• Journal of the Optical Society of Korea
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• v.15 no.2
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• pp.146-151
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• 2011

We describe, throughout a Mach-Zehnder interferometric configuration, a new test sieves calibration method based on off-axis digital holography. The experiment is conducted on a test sieve of square openings. The nominal sieve opening is 1.00 mm with maximum individual opening of 1.14 mm in size. The recorded off-axis hologram is numerically processed using Fresnel transforms to obtain an object wave (amplitude and phase). From the reconstructed phase, the average size of the illuminated openings has been measured precisely. The proposed method can provide a real time solution for calibrating test sieves very precisely and with moderate accuracy.

• Korean Journal of Optics and Photonics
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• v.25 no.2
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• pp.85-89
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• 2014

In this paper, we present a speckle-free digital hologram with conversion to an off-axis horizontal-parallax-only (HPO) hologram. First, we record the speckle-free hologram using optical scanning holography. Second, we digitally convert the full-parallax hologram to a horizontal-parallax-only hologram. Third, we convert the horizontal-parallax-only hologram to an off-axis hologram. Finally, we show that the off-axis HPO hologram can be numerically reconstructed in space.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.79.1-79.1
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• 2019

The Schwarzchild-Chang telescope is a confocal off-axis two mirror telescope with D = 50 mm, F = 100 mm and FOV = 8 ° × 8 °. Unlike common off-axis telescopes, the mirrors of the Schwarzchild-Chang telescope share their focal points to remove the linear astigmatism. In this poster, we show the alignment process of the Schwarzchild-Chang telescope with wavefront measurement and the sensitivity table method. Wavefront is measured using the Shack-Hartmann sensor, and Zernike polynomials are obtained from measured wavefront. Sensitivity table method is to calculate alignment errors from the Zernike coefficients. As a result, we evaluate tilt, decenter, and despace of each mirror of linear astigmatism-free con-focal off-axis system.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 1999.11a
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• pp.111-114
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• 1999

Off-vertical axis rotator was developed to differentiate each function of the canal and otolith in the vestibular system and evaluate subjective symptoms during postural change. Eye movement induced by various types of rotation was measured in normal subjects. Nystagmus with fast component corresponding to direction of rotation was occurred by sinusoidal earth vertical axis rotation, and the gain of eye movement in vestibuloocular reflex (VOR) was lower than in visual vestibuloocular reflex (VVOR) and higher than in visual fixed vestibuloocular reflex (VFX). Degree of dizziness was proportioned to degree of gain. off-vertical axis rotation was produced severe dizziness than earth vertical axis rotation. These results suggest stimulation of the otolith should be minimized to make a stable and pleasant condition in work and travel.

• Korean Journal of Optics and Photonics
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• v.32 no.1
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• pp.9-14
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• 2021

In this paper we have studied an optical system according to the aperture position of an off-axis TMA telescope for satellites. An off-axis TMA telescope should have high resolution and wide field of view (FOV). In addition, the optical system should have a wide tolerance range, because it is structurally located off-axis and is difficult to assemble. However, there are differences in performance and sensitivity according to the aperture-stop position, so it is important to select a suitable aperture-stop position. Therefore, in this paper we have designed each off-axis TMA telescope according to the aperture-stop position, and have analyzed the performance and sensitivity to suggest a suitable aperture-stop position.

• Current Optics and Photonics
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• v.6 no.1
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• pp.44-50
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• 2022

An off-axis zone plate is able to focus on a single order while neglecting the zeroth order in a visible imaging system. This allows one to enhance the contrast quality in diffractive images, which is the major advantage of this type of zone plate. However, most previous reflection zone plates are used in focusing X-rays with a small grazing incident angle and are intricately designed with the use of a local grating period. In this study, we suggest the design of an off-axis elliptical zone plate (EZP) that is used to focus a monochromatic light beam with separation between the first and unfocused orders under a large grazing incident angle of 45°. An assumption using the total grating period, which depends on the average and constant grating period, is proposed to calculate the desired distance between the first and zeroth order and to simplify the construction of a novel model off-center EZP. Four diffractive optical elements (DOEs) with different parameters were subsequently fabricated by direct laser lithography and then verified using a performance evaluation system to compare the results from the assumption with the experimental results.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.150-150
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• 2010

질화물 기반의 LED의 경우 c-plane 사파이어에 GaN을 성장 하는 방법이 많이 연구되어 왔다. 그러나 c-plane 위에 성장시킨 LED는 분극현상이 발생하여 양자효율의 저하와 발광파장의 적색 편이를 야기한다[1]. 이런 문제를 해결하기 위하여 a-plane (11-20), m-plane (10-10) 등의 비극성면을 갖는 GaN을 성장을 통해 분극문제를 해결하고자 하는 방법이 제안되었다 [2] 하지만, 현재 비극성 면을 갖는 고품질의 박막을 성장시키기 어렵다는 단점이 존재한다. 고품질의 박막을 성장시키는 방법으로는 ELO와 다중 버퍼층의 사용처럼 여러가지 방법이 연구되고 있다. 하지만 사파이어의 tilt와 열처리에 따른 표면 개질에 대한 연구는 많이 진행되어지고 있지 않다. 본 연구에서는 사파이어에 열처리를 통하여 표면의 특성 변화를 관찰하고 이를 이용하여 고품위 GaN 박막의 품질을 높이려 하였다. r-plane 사파이어에 유기금속화학증착법(MOCVD)을 이용하여 a-plane GaN을 성장하였다. 이 공정에서 사용한 pre-treatment는off-axis angle을 가진 기판의 표면 열처리이다A-plane GaN 성장전에 m-direction으로 off-axis angle을 가진 r-plane 사파이어 기판을 1300도로 가열한 후 각각의 다른 시간에서 열처리를 진행하였다. Off-axis angle을 가진 사파이어는 표면에 step구조를 가지고 있으며, 이 step의 width를 비롯한 표면의 morphology는 off-axis angle에 따라 달라진다. Off-axis angle을 변화시킨 사파이어를 1300도에서 1시간, 3시간, 5시간 annealing하여 표면을 AFM을 사용하여 관측한 결과 step width가 증가하고 step의 형태가 뚜렷해지며 rms-roughness가 변화한 것을 관찰할 수 있었다. 그리고 이 각각의 기판을 동일한 조건으로 a-plane GaN을 성장하여 박막의 특성을 측정하였다. 본 발표에서는 사파이어 기판의 표면 처리에 따른 비극성 GaN의 특성 변화에 대한 분석 결과를 논의할 것이다.

• Korean Journal of Optics and Photonics
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• v.2 no.3
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• pp.121-126
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• 1991

The knife-edge scanning type OTF measuring equipment is improved to enhance the accuracy in off-axis OTF measurement and the accuracy of this equipment of evaluated by measuring the OTF of 50 mm plano-convex standard lens developed by SIRA group. Measured MTF values of the standard lens are in good agreement with SIRA results within $\pm$0.02 on axis and % $\pm$0.03 off-axis in 0-100 clmm frequency range except only a few spatial frequencies. Measured PTF values are good agreement with SIRA results within $\pm$$5^{\circ}$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.10
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• pp.3789-3793
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• 2010

To investigate accuracy of graduated scale of schematic retinoscope training eye(schematic eye) and induced effect when measured at off-axis from visual axis. Two skilled retinoscopist measured refractive power using retinoscope in random order. Seven schematic eyes from a single manufacturer were recruited and set to mark +4.00 to -6 diopter(+4, +3, +2, +1, 0, -1, -2, -3, -4, -5, -6). After introducing +2.00 diopter trial lens(50cm working lens), neutral distance was measured at 180 degree to estimate accuracy of scale, and refractive power measured at 0, 5, 10, 15 and 20 degree off-axis to see if any error was induced. According to the results measured by two specialists, in six of seven schematic eye, scale setting varied (p<0.05) and measured refractive power at 5, 10, 15 and 20 degree off-axis from visual axis were $-0.13{\pm}0.06$, $-0.29{\pm}0.06$, $-0.58{\pm}0.11$, and $-0.83{\pm}0.16$ diopter respectively. In some schematic eye, scale graduated on the schematic eye and scale measured by retinoscopy could be different and if retinoscopy is performed off-axis from visual axis, any measuring error can be caused.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.3
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• pp.97-101
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• 2005

ZnO thin films were grown at different plume-substrate (P-S) angles of 90$^{\circ}$ (on-axis PLD), 45$^{\circ}$ and 0$^{\circ}$ (off-axis PLD) using pulsed laser deposition. The x-ray diffraction pattern exhibiting a dominant (002) and a minor (101) peak of ZnO indicates all films were strongly c-axis oriented. By observing of (002) peak, the FWHMs of ZnO (002) peaks decreased and c-axis lattice constant approached the value of bulk ZnO as P-S angle decreased. Whereas the carrier concentration of ZnO thin film deposited at P-S angle of 90$^{\circ}$ was ~ 10$^{19}$ /cm$^{3}$, the Hall measurement of ZnO thin films deposited at P-S angles of 0$^{\circ}$ and 45$^{\circ}$ was impossible due to the decrease of the carrier concentration by the improvement of stoichiometry and crystalline quality. By decreasing P-S angle, the grain size of the films and the UV intensity investigated by photoluminescence (PL) increased and UV peak position showed red shift. The improvement of properties in ZnO thin films deposited by off-axis technique was due to the decrease of repulsive force between a substrate and the particle in plume and the relaxation of supersaturation.