• 한국레이저가공학회지
• /
• 제18권1호
• /
• pp.12-17
• /
• 2015

This work performed numerical analysis of electromagnetic field and thermal phenomena occurring in femtosecond laser irradiation of silver nanowires. The local electric field enhancement was computed to calculate the optical energy dissipation as a Joule heating source and the thermal transport was analysed based on the two-temperature model (TTM). Electron temperature increased up to 1000K after 50fs and its spatial distribution became homogeneous after 80fs at the fluence of 100mJ/cm2. The result of this work is expected to contribute to revealing the photothermal effects on silver nanowires induced by femtosecond laser irradiation. Although the highest increase of lattice temperature was substantially below the melting point of silver, the experimental results showed resolidification and fragmentation of the silver nanowire into nanoparticles, which cannot be explained by the photothermal mechanism. Further studies are thus needed to clarify the physical mechanisms.

• 한국산학기술학회논문지
• /
• 제1권2호
• /
• pp.63-68
• /
• 2000

어븀 첨가된 고리형 광섬유 레이저를 제작하여 외부 조절기를 적용하지 않은 수동형 모드로킹을 구현하였다. 모드로킹 현상은 단일 모드로킹 과정과 이중 모드로킹 과정이 관측되었고 분산천이 광섬유의 길이를 변화시켜 65 fs의 시간폭을 갖는 초단 펄스를 얻었다. 한편 고차조화모드로킹과 Q스위치된 고차조화 모드로킹도 구현하였는데, 연속파 고차조화 모드로킹은 17차까지 구현하였으며, 펌프 전력의 감소가 연속파 고차 조화 모드로킹에서 Q스위치된 고차조화 모드로킹으로 변화시키며 이러한 과정이 편광조절기에 의해서도 이루어 졌다 이러한 일련의 초단 펄스열의 연구는 광통신용 신호원으로 개발에 중요한 역할을 한다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2006년도 제31회 학술논문발표회 초록집
• /
• pp.52-52
• /
• 2006

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2013년도 춘계학술대회 논문집
• /
• pp.907-908
• /
• 2013

• Journal of information and communication convergence engineering
• /
• 제1권1호
• /
• pp.39-43
• /
• 2003

The technology required to advance the state of the art of ultra-high-intensity excimer amplifier construction to the 100 J/100fs output pulse level is identified. The preliminary design work for very large final amplifier pumped by electron beam module is described, and key design problems and approaches are presented and discussed in detail based on the recent experimental and theoretical results.

• 한국전기전자재료학회논문지
• /
• 제30권7호
• /
• pp.427-431
• /
• 2017

In this paper, we discuss ${\beta}-Ga_2O_3$ thin films that have been grown on freestanding GaN (FS-GaN) using furnace oxidation. A GaN template was grown by horizontalhydride vapor phase epitaxy (HVPE), and FS-GaN was fabricated using the laser lift off (LLO) system. To obtain ${\beta}-Ga_2O_3$ thin film, FS-GaN was oxidized at $900{\sim}1,100^{\circ}C$. Surface and cross-section of prepared ${\beta}-Ga_2O_3$ thin films were observed by field emission scanning electron microscopy (FE-SEM). The single crystal FS-GaNs were changed to poly-crystal ${\beta}-Ga_2O_3$. The oxidized ${\beta}-Ga_2O_3$ thin film at $1,100^{\circ}C$ was peel off from FS-GaN. Next, oxidation of FS-GaNwas investigated for 0.5~12 hours with variation of the oxidation time. The thicknesses of ${\beta}-Ga_2O_3$ thin films were measured from 100 nm to 1,200 nm. Moreover, the 2-theta XRD result indicated that (-201), (-402), and (-603) peaks were confirmed. The intensity of peaks was increased with increased oxidation time. The ${\beta}-Ga_2O_3$ thin film was generated to oxidize FS-GaN.

• Current Optics and Photonics
• /
• 제7권6호
• /
• pp.738-744
• /
• 2023

Graphene-based saturable absorbers (SAs) are widely used as laser mode-lockers at various laser oscillators. In particular, transmission-type graphene-SAs with ultrabroad spectral coverage are typically manufactured on transparent substrates with low nonlinearity to minimize the effects on the oscillators. Here, we developed two types of transmitting graphene SAs based on CaF₂ and ZnSe. Using the graphene-SA based on CaF₂, a passively mode-locked mid-infrared Cr:ZnS laser delivers relatively long 540 fs pulses with a maximum output power of up to 760 mW. In the negative net cavity dispersion regime, the pulse width was not reduced further by inhomogeneous group delay dispersion (GDD) compensation. In the same laser cavity, we replaced only the graphene-SA based on CaF₂ with the SA based on ZnSe. Due to the additional self-phase modulation effect induced by the ZnSe substrate with high nonlinearity, the stably mode-locked Cr:ZnS laser produced Fourier transform-limited ~130 fs near 2,340 nm. In the stable single-pulse operation regime, average output powers up to 635 mW at 234 MHz repetition rates were achieved. To our knowledge, this is the first attempt to achieve shorter pulse widths from a polycrystalline Cr:ZnS laser by utilizing the graphene deposited on the substrate with high nonlinearity.

• 한국광학회지
• /
• 제4권1호
• /
• pp.66-72
• /
• 1993

파장이 $1.053{\mu}m$에서 연속 발진하는 Nd:YLF 레이저에, 비선형 매질로서 단일모드 광섬유를 이용한 외부 공진기를 연결하여 additive-pulse mode-locking(APM)된 펄스를 얻었다. APM 펄스의 펄스폭은 4.5 ps이며 평균 출력은 1.5W이다. APM 펄스를 광섬유와 회절격자쌍을 이용하여 peak power가 17 kW인 210 fs의 극초단 펄스로 압축하였다.

• 한국레이저가공학회지
• /
• 제11권1호
• /
• pp.19-24
• /
• 2008

It has been recognized that laser dicing of wafers results in low mechanical strength compared to the conventional sawing techniques. Thermal shock generated by rapid thermal loading is responsible for this problem. This work presents a two-dimensional ultra-short thermo elastic model for numerical simulation of femtosecond laser ablation of metals in the high-fluence regime where the phase explosion is dominant. Laser-induced thermoelastic stress is analyzed for Ni. The results show that the laser-induced thermal shock is large enough to induce mechanical damages.

• 한국레이저가공학회지
• /
• 제11권2호
• /
• pp.20-25
• /
• 2008

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.