• Journal of Korean Ophthalmic Optics Society
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• v.9 no.2
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• pp.417-421
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• 2004

We can see that two images of reflection are observed on the surface of a ophthalmic lens. These are the image reflected from front surface and back surface of lens, respectively. The reflective image shows to be affect by surface refractive power of front and back surface of lens. Total refractive power of lens is calculated by refractive power of front and back surface of lens. Accordingly, the ratio of image on the lens surface is able to measure refractive power of ophthalmic lens without helping of the lensmeter. The ratio of two reflective image measured on the lens surface is compared with the calculated ratio by the power measurement.

• Korean Journal of Optics and Photonics
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• v.20 no.1
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• pp.53-56
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• 2009

We applied an ellipsometric technique to get quantitative information about the thickness and refractive index of human Mesenchymal Stem Cells (hMSCs). The images of ellipsometric constants $\Delta$, $\Psi$ for the nucleus region and for the cell body region of hMSCs were obtained by using an Imaging Ellipsomter (IE) for their in vitro state. A numerical inversion method was applied to deduce the refractive index and the thickness of hMSCs from the measured $\Delta$, $\Psi$. Thus the images of the refractive index and those of the thickness of hMSCs for the nucleus region and for the cell body region are reported.

• Journal of Advanced Engineering and Technology
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• v.11 no.4
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• pp.245-251
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• 2018

Terahertz waves (T-ray) was extensively studied for the NDE (nondestructive evaluation) of characterization of trailing edges for a use of turbines composed with composite materials. The used NDE system were consisted of both CW(Continuous wave) and TDS (Time domain spectroscopy). The FRP composites were utilized for two kinds of both trailing edges of wind energy (non-conducting polymeric composites) and carbon fiber composites with conducting properties. The signals of T-ray in the TDS (Time domain spectroscopy) mode resembles almost that of ultrasound waves; however, a terahertz pulse could not penetrate a material with conductivity unlike ultrasound. Also, a method was suggested to obtain the "n" in the materials, which is called the refractive index (n). The data of refractive index (n) could be solved for the trailing edges. The trailing edges were scanned for characterization and inspection. C-scan and B-scan images were obtained and best optimal NDE techniques were suggested for complicated geometry samples by terahertz radiation. Especially, it is found that the defect image of T-ray corresponded with defect locations for the trailing edges of wind mill.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.5
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• pp.72-78
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• 2009

We propose the separation algorithm to simultaneously measure two-dimensional refractive index distribution and thickness profile of transparent samples using three wavelengths. The optical system was based on the Mach-zehnder interferometer with LD (Laser Diode)-based multi-wavelength sources. A LCR (Liquid Crystal Retarder) was used to obtain interference images at four phase states and then the optical phase of the object is calculated by four-bucket algorithm. Experimental results with a glass rod are provided at the different wavelengths of 635nm, 660nm and 675nm. The refractive indices of the sample are distributed with accuracy of less than 0.0005 and the thickness profile of sample was cylindrical type. This result demonstrates that it is possible to separate refractive index distribution and thickness profile of samples in two dimensions using the proposed algorithm.

• Current Optics and Photonics
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• v.3 no.6
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• pp.597-604
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• 2019

This study was performed to evaluate objective visual quality and ocular scattering in myopic refractive-surgery patients, compared to emmetropes. Optical vision-quality parameters (modulation transfer function (MTF) cutoff and Strehl ratio) and objective scattering index (OSI) were measured using an optical quality analysis system (OQAS II) based on the double-pass technique. In all subjects, the higher the MTF cutoff and Strehl ratio, the lower the OSI and ocular higher-order aberrations (HOAs). The MTF cutoff and Strehl ratio for the laser-assisted subepithelial keratectomy (LASEK) group were lower than those for the emmetropia group, while the OSI, ocular HOAs, and spherical aberration (SA) for the LASEK group were higher than those for emmetropia group. Ocular scattering would be one of the important factors in regard to visual quality. Therefore, the quality of the retinal image in the LASEK patients has been shown to reduce the quality of vision more than in the emmetropes.

• Journal of the Optical Society of Korea
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• v.18 no.6
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• pp.691-697
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• 2014

Optical measurements of the morphological and biochemical imaging of phytoplankton are presented. Employing quantitative phase imaging techniques, 3-D refractive index maps and high-resolution 2-D quantitative phase images of individual live phytoplankton are simultaneously obtained without exogenous labeling agents. In addition, biochemical information of individual phytoplankton including volume, mass, and density of individual phytoplankton are also quantitatively obtained from the measured refractive index distributions. We expect the present method to become a powerful tool for the study of phytoplankton.

• Journal of the Korean Vacuum Society
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• v.9 no.1
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• pp.60-68
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• 2000

The optical constants ($E_g^d$, n, K) of the polycrystalline CdSe thin films deposited on the glass substrate by the electron-beam evaporation technique are determined over 400~2,500 nm photon wavelengths. In order to explain the variation of the optical contents with film thickness and substrate temperatures, the surface microstructural parameter are investigated by AFM (atomic forced microscope( images for the films deposited by different growth conditions. It is shown that the variations of optical constants are close related to changes of the surface morphology of the CdSe thin films. The decrease in the band gap with film thickness is connected with quantum size effects due to increase of the grain size. The refractive index of CdSe films decrease with increasing the grain size of the films, and the dispersion of the refractive index followed a single oscillator model according to the Sellmeier formulation.

• Journal of Integrative Natural Science
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• v.7 no.1
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• pp.1-4
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• 2014

Distributed Bragg reflector porous silicon of different characteristics were formed to determine their optical constants in the visible wavelength range using a periodic square wave current between low and high current densities. The surface and cross-sectional SEM images of distributed Bragg reflector porous silicon were obtained using a cold field emission scanning electron microscope. The surface image of distributed Bragg reflector porous silicon indicates that the distributions of pores are even. The cross-sectional image illustrates that the multilayer of distributed Bragg reflector porous silicon exhibits a depth of few microns and applying of square current density during the etching process results two distinct refractive indices in the contrast. Distributed Bragg reflector porous silicon exhibited a porosity depth profile that related directly to the current-time profile used in etch. Its free-standing film was obtained by applying an electro-polishing current.

• Journal of the Optical Society of Korea
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• v.15 no.1
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• pp.78-81
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• 2011

We demonstrate a high-spatial-resolution imaging and spectroscopy tool using a solid immersion lens (SIL), a hemispherical lens made of high refractive index glass (n ~2). Photoluminescence (PL) images of single CdSe nanocrystals confirm a numerical aperture enhancement factor of ~2, close to the refractive index of the SIL. In particular, a bare-eye observation of PL signals emitted by single nanocrystals with ${\sim}10\;{\mu}m^{-2}$ densities was possible over an ${\sim}30\;{\mu}m$ diameter region. In addition, the PL spectra of single CdSe nanocrystals were successfully measured at room temperature. Thus, this SIL microscope ensures a simple but powerful method for nanostructure spectroscopy.

• Korean Journal of Remote Sensing
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• v.27 no.2
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• pp.163-170
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• 2011

In this paper, we analyzed the phase change of 5-triangular trihedral comer reflectors by using X-band Ground-Based Synthetic Aperture Radar (GB-SAR) system. Each reflector was set as a stationary target at a different distance from the system. We obtained total 123 full-polarization images during 40 hours continuously at 20 minute interval. Results of SAR interferometric analysis showed phase changes of maximum 2 radians and followed similar pattern with atmospheric data. Through a GB-SAR phase formula that includes refractive index in the air, we performed regression analysis for refractive index as a function of atmospheric humidity, temperature and pressure. As a result, refractive index of air in X-band showed relatively high coefficient of determination with humidity and temperature (0.72 and 0.76 on average, respectively) but not so with pressure (0.34). The refractive index of air in X -band changed by 3.14\;{\times}\;10^{-5}$ during the measuring time with a humidity range of 50% ~ 90% and a temperature range of $-1^{\circ}C$ ~ $9^{\circ}C$. We expect that a total expression of refractive index of air including humidity, temperature and pressure can be calculated when more extensive data would be collected at various atmospheric conditions.