• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.891-894
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• 2014

The ultrashort electron pulse, laser-emitted from the metal tip apex has been characterized and used as a probing source for a new electron microscope to visualize the morphology of the gold-mesh in the nanometric resolution. As the gap between the tungsten tip and Au-surface is approached within a few nm, the large electromagnetic field enhancement for the incident P-polarized laser pulse with respect to the tip-sample axis is strongly observed. Here, we demonstrate that the time-resolved tip-enhanced electron emission microscope (TEEM) can be implemented on the laboratory table top to give the two-dimensional image, opening lots of challenges and opportunities in the near future.

• 비파괴검사학회지
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• 제33권2호
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• pp.160-164
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• 2013

레이저 초음파검사 장치는 레이저 빔을 이용하여 초음파 신호를 발생시키고 측정하는 비접촉식 결함 검사 장치이다. 이 장치는 펄스 레이저 빔을 이용하여 광대역 주파수 범위를 갖는 초음파 신호를 발생시키고 작은 점으로 집속된 레이저 빔을 이용하여 초음파 신호를 측정하므로 우수한 측정 분해능을 제공한다. 본 연구에서는 이종금속 접촉부식(갈바닉 부식) 현상을 레이저를 이용한 비파괴, 비접촉 방법으로 측정하였다. 부식된 부분에 이물질이 혼합되는 경우를 가정하고, 레이저 초음파 실험을 진행하였다. 시편의 뒷면에서 펄스 레이저로 초음파를 발생시키고, 같은 위치의 앞면에서 CW 레이저와 CFPI를 이용하여 초음파 신호를 획득하였다. 이물질이 존재하는 부분의 초음파 신호 특성을 분석하여 이물질의 위치 및 크기를 측정하였다.

• Journal of Periodontal and Implant Science
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• 제52권1호
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• pp.77-87
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• 2022

Purpose: This pilot study assessed the immediate in vivo effect of high peak pulse power neodymium-doped yttrium aluminum garnet (Nd:YAG) laser monotherapy on selected red/orange complex periodontal pathogens in deep human periodontal pockets. Methods: Twelve adults with severe periodontitis were treated with the Laser-Assisted New Attachment Procedure (LANAP®) surgical protocol, wherein a free-running, digitally pulsed, Nd:YAG dental laser was used as the initial therapeutic step before mechanical root debridement. Using a flexible optical fiber in a handpiece, Nd:YAG laser energy, at a density of 196 J/cm² and a high peak pulse power of 1,333 W/pulse, was directed parallel to untreated tooth root surfaces in sequential coronal-apical passes to clinical periodontal probing depths, for a total applied energy dose of approximately 8-12 joules per millimeter of periodontal probing depth at each periodontal site. Subgingival biofilm specimens were collected from each patient before and immediately after Nd:YAG laser monotherapy from periodontal pockets exhibiting ≥6 mm probing depths and bleeding on probing. Selected red/orange complex periodontal pathogens (Porphyromonas gingivalis, Tannerella forsythia, Prevotella intermedia/nigrescens, Fusobacterium nucleatum, Parvimonas micra, and Campylobacter species) were quantified in the subgingival samples using established anaerobic culture techniques. Results: All immediate post-treatment subgingival biofilm specimens continued to yield microbial growth after Nd:YAG laser monotherapy. The mean levels of total cultivable red/orange complex periodontal pathogens per patient significantly decreased from 12.0% pretreatment to 4.9% (a 59.2% decrease) immediately after Nd:YAG laser monotherapy, with 3 (25%) patients rendered culture-negative for all evaluated red/orange complex periodontal pathogens. Conclusions: High peak pulse power Nd:YAG laser monotherapy, used as the initial step in the LANAP® surgical protocol on mature subgingival biofilms, immediately induced significant reductions of nearly 60% in the mean total cultivable red/orange complex periodontal pathogen proportions per patient prior to mechanical root instrumentation and the rest of the LANAP® surgical protocol.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.620-623
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• 2003

The material processing by using ultrashort pulse laser, in recently, is actively applying into the micro machining and nano-machining technology since ultrashort pulse has so faster than the time which the electrons energy absorbing photon energy is transmitted to surrounding lattice-phonon that it has many advantages in point of machining. The micro machining of metallic thin film on the plain glass is widely used in the fields such as mask repairing for semiconductor, fabrication of photonic crystal, MEMS devices and data storage devices. Therefore, it is important to secure the machining technology of the sub-micron size. In this research, we set up the machining system by using ultrashort pulse laser and conduct on the Cr 200nm thin film ablation experiments of spot and line with the variables such as energy, pulse number, speed, and so on. And we observed the characteristics of surrounding heat-affected zone and by-products appeared in critical energy density and higher energy density through SEM, and also examined the machining features between in He gas atmosphere which make pulse change minimized by nonlinear effect and in the air. Finally, the pit size of 0.8${\mu}{\textrm}{m}$ diameter and the line width of 1${\mu}{\textrm}{m}$ could be obtained.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.75-78
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• 1995

This paper presents the feasibility of laser ablation process in 3-D micro machining of MEMS (micro Electro Mechanical System)parts. The micro machining characteristics of polymer(Energy fluence, pulse repetition rate, number of pulse, ablation rate)are investigated and 3-D micro machined samples are demonstrated.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2004년도 춘계종합학술대회
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• pp.324-326
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• 2004

엑시머 레이저로 여기되는 분포제환 색소레이저(DFDL: Distributed Feedback Dye Laser)로부터 616nm의 레이저 펄스를 얻고, 이를 제2고조파 발생에 의한 파장변환을 통해 308nm의 극초단 자외 광펄스를 얻었다. 또한 3단의 XeCl 엑시머 레이저 증폭기를 구성하여 자외 광펄스의 증폭을 행하였다.

• 반도체디스플레이기술학회지
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• 제6권1호
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• pp.11-15
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• 2007

Low-k wafer engraving process has been investigated by using UV pico-second laser with high repetition rate. Wavelength and repetition rate of laser used in this study are 355 nm and 80 MHz, respectively. Main parameters of low-k wafer engraving processes are laser power, work speed, assist gas flow, and protective coating to eliminate debris. Results show that engraving qualities of low-k layer by using a laser with UV pico-second pulse width and high repetition rate had better kerf edge and higher work speed, compared to one by conventional laser with nano-second pulse width and low repletion rate in the range of kHz. Assist gas and protective coating to eliminate debris gave effects on the quality of engraving edge. Total engraving width and depth are obtained less than $20\;{\mu}m$ and $10\;{\mu}m$ at more than 500 mm/sec work speed, respectively. We believe that engraving method by using UV pico-second laser with high repetition rate is useful one to give high work speed in laser material process.

• 한국광학회지
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• 제19권4호
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• pp.320-326
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• 2008

광섬유 연결 반도체레이저 여기 세라믹 Nd:YAG 레이저의 전기광학 Q-스위칭 출력 특성에 대해 연구하였다. 세라믹 Nd:YAG 레이저의 Q-스위칭은 여기원의 펄스폭 $1,000\;{\mu}s$, 출력 거울의 반사율 77% 및 지연시간 $985\;{\mu}s$에서 최적화되었다. 여기 에너지 17.9 mJ에서 0.35 mJ의 Q-스위칭된 출력 에너지와 약 4 ns의 펄스폭이 측정되어 1.9%의 출력 효율과 87.5 kW의 첨두 출력을 나타내었다.

• 한국광학회지
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• 제21권6호
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• pp.254-258
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• 2010

타원형 모양의 모드 형태를 갖는 펄스형 레이저 다이오드 (laser diode)의 펄스 형태를 유지하면서 단일 모드 및 Gaussian 형태로 광 모드 변환을 유도하고 광출력을 증폭할 수 있는 기술에 대해서 연구하였다. 실험에서 사용한 펼스형 레이저 다이오드의 구경이 가로는 $300{\mu}m$이며, 세로는 $2{\mu}m$이고 출력은 $1.1mW/cm^2$이다. 렌즈형 광섬유를 사용하여 광결합을 유도하여 단일 모드 및 Gaussian 형태의 출력으로 변환시켰다. 그러나, 다중모드의 펄스형 레이저 다이오드의 출력을 단일모드 렌즈형 광섬유에 결합시키면 출력이 급격하게 감소한다. 따라서 master oscillator power amplifier (MOPA) 기반의 광증폭 기술을 이용하여 레이저 다이오드의 광출력을 증폭시켰다. 증폭 후에도 펄스 성질은 그대로 유지되었고, MOPA구조를 지나 증폭된 광 출력은 $29mW/cm^2$로 측정되었다.

• Current Optics and Photonics
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• 제6권4호
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• pp.407-412
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• 2022

We report on a diode-laser-pumped mode-locked Yb:KGW laser system, which delivers ultrashort pulses down to 89 fs at a repetition rate of 63 MHz, with an average power of up to 5.6 W. A fiber-coupled diode laser at 981 nm, operated with a compact driver, is used to optically pump the gain crystal via an off-axis parabolic mirror. A semiconductor saturable-absorber mirror is used to initiate the pulsed operation. Laser characteristics such as the pulse duration, spectrum bandwidth, and output power are investigated by varying the intracavity dispersions via changing the number of bounces between negative-dispersive mirrors within the cavity. Short pulses with a duration of 89 fs, a center wavelength of 1,027 nm, and 3.6 W of output power are produced at a group-velocity dispersion (GVD) of -3,300 fs². As the negative GVD increases, the pulse duration lengthens but the output power at the single-pulse condition can be enhanced, reaching 5.6 W at a GVD of -6,600 fs². Because of pulse broadening at high negative GVDs, the highest peak intensity is achievable at a moderate GVD with our system.