• Proceedings of the Optical Society of Korea Conference
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• 1989.02a
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• pp.13-19
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• 1989

Passive mode-locking of a pulsed Nd:YAG laser is achieved with saturable absorbers, BDN dye in iodoethane solvent and Kodak Eastman # 26 dye in 1,2-dichloroethane solvent, and its optimum conditions are investigated. The thickness of saturable absorbers employed in the laser mode-locking is 0.16~0.50mm. The PBR (peak-to-background ratio) measured in the oscilloscope is 79.8% in Kodak Eastman # 26 dye at the neighbourhood of the peak power, whereas the passive mode-locking with BDN dye gives PBR of 67.7%. BDN and Kodak Eastman # 26 dyes are superior in photostability over Kodak eastman # 9860 and # 9740 dyes which were used previously in passive mode-locking. From the PBR curve, we find that Kodak Eastman # 26dye is more effective than BDN dye in passive mode-locking. The spacing between the adjacent pulses of the pulse train, which depends on the laser cavity length, is measured and is found to be 7 nsec for the cavity length of 100cm.

• Bulletin of the Korean Chemical Society
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• v.18 no.2
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• pp.171-174
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• 1997

The initial kinetic energy of laser-ablated Zn cation has been investigated via time-of-flight mass spectrometry. The flight times of the ions have been measured with a high voltage pulse on the extract electrode in the mass spectrometer, which has been delayed from the laser pulse. The time-of-flight equation including the initial kinetic energy term of the ion has been derived for the mass spectrometer. The optimum value of the initial kinetic energy has been extracted by fitting the measured flight times into the time-of-flight equation. The initial kinetic energy of the ions generated by Nd:YAG laser (532 nm) at the power density of 5 × 107 W/cm2 has been determined to be 22-44 kJ/mol.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.4
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• pp.101-107
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• 2007

The objective of this research work is to investigate into effects of an auto tracking of the focal distance on the quality of the cut part in the cutting of a low carbon sheet using a high-power CW Nd:YAG laser. An auto-tracking system with a capacitance based distance control loop has been employed to perform a real control of the focal distance. In order to examine the influence of the auto-tracking of a focal distance on the optimum focal distance, the kerfwidth, surface roughness and the formation of the cut section, several linear cutting tests have been carried out using the auto-tracking system. The results of experiments have been shown that the optimum focal distance is 0.9mm. In addition, it has been shown that the variation of kerfwidth and the surface roughness of the cut part with control of the focal distance are reduced 40-80% and 30-55% in comparison with those of the cut part without tracking of the focal distance. From the results of the experiments, it has been found that the real time tracking of the focal distance can improve the part quality.

• Korean Journal of Optics and Photonics
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• v.1 no.1
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• pp.22-27
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• 1990

The cavity-length detuning characteristics of the hybridly mode-locked dye laser have been studied with a collinear autocorrelator. In the optimum condition, the pulse width is 0.65 ps about three times as short as that of the synchronously mode-locked dye laser. As the cavity length is increased, the pulse width becomes broader than that at the optimum cavity length because of the effect of spontaneous emission. Also, the spectrum width becomes broad, therefore the time bandwidth product ($\Deltat\Deltav$) is increased. The peak power of autocorrelation is maximum at $\Deltat=5.0\umm$ longer than the optimum cavity length. On the other hand, as the cavity length is decreased, the pulse width becomes broader and the satellite pulses appear because of the gain recovery. Also the spectrum width becomes narrower than that at the optimum cavity length. In particular, at the mismatched cavity length the center of the lasing spectrum moves to shorter wavelengths. ngths.

• Korean Journal of Optics and Photonics
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• v.19 no.3
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• pp.229-236
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• 2008

The optimum conditions of second harmonic generation (SHG) can be successfully achieved experimentally using single pass and double pass methods of a pumping beam. The beam has a power of several Watts radiated by a DOFA (Diode Laser Oscillator & Fiber Amplifier) system, which is a high power CW wavelength tunable infrared laser system, in a PPLN (Periodically Poled MgO doped Lithium Niobate) nonlinear crystal. In the case of a single pass method, the parameters are the wavelength of 535 nm for SHG and the output power of 245 mW generated from the pumping input beam with wavelength of 1070 nm and the power of 2.45 W at phase matching temperature of $108.9^{\circ}C$. The conversion efficiency of SHG was 10%. In order to enhance the output of SHG, the double pass method of the SHG system of a PPLN using a concave mirror for the retroreflection and a pair of wedged flat windows for phase compensation was also presented. In this double pass system, we obtained the SHG output beam with the wavelength of 535 nm and the maximum power of 383 mW at optimum phase matching temperature of $108.5^{\circ}C$ by using an incident pumping beam with wavelength of 1070 nm and the power of 2.45 W. The maximum conversion efficiency is 15.6%, which is more than that of the single pass method.

• Laser Solutions
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• v.15 no.2
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• pp.15-20
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• 2012

A novel joining technology was developed to compensate the camber in polymers. The preheating laser beam circulates on the joining location and the accumulated heat serves to increase the flexibility of neighboring polymers. The temperature rises up to the glass transient temperature of the polymers and continually loading spring force closes the gap of camber. The irradiated laser was 808nm central wavelength and the power varied between 2Watt and 5Watt. The laps were adjusted between 3 and 10 and the optimum process parameters were 3Watt and 5 laps for the specific application. An FEM analysis was introduced to understand the mechanism of joining by the transient temperature distribution on the polymers. Thermocouples experiments were also tried to correlate the numerical analysis results and it showed the trend of heat accumulation in experiments.

• Journal of Welding and Joining
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• v.32 no.4
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• pp.20-25
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• 2014

Laser heat source was applied on 3D poly urethane model built by 3D printer and cellulous acetate for joining. A diode laser with 808nm wavelength was transmitted through the 3D model and applied on the boundary of ABS/Acetate and 3D poly urethane model. Based on the experimental result, the ABS and 3D built poly-urethane polymers was successfully joined, but the mechanical strength was not enough at the joining boundaries in the range of 6watt to 8watt of laser heat source. However, biodegradable acetate was successfully joined without damaging the 3D built model and mechanical strength was properly achieved. The optimum laser power was found between 5watt and 8watt with scanning speed of 500mm/min, 700mm/min and 1,000mm/min. Based on the SEM analysis the filling mechanism was that the applied pressure on 3D built model squeezed the fluidic thermoplastics, ABS and acetate, into the structure of 3D model. Therefore soundness of joining was strongly depending on the viscosity of thermoplastics in polymers. The developed laser process is expected to increase productivity and minimize the cost for the final products.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.2
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• pp.91-95
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• 2005

A feasibility study was performed to see the welding possibility of dissimilar thin-plat materials. These materials were welded for finding the optimum welding condition and evaluating the soundness of welding zone. The welding was attempted under the condition of laser power 500~600w, Pulse width 1.0~2.5ms and frequency 11~18Hz. In this study, the highest tensile-shear strength was observed at laser the low frequency. The suitable welding condition can be obtain at the large pulse width and the low frequency.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.46-50
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• 2004

The curing characteristics of a liquid photopolymer during microstereolithography and the shape accuracy of thereby fabricated microstructures were investigated experimentally. A He-Cd laser with a wavelength of 442nm and a photopolymer consisted of a commercial resin from SK chemical and a photoinitiat or were used for the experiment. By varying the laser beam power and scanning speed of the focused laser beam, minimum curing thickness of 50 ${\mu}ㅡ$ was obtained. The distortion of solidified structure due to adhesion force was measured and the optimum fabrication conditions were determined. Also, the feasibility of direct fabrication of three-dimensional microstructures by Super IH process was examined.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.190-192
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• 2006

The 3-dimensional(3D) chip stacking technology is one of the leading technologies to realize a high density and high performance system in package(SIP). It could be found that it is the advanced process of through-hole via formation with the minimum damaged on the Si-wafer. Laser ablation is very effective method to penetrate through hole on the Si-wafer because it has the advantage that formed under $100{\mu}m$ diameter through-hole via without using a mask. In this paper, we studied the optimum method for a formation of through-hole via using femto-second laser heat sources. Furthermore, the processing parameters of the specimens were several conditions such as power of output, pulse repetition rate as well as irradiation method and time. And also the through-hole via form could be investigated and analyzed by microscope and analyzer.