• 한국레이저가공학회:학술대회논문집
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• 한국레이저가공학회 2004년도 추계학술대회논문집
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• pp.68-72
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• 2004

• 한국광학회:학술대회논문집
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• 한국광학회 2002년도 제13회 정기총회 및 2002년도 동계학술발표회
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• pp.300-301
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• 2002

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.40.1-40.1
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• 2009

생체용 금속 임플란트의 표면개질은 생체활성화를위하여 오래 전 부터 관심을 가지고 연구해오고 있다. 최근에 표면개질을위하여 화학적 에칭, 샌드 블래스팅, 또는 나노튜브형성등 표면에 임의의 요철을 만들어서 사용하는방법이 가장 일반적으로 적용되어 상용화되고있다. 그러나 샌드블래스팅이나 화학적 에칭은 가공은 쉽지만 가공표면에 인체에 해로운 잔류물의존재로 생체적합성에 해로운 영향을 미칠 수 있다. 이러한 문제점들을 해결하기위하여 레이저를 사용하여 임플란트 표면을 개질한 예가 보고 되었다. 레이저를 사용한 표면처리 방법의큰 장점은 잔류물이 남지 않고 비교적 표면 거칠기의 제어가 용이하다. 금속합금의 표면개질에사용되는 레이저는 주로 Nd:YAG 레이저의 파장을 반으로 줄인 녹색레이저 ($\lambda$=532nm)를 사용하거나, 자외선파장영역의레이저를 사용하는 경우가 일반적으로 가장 보 편화된 가공방법으로 연구되었다. 표면의 거칠기는 수마이크로의크기와 수십나노의 크기를 갖는 표면을 생체적합적인 측면에서 요구하고 있다. 따라서 이러한 표면의 거칠기를조절할 수 있는 펨토레이저를 사용하여 표면에 균질한 표면의 텍스춰링을 통하여 그 특성을 개선할 수 있는지를 확인하는 것이 본 과제이다. 본 실험에서는 Ti합금을 진공 아크로를 이용하여 3원계합금을 제조하고 $1000^{\circ}C$에서 24시간 열처리 후 급냉(water quenching)하였다. 열처리 후 시편은 두께 2mm로 절단 하여 #2000까지 연마 후 하여 펨토 초(10-15 second) 펄스폭 대역을 갖는 레이저를 이용하여 수마이크로 크기의 미세 요철을 표면에 형성한 후, 표면의 특성을 조사해 보았다.(NRF-2009-0074672)

• 한국정밀공학회지
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• 제22권12호
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• pp.184-189
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• 2005

An experimental study of the femtosecond laser machining of Si materials was carried out. Direct laser machining of the materials for the feature size of a few micron scale has the advantage of low cost and simple process comparing to the semiconductor process, E-beam lithography, ECM and other machining process. Further, the femtosecond laser is the better tool to machine the micro parts due to its characteristics of minimizing the heat affected zone(HAZ). As a result of line cutting of Si, the optimal condition had the region of the effective energy of 2mJ/mm-2.5mJ/mm with the power of 0.5mW-1.5mW. The polarization effects of the incident beam existed in the machining qualities, therefore the sample motion should be perpendicular to the projection of the electric vector. We also observed the periodic ripple patterns which come out in condition of the pulse overlap with the threshold energy. Finally, we could machined the groove with the linewidth of below $2{\mu}m$ for the application of MEMS device repairing, scribing and arbitrary patterning.

• 한국정밀공학회지
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• 제24권12호
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• pp.50-56
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• 2007

Femtosecond laser ablation of the Invar alloy and hole drilling for a shadow mask are studied. We used a regenerative amplified Ti-sapphire laser with a 1kHz repetition rate, 184fs pulse duration and 785nm wavelength. Femtosecond laser pulse was irradiated on the Invar alloy with air blowing at the condition of various laser peak power. An ablation characteristic of the Invar alloy was appeared non-linear at $125J/cm^2$ of energy fluence. For the application to a shadow mask, the hole drilling of the Invar alloy with the cross section of a trapezoidal shape was investigated. The ablated micro-holes were characterized using an atomic force microscopy(AFM). The optimal condition of hole pattern f3r a shadow mask was $4\;{\mu}m$ z-axis feed rate, 0.2mm/s circular velocity, $26.4{\mu}J$ laser peak power. With the optimal processing condition, the fine circular hole shape without burr and thermal damage was achieved. Using the femtoseocond laser system, it demonstrates excellent tool for the Invar alloy micro-hole drilling without heat effects and poor edge.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.1365-1368
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• 2004

A scheme to control the laser power and the exposure time was studied to fabricate precise microstructures using the nanostereolithography (nSL) process. Some recent works have shown that a three-dimensional (3D) microstructure can be fabricated by the photopolymerizing process which is induced by two-photon absorption (TPA) with a femtosecond pulse laser. TPA provides the ability to confine photochemical and physical reactions within the order of laser wavelength, so neardiffraction limit features can be produced. In the nSL process, voxels are continuously generated to form a layer and then another layer is stacked in the normal direction of a plane to construct a 3D structure. Thus, fabrication of a voxel with low aspect ratio and small diameter is one of the most important parameters for fabricating precise 3D microstructures. In this work, the mechanism of a voxel formation is studied and a scheme on the control of laser power and exposure for minimizing aspect ratio of a voxel is proposed.

• 한국정밀공학회지
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• 제27권11호
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• pp.17-23
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• 2010

Titanium alloy is one of the hard processing materials made by the traditional manufacturing method because of the excellent mechanical strength. Ablation of titanium alloy is investigated by using a femtosecond laser which is a regenerative amplified Ti:sapphire laser with 1kHz repetition rate, 184fs pulse duration time and 785nm wavelength. Experiments are carried out under various ablation conditions with different pulse overlap ratios for the rectangular shape and micro hole. Test results show that the ablation characteristic according to pulse overlap ratio of titanium alloy seems to be as non-linear type at the different zone of energy fluence. The optimal condition of rectangular shape processing is obtained at the laser peak power 1.3mW, pulse overlap ratio of 90%, beam gap of $1\;{\mu}m$. The micro hole has a good quality from the pulse overlap ratio of 99% at the same laser peak power. With the optimal processing condition, the fine rectangular shape and micro hole without burr and thermal damage are achieved.

• 대한기계학회논문집A
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• 제28권9호
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• pp.1270-1275
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• 2004

Standard positive photoresist techniques were adapted to generate nano-scale patterns of gold substrate using self-assembled monolayers (SAMs) and femtosecond laser. SAMs formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists, Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200nm is necessary for oxidation to occur. In this study, ultrafast laser of wavelength 800nm and pulse width 200fs is applied for photolithography. Results show that ultrafast laser of visible range wavelength can replace deep UV laser source for photo patterning using thin organic films. Femtosecond laser coupled near-field scanning optical microscopy facilitates not only the patterning of surface chemical structure, but also the creation of three-dimensional nano-scale structures by combination with suitable etching methods.

• 한국레이저가공학회지
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• 제17권4호
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• pp.7-13
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• 2014

In this work, the application of laser induced breakdown spectroscopy (LIBS) for the composition analysis of thin $Cu(In,Ga)Se_2$ (CIGS) solar cell films ($1-2{\mu}m$ thickness) is reported. For the ablation of CIGS films, femtosecond (fs) laser (wavelength = 343nm, pulse width = 500fs) and nanosecond (ns) laser (wavelength = 266nm, pulse width = 5ns) were used under atmospheric environment. The emission spectra were detected with an intensified charge coupled device (ICCD) spectrometer and multichannel CCD spectrometer for fs-LIBS and ns-LIBS, respectively. The calibration curves for fs-LIBS and ns-LIBS intensity ratios of Ga/Cu, In/Cu, and Ga/In were generated with respect to the concentration ratios measured by inductively coupled plasma optical emission spectrometry (ICP-OES).

• 한국레이저가공학회지
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• 제17권4호
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• pp.1-6
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• 2014

Femtosecond laser induced shock generation in water and vitreous humor of enucleated porcine eyeball was investigated. When focusing the femtosecond laser into the liquid mediums, the acoustic waves with a frequency of about 15.6kHz could be observed by using wide-band microphone. The amplitude of the acoustic signals from water has attained a maximum under a laser power of about 5mW. Further increment of the power results in a decrement of the acoustic signals due to nonlinear optical process including filamentation of laser beam. We have further investigated the effect of femtosecond laser induced acoustic waves by applying the laser pulse into enucleated porcine eyeball. The comparative studies on both healthy and diseased eyeballs led us propose that the femtosecond laser pulses could be utilized as a novel tools for treatment of partially detached retina layers from their choroid structures.