• Current Optics and Photonics
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• v.8 no.4
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• pp.366-374
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• 2024

This paper presents an optimum method for determining the parameters to athermalize a long-wavelength infrared (LWIR) zoom camera by introducing the defocus sensitivity analysis. To effectively find parameters that significantly affect thermal defocus, we simulated athermal analysis with temperature changes for all variables. Consequently, we found that the optimum parameter to correct thermal defocus is the compensation lens, and its movements with temperature at each zoom position are obtained from the simulated athermal analysis. To verify the efficiency of our athermal approach, we performed actual athermal tests in a broad temperature range at each zoom position. The simulated athermal analysis provides the initial position of the compensation lens at the corresponding temperature and zoom position. Then the compensation lens is elaboratively moved to serve the highest live contrast ratio (LCR) for the target. This experiment shows that the compensation lens locations in the actual test are closely matched to those in the simulated athermal analysis. In addition, two outdoor tests conducted in two different environments confirm that the autofocus system suggested in this study performs well at all zoom positions. Using the proposed athermal analysis approach in this paper, we efficiently realize an athermal system over the specified temperature and zoom ranges.

• Journal of the Korean Vacuum Society
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• v.21 no.3
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• pp.136-141
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• 2012

We report investigation of structural and optical characteristics of $In_2Se_3$ thin films fabricated by thermal annealing process. Indium (In) is deposited on substrates by sputtering methods and $In_2Se_3$ thin films are fabricated by thermal annealing it with selenium vapor. The annealing temperature was changed from $150^{\circ}C$ to $400^{\circ}C$. We observe formation and phase changes of $In_2Se_3$ thin films with increase of annealing temperature. Conglomeration of In is observed at low annealing temperature (${\leq}150^{\circ}C$). $In_2Se_3$ phases are started to form at $200^{\circ}C$ and ${\gamma}-In_2Se_3$ phase form at $350^{\circ}C$. High-quality ${\gamma}-In_2Se_3$ thin film with wurtzite structure is obtained at $400^{\circ}C$ of annealing temperature. Furthermore, we confirm that band gaps of $In_2Se_3$ thin films are increased according to increase of annealing temperature. Optical band gap of high-quality ${\gamma}-In_2Se_3$ is found to be 1.796eV.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.4
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• pp.475-480
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• 2010

The thermal barrier coating of a gas turbine blade was degraded by isothermal heating in a furnace and by varying the exposure time and temperature. Then, a micro-Vickers hardness test was conducted on the cross section of the bond coat and Ni-based superalloy substrate. Further, the thickness of TGO(Thermally Grown Oxide) was measured by using an image analyzer, and the changes in the microstructure and element contents in the coating were analyzed by using an optical microscope and by performing SEM-EDX analysis. No significant change was observed in the Vickers hardness of the bond coat when the coated specimen was degraded at a high temperature; delamination was observed between the top coat and the bond coat when the coating was degraded for 50 h at a temperature $1,151^{\circ}C$.

• Journal of the Korea Institute of Military Science and Technology
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• v.15 no.2
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• pp.201-207
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• 2012

Pulsed lasers at the 613 nm and 1064 nm wavelengths on nanoseconds have been utilized to characterize the damage on Si photodiode exposed to intense illumination. Morphological damages and structural changes at sites on the photodiode irradiated during microseconds of laser pulses were analyzed by FE-SEM images and XRD patterns, respectively. The removal of oxide coating, ripple, melting marks, ridges, and crater on photodiodes were definitely observed in order of increasing the pulse intensities generated above the damage threshold. Then, the degradation in photosensitivity of the Si photodiode irradiated by high power density pulses was measured as a function of laser irradiation time at the various wavelengths. The free charge carrier and thermal diffusion mechanisms could have been invoked to characterize the damage. The relative photosensitivity data calculated using the thermal diffusion model proposed in this paper have been compared with the experimental data irradiated above the damage threshold.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.843-846
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• 1992

This thesis was investigated on optical-and ion-induced characteristics in positive(a-$Se_{75}Ge_{25}$) and negative (Ag/a-$Se_{75}Ge_{25}$) resists for focused-ion-beam microlithogaphy. The a-$Se_{75}Ge_{25}$ inorganic thin film shows an increase in optical absorption after exposure to$\sim$$10^{16}$ dose(ions/$cm^{2}$) of Ga ions. The observed shift in the absorption edge toward longer wavelengths is consistent with that in films exposed to band-gap photons ($\sim$$10^{20}$ photons/$cm^{2}$). But, ion induced shift is twice as much as that in film exposed to optical radiation. This result may be related with microstructural rearrangements with in the short range of SeGe network. Due to changes in the short range order, the chemical bonding may be affected, which results in increased chemical dissolution in ion-induced film. Also, this resist exhibits good thermal stability because of its high Tg(~220$^{\circ}C$). The composition of deposited film measured by AES is consistent with that of bulk.

• Korean Journal of Optics and Photonics
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• v.30 no.6
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• pp.249-254
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• 2019

An optical current sensor device that measures electric current by the principle of the Faraday effect was designed and fabricated. The polarization-rotated reflection interferometer and the quadrature phase interferometer were introduced so as to improve the operational stability. Complex structures containing diverse optical components were integrated in a polymeric optical integrated circuit and manufactured in a small size. This structure allows sensing operation without extra bias feedback control, and reduces the phase change due to environmental temperature changes and vibration. However, the Verdet constant, which determines the Faraday effect, still exhibits an inherent temperature dependence. In this work, we tried to eliminate the residual temperature dependence of the optical current sensor based on polarization-rotated reflection interferometry. By varying the length of the fiber-optic wave plate, which is one of the optical components of the interferometer, we could compensate for the temperature dependence of the Verdet constant. The proposed optical current sensor exhibited measurement errors maintained within 0.2% over a temperature range, from 25℃ to 85℃.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.26-32
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• 2021

The photovoltaic properties and microstructure changes were observed while perovskite solar cells (PSCs) with a fabricated carbon electrode were formed using the following annealing processes: hot-plate, oven, and rapid thermal annealing (RTA). Perovskite solar cells with a glass/FTO/compact TiO2/meso TiO2/meso ZrO2/carbon structure were prepared. The photovoltaic properties and microstructure changes in the PSCs were analyzed using a solar simulator, optical microscopy, and field emission scanning electron microscopy. An analysis of the photovoltaic properties revealed outstanding properties when RTA was applied to the cells. Microstructure analysis showed that perovskite was formed locally on the carbon electrode surface when hot-plate and oven annealing were applied. On the other hand, PSC with RTA showed a flat surface without extra perovskite agglomeration. Denser perovskite formed on the porous carbon electrode layer with RTA showed superior photovoltaic properties. These results suggest that the RTA process might be appropriate for the massive production of carbon electrode PSCs considering the processing time.

• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.1108-1110
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• 2003

MSC(Multi-Spectral Camera) which is a unique payload for KOMPSAT-2, comprises main three subsystems of PMU(Paylaod Management Unit), EOS(Electro -Optical Subsystem) and PDTS(Payload Data Transmission Subsystem). The PMU, as a main controller of MSC, performs major tasks such as interfacing with S/C(Space Craft), controlling the MSC operation, distributing and controlling of operating power to all MSC including thermal unit, etc. In this paper the H/W configurations as well as the functions of PMU are introduced and possible changes for the future development are suggested.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1992.05a
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• pp.30-33
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• 1992

This thesis was investigated on ion-induced characteristics in a-$Se_{75}Ge_{25}$ positive and negative resists for focused-ion-beam microlithogaphy. The exposed a-$Se_{75}Ge_{25}$ inorganic thin film shows an increase in optical absorption after exposure to~$10_{16}$ dose of Ga+. The observed shift in the absorption edge toward longer wavelengths is consistent with that in films exposed to band-gap photons(~$10^{21}$photons/cm2). This result may be related with microstructural rearrangements with in the short range of SeGe network. Due to changes in the short range order, the chemical bonding may be affected, which results in increased chemical dissolution in ion-induced film. Also, this resist exhibits good thermal stability because of its high Tg(~$220^{\circ}C$). When focused ion beams are used for direct exposure of resist over a substrate, unwanted implantation of the substrate may be an issue. A possible way to avoid this is to match the thickness of the resist to the range of ions in the resist. Thin aspect is currently under investigation.

• Korean Journal of Optics and Photonics
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• v.29 no.3
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• pp.110-118
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• 2018

We have designed a mid-infrared optical system for an airborne electro-optical targeting system. The mid-IR optical system is a dual-field-of-view (FOV) optics for an airborne electro-optical targeting system. The optics consists of a beam-reducer, a zoom lens group, a relay lens group, a cold stop conjugation optics, and an IR detector. The IR detector is an f/5.3 cooled detector with a resolution of $1280{\times}1024$ square pixels, with a pixel size of $15{\times}15{\mu}m$. The optics provides two stepwise FOVs ($1.50^{\circ}{\times}1.20^{\circ}$ and $5.40^{\circ}{\times}4.23^{\circ}$) by the insertion of two lenses into the zoom lens group. The IR optical system was designed in such a way that the working f-number (f/5.3) of the cold stop internally provided by the IR detector is maintained over the entire FOV when changing the zoom. We performed two analyses to investigate thermal effects on the image quality: athermalization analysis and Narcissus analysis. Athermalization analysis investigated the image focus shift and residual high-order wavefront aberrations as the working temperature changes from $-55^{\circ}C$ to $50^{\circ}C$. We first identified the best compensator for the thermal focus drift, using the Zernike polynomial decomposition method. With the selected compensator, the optics was shown to maintain the on-axis MTF at the Nyquist frequency of the detector over 10%, throughout the temperature range. Narcissus analysis investigated the existence of the thermal ghost images of the cold detector formed by the optics itself, which is quantified by the Narcissus Induced Temperature Difference (NITD). The reported design was shown to have an NITD of less than $1.5^{\circ}C$.