experimental REELS with a rigorous model calculation based on the dielectric response theory, using available software package, good agreement between the experimental and fitting results gives confidence in the accuracy of the determined dielectric function. The main peak of Energy Loss Function (ELF) obtained from IZO shows at 18.42 eV, which shifted to 19.43 eV and 18.15 eV for GIZO and HIZO respectively, because indicates the corporation of cation Ga and Hf in the composition. The optical properties represented by the dielectric function e, the refractive index n, the extinction coefficient k, and the transmission coefficient, T of HIZO and IZO thin films were determined from a quantitative analysis of REELS. The transmission coefficient was increased to 93% and decreased to 87% in the visible region with the incorporation of Hf and Ga in the IZO compound.