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최준하(Junha Choi),신영관(Young Gwan Shin),김훈영(Hoon Young Kim),최원석(Wonsuk Choi),김재구(Jae-Gu Kim),장원석(Won-Seok Chang),윤재성(Jae-sung Yoon),조성학(Sung-Hak Cho) Korean Society for Precision Engineering 2020 한국정밀공학회지 Vol.37 No.12
A femtosecond laser is used in various fields such as microscale machining, OLED repair, micro 3D structure fabrication, and eye surgery. Particularly, because of non-thermal property, ablation and ablation threshold are the most representative characteristics of femtosecond laser. The ablation system is accompanied by many optics, stage, or gantry. In the case of the gantry, an ordinary optic system delivers a beam where mirrors and lens are required. If the gantry moves to the sample, external stimulation such as vibration will occur. Vibration has an influence on optics such as transforming beam path and becomes an error that decreases accuracy, precision, and spatial resolution. Generally, Fiber Optic Beam Delivery System (FOBDS) is used to solve this issue. But in the case of the femtosecond laser, FOBDS is incompatible. Recently, another FOBDS model that is compatible with the femtosecond laser has been developed. In this paper, the ablation threshold was obtained by FOBDS and femtosecond laser. The results present a possibility of ablation without external stimulation.
신동식(D. S. Shin),이제훈(J. H. Lee),서정(J. Suh),노지환(J. W. Noh),정용운(Y. W. Chung),김재구(J. G. Kim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
In contrast to dielectric materials, metals are characterized by a high density of quasi-free electrons causing strong absorption of laser light from the beginning of the ultrashort laser pulse without the need of nonlinear absorption effects like multiphoton absorption. The transfer of energy from the electronic system causing strong absorption of laser light to the lattice needs relaxation times of the order of some picoseconds. Under the above theoretical background, nickel was chiefly ablated using femtosecond, picosecond and nanosecond laser. As a result, nickel ablation by picosecond laser and femtosecond laser, which are called ultrashort laser, has similar machinability because of relaxation time of metals, whereas nanosecond Nd:YAG laser has lower absorption, higher thermalization effect in comparison with ultrashort laser.
AMOLED 제조공정에 사용되는 Fine Metal Mask 용 얇은 Invar 합금의 진동자를 이용한 펨토초 레이저 응용 홀 드릴링
최원석,김훈영,신영관,최준하,장원석,김재구,조성학,최두선,Choi, Won-Suk,Kim, Hoon-Young,Shin, Young-Gwan,Choi, Jun-ha,Chang, Won-Seok,Kim, Jae-Gu,Cho, Sung-Hak,Choi, Doo-Sun 한국금형공학회 2020 한국금형공학회지 Vol.14 No.3
One of display trends today is development of high pixel density. To get high PPI, a small size of pixel must be developed. RGB pixel is arranged by evaporation process which determines pixel size. Normally, a fine metal mask (FMM; Invar alloy) has been used for evaporation process and it has advantages such as good strength, and low thermal expansion coefficient at low temperature. A FMM has been manufactured by chemical etching which has limitation to controlling the pattern shape and size. One of alternative method for patterning FMM is laser micromachining. Femtosecond laser is normally considered to improve those disadvantages for laser micromachining process due to such short pulse duration. In this paper, a femtosecond laser drilling for thickness of 16 ㎛ FMM is examined. Additionally, we introduce experimental results for controlling taper angle of hole by vibration module adapted in laser system. We used Ti:Sapphire based femtosecond laser with attenuating optics, co-axial illumination, vision system, 3-axis linear stage and vibration module. By controlling vibration amplitude, entrance and exit diameters are controllable. Using vibrating objective lens, we can control taper angle when femtosecond laser hole drilling by moving focusing point. The larger amplitude of vibration we control, the smaller taper angle will be carried out.
민철기,이만섭 한국레이저가공학회 2008 한국레이저가공학회지 Vol.11 No.2
Polyimide iS one of the useful materials in industry. The surface treatment of polyimide by a femtosecond laser can help accurate and fine fabrication of microstructure. And it can change the transmittance and reflectance of polyimide, too. We put femtosecond laser pulses on polyimide for rectangular or square type surface treaments and observe the change of transmittance and reflectance. Pulsewidth is 172 fs, laser power changes for fabrication are from 5 mW to 20 mW, and transmittance and reflectance are measured under 20m W, 300m W, and 920 mW. Pulse patterning is stable and almost no unwanted surface damage is shown. As power increases, working depth increases but working line width does not increase significantly. As speed changes, they also have same results. It shows the efficiency of a femtosecond laser is good and thermal damage is small for polyimide.
진동자를 이용한 하이브리드 극초단 펄스 레이저 초정밀가공시스템 개발 및 Cu-Zn합금 응용
최원석,윤지욱,조성학,강명창,Choi, Won-Suk,Yoon, Ji-Wook,Cho, Sung-Hak,Kang, Myung-Chang 한국분말야금학회 2013 한국분말재료학회지 (KPMI) Vol.20 No.4
In this paper, we describe experiment results using a vibration assisted hybrid femtosecond laser (${\lambda}$:795 nm) ultra-precision machining system. The hybrid system we have developed is possible that optical focal point of the femtosecond laser constantly and frequently within the range of PZT(piezoactuator) vibrator working distance. Using the hybrid system, We have experimented on brass and studied about differences of result of hole aspect ratio compare to general experiment setup of femtosecond laser system. Aspect ratio of a micro hole on brass is increased as 54% with 100 Hz vibration frequency and surface roughness of the side wall also improved compare to non-vibration.