• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.101-103
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• 2012

Characteristic of aluminum ignition under high temperature and high pressure is studied using lasers. The laser ablation method is used to generate aluminum particles exposed to a high pressure by using a nanosecond pulsed laser where the range of ablation pressure varies between 0.35 and 2.2 GPa. A $CO_2$ laser is used to supply radiative heat to the aluminum target surface for providing high temperature ranging between 5000~9300 Kelvin. The ignition is confirmed using spectroscopy analysis of AlO vibronic band 484 nm wavelength. Also the radiative temperature is measured in various high pressure range for tracing the ignition temperature in high pressure conditions.

• 한국기계가공학회지
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• 제21권4호
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• pp.77-83
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• 2022

Amorphous alloys exhibit excellent mechanical properties; therefore, application technology development is being attempted in various fields. However, industrial use of application technology is limited owing to the limitations in fabrication. In this study, micropattern fabrication of an amorphous alloy was conducted using laser beam machining. Although microhole fabrication is possible without the deformation of the amorphous phase through nanosecond pulsed laser beam machining, there are limitations in the generation of recast layers and spatters. In cover plate laser beam machining (c-LBM), a cover plate is used to reduce the thermal deformation and processing area. Therefore, it is possible to fabricate holes at the level of several micrometers. In this study, it was confirmed that recast layers are hardly generated in c-LBM. Furthermore, square-shaped micropatterns were successfully fabricated using c-LBM.

• Bulletin of the Korean Chemical Society
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• 제17권4호
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• pp.365-373
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• 1996

Time profile of the transient grating signal induced by a nanosecond pulsed laser excitation of methyl red is investigated in alcohols and toluene at several solvent temperatures. The signal decays biexponentially with well-separated time constants; the faster decay is identified as due to thermal diffusion of the solvents and the slower one as mainly due to translational diffusion of the solute. The measured translational diffusion constants of methyl red in toluene are close to a hydrodynamic prediction with a slip boundary condition while those in alcohols are larger by 30% and increase slightly with the size of alcohols. We compare the results with modified hydrodynamic models.

• 한국정밀공학회지
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• 제27권2호
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• pp.20-24
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• 2010

High speed cutting processes of rigid flexible printed circuit board by making use of high power UV laser with nano-second pulse width have been proposed and investigated experimentally. Also robust laser cutting system has been designed and developed in order to obtain a good cutting quality of rigid and flexible PCB with multi-layers (2-6 layers). Power controller module developed for ourselves is adapted to control the laser output power in the range less than 1%. The systems show the good performance of cutting speed, cutting width and cutting accuracy, respectively. Especially we have confirmed that the short circuit problem due to the carbonized contamination occurred in cross section of multi-layers by thermal effect of high power laser has been improved largely by using multi-pass cutting process with low power and high speed.

• 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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.348-353
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• 2001

Experimental schemes that enable characterization of phase-change phenomena in the micro scale regime is essential for understanding the phase-change kinetics. Particularly, monitoring rapid vaporization on a submicron length scale is an important yet challenging task in a variety of laser-processing applications, including steam laser cleaning and liquid-assisted material ablation. This paper introduces a novel technique based on Michelson interferometry for probing the liquid-vaporization process on a solid surface heated by a KrF excimer laser pulse (${\lambda}=248nm,\;FWHM=24\;ns$) in water. The effective thickness of a microbubble layer has been measured with nanosecond time resolution. The maximum bubble size and growth rate are estimated to be of the order of $0.1{\mu}m\;and\;1\;m/s$, respectively. The results show that the acoustic enhancement in the laser induced vaporization process is caused by bubble expansion in the initial growth stage, not by bubble collapse. This work demonstrates that the interference method is effective for detecting bubble nucleation and microscale vaporization kinetics.

• 대한기계학회논문집B
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• 제25권8호
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• pp.1140-1147
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• 2001

Experimental schemes that enable characterization of phase-change phenomena in the microscale regime are essential for understanding the phase-change kinetics. Particularly, monitoring rapid vaporization on a submicron length scale is an important yet challenging task in a variety of laser-processing application, including steam laser cleaning and liquid-assisted material ablation. This paper introduces a novel technique based on Michelson interferometry for probing the liquid-vaporization process on a solid surface heated by a KrF excimer laser pulse(λ=248nm, FWHM=24ns) in water. The effective thickness of a microbubble layer has been measured with nanosecond time resolution. The maximum bubble size and growth rate are estimated to be of the order of 0.1㎛ and 1m/s, respectively. The results show that the acoustic enhancement in the laser induced vaporization process is caused by bubble expansion in the initial growth stage, not by bubble collapse. This work demonstrates that the interference method is effective for detecting bubble nucleation and microscale vaporization kinetics.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.226-226
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• 2010

Boron Nitride (BN) doped GeSbTe films were grown by the ion beam sputtering deposition (IBSD). The in-situ sheet resistance data and the x-ray diffraction patterns showed the crystallization is suppressed due to the BN incorporation. The phase change speed in BN doped GeSbTe films were investigated using the static tester equipped with nanosecond pulsed laser. The phase change speed for BN doped GST films become faster than the corresponding values for an undoped GST film. The Johnson-Mehl-Avrami(JMA) plot and Avrami coefficient for laser crystallization showed that the change in growth mode during the laser crystallization is a most important factor for the phase change speed in the BN doped GST films. The JMA results and the atomic force microscopy (AFM) images indicate that the origin of the change in the crystalline growth mode is due to an increase in the number of initial nucleation sites which is produced by the incorporated BN. In addition, the retension properties for the laser writing/erasing are remarkably improved in BN doped GeSbTe films owing to the stability of the incorporated BN.

• 한국광학회지
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• 제26권5호
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• pp.261-264
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• 2015

본 논문에서는 인쇄회로기판의 감광층 보호필름을 532 nm 파장의 나노초 레이저의 단일펄스로 박리할 수 있음을 보여준다. 인쇄회로기판의 가장자리를 9 mm 크기의 레이저 빔으로 국부적으로 박리시킨 후 스카치테이프를 레이저 조사에 의해 초기 박리 된 영역에 붙여 전체 보호필름을 떼어내었는데, 160 - 170 mJ의 펄스에너지 범위에서는 10회의 반복된 실험 모두에서 감광층 손상 없는 박리에 성공하였다. 보호필름 초기 박리에 레이저를 사용하는 방식은 기계적 압착에 바탕을 둔 기존의 널링방식과는 달리 감광층에 손상을 유발하지 않는 비접촉 방식으로써, 인쇄회로기판 제조공정에 보다 효율적으로 사용될 수 있을 것으로 판단된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.377-377
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• 2016

Under nanosecond-pulsed laser irradiation, light-absorbing thin films have been used for photoacoustic transmitters for ultrasound generation. Especially, nanostructured absorbers are attractive due to high optical absorption and efficient thermoacoustic energy conversion: for example, 2-dimensional (2-D) gold nanostructure array, synthetic gold nanoparticles, carbon nanotubes (CNTs), and reduced graphene oxides. Among them, CNT has been used to fabricate a composite film with polydimethylsiloxane (PDMS) that exhibits excellent photoacoustic conversion performance for high-frequency, high-amplitude ultrasound generation. Previously, CNT-PDMS nanocomposite films were made by using a high-temperature chemical vapor deposition (HTCVD) process for CNT growth. However, this approach is not suitable to fabricate large-area CNT films (>several cm2). This is because a chamber dimension of HTCVD is limited and also the process often causes nonuniform CNT growth when the film area increases. As an alternative approach, a solution-based process can be used to overcome these issues. We develop PDMS composite transmitters, based on the solution process, using several nanostructured light-absorbers such as CNTs, nanoink powders, and imprinted regular arrays of gold nanostructure. We compare fabrication processes of each composite transmitters and photoacoustic output performance.