• Korean Journal of Heritage: History & Science
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• v.39
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• pp.281-314
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• 2006

Several explanations exist about the usage of disk-shaped bronze implements in the ancient society. Some argue that they were used as mirrors, others suggest percussion instruments, and still others bronze ornaments. Differences between disk-shaped bronze implements and mirrors with multiple knobs are that the former have no visible design, only one handle, and a sharp curvature unlike the latter with smooth curvature. The question is whether disk-shaped bronze implements excavated from Korean peninsula have any light reflecting function. To answer this question, I carefully studied the concave surfaces of disk-shaped bronze implements excavated from Goejeong-dong, Tongso-ri and Hapsong-ri sites. The main findings are as follows: (1) The concave sides of the disk-shaped bronze implements excavated from Goejeong-dong and Tongso-ri sites were highly polished, and they were as reflective as bronze mirrors. (2) The concave side of the disk-shaped bronze implement from Hapsong-ri site was unpolished, and it was different from bronze mirrors. (3) As for the convex sides of the disk-shaped bronze implements, they did not appear to have been polished with care. Considering the above findings, the disk-shaped bronze implements excavated from Goejeong-dong and Tongso-ri sites belong to the stage where they could act as both mirrors and instruments. On the contrary, the disk-shaped bronze implement from Hapsong-ri site can belong to the stage where it lost the function of being a mirror as the result of maintaining only its function as an instrument. Even though disk-shaped implements had two functions, it can be considered that the light reflecting function expanded the role of a mirror with multiple knobs and the sound function helped the engraved round bronze implement to be converted into an eight-armed bronze rattle. Since it has been reported that shamans used bronze mirrors as percussion instruments in their performances in Korean peninsula and Siberia, I propose a reconsideration of the usage of mirrors in the ancient East Asia. Although the essential function of a mirror is to reflect light, other possible usages involving important functions need to be further investigated.

• 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.

• Korean Journal of Optics and Photonics
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• v.4 no.2
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• pp.206-211
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• 1993

We carried out the second harmonic generation of low power CW laser diode with maximum power of 30 mW in $LilO_3$ crystals. We used a ring enhancement cavity to increase the second harmonic conversion efficiency. The ring enhancement cavity was Composed of two flat mirrors and two concave mirrors. The focal length of concave mirrors was 25 mm, and 5 mm long and 10 mm long $LilO_3$ crystals were used. We measured the second harmonic power according to the pumping power and compared with theoretical value. We obtained 397 nm second harmonic power of about $6.6{\mu}W$ in 10 mm long $LilO_3$ crystal with the fundumental 794 nm pumping power of 28 mW.

• Korean Journal of Optics and Photonics
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• v.15 no.6
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• pp.495-502
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• 2004

We proposed an analysis model for a Fabry-Perot cavity constructed with a plane-mirrored optical fiber and a concave-mirrored one. We presented the analysis results calculated by inserting practical values into the equations derived. The coupling loss of the cavity and the mirror loss are the most important parameters in reducing the insertion loss of the filter. In order to build a filter of finesse 600, FSR 57 nm, and insertion loss < 3 dB, the plane-concave cavity using mirrors of loss < 0.09% should be aligned for the coupling loss to be less than 0.1 %.

• Journal of the Optical Society of Korea
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• v.5 no.4
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• pp.136-139
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• 2001

We investigated a high-output ower, periodically poled lithium niobate(PPLN) optical parametric oscillator(OPO) pumped by a Q-switched Nd:YAG laser. Given the low optical damage threshold and the limited aperture (0.5mm thick) of PPLN, we tried to maximize the signal output power in a linear cavity consisting of two flat mirrors with a loosely focused pump beam. It is found that this simple cavity structure allowed a robust OPO operation, which was not sensitive to alignment compared with the conventional ones using concave mirrors. A maximum energy of 100$\mu$J/pulse was achieved for the signal at 1.36${\mu}{\textrm}{m}$, while the oscillation threshold was 0.3 mJ/pulse for the pump at 1064 nm.

• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.7
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• pp.628-634
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• 2005

We have simulated and proposed novel optical cavity, which has two elliptical mirrors, for NDIR gas sensor module and have tested it from 0 ppm to 2,000 ppm $CO_2$ concentration. The proposed sensor module shows the maximum peak voltage at 500 ms pulse modulation time, however, it shows a maximum voltage changes at 200 ms pulse duration with 18,000 times amplification gain. From 0 ppm to 2,000 ppm, the voltage difference of sensor module $({\Delta}V)$ shows 360 mV at 200 ms pulse duration and 3 sec turn-off time. The response time of designed sensor module is about 30 seconds.

• Journal of the Optical Society of Korea
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• v.20 no.2
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• pp.314-320
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• 2016

The glass thermal forming process provides a high volume, low cost approach to producing aspherical reflectors for x-ray optics. Thin glass sheets are shaped into mirror segments by replicating the mold shape at high temperature. Heating parameters in the glass thermal slumping process are crucial to improve surface quality of the formed glass. In this research, the heating process of a thermal slumping glass sheet on a concave parabolic mold was simulated with the finite-element method (FEM) to investigate the effects of heating rate and soaking temperature. Based on the optimized heating conditions, glass samples 0.5 mm thick were formed in a furnace with a steel concave parabolic mold. The figure errors of the formed glass were measured and discussed in detail. It was found that the formed glass was not fully slumped at the edges, and should be trimmed to achieve better surface deviation. The root-mean-square (RMS) deviation and peak-valley (PV) deviation between formed glass and mold along the axial direction were 2.3 μm and 4.7 μm respectively.

• Journal of the Optical Society of Korea
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• v.18 no.1
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• pp.32-36
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• 2014

A tangible floating display that can provide different perspective views without special glasses being introduced. The proposed system can display perspective floating images in the space in front of the system with the help of concave mirrors. In order to avoid wearing special equipment to interact and deliver the sense of touch, the proposed system adopted an ultrasound focusing technology. For providing an immersive experience to the viewers, the proposed system consists of a tangible floating display system and a multiple-view imaging system for generating three lenticular displays in front of the users.

• Korean Journal of Optics and Photonics
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• v.19 no.4
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• pp.327-333
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• 2008

In general, a lens with large NA makes image quality better. There are many kinds of cheap concave mirrors with large aperture and NA. This paper presents a method that uses a large aperture projection imaging system to enhance the image used for 3D shape measurement. This method makes it possible to enhance reflection uniformity on the object surface and increases SNR (Signal to Noise Ratio). Using a large aperture lens, it is possible to obtain a brighter image, reducing the shading nature in the image boundary, and enhancing the reflection uniformity even on woven surfaces. Because of the exorbitant cost of a large aperture projection lens larger than 150 mm in diameter, a refractive lens was exchanged with a concave mirror resulting in the same optical effect. In experiment, changing NA $0.15{\sim}0.8$, image contrast was enhanced from 46 to 1.33. Incidentally, the effect of the concave mirror was tested successfully through the experiment.