DPSS UV laser를 이용한 롤 금형 미세가공

민복기(Bokki Min),김재구(Jaegu Kim),조성학(Sunghak Cho),최두선(Doosun Choi),황경현(Kyunghyun Whang) 한국레이저가공학회 2008 한국레이저가공학회 학술대회 논문집 Vol.2008 No.-

This paper presents the method to fabricate a roll mold with microstructure using DPSS(diode pumped solid-states) UV laser. DPSS laser ablation makes it possible to micromachine by controlled energy density and pulse repetition rate of laser. But, In case of metal ablation, molten debris is caused by thermal damage. Hence, We suggest the process of the ablation of a photoresist(PR) coated on roll mold. And we design a roll coater for laminating the photoresist onto the curby surface of a copper roll mold. The microstructure on roll mold is fabricated by controlled laser pulse energy, pulse repetition rate, rotation speed and rotation number of roll. We compare and analyze the quality of microstructure by the wet etching process with the quality by the direct write process.

어블레이션 영역 레이저 초음파의 시뮬레이션과 내부결함 검사

김진겸(Jin-Gyum Kim),최성호(Sungho Choi),장경영(Kyung-Young Jhang) 한국비파괴검사학회 2014 한국비파괴검사학회지 Vol.34 No.3

본 연구에서는 고출력 레이저를 재료 표면에 조사하였을 때 나타나는 어블레이션 현상에 의한 레이저 초음파의 특성을 시뮬레이션과 실험을 통해 분석하였다. 레이저 초음파 기법은 비파괴검사 분야에서 기존의 접촉식 초음파 기법을 적용하기 어려운 환경요인(고온 등)을 극복할 수 있는 장점들을 가지고 있다. 특히, 어블레이션 영역에서는 종파의 신호 세기 및 직진성이 강하므로, 투과 및 반사 신호를 통한 내부결함 검사법으로 활용하기 적합하다. 본 논문에서는 유한요소해석을 통해 어블레이션 영역에서의 레이저 초음파의 발생 및 전파를 해석하였다. 그리고 개발된 유한요소해석 모델을 활용해 결함모사시편을 대상으로 B-Scan을 수행한 결과, 실험 결과와 동일하게 나타나는 것을 확인하였고, 이로부터 개발된 해석모델의 타당성을 검증할 수 있었다. In the present study, the characteristics of laser ultrasound in the ablation regime are investigated using simulations and experiments. The laser ultrasonic technique has been recognized as a noncontact method in the field of nondestructive tests (NDTs). In hostile environments (such as hot temperatures), this method has various advantages over the conventional contact ultrasonic method. In particular, in the ablation regime, the laser ultrasonic technique is suitable for inspecting internal defects because of the high amplitude and directivity of the longitudinal wave. In this paper, a simulation model for laser ultrasound in the ablation regime was developed. This model was subsequently applied to a defective specimen using the B-scan method to locate defects. Finally, we performed an experimental test to verify the simulation results. Consequently, the simulation demonstrated good agreement with the experimental test.

레이저 어블레이션 기반 가공 및 계측에서 공정변수의 영향

정성호(Sungho Jeong),이석희(Seok Hee Lee) Korean Society for Precision Engineering 2011 한국정밀공학회지 Vol.28 No.12

The changes of ablation characteristics with respect to laser parameters and material parameters during pulsed laser ablation of solids were discussed with experimental results. Although laser wavelength, laser pulse width, and laser pulse energy are the primary factors to be considered, it is shown that other parameters such as laser spot size and material properties also critically influence on the ablation results. It is further demonstrated that the microstructural characteristics of the target can lead to completely different ablation rate and surface morphology.

피코초 레이저를 이용한 니켈의 미세가공 특성

신동식(D. S. Shin),이제훈(J. H. Lee),서정(J. Suh),노지환(J. H. Noh),정용운(Y. W. Chung),김재구(J. G. Kim) 한국정밀공학회 2006 한국정밀공학회 학술발표대회 논문집 Vol.2006 No.5월

In case of ultrashort laser ablation of metals, 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 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.

355㎚ UV 레이저를 이용한 구리 박판 가공 시 어블레이션에 관한 연구

오재용(Jae Yong Oh),신보성(Bo Sung Shin) Korean Society for Precision Engineering 2007 한국정밀공학회지 Vol.24 No.2

Usually nanosecond pulsed laser processing of metal is mainly affected by the thermal ablation. Many studies of the theoretical analysis and modeling to predict the laser ablation of metal are suggested on the basis of the photothermal mechanism at higher laser fluence. In this paper, we investigate the etching depth and laser fluence of laser ablation of copper foils and propose the simplified SSB Model(Srinivasan-Smrtic-Babu model) to study the photothermal effect of nanosecond pulsed laser ablation. The experimental results show that the photothermal ablation of the 355㎚ DPSS Nd:YV04 laser is useful to process the copper thin foils.

피코초 레이저를 이용한 금속의 미세가공 특성

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.

피코초 레이저를 이용한 Eagle Glass 절단 시 가공성 평가

이상균(Sang Kyun Lee),이영곤(Young Gon Lee),김재도(Jae Do Kim) Korean Society for Precision Engineering 2013 한국정밀공학회지 Vol.30 No.4

In this paper, the characteristics of ablation processing of the eagle glass by pico-second laser are investigated. The laser ablation is used to process micro forms on materials. The ablation causes little thermal effect and little burr on the surface of eagle glass. In order to examine the characteristics of panic cracks, experiments are conducted under various cutting conditions such as a frequency of 600 kHz, laser powers, scan speeds and number of scan(NS). To minimize the panic cracks, the specimens are heated at 30℃, 45℃, and 60℃ for ten minutes respectively and then they are broken by hands. Laser powers, NS and scan speeds have an effect on glass cutting results. The ablation depths increase with an increase in the laser power and NS whereas the panic cracks decrease with an increase in scan speed. The high temperature on processed specimens reduces the panic cracks and makes good results of laser cutting. The optimal condition for eagle glass laser cutting is found to be at 30 W of laser power, 3 mm/s of scan speed and 500 of NS, respectively.

레이저 유도 충격파를 이용한 첨단 약물전달시스템 개발

한태희(Tae-hee Han),이현희(Hyun Hee Lee),Ardian B. Gojani,여재익(Jai-ick Yoh) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.1

1 GW/㎠ 이상의 고강도의 레이저 빔을 얇은 금속 호일의 한 점에 집중시키면, 레이저 삭마현상에 의해 발생된 충격파가 금속 호일 안으로 전파하게 된다. 이 충격파는 금속 호일의 반대 면에서 팽창파로 반사되고, 그 과정에서 금속 호일에 급격한 변형이 일어난다. 이 때, 금속 호일의 반대 면에 미세한 마이크로 단위 크기의 입자들을 코팅하면, 금속의 순간적인 변형으로 인해 입자들이 큰 운동량을 얻으며 가속되어 빠른 속도로 튕겨져 나가게 되는데 이것이 바이오리스틱 약물 전달의 원리이다. 이번 연구에서는 바이오리스틱 시스템의 제어성, 안정성, 효율을 향상시키고자 컨파인 조건을 변화시키며, 인체의 연한 조직을 모사하는 3% 젤라틴 용액으로의 침투 모습을 파악하였다. 사용한 컨파인 매질은 BK7 유리, 물, 그리고 초음파젤(RHAPAPHRM Co. Ltd)이다. 실험결과, 컨파인 매질과 그 두께를 조절함으로써 마이크로 입자들의 침투 양상을 제어할 수 있음을 확인하였다. Impingement of a high power laser pulse (above 1 GW/㎠) on a metal foil causes its ablation, which is characterized by a rapid expulsion of matter and the initiation of a strong shock wave inside the solid metal. The shock propagates through the foil and reverberates on the rear side, causing its deformation and microparticle ejection, which were deposited on the foil prior to ablation. Based on this principle, we are developing a new drug delivery system - Biolistic gun. Current study is focused on the controllability, stability, efficiency of the system, and characterization of the penetration shapes in various conditions. We have tested the system by applying direct and confined ablation. Several different media combinations were used for confinement-BK7 glass, water, BK7 glass with water, and succulent jelly(ultrasono jelly, RHAPAPHRM). Biological tissue was replicated by a 3% gelatin solution. Present data shows that the confinement results in enhancement of penetration shape reached by 5 um cobalt microparticles. Based on the analysis of the experimental results we observe that the penetration shape of microparticles can be controlled by adjusting the thickness of confinement media.

엑시머 레이저를 이용한 PMMA와 PET의 가공

신동식,이제훈,서정,김도훈 한국레이저가공학회 2003 한국레이저가공학회지 Vol.6 No.1

The ablative decomposition mechanism of PMMA(polymethyl methacrylate) and PET(polyethylene terephthalate) with KrF excimer laser(λ : 248nm, pulse duration: 5ns) is investigated. The UV/Vis spectrometer analysis showed that PMMA is a weak absorber and PET is a strong absorber at the wavelength of 248nm. The results(surface debris, melt, etch depth, etching shape) from drilling and direct writing experiments imply that ablation mechanism of PMMA is dominated by photothermal process, while that of PET is dominated by photochemical process.

단일 펨토초 레이저펄스를 이용한 실리콘 표면에서의 시분해 반사율 측정 연구

문혜영(Heh-Young Moon),시두 메라 씽(Mehra Singh Sidhu),이현규(Hyun-Kyu Lee),정세채(Sae-Chae Jeoung) 한국레이저가공학회 2011 한국레이저가공학회지 Vol.14 No.4

In this work, we have studied on time-resolved transient reflective image of single crystalline Si surface after single-shot fs-laser irradiation with varying the laser fluence under two different laser spot sizes. The temporal profiles of transient reflectivity changes as well as its maximum values at the early delay time were found to be strongly dependent on both the laser beam spot size and laser fluence. We have interpreted the dependence of transient reflectivity changes on the laser spot size in terms of a relaxation of the generated free carriers to the bulk silicon, which should be interacted with the plasma.