• 한국레이저가공학회지
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• 제15권3호
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• pp.16-19
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• 2012

We have successfully formed brown colored patterns inside of a transparent borosilicate glass generally known as BK7, laying the focus of near infrared Ti: sapphire femtosecond laser beam in the bulk BK7 glass. It is important to keep the laser power well below the damage threshold of BK7 in forming the color center. According to the low laser power, there was no laser induced mechanical damage such as cracks or threads in the color formed area. From the absorbance spectrum and its gaussian fitting, we found the band gap of BK7, 4.21eV, and three absorption edges.

• 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.

• 한국레이저가공학회지
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• 제18권4호
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• pp.17-22
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• 2015

In this paper, ablation rate of $Al_2O_3$ ceramics by femtosecond laser fluence is derived with experimental method. The automatic three axis linear stage makes laser optics to move with high spatial resolution. With 10 times objective lens, minimal pattern width of $Al_2O_3$ is measured in the focal plane. Ablated surface area is shown as linear tendency increasing number of machining times with various laser power conditions. Machining times is most sensitive condition to control $Al_2O_3$ pattern width. Also, the linear increment of pattern width with laser power change is investigated. In high machining speed, the ablation volume rate is more linear with fluence because pulse overlap is minimized in this condition. Thermal effect to surrounding medium can be minimized and clean laser process without melting zone is possible in high machining speed. Ablation volume rate decelerates as increasing machining times and multiple machining times should be considered to achieve proper ablation width and depth.

• 한국레이저가공학회지
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• 제17권2호
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• pp.19-25
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• 2014

Optical embedded diffraction gratings with the bulk modification in BK-7 glass plates excited by tightly focused high-intensity femtosecond (130fs) Ti: sapphire laser (peak wavelength = 790nm) were demonstrated. The structural modifications with diameters ranging from 400nm to $4{\mu}m$ were photo-induced after plasma formation occurred upon irradiation with peak intensities of more than $1{\times}1013W/cm^2$. The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which low-density plasma occurred. The maximum refractive index change was estimated to be $1.5{\times}10^{-2}$. The two optical embedded gratings in BK-7 glass plate were demonstrated with refractive index modification induced by the scanning of low-density plasma formation.

• 한국레이저가공학회지
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• 제11권2호
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• pp.20-25
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• 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.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.209-210
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• 2006

We have successfully termed brown colored patterns inside of a transparent borosilicate glass generally known as BK7, laying the focus of near infrared Ti: sapphire femtosecond laser beam in the bulk BK7 glass. It is important to keep the laser power well below the damage threshold of BK7 in forming the color center. Thanks to the low laser power, there was no laser induced mechanical damage such as cracks or threads in the color formed area. From the absorbance spectrum and its gaussian fitting, we found the band gap of BK7, 4.21eV, and three absorption edges.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.239-240
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• 2006

For longer than picosecond pulses, bulk damage inside defect-free dielectrics involves the heating and multiplication of spurious electrons by the incident laser beam and transfer of this energy to the lattice. The situation is quite different for femtosecond pulses which are shorter than the time scale for electron energy transfer to the lattice. Damage caused by these pulses is produced with smaller statistical uncertainty and is controllable on a microscopic scale. These properties can be exploited to produce laser devices such as arrays of damage dots for all optical memories with high data storage density or arrays of parallel grooves to form transmission gratings. In this work, we observed characteristic of the femtosecond laser machining in BK7 and fused silica.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2013년도 춘계학술대회 논문집
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• pp.235-236
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• 2013

• 한국정밀공학회지
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• 제29권3호
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• pp.339-345
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• 2012

Electrospun meshed poly-caprolactone PCL was patterned by femtosecond laser with linear grooves. As parametric variables, focus spot size, pulse energy, and scanning speed were varied to determine the affects on groove size and the characteristics of the electrospun fiber at the edges of these grooves. The femtosecond laser was seen to be an effective means for flexibly structuring the surface of ES PCL scaffolds and the width of the ablated grooves was well controlled by laser energy and focus spot size. The ablation threshold was measured to be $14.9J/cm^2$ which is a little higher than other polymers. These affects were attributed to optical multiple reflections inside nano-fibers. By the laser-induced plasma at higher pulse energies, some melting of fibers was observed.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.653-654
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• 2006

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.