• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.291-296
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• 1997

The slotted type of hollow copper cathode was constructed and tested for its geometric stability and usability for laser operation at 780nm. The peak output power of copper ion laser emission was measured for different operating conditions. The IR-laser power was dependent on the parameters of the geometry of the hollow cathodes, discharge current and gas fillings. The peak power decreased with increasing neon pressure over 60%. One reason for this decrease in output power may be conjectured as hier due to the decreasing population of the upper laser level. The copper ion laser transition at 780 nm populated at the 5p level. The hollow cathode copper ion laser is operated in He and Ne mixture by electric discharge excitation and could be operated for more than 100 hours with only a 35% drop in the output power(2.8mW cw for 9.6cm active length).

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.530-536
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• 2002

The accurate measurements of thermal expansion coefficients is one of the most important techniques required not only in material science but also in industries. A high precision interferometric dilatometer, using acoustic optical modulator, has been constructed and its performance has been tested. The system consists of a double-path optical heterodyne interferometer and a radiant heating furnace. This provides highly accurate length measurement, and allows rapid heating and cooling method for the specimen. A three longitudinal mode frequency stabilized He-Ne laser, using the secondary beat frequency, is constructed. Its stability is found to be $5{\times}10^{-9}$. The uncertainty in the length measurement is estimated to be of nanometer order in the range between room temperature to 1100 K.

• Korean Journal of Optics and Photonics
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• v.13 no.1
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• pp.58-64
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• 2002

Using Mach-Zehnder type intensity modulator, we stabilized a 10 GHz harmonically mode-locked dispersion-compensated fiber ring laser using a feedback controlling system, and we measured its stability. The laser was stabilized for more than 16 hours by controlling the cavity length to suppress the relaxation oscillation frequency component which had caused the laser output instability. The ms timing jitter and ms amplitude noise were measured to be 260-524 fsec and 4~11.5%, respectively, and BER test measurement showed a value of 10$^{-13}$ .

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.66.3-66.3
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• 2017

Korea Astronomy and Space Science Institute (KASI) is developing a coronagraph in collaboration with National Aeronautics and Space Administration (NASA) which will be installed on the International Space Station (ISS). The coronagraph can measure speed and temperature by using four filters approximately 400 nm and polarization filter in three different angles, differently with older coronagraphs. For the successful mission, it has development and experiment progress in three phases; total solar eclipse experiment in 2017, balloon experiment in 2019, and the ISS installation in 2021. As a first experiment, we developed a coronagraph without an occulter named with Diagnostic Coronagraph Experiment (DICE) for experiment for filter system and imaging sensor. We designed optics with a field of view from 2.5 to 15 solar radii. It has four filters approximately 400 nm and polarizer to measure speed and velocity of the solar corona. For the selection of filter or polarization angle, it has two mechanism parts; filter wheel assembly and a polarizer wheel assembly. Especially we used Core Flight System (CFS) platform which was developed by NASA, when we develop the coronagraph operation software. It provides us stability, reusability, and compatibility.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.2
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• pp.27-31
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• 2000

As the functional test of cornea. The clinical value of keratometric information was important for assessment the curvature of the cornea, the quality of the corneal surface, the stability of the corneal curvature, and the direction of the corneal astigmatism. This study was performed the comparative analysis of male and female of adult on the base curve, power and astigmatism of the Cornea. On the corneal base curve, the male right eye was 7.656 mm in vertical and 7.966 mm in horizontal. But, the male left cornea was 7.714 mm in vertical base curve and 8.026 mm in horizontal base curve. On the other hand, the female right eye cornea was 7.559 mm in vertical base curve and 7.695 mm in horizontal base curve. But, the female left eye cornea was 7.444 mm in vertical base curve and 7.742 mm in horizontal base curve. On the corneal diopter power, the male right eye was 44.063 diopter in vertical and 43.738 diopter in horizontal. But the male left eye was 44.046 diopter in vertical and 42.304 diopter in horizontal. On the other hand, the female right eye was 44.082 diopter in vertical and 43.77 diopter in horizontal. But, the female left eye was 44.347 diopter in vertical and 43.495 diopter in horizontal. According to the corneal astigmatism axis. The male right eye have 89.9% positive for with the - rule astigmatism, and 8.1 % positive for against - the - rule astigmatism. But, he male left eye have 91.89% positive for with - the - rule astigmatism, and 8.11 % positive for against - the - rule astigmatism. On the other hand, The female right eye have 76.92% positive for with - the - rule astigmatism, and 23.08 % positive for against - the - rule astigmatism. But, the female left have 80.76 % positive for with - the - rule astigmatism, and 17.31 % positive for against - the - rule as tigmatism. The diopter power of corneal astigmatism have 25.57% positive for behind 1 diopter, 44.89% positive for 1 diopter, 18.18% positive for 2 diopter, 5.11% positive for 3 diopter and 6.25% positive for over 4 diopter.

• Journal of Korean Ophthalmic Optics Society
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• v.21 no.3
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• pp.191-201
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• 2016

Purpose: In the present study, the effect of artificial tears with different ingredients on tear film stability and subjective symptoms of dry eyes in the early stage of soft contact lenses wear was investigated. Methods: The three kinds of artificial tears and saline solution were respectively applied onto 50 dry eyes which wore soft contact lenses made of etafilcon A. Then, non-invasive tear film break-up time (NIBUT) was measured at every five minutes for 30 minutes right after the instillation of artificial tears, and the changes in blink rate and subjective symptoms were estimated after 30 minutes from the instillations. Results: All three kinds of artificial tears increased NIBUT larger than saline. The effect of increasing NIBUT immediately after the instillation of artificial tears was the largest when the artificial tear containing viscosity enhancer was used. The duration time of the effect was the longest when the artificial tear having both surfactant and viscosity enhancer was applied. The blink rate was not significantly changed when both artificial tears and saline solution were instilled. Subjective symptoms were significantly improved by the instillation of both artificial tears and saline solution and dryness, irritation, tiredness, stiffness, dazzling were improved by the use of most solutions. However, the subjective symptoms were rebounded to the level before the instillation of artificial tears after 30 minute-instillation. Conclusions: It was revealed that both artificial tears and saline solution could improve the subjective symptoms of dry eye in the early stage of soft contac lenses however, the effect of these solutions on the tear film stability was different according to the components. From the results, it is suggested that the proper selection of artificial tears is necessary for the improvement of dry eye symptoms at the early stage of soft contact lenses wear in dry eye.

• Journal of Korean Ophthalmic Optics Society
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• v.17 no.1
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• pp.1-10
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• 2012

Purpose: Cellulose acetate (CA) was blended with polyethyleneglycol (PEG) having different molecular weight at various mixing conditions to enhance melt-processibility of CA, which might prevent the harmful effect resulted from the introduction of phthalic plasticizer. Methods: To establish optimal plasticizing conditions, CA/PEG blends were examined under various plasticizing conditions: PEG concentration, molecular weight of PEG, and plasticzing temperature. Mechanical properties of the CA/PEG blends, as well as migration and exudation of the PEG, were performed in order to evaluate the efficiency of plasticization. Results: Compared to industrial CA resin plasticized by diethyl phthalate, CA/PEG blends exhibited similar thermal plasticization. It was established that the optimum condition was to blend 30~40 phr PEG with molecular weight 400 at $175{\sim}180^{\circ}C$. CA/PEG blend showed superior glassness, PEG stability, and mechanical properties. Conclusions: CA/PEG blends would be a eco-friendly glasses frame to substitute traditional CA glasses frame prepared phthalate plasticizers.

• Korean Journal of Optics and Photonics
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• v.33 no.5
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• pp.218-229
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• 2022

We have investigated reliable inspection methods for finding the defects generated during the manufacturing process of lightweight, large-aperture satellite telescope mirrors using silicon carbide, and we have measured the basic physical properties of the mirrors. We applied the advanced ceramic material (ACM) method, a combined method using liquid-silicon penetration sintering and chemical vapor deposition for the carbon molded body, to manufacture four SiC mirrors of different sizes and shapes. We have provided the defect standards for the reflectors systematically by classifying the defects according to the size and shape of the mirrors, and have suggested effective nondestructive methods for mirror surface inspection and internal defect detection. In addition, we have analyzed the measurements of 14 physical parameters (including density, modulus of elasticity, specific heat, and heat-transfer coefficient) that are required to design the mirrors and to predict the mechanical and thermal stability of the final products. In particular, we have studied the detailed measurement methods and results for the elastic modulus, thermal expansion coefficient, and flexural strength to improve the reliability of mechanical property tests.

• Journal of Korean Ophthalmic Optics Society
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• v.18 no.3
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• pp.279-289
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• 2013

Purpose: To evaluate the changes of refractive power when worn soft contact lenses were temporarily removed. Methods: 91 soft contact lens wearers (15 males and 76 females; total 182 eyes) from 17 to 39 years of age (average: $24{\pm}4.8$ years) were participated. Objective and subjective refraction, and corneal radius were measured at 0, 30, 60 and 90 min after lens removal. The changes in refractive power were evaluated between measurements over time. The other parameters such as types of lenses, fitting and wearing conditions were also assessed. Results: Objective refraction, subjective refraction and corneal radius were significantly changed according to measured time (p<0.0001). A moderate myopic shifts was observed at the beginning (30 min after lens removal) and a slight myopic shift at the late of measurement (60 min to 90 min after lens removal). There are no significant differences between lens types, fitting states, wearing time, wearing days and sleeping time in the previous day. However, there was significant interaction in changes for corneal radius between measuring time and lens type (p=0.017), fitting state (p=0.019), and sleeping time prior to the test (p=0.010). Conclusions: Time to reach refractive and corneal radius stability after contact lens removal revealed at least more than 60 min, regardless of types of lenses, fitting and wearing conditions. Therefore, refraction for correction should be performed after waiting for more than that time as possible.

• Journal of Korean Ophthalmic Optics Society
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• v.15 no.2
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• pp.137-144
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• 2010

Purpose: This study was to evaluate the clinical performance of 1-Day disposable toric soft contact lenses (TSCL) and to compare the visual performance with glasses and TSCL. Methods: In a two-week investigation of 'prism ballast' designed TSCL, occular refractions in 15 (30 eyes) healthy subjects were within the range of -2.75 D TO -8.00 D spherical power and -0.75 DC to -2.25 DC cylinderical power (with-the-rule). Subjects were assessed the clinical performance (orientation, centration, movement, tightness, rotation recovery, symptoms) of TSCL and compared binocular vision and contrast sensitivity with corrected glasses and TSCL at initial and two-week follow-up visits. Results: The prism-ballast design TSCL achieved better orientation, rotation recovery and symptoms over 2 week period. There was no statistically significant difference between spectacles and TSCL with respect to measuring binocular vision and contrast sensitivity. Conclusions: The clinical performance was good with prism-ballast design toric soft contact lenses. Evaluation of binocular vision and contrast sensitivity did not show the differences between spectacles and TSCL correction. This study suggests that TSCL wearers can be achieved similar visual performance for spectacles wearers.