• Laser Solutions
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• v.14 no.2
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• pp.13-16
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• 2011

We fabricated the Fresnel zone plate using femtosecond laser lithography-assisted micro-machining, which is a combined process of nonlinear lithography and wet etching. We investigated the focusing properties by launching a 632.8nm wavelength He-Ne laser beam into the zone plate. The spot size of the primary focal point was $27{\mu}m$ and the intensity of focal point was 0.565W/$cm^2$.

• Laser Solutions
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• v.12 no.1
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• pp.14-18
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• 2009

Ripple formation of femtosecond laser in stainless steel is investigated using 184 fs pulses with a center wavelength of 785 nm. The effect of the laser polarization relative to the translation direction is observed. For drilling with a certain aspect ratio, reflections at the hole walls take place, leading to a non-uniform intensity distribution deep inside the formed hole. Finally, it is shown that a circular polarization during the drilling process significantly improves the quality of the produced holes.

• Laser Solutions
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• v.14 no.2
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• pp.17-23
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• 2011

Active thin films are ubiquitous in the manufacture of all forms of flat panel display (FPD). One of the most widely employed thin films is indium tin oxide (ITO) and metal films used electrically conductive materials in display industries. ITO is widely used for fabrication of LCD, OLED device, and many kinds of optical applications because of transparency in visible range and its high conductivity and metal films are also widely employed as electrodes in various electric and display industries. It is important that removing specific area of layer, such as ITO or metal film on substrate, to fabricate and repair electrode in display industries. In this work, we demonstrate efficient selective ablation process to ITO and aluminum film on glass using a femtosecond laser (${\lambda}p=1025nm$) respectively. The femtosecond laser with wavelength of 1025nm, pulse duration of 400fs, and the repetition rate of 100kHz was used for selectively removing ITO and Al on glass in the air. We can successfully remove the ITO and Al films with various pulse energies using a femtosecond laser.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.5
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• pp.150-156
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• 2009

The removal of tiny particles adhered to surfaces is one of the crucial prerequisite for a further increase in IC fabrication, large area displays and for the process in nanotechnology. Various cleaning techniques (wet chemical cleaning, scrubbing, pressurized jets and ultrasonic processes) currently used to clean critical surfaces are limited to removal of micrometer-sized particles. Therefore the removal of sub-micron sized particles from silicon wafers is of great interest. For this purpose various cleaning methods are currently under investigation. In this paper, we report on experiments on the cleaning effect of 100nm sized fluorescence particles on silicon wafer using the plasma shockwave occurred by femtosecond laser. The plasma shockwave is main effect of femtosecond laser cleaning to remove particles. The removal efficiency was dependent on the gap distance between laser focus and surface but in some case surface was damaged by excessive laser intensity. These experiments demonstrate the feasibility of femtosecond laser cleaning using 100nm size fluorescence particles on wafer.

• Laser Solutions
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• v.17 no.1
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• pp.1-6
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• 2014

Indium tin oxide (ITO) is an important transparent conducting oxide (TCO). ITO films have been widely used as transparent electrodes in optoelectronic devices such as organic light-emitting devices (OLED) because of their high electrical conductivity and high transmission in the visible wavelength. Finding ways to control ITO micromachining depth is important role in the fabrication and assembly of display field. This study presented the depth control of ITO patterns on glass substrate using a femtosecond laser and slit. In the proposed approach, a gaussian beam was transformed into a quasi-flat top beam by slit. In addition, pattern of square type shaped by slit were fabricated on the surfaces of ITO films using femtosecond laser pulse irradiation, under 1030nm, single pulse. Using femtosecond laser and slit, we selectively controlled forming depth and removed the ITO thin films with thickness 145nm on glass substrates. In particular, we studied the effect of pulse number on the ablation of ITO. Clean removal of the ITO layer was observed when the 6 pulse number at $2.8TW/cm^2$. Furthermore, the morphologies and fabricated depth were characterized using a optical microscope, atomic force microscope (AFM), and energy dispersive X-ray spectroscopy (EDS).

• Laser Solutions
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• v.15 no.1
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• pp.15-19
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• 2012

The fabrication of internal diffraction gratings with photoinduced refractive index modification in transparent materials was demonstrated using low-density plasma formation excited by a femtosecond (130 fs) Ti: sapphire laser (${\lambda}_p$=800 nm). The refractive index modifications with diameters ranging from $1{\mu}m$ to $3{\mu}m$ were photoinduced after plasma formation occurred upon irradiation with peak intensities of more than $2.0{\times}10^{13}W/cm^2$. The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which low-density plasma occurred.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.640-643
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• 2003

We present investigations of the surface micromachining for transparent glass substrate, e.g. soda lime glass using tightly focused 800nm Ti:sapphire femtosecond laser. In this study, experiment conditions such as laser intensity, scanning speed, focus position were controlled as variable parameters to decide optimal machining conditions. This study shows clearly that laser intensity and scanning speed are dominant factors for good surface morphology. Using the optimal conditions, grooves with 50${\mu}{\textrm}{m}$ line width were fabricated on glass substrate and their surface morphologies were investigated from SEM image.

• Laser Solutions
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• v.10 no.4
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• pp.18-22
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• 2007

In this paper, we suggested the femtosecond laser processing using the mask which makes Gaussian spatial beam distribution to a normalized distribution by Fresenel diffraction. Holography pattern of the size of $320{\times}320{\mu}m^2$ on the Cr thin film on glass substrate with a pixel size of $5{\times}5{\mu}m^2$ was fabricated according to the pattern generated by the iterative Fourier transform algorithm(IFTA) algorithm. We analysed the damage threshold with an assumption the power distribution as Gaussian profile as 45 $mJ/cm^2$. The regenerated image of letters through the diffractive pattern was well recognized at the screen.

• Current Optics and Photonics
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• v.7 no.6
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• pp.732-737
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• 2023

A high-power Yb-doped femtosecond (fs) fiber laser at a repetition rate of 1.83 GHz is reported. By employing a 5-stage repetition rate multiplier, the repetition rate of the mode-locked master oscillator was multiplied from 57.1 MHz to 1.83 GHz. The ultrashort pulse output at 1.83 GHz was amplified in a two-stage Yb-doped fiber amplifier, leading to >100 W of fs laser output with a pulse duration of 290 fs. The theoretical pulse width along the fiber was simulated, showing that it was in good agreement with experimental results. Further improvement in power scaling is discussed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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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.