• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1213-1218
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• 2004

The present article reports extensive numerical results on the non-local characteristics of ultra-short pulsed laser-induced breakdowns of fused silica ($SiO_{2}$) by using the multivariate Fokker-Planck equation. The nonlocal type of multivariate Fokker-Planck equation is modeled on the basis of the Boltzmann transport formalism to describe the ultra-short pulsed laser-induced damage phenomena in the energy-position space, together with avalanche ionization, three-body recombination, and multiphoton ionization. Effects of electron avalanche, recombination, and multiphoton ionization on the electronic transport are examined. From the results, it is observed that the recombination becomes prominent and contributes to reduce substantially the rate of increase in electron number density when the electron density exceeds a certain threshold. With very intense laser irradiation, a strong absorption of laser energy takes place and an initially transparent solid is converted to a metallic state, well known as laser-induced breakdown. It is also found that full ionization is provided at intensities above threshold, all further laser energy is deposited within a thin skin depth.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -1
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• pp.540-541
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• 2002

In this paper, the performance of upidirectional and hi-directional regenerative erbium-doped fiber amplifier (EDFA) is compared. The systems are operating above laser oscillation threshold. The experimental results show that the unidirectional regenerative EDFA has a better performance than the hi-directional.

• 전자공학회논문지D
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• 제35D권4호
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• pp.101-108
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• 1998

We examine experimentally the dependence of output width on DC bias, RF power, and RF frequency in a gain-switched semiconductor laser. The optimum short pulses are obtained around threshold DC bias. The DC bias to generatoe shorter pulses decreases the RF power increases, whereas it increases to above threshold as the RF freqnecy increases. The pulse width becomes less sensitive to the variations of the DC bias, as the RF bias, or frquency increases.

• Journal of Communications and Networks
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• 제10권1호
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• pp.1-4
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• 2008

This paper reports the design of a multiwavelength fiber laser source that utilizes a linear cavity of hybrid Brillouin/Erbium fiber laser (BEFL). The output power, threshold power and free running cavity modes were investigated against the pump powers. The structure exhibited low threshold operation of 4 mW at 2.3 mW injected Brillouin pump power. The optimization of Brillouin pump wavelength, power and Erbium gain led to a maximum possible number of channels generated. Simultaneous and stable operation of 21 channels with 10.88 GHz channels spacing were obtained from this architecture at 1 mW injected Brillouin pump power and 90 m W Erbium doped fiber pump power in the 1555 nm region.

• Journal of the Optical Society of Korea
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• 제20권3호
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• pp.407-412
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• 2016

We analyzed through numerical simulations the properties of a square beam homogenizer near the target for laser shock peening. The efficiency was calculated near the target by considering the plasma threshold of the metals. We defined the depth of focus of the square beam homogenizer with a given efficiency near the target. Then, we found the relationship between the depth of focus for the laser shock peening and four main parameters of the square beam homogenizer: the plasma threshold of the metal, the number of lenslets in the array-lens, the focal length of the condenser lens and the input beam size.

• 대한전자공학회논문지
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• 제15권5호
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• pp.34-38
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• 1978

rate equation을 사용하여 DH Laser Diode에서 나타나는 전기적 포화현상이 이론적으로 설명되었다. Carrier density는 threshold 이후에 서서히 ns에 접근해가며 이론적으로 계산된 곡선과 예측된 ΔVj는 전에 보고된 실험결과를 정확히 설명한 수 있음이 입증되었다. carrier saturation factor kβ를 제안하였으며 kβ는 L.D의 이상성을 결정하는 중요한 factor 임이 설명되었다. kβ와 β와의 관계를 통해 β가 작으면 작을수록 diode의 특성은 이상적 diode에 가까와짐이 밟혀졌다.

• 한국기계가공학회지
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• 제18권5호
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• pp.74-81
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• 2019

This study reports the CW $CO_2$ laser scribing of soda lime glass. In this study, scribing experiments are carried out at different laser powers, scan speeds, and focal positions to investigate the effect of the process parameters on the interaction characteristics between a laser beam and glass. In particular, the interaction characteristics are analyzed and described with the input laser energy per unit length. According to the experimental results, the damage threshold for the glass surface was found to exist between 0.072 and 0.08 J/mm. The input laser energy in this region induced partial melting of the surface and grain-shaped cracks. These cracks tended to increase as the input laser energy increased. At the laser input energy larger than 1 J/mm, a huge crack propagating along the scan direction was produced, and the volume below the scribed area was fully melted. The growth of this crack finally resulted in the complete cutting of the glass at the input laser energy above 8 J/mm. It was found that both the width and depth of the scribed line increased with increasing input laser energy. For the beam focusing at the rear surface, the width of the scribed line varied irregularly. This could be ascribed to the increased asymmetry of the beam intensity distribution when the laser beam was focused at the rear surface. Under this condition, a large burr was only produced on one side of the scribed line.

• 대한전자공학회논문지SD
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• 제43권7호
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• pp.1-6
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• 2006

본 연구에서는 광 논리 및 광 접속에 응용할 수 있는 GaAs/AlGaAs 구조의 완전 공핍 광 싸이리스터(depleted optical thyristor, DOT)에 VCSEL(vertical-cavity surface-emitting laser diode)을 응용하여, 활성층 위, 아래에 1/4 파장 거울층(quarter wavelength reflector stacks)을 제작함으로서 본 구조에서 최초의 레이징 특성을 구현하였고, 그 특성을 측정, 분석하였다. 스위칭 특성을 알아보기 위하여 순방향 전압에서는 비선형 s-자형의 전류-전압 특성을, 역방향 전압에서는 완전 공핍 전압을 모의실험으로 알아보았다. 모의실험을 바탕으로 설계, 제작한 VCL-DOT(Vertical Cavity Laser - Depleted Optical Thyristor)의 스위칭 전압과 전류는 5.24 V, $5{\mu}A$ 이고, 홀딩 전압과 전류는 각각 1.50 V, $100{\mu}A$가 나왔다. 측정된 레이징 문턱 전류는 0.65 mA 이고, 출력 파장은 854.5 nm의 레이징 특성을 확인하였다.

• 한방재활의학과학회지
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• 제20권1호
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• pp.183-192
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• 2010

Objectives : The purpose of this study is to investigate the clinical effects of low level laser therapy on shoulder pain. Methods : From October 1, 2009 to November 14, 2009, we applied 15 participants who consented to an assignment had a shoulder pain to low level laser therapy(LLLT). We treated LLLT 8 times on both upper trapezius, levator scapular, pectoralis, suboccipital, rhomboid, rotator cuff tender point for 2 weeks. To evaluate the efficiency of low level laser therapy, we used questionnaire of shoulder pain symptom, questionnaire of a day living discomfort scale, shoulder pain and disability index(SPADI) and pressure pain threshold(PPT) at before treatment and after treatment 4 times and 8 times. Results : There was a significant difference in questionnaire of shoulder pain symptom, questionnaire of a day living discomfort scale, SPADI and PPT after 8th treatment. Conclusions : Low level laser therapy for shoulder pain is effective to improve patients' symptoms measured with questionnaire of pain and a day living discomfort score, SPADI and PPT significantly.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.487-488
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• 2006

Picosecond (ps) laser micro-machining has emerged as an attractive method of fabricating high-precision microstructures, especially in metals. In this paper, a metallic mold for diffraction gratings is fabricated with a mode-locked 12 Ps $Nd:YVO_4$ laser. Laser pulses with a wavelength of 355nm are irradiated on the surface of NOK 80, a mold material, to generate line patterns. In order to minimize the line width, laser power is set just above the ablation threshold of NOK 80. Results show that the spectrum from the fabricated mold is good enough for some industrial application.