• Publications of The Korean Astronomical Society
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• v.19 no.1
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• pp.65-70
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• 2004

An imaging spectrograph concept optimized for extended far-ultraviolet emission sources is presented. Although the design was originally developed for FIMS aboard the first Korean science satellite STSAT-l launched on September 27, 2003, no rigorous theoretical background of the spectrograph design has been published. The spectrograph design employs an off-axis parabolic cylinder mirror in front of a slit that guides lights to a diffraction grating. The concave grating provides moderate spatial resolution over a large field of view. This mapping capability is absent in most astronomical instruments but is crucial to the understanding of the nature of a variety of astrophysical phenomena. The aberration theory presented in this paper can be extended to holographic gratings in order to improve the spatial as well as the spectral resolutions.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.3
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• pp.37-41
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• 2014

In this work, we investigated the efficiency improvement of concave mirror based solar daylighting system that does not convert light to electricity. Total efficiency of the system is substantially affected by external environment and focusing position, alignment of reflectors, lenses. As a result of simulation, we obtained the max. efficiency in which depends on convex lens position.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.11
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• pp.955-959
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• 2013

It is possible to obtain an omnidirectional stereo image via a single camera by using a catadioptric approach with a convex mirror and concave lens. In order to measure three-dimensional distance using the imaging system, the optical parameters of the system are required. In this paper, a calibration procedure to extract the parameters of the imaging system is described. Based on the parameters, experiments are carried out to verify the performance of the three-dimensional distance measurement of a single camera omnidirectional stereo imaging system.

• Journal of Mechanical Science and Technology
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• v.19 no.8
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• pp.1576-1581
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• 2005

Generally, the optical components are fabricated by grinding, lapping, and polishing. And, those processes take long time to obtain such a high surface quality. Therefore, in the case of large optical component, the on-machine inspection (OMI) is essential. Because, the work piece is fragile and difficult to set up for fabricating and measuring. This paper is concerned about a swing-arm method for measuring surface profile of large optical concave mirror. The measuring accuracy and uncertainty for suggested method are studied. The experimental results show that this method is useful specially in lapping process with the accuracy of $3\~5\;{\mu}m$. Those inspection data are provided for correcting the residual figuring error in lapping or polishing processes.

• Bulletin of the Korean Space Science Society
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• 2004.10b
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• pp.254-257
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• 2004

Both ground and space telescopes are being built larger and larger. Accordingly, the secondary mirrors become larger which are convex mostly on the surface form. Testing convex mirrors becomes more difficult and delicate than testing concave mirrors in optics, because additional optical components are needed to make the reflected rays converge. Hindle type tests are frequently used for measuring the surface deforms of convex mirrors, which employs a meniscus lens to reverse the diverted rays from the mirrors. In case of testing large convex mirrors by using Hindle type tests, attention would be needed as larger meniscus lens is required. A method of modified Hindle test has been studied and the characteristics are analyzed. In this paper, current method of testing convex mirrors is presented, and a new method is discussed.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.12
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• pp.586-591
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• 2003

We have developed the radio frequency excited slab waveguide $CO_2$ laser, The dimension of active area is $2{\times}40{\times}400$ mm to get a laser gain. Two pieces of concave mirror are used to make the unstable resonator of negative branch. The radio frequency is 123 MHz and RF input power is from 100 to 900 W. The laser gas is set to a pressure of 10 ∼ 60 torr and the mixing ration is $CO_2$:$N_2$:He=1:1:3. The laser output power of 50.9 W was obtained with laser power to RF power efficiency of 6.5 %.

• Korean Journal of Optics and Photonics
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• v.3 no.1
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• pp.37-42
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• 1992

Nd:YLF regenerative amplifiers have proved to be reliable source for producing stable short pulses of high repetition rate. We used a convex-concave mirror design to optimize output energy and stability while minimizing the energy density on critical intracavity optical components. The Kd:YLF laser pulse is used as a seed pulse which has pulse width of 40 ps, energy of 100pJ, and wavelength of 1053 nm. The amplifier yields stable 1 mJ pulses at 3.5 kHz repetition rate, and the maximum energy is measured as 5 mJ.

• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.392-398
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• 2003

We present a novel concept of a phase-shifting diffraction-grating interferometer, which is intended for the optical testing of concave mirrors with high precision. The interferometer is configured with a single reflective diffraction grating, which performs multiple functions of beam splitting, beam recombination, and phase shifting. The reference and test wave fronts are generated by means of reflective diffraction at the focal plane of a microscope objective with large numerical aperture, which allows testing fast mirrors with low f-numbers. The fiber-optic confocal design is adopted for the microscope objective to focus a converging beam on the diffractive grating, which greatly reduces the alignment error between the focusing optics and the diffraction grating. Translating the grating provides phase shifting, which allows measurement of the figure errors of the test mirror to nanometer accuracy.

• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.230-235
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• 1997

Coupling loss variation as the shape of fiber ends and the fiber arrangement in a fiber Fabry-Perot cavity, formed with two optical fibers with dielectric mirror coatings on their ends, is analyzed. For the intended features it is assumed that one of two fibers is processed to have a concave mirror whose curvature is the same as that of the wavefront of the Gaussian beam from the first fiber. In this assumption, it was turned out that the coupling loss at the cavity length of 15 ${\mu}{\textrm}{m}$ is less than 0.5% even with tilt angle of 0.2$^{\circ}$, curvature error of 70 ${\mu}{\textrm}{m}$, cavity length error of 8 ${\mu}{\textrm}{m}$, and lateral alignment error of 0.5 ${\mu}{\textrm}{m}$. Thus, low loss and high-finesse fiber Fabry-Perot filters whose cavity length is greater than several ${\mu}{\textrm}{m}$ can be obtained easily if the receiving fiber end is properly formed.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.76.3-77
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• 2021

GMT secondary mirror system consists of 7 segmented adaptive mirrors. Each segment consists of a thin shell mirror, actuators and a reference body. The thin shell has a few millimeters of thickness so that it can be easily bent by push and pull force of actuators to compensate the wavefront disturbance of light due to air turbulence. The one end of actuator is supported by the reference body and the other end is adapted to this thin shell. One of critical role of the reference body is to provide the reference surface for the thin shell actuators. Therefore, the reference body is one of key components to succeed in development of GMT ASM. Recently, Korea Research Institute of Standards and Science (KRISS) and University of Arizona (UA) has signed a contract that they will cooperate to develop the first set of off-axis reference body for GMT ASM. This project started August 2021 and will be finished in Dec. 2022. The reference body has total 675 holes to accommodate actuators and 144 pockets for lightweighting. The rear surface has a curved rib shape with radius of curvature of 4387 mm with offset of 128.32mm. Since this reference body is placed just above the thin shell so that the front surface shape needs to be close to that of thin shell. The front surface has a concave off-axis asphere, of which radius of curvature is 4165.99 mm and off-axis distance is about 1088 mm. The material is Zerodur CTE class 1 (CTE=0.05 ppm/oC) from SCHOTT. All the actuator holes and pockets are machined normal to the front surface. It is a very complex challenging optical elements that involves sophisticated machining process as well as accurate metrology. After finishing the fabrication of reference body in KRISS, it will be shipped to UA for final touches and finally sent to Adoptica in Italy, in early 2023. This paper presets the development plan for the GMT ASM Reference Body and relevant fabrication and metrology plans.