• The Journal of the Convergence on Culture Technology
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• v.6 no.4
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• pp.727-732
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• 2020

In this paper, when a refractive index grating and a gain grating were simultaneously present in a DFB laser having a wavelength of 1.55 ㎛, a dielectric film coating was applied so that reflection did not occur on the right mirror surface, so that 𝜌_r=0. In case of δL > 0, the threshold gain and the beam distribution in the longitudinal direction and the radiated power ratio P_l/P_r of the oscillation mode were compared for the cases of the phase of 𝜌_l=π and π/2. If the phase of 𝜌_l=π, in order to obtain a low threshold current and high frequency stability, κL should be greater than 8. In the case of the phase of 𝜌_l= π/2, when κL is larger than 4.0, the oscillation gain starts to be lower than when the phase of 𝜌_l=π. In order to lower the threshold current of a oscillation mode and enhance the frequency stability, κL should be greater than 8.

• Tribology and Lubricants
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• v.38 no.3
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• pp.93-100
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• 2022

Micro-light emitting diode (micro-LED) displays offer numerous advantages such as high brightness, fast response, and low power consumption. Hence, they are spotlighted as the next-generation display. However, defective LEDs may be created due to non-uniform contact loads or LED alignment errors. Therefore, a repair process involving the replacement of defective LEDs with favorable ones is necessitated. The general repair process involves the removal of defective micro-LEDs, interconnection material transfer, as well as new micro-LED transfer and bonding. However, micro-LEDs are difficult to repair since their size decreases to a few tens of micron in width and less than 10 ㎛ in thickness. The conventional nozzle-type dispenser for fluxes and the conventional vacuum chuck for LEDs are not applicable to the micro-LED repair process. In this study, transfer conditions are determined using a micro stamp for repairing micro-LEDs. Results show that the aging time should be set to within 60 min, based on measuring the aging time of the flux. Additionally, the micro-LEDs are subjected to a compression test, and the result shows that they should be transferred under 18.4 MPa. Finally, the I-V curves of micro-LEDs processed by the laser and hot plate reflows are measured to compare the electrical properties of the micro-LEDs based on the reflow methods. It was confirmed that the micro-LEDs processed by the laser reflow show similar electrical performance with that processed by the hot plate reflow. The results can provide guidance for the repair of micro-LEDs using micro stamps.

• Journal of Software Assessment and Valuation
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• v.15 no.1
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• pp.71-78
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• 2019

Lasers for optical broadband communication systems should have excellent frequency selectivity and modal stability. DFB lasers have low lasing frequency shift during high speed current modulation. In this paper, we have developed a simulation software and analysed beam profiles of a lasing mode in longitudinal direction of an 1.55um DFB laser with two mirrors and without anti-reflection coatings, that have both an index- and gain-gratings. As the phases of the index and gain gratings on the mirror faces are varied, the beam profiles |R(z)| and |S(z)| of the lasing mode with the emitted power ratio P_l/p_r are analysed and examined. In order to reduce the threshold current of a lasing mode and enhance the frequency stability, κL should be greater than 8, regardless of the grating phases on the mirror faces.

• Journal of Software Assessment and Valuation
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• v.16 no.1
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• pp.55-63
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• 2020

Lasers for optical broadband communication systems should have excellent frequency selectivity and modal stability. DFB lasers have low lasing frequency shift during high speed current modulation. In this paper, when a refractive index grating and a gain grating are simultaneously present in a DFB laser having a wavelength of 1.55 ㎛, the dielectric film is coated so that reflection does not occur on the right mirror surface, so that ρ_r=0. For the first mode, which requires a minimum gain at the threshold, the beam distribution of the oscillation mode in the longitudinal direction and the radiated power ratio P_l/P_r were analyzed and compared for the cases of the phase of ρ_l=π and π/2. If the phase of ρ_l=π, in order to obtain a low threshold current and high frequency stability, κL should be greater than 8. In the case of the phase of ρ_l=π/2, for low threshold current, κL is necessary to be 1.0, where the oscillation frequency coincides with the lattice frequency. DFB lasers with an anti-reflection coated mirror have excellent mode selectivity than 1.55um DFB lasers with two mirror facets

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.10 no.2
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• pp.45-56
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• 2004

OBJECTIVE: The objective of this study was to know the effects of the postoperative lumbar extensor strengthening exercise program on back muscles strength and volume, pain, and the time of return to work. METHODS: A prospective controlled trial of lumbar extensor exercise program in patients who underwent microdiscectomy or percutaneous endoscopic discectomy for prolapsed lumbar intervertebral disc. Seventy-five patients were randomized into exercise group (20 male, 15 female) and non-exercise group (18 male, 22 female). Six weeks after surgery, patients in exercise group undertook a 12-week lumbar extension exercise (MedX) program. Assessment of spinal function was performed in all patients on postoperative 6 weeks, 18 weeks. The assessment included measures of lumbar extensor power, muscle mass of erector spinalis. All patients completed the visual analog scale (VAS) for evaluation of pain, and return to work. RESULTS: In muscle power, there were statistically significant improvements between pre and post test on muscle power in exercise group. But there were not statistically significant difference on muscle power in non-exercise group. In muscle mass, there were statistically significant difference between pre and post test on muscle mass in exercise group. But there were not statistically significant difference on muscle mass in non-exercise group. In the pain, there were statistically significant decrease between pre and post test on both group. But there were not statistically significant difference on fatty tissue and obesity in non-exercise group. The percentages of return to work in postoperative 4 months were significantly greater in the exercise group than in the non -exercise group. CONCLUSIONS: Postoperative lumbar extensor strengthening exercise program appears to be more beneficial to the patients who underwent operation for prolapsed lumbar intervertbral disc.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.126-126
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• 2012

In past decades, the themal inkjet (TIJ) printer has been widely used as one of the most well-known digital printing technology due to its low cost, and high printing quality. Since the printing speed of TIJ printers are much slower than that of laser printers, however, there has been intensive efforts to raise the printing speed of TIJ printers. One of the most plausible methods to raise the printing speed of TIJ printers is to adopt a page-wide array TIJ printhead. To accomplish this goal, the high efficiency inkjet heating resistor films should be developed to settle the high power consumption problem of a page-wide array TIJ printhead. In this study, we investigated noble metal based multicomponent thin film resistor films prepared by atomic layer deposition (ALD) for a high efficiency inkjet printhead. Design concept, preparation, material properties of noble metal based multicomponent thin films will be discussed in terms of mutlfunctionality.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.4
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• pp.381-385
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• 2005

The plasma temperature of Ar gas in hollow cathode discharge were measured. This is done by measuring the line profile of the 1s/sub 8/-2p/sub 8/ transition in Ar, using a single-frequency diode laser. Low power diode lasers have been successfully used for investigation of the line profiles of Ar transitions in hollow cathode discharges. It turns out that the plasma temperature of Ar is 640∼783 K in the discharge current range at 7∼10 mA.

• Journal of the Korean Vacuum Society
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• v.8 no.4B
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• pp.530-535
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• 1999

W made a near-field optical microscope(NSOM) apparatus and evaluated it. To control the distance between a tip and a sample, we used a piezoelectric translator and a He-Ne laser, and consequently obtained the spatial resolution better than 100nm. For the semiconductor spectroscopic applications, we performed photoluminescence and photocurrent experiments on the GaAs/AlGaAs MQWs samples. In the case of PL experiment, we obtained the low signal to nose ration due to the extremely small power of a light source passing through the nanometric optical fiber tip. However photocurrent experiment shows a hundred times better signal to noise than that of PL experiment. This suggests that photocurrent experiment using NSOM have the possibility to provide the spatial resolution better than 10nm.

• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1988.05a
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• pp.74-77
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• 1988

This paper reports the properties of antireflection structure and hole formation of Te-based systems. The optical-recording characteristics of metallic recording media are enhanced significantly by incorporating the metal(Al) layer into an antreflection trilayer structure. Due to the interface condition inherent in the design of the trilayer structure, reflectivity from holes is ranked low fraction (<10%). The hole formation is carried by $Ar^+$ Laser(488nm). For 20nsec pulse duration, hole opening power(threschold) of $(Te_{86}Se_{14})_{50}Bi_{50}$ trilayer is lower than that of monolayer that used in this experiment. Hole shapes of the whole sample were clean.