• International Journal of Precision Engineering and Manufacturing
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• v.1 no.1
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• pp.49-55
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• 2000

The semiconductor industry relies on digital optical imaging for the overlay metrology of integrated circuit patterns. One critical performance demand in the particular application of digital imaging is placed on the edge resolution that is defined as the smallest detectable displacement of an edge from its image acquired in digital from. As the critical feature size of integrated circuit patterns reaches below 0.35 micrometers, the edge resolution is required to be less than 0.01 micrometers. This requirement is so stringent that fundamental behaviors of digital optical imaging need to be explored especially for the precision coordinate metrology. Our investigation reveals that the edge resolution shows quasi-random characteristics, not being simply deduced from relevant opto-electronic system parameters. Hence, a stochastic upper bound analysis is made to come up with the worst edge resolution that can statistically well predict actual indeterminate edge resolutions obtained with high magnification microscope objectives.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.140-141
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• 2003

인공위성 카메라는 발사 시 발생하는 하중조건(진동, 충격 등)과 우주 환경(무중력, 진공, 복사 등)하에서 카메라 내부의 각종 광학부품과 그를 지지하는 구조물의 변형으로 인해 광학적 성능 전반에 큰 영향을 받는다. 특히 높은 신뢰성이 요구되는 고해상도 지구관측용 광학카메라의 경우 광학적 현상과 기계적 현상을 동시에 체계적으로 고려하는 광기계 해석 및 설계(opto-mechanical analysis and design)가 필수적이다. 그 중에서도 목표로 하는 광학적 성능을 얻기 위한 위성용 카메라 주반사경의 설계기술이 가장 중요한 부분에 속한다. (중략)

• Journal of Astronomy and Space Sciences
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• v.20 no.4
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• pp.393-402
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• 2003

The Multi-Spectral Camera (MSC) is the payload of KOMPSAT-2 which is designed for earth imaging in optical and near-infrared region on a sun-synchronous orbit. The telescope in the MSC is a Ritchey-Chretien type with large aperture. The telescope structure should be well stabilized and the optical alignment should be kept steady so that best images can be achieved. However, the MSC is exposed to adverse thermal environment on the orbit which can give impacts on optical performance. Solar incidence can bring non-uniform temperature rise on the telescope tube which entails unfavorable thermal distortion. Three ways of preventing the solar radiation were proposed, which were installing external mechanical shield, internal shield, and maneuvering the spacecraft. After trade-off study, internal sun shield was selected as a practical and optimal solution to minimize the effect of the solar radiation. In addition, detailed designs of the structure and sunshield were produced and analyses have been performed. The results were assessed to verify their impacts to the image quality. It was confirmed that the internal sunshield complies with the requirements and would improve image quality.

• Journal of The Korean Astronomical Society
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• v.56 no.2
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• pp.169-185
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• 2023

The GMT-Consortium Large Earth Finder (G-CLEF) is the first instrument for the Giant Magellan Telescope (GMT). G-CLEF is a fiber feed, optical band echelle spectrograph that is capable of extremely precise radial velocity measurement. G-CLEF Flexure Control Camera (FCC) is included as a part in G-CLEF Front End Assembly (GCFEA), which monitors the field images focused on a fiber mirror to control the flexure and the focus errors within GCFEA. FCC consists of an optical bench on which five optical components are installed. The order of the optical train is: a collimator, neutral density filters, a focus analyzer, a reimager and a detector (Andor iKon-L 936 CCD camera). The collimator consists of a triplet lens and receives the beam reflected by a fiber mirror. The neutral density filters make it possible a broad range star brightness as a target or a guide. The focus analyzer is used to measure a focus offset. The reimager focuses the beam from the collimator onto the CCD detector focal plane. The detector module includes a linear translator and a field de-rotator. We performed thermoelastic stress analysis for lenses and their mounts to confirm the physical safety of the lens materials. We also conducted the global structure analysis for various gravitational orientations to verify the image stability requirement during the operation of the telescope and the instrument. In this article, we present the opto-mechanical detailed design of G-CLEF FCC and describe the consequence of the numerical finite element analyses for the design.

• Journal of the Korea Institute of Military Science and Technology
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• v.27 no.2
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• pp.127-139
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• 2024

This paper discusses a gravity compensation technique designed to reduce wavefront error caused by gravity during the assembly and alignment of satellite multi-band optical sensor. For this study, the wavefront error caused by gravity was analyzed for the opto-mechanical structure of multi-band optical sensor. Wavefront error, an indicator of optical performance, was computed by using the displacements of optics calculated through structural analysis and optical sensitivity calculated through optical analysis. Since the calculated wavefront error caused by gravity exceeded the allocated budget, the gravity compensation technique was required. This compensation technique reduces wavefront error effectively by applying the compensation load to the appropriate position of the housing tube. This method successfully meets the wavefront error budget for all bands. In the future, a gravity compensation equipment applying this technique will be manufactured and used for assembly and alignment of multi-band optical sensor.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.39.2-39.2
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• 2010

In this paper, I present the domestic development of near infrared camera systems for the ground telescope and the space satellite. These systems are the first infrared instruments made for astronomical observation in Korea. KASINICS (KASI Near Infrared Camera System) was developed to be installed on the 1.8m telescope of the Bohyunsan Optical Astronomy Observatory (BOAO) in Korea. KASINICS is equipped with a $512{\times}512$ InSb array enable L band observations as well as J, H, and Ks bands. The field-of-view of the array is $3.3'{\times}3.3'$ with a resolution of 0.39"/pixel. It employs an Offner relay optical system providing a cold stop to eliminate thermal background emission from the telescope structures. From the test observation, limiting magnitudes are J=17.6, H=17.5, Ks=16.1 and L(narrow)=10.0 mag at a signal-to-noise ratio of 10 in an integration time of 100 s. MIRIS (Multi-purpose InfraRed Imaging System) is the main payload of the STSAT-3 in Korea. MIRIS Space Observation Camera (SOC) covers the observation wavelength from $0.9{\mu}m$ to $2.0{\mu}m$ with a wide field of view $3.67^{\circ}{\times}3.67^{\circ}$. The PICNIC HgCdTe detector in a cold box is cooled down below 100K by a micro Stirling cooler of which cooling capacity is 220mW at 77K. MIRIS SOC adopts passive cooling technique to chill the telescope below 200K by pointing to the deep space (3K). The cooling mechanism employs a radiator, a Winston cone baffle, a thermal shield, MLI of 30 layers, and GFRP pipe support in the system. Opto-mechanical analysis was made in order to estimate and compensate possible stresses from the thermal contraction of mounting parts at cryogenic temperatures. Finite Element Analysis (FEA) of mechanical structure was also conducted to ensure safety and stability in launching environments and in orbit. MIRIS SOC will mainly perform the Galactic plane survey with narrow band filters (Pa $\alpha$ and Pa $\alpha$ continuum) and CIB (Cosmic Infrared Background) observation with wide band filters (I and H) driven by a cryogenic stepping motor.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.181.2-181.2
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• 2014

A single-layer graphene has been uniformly grown on a Cu surface at elevated temperatures by thermally processing a poly (methyl methacrylate) (PMMA) film in a rapid thermal annealing (RTA) system under vacuum. The detailed chemistry of the transition from solid-state carbon to graphene on the catalytic Cu surface was investigated by performing in-situ residual gas analysis while PMMA/Cu-foil samples being heated, in conjunction with interrupted growth studies to reconstruct ex-situ the heating process. We found that the gas species of mass/charge (m/e) ratio of 15 ($CH_3{^+}$) was mainly originated from the thermal decomposition of PMMA, indicating that the formation of graphene occurs with hydrocarbon molecules vaporized from PMMA, such as methane and/or methyl radicals, as precursors rather than by the direct graphitization of solid-state carbon. We also found that the temperature for dominantly vaporizing hydrocarbon molecules from PMMA and the length of time, the gaseous hydrocarbon atmosphere is maintained, are dependent on both the heating temperature profile and the amount of a solid carbon feedstock. From those results, we strongly suggest that the heating rate and the amount of solid carbon are the dominant factors to determine the crystalline quality of the resulting graphene film. Under optimal growth conditions, the PMMA-derived graphene was found to have a carrier (hole) mobility as high as ${\sim}2,700cm^2V^{-1}s^{-1}$ at room temperature, which is superior to common graphene converted from solid carbon.

• Journal of Magnetics
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• v.21 no.3
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• pp.379-386
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• 2016

To satisfy the requirement of magnetically suspended control moment gyroscope (MSCMG) that magnetic bearing can provide torque, a novel 4DOF hybrid magnetic bearing (HMB) with integrated structure was designed. Mathematical models of forces and torques are established by using equivalent magnetic circuit method. The current stiffness, displacement stiffness, tilting current stiffness and angular stiffness of the 4DOF hybrid magnetic bearing are derived by the mathematical models. Equivalent magnetic circuit method and finite element method (FEM) simulation results indicate that the force has a good linear relationship with both displacement and current, and the torque has a good linear relationship with angular displacement and current. The novel 4DOF HMB is capable of achieving control in both two radial translational degrees of freedom (DOF) and also two radial rotational DOFs. The 4DOF HMB is well adapted to MSCMG system, exhibiting advantages in the controllable DOF, light weight and easy to control.

• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.30.4-31
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• 2011

The Korea Astronomy and Space Science Institute (KASI) and the Department of Astronomy at the University of Texas at Austin (UT) are developing a near infrared wide-band high resolution spectrograph, IGRINS (Immersion Grating Infrared Spectrograph). The white-pupil design of the instrument optics uses 7 cryogenic mirrors including 3 aspherical off-axis collimators and 4 flat fold mirrors. Two of the 3 collimators are H- and K-band pupil transfer mirrors and they are designed as compensators for the system alignment in each channel. Therefore, their mount design will be one of the most sensitive parts in the IGRINS optomechanical system. The design work will include the computer-aided 3D modeling and finite element analysis (FEA) to optimize the structural stability of the mount models. The mount body will also include a tip-tilt and translation adjustment mechanism to be used as the alignment compensators.

• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.31.2-31.2
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• 2011

IGRINS (Immersion GRating INfrared Spectrometer) is a high resolution wide-band infrared spectrograph developed by Korea Astronomy and Space Science Institute (KASI) and the University of Texas at Austin (UT). The slit-viewing camera is one of four re-imaging optics in IGRINS including the input relay optics and the H- and K- band spectrograph cameras. Consisting of five lenses and one Ks-band filter, the slit viewing camera relays the infrared image of $2'{\times}2'$ field around the slit to the detector focal plane. Since IGRINS is a cryogenic instrument, the lens barrel is designed to be optimized at the operating temperature of 130 K. The barrel design also aims to achieve easy alignment and assembly. We use radial springs and axial springs to support lenses and lens spacers against the gravity and thermal contraction. Total weight of the lens barrel is estimated to be 1.2 kg. Results from structural analysis are presented.