• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 C
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• pp.1631-1633
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• 2001

In manufacturing processes, various and suitable pulse shapes are required for the purpose of material processing and the pulseshape is regarded as a dominant factor due to the specific property of processing materials. Therefore, in this study, a variable pulse width, high duty cycle Pulse Forming Network(PFN) is constructed by time sequently. The power supply for this experiment consists of three switching circuits. The PFN elements operate at low voltage and drive the primary of HV leakage transformer. The secondary of the transformer has a full-wave rectifier, which passes the pulse energy to the load in a continuous sequence of properly phased and nested increments. We investigated laser pulse width as various delay time among three switching circuit. As a result, we tan obtain various laser pulse width from about 4ms to 10ms. The maximum laser pulse width obtained at this experiment was about 10ms at delay time of 4ms among each switching circuit.

• 한국레이저가공학회지
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• 제9권3호
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• pp.15-21
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• 2006

A Polypropylene (PP) film was ablated using a femtosecond laser with a center wavelength of 785 nm, a pulse width of 184 fs and a repetition rate of 1 kHz. Increments of both pulse energy and the shot number of pulses lead to co-occurrence of photochemical and thermal effect, demonstrated by the spatial expansion of rim on the surface of PP. The shapes of the laser-ablated PP films were imaged by a scanning electron microscope (SEM) and measured a 3D optical measurement system (NanoFocus). And, the oxygen transmission rate (ORT) of periodically laser-ablated PP film were characterized by oxygen permeability tester for modified atmosphere packaging (MAP) of fresh fruit and vegetable. Our results demonstrate that femtosecond pulsed laser is efficient tools for breathable packaging films in modifying the flow of air and gas into and out of a fresh produce container, where the micropatterns are specifically tailored in size, location and number which are easily controlled by laser pulse energy and pulse patterning system.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1999년도 특별강연 및 추계학술발표대회 개요집
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• pp.37-38
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• 1999

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.373-375
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• 1997

In this study, we designed multiple mesh circuit consisting of 3-6 meshes and pulse superposition one consisting of a 3 mesh, and fabricated the electrical power supply and the single elliptical resonator. We developed the two pulse superposition technique forming the step pulse shapes of pulsed Nd:YAG laser with single shot multivibrator and 2 SCRs. Laser beam generated by multiple mesh circuit and superposition one respectively irradiated target surface to analyze process state of surface with spark and vapor. And it was obtained experimental results that all superposition meshes had common points which the best efficiency was obtained at delay time 0[${\mu}s$], followed by, no superposition and obtained at delay time 250[${\mu}s$].

• Journal of the Optical Society of Korea
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• 제12권1호
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• pp.38-41
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• 2008

Precise micropatterning of polypropylene film, which is highly transparent in the wavelength range over 250 nm has been demonstrated by 355 nm nano/picosecond laser and 785 nm femtosecond laser. Increments of both the pulse energy and the shot number of pulses lead to cooccurrence of photochemical and thermal effects, demonstrated by the spatial expansion of rim on the surface of PP. The shapes of the laser-ablated polypropylene films were imaged by optical microscope and measured by a 3D optical measurement system. And, the ablation depth and width of polypropylene film ablated by femtosecond laser at various pulse energy and pulse number were characterized. Our results demonstrate that a femtosecond pulsed laser is an efficient tool for fabricating micropatterns of polypropylene films, where the micropatterns are specifically tailored in size, location and number easily controlled by laser processing conditions.

• 한국컴퓨터산업학회논문지
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• 제2권7호
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• pp.975-982
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• 2001

펄스형 Nd：YAG레이저는 연속형에 비해 효율이 높고 높은 첨두출력이 가능하므로 가공에 있어서 여러 가지 장점이 있다. 더구나 레이저 펄스모양을 가변 시키는 기능은 펄스형 Nd：YAG레이저로 가공하기 힘든 특수분야에까지 가공을 가능하게 하였다. 본 연구에서는 3개의 플래쉬 램프를 순차 점등시키는 방식의 레이저시스템을 설계, 제작하여, 램프 점등시간의 변화에 따른 레이저빔의 펄스 폭과 펄스 세기를 조사하였다. 즉 PIC-Onechip microprocessor를 이용하여 실시간으로 3개의 플래쉬 램프를 순차적으로 점등시켜 보다 다양한 펄스모양을 만드는 기술을 개발하였다. 위 방식의 장점은 램프의 점등 지연시간을 0∼10ms까지 다양하게 변화시킬 수가 있고, 외부의 키보드로 실시간 제어가 가능하므로 보다 편리하게 펄스모양을 변화시킬 수가 있다. 또한, 긴 펄스를 만들 수가 있어 산업용 가공이나 의료용으로 널리 사용될 수가 있을 것이다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1852-1854
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• 2003

In manufacturing processes, various and suitable pulse shapes are required for the purpose of material processing. In order to make various pulse shapes with variable pulse length and high duty cycle, We have fabricated the power supply consisting 6 SCRs and the Pulse Forming Network(PFN) with the precise delay time control. So our control system has three switching circuits, 3 mesh PFN, and simmer circuit. In addition, we have designed and fabricated the PIC one-chip microprocessor(16F877) to control the delay time of sequential switching.

• 한국항공우주학회지
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• 제39권5호
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• pp.451-457
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• 2011

레이저 조사 시 발생되는 플라즈마는 물질에 따라 특정한 파장의 빛을 방출하므로, 이 빛을 수집하여 물질의 구성 성분을 정성 정량적으로 분석할 수 있다. LIBS(Laser-Induced Breakdown Spectroscopy)는 실시간에 가까운 분석과 원거리 검출이 가능하다는 점에서 우주 자원 탐사 기술로 주목받고 있다. 본 연구에서는 달 환경, 즉 고진공 하에서의 성분 분석을 위하여 double-pulse LIBS 기법을 이용하여 LIBS 신호 세기를 크게 증가시켰다. 또한 시편에 레이저가 조사되는 각도를 조절하여 임의 형상 물질의 분석을 모사하였다.

• 소성∙가공
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• 제19권8호
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• pp.517-522
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• 2010

Selective laser melting (SLM) is emerged as a new manufacturing technique to directly fabricate precise parts using metallic materials. The final characteristics of a component fabricated through the SLM process are strongly dependent upon various parameters such as laser power, scan rate and pulse duration, etc. This paper, therefore, focuses on the dimensional characteristics of melted $20{\mu}m$ Fe-Cr-Ni powder by fiber laser for the selective laser melting process. With energy density decrease, the height and depth were decreased. Although the conditions are of the same energy density, the shape is different by laser power and scan rate. The shapes at various laser parameters were divided into 3 groups based on depth over height. The smooth regular shape is obtained under the conditions of $50{\mu}m$ of powder height and $15-20{\mu}s$ of pulse duration. And the laser power influenced the variation of shape more significantly than the scan rate.

• 한국통신학회논문지
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• 제22권11호
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• pp.2401-2408
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• 1997

The measured pulse shapes provided in the given data package demonstrated pulse distortions due to laser speckle. the distorted pulse shapes were carefully analyzed, modeled, and then applied to the DTTL(Digital-data Transition Tracking Loop)[1] bit synchronizer simulator to measure the mean time delay and its delay variation performance. The result showed that the maximum mean time delay variation with the modeled data was 12.5% when window size equals 1. All the data given were located within this modeled boundary and the maximum eman time delay variation was 7% in this case. The mean time delay variation was known to be smaller by reducing the window size [2][5][6]. The mitigated delay variation was 2.5% in the modeled case and 1.4% in the data set given when the windown size equals 0.1. With the digital DTTL insteal of analog DTTL, similar results was obtained.