• Korean Journal of Optics and Photonics
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• v.11 no.4
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• pp.289-293
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• 2000

Diode-laser-pumped Tm:YAG laser of wavelength $2.02\mu\textrm{m}$has been manufactured and its excitation efficiency and output characteristics have been investigated. The excitation efficiency was varied from 66 to 68% with respect to the pump power, yielding pump power absorption of 87-89%. The output power was sensitively varied with the temperature of Tm:YAG rod. When the concave output coupler with a focal length of 25 mm and a transmittance of 3% was used, the maximum output power reached up to 1.2 W. The slope and optical efficiency of this Tm: YAG laser was 29% and 20% at $6^{\circ}C$, respectively.tively.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.2
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• pp.192-200
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• 2006

The aim of this study was to assess the microleakage underneath a pit and fissure sealant bonded to occlusal surfaces treated by Er:YAG laser To determine the most effective energy density of laser, fourteen specimens were irradiated from 50mJ to 300mJ at 3Hz. After irradiation, the lased specimens were observed under the scanning electron microscope. Thirty six non-carious extracted premolars were randomly assigned to four groups of nine teeth: group 1, no treatment on the occlusal surface; group 2, acid etching for 15 seconds; group 3, Er:YAG laser irradiation; group 4, acid etching followed by Er:YAG laser irradiation. The pits and fissures were sealed with unfilled sealant(Helioseal F) and the specimen teeth were thermo-cycled, immersed in 2% Rhodamine B solution, longitudinally sectioned and analyzed for microleakage with fluorescent microscope. The results were as follows: 1. Er:YAG lased surfaces with 50mJ, 3Hz showed a similar pattern of irregularity with acid etched enamel surfaces 2. The mean microleakage score increased in the order of group 2, 4, 3 and 1. There was no significant difference among group 1, 3 and 4(p>0.05), however group 2 showed significantly less microleakage compared with group 1 and 3. Conclusively, the laser irradiation seemed not enough to replace the acid etching for proper retention of pit and fissure sealants.

• Journal of Korean Dental Science
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• v.9 no.1
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• pp.19-27
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• 2016

Purpose: Laser treatment has become a popular method in implant dentistry, and lasers have been used for the decontamination of implant surfaces when treating peri-implantitis. This study was performed to evaluate the effects of an Erbium-doped:Yttrium-Aluminum-Garnet (Er:YAG) laser with different settings on machined (MA), sand-blasted and acid-etched (SA), and resorbable blast media (RBM) titanium surfaces using scanning electron microscopy and confocal microscopy. Materials and Methods: Four MA, four SA, and four RBM discs were either irradiated at 40 mJ/20 Hz, 90 mJ/20 Hz, or 40 mJ/25 Hz for 2 minutes. The specimens were evaluated with scanning electron microscopy and confocal microscopy. Result: The untreated MA surface demonstrated uniform roughness with circumferential machining marks, and depressions were observed after laser treatment. The untreated SA surface demonstrated a rough surface with sharp spikes and deep pits, and the laser produced noticeable changes on the SA titanium surfaces with melting and fusion. The untreated RBM surface demonstrated a rough surface with irregular indentation, and treatment with the laser produced changes on the RBM titanium surfaces. The Er:YAG laser produced significant changes on the roughness parameters, including arithmetic mean height of the surface (Sa) and maximum height of the surface (Sz), of the MA and SA surfaces. However, the Er:YAG laser did not produce notable changes on the roughness parameters, such as Sa and Sz, of the RBM surfaces. Conclusion: This study evaluated the effects of an Er:YAG laser on MA, SA, and RBM titanium discs using confocal microscopy and scanning electron microscopy. Treatment with the laser produced significant changes in the roughness of MA and SA surfaces, but the roughness parameters of the RBM discs were not significantly changed. Further research is needed to evaluate the efficiency of the Er:YAG laser in removing the contaminants, adhering bacteria, and the effects of treatment on cellular attachment, proliferation, and differentiation.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.171-174
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• 2000

In this study, the laser patterning of sputter-deposited amorphous CoNbZr films has been tried usig Nd: YAG laser. However, the metal film was not removed because of its high reflectance of the alser on the metal surface. To solve this problem, authors tried to screen-print a block polymer on the metal film and then irradiate the laser on the polymer. This is a new method which was suggested by this study. Using this new method, the metal films were effectively removed with the laser power of 114W even though the metal films was not removed with the laser power of 332W using the conventional method. This result leads to the conclusion that the block polymer acts as a laser energy absorbing and transferring layer.

• Laser Solutions
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• v.4 no.1
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• pp.29-38
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• 2001

This work was carried out to investigate the welding behavior of thin A3003 Al alloy sheets by Nd : YAG laser beam. Considering bead shape and mechanical properties, the laser pulse shapes selected were two kinds of 2-division and 3-division by varying power level and pulse duration. In order to obtain optimum conditions, the factorial design method and central composite design method were applied. Tensile test, optical microscopy, micro hardness test and TEM analysis were performed. Due to the annealing caused by thermal effect during laser welding, precipitates were coarsended. The HAZ was softened and failed during tensile test. The hardness of HAZ was lower than that of base metal, since the heat input relieved the work hardening effect and caused grain growth.

• Current Optics and Photonics
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• v.4 no.2
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• pp.127-133
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• 2020

We successfully constructed a passively Q-switched Yb:YAG laser ignitor pumped by a diode laser with low power and long pulse width. To the best of our knowledge, this is the first study to achieve a quasi-MW output power from an optimized Q-switch Yb:YAG laser ignitor by using a pumping diode laser module emitting at under a power of 23 W. The output pulse energy of our optimized laser is 0.98 mJ enclosed in a 1.06 ns pulse width, corresponding to a peak power of 0.92 MW.

• Laser Solutions
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• v.3 no.1
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• pp.12-20
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• 2000

The nuclear steam generators are subjected to corrosion environmental condition during operation that can result in stress corrosion in the tube wall. If any tube wall degradation is recognized, the tube must be repaired by plugging or sleeving. For the sleeving repair, Nd : YAG laser welded sleeving technology is one of the most promising when considering radioactive working conditions in the nuclear power plant. In this paper, the laser welding characteristics of steam generator tube and sleeve materials are investigated. The effects of average laser power, laser energy, welding speed, pulse duration and frequency are evaluated. Based on these results, Nd : YAG laser welded sleeving repair was applied to the degraded steam generator tubes in real environment.

• Journal of the korean academy of Pediatric Dentistry
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• v.27 no.4
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• pp.558-563
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• 2000

The lasers have been used in dentistry for more than 30 years and the application of lasers for drilling dental hard tissue has been investigated since the early developement of lasers. Recently, the Er:YAG laser was invented for hard tissue ablation. The Er:YAG laser, having a wavelength of 2.94um, is highly absorbed in both water and hydroxiapatite, leading to a very effective material for hard tissue removal by bursting off the solid tissue component that is, enamel and dentin are removed by the Er :YAG laser by water vaporization and microexplosion, without any melting of inorganic tissues. Therefore, the Er:YAG laser produced round craters with well defined margins and the surrounding tissues had no cracks and no charring. When used for cavity preparation, pulpal damage should not occur if hear buildup is minimized by careful selection of exposure parameters and by use of a water spray. The present study demonstrated that the Er:YAG laser cut the tooth substance adequately for composite resin restoration, without having undesirable side effects such as harmful effects on the pulp, discoloration or cracking etc. Also, the child patients were well cooperative during laser treatment mainly because of little noise, lesser vibration and minimal pain compared to conventional means of cavity preparation.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.7 s.172
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• pp.19-26
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• 2005

The objective of this study is to investigate the influence of process parameters, such as power of laser, cutting speed of laser and material thickness, on the practical cutting region and the kerfwidth fer the case of cutting of CSP IN sheet using high power Nd:YAC laser in continuous wave(CW) mode. In order to obtain the practical cutting region and the relationship between process parameters on the kerfwidth, several laser cutting experiments are carried out. The effective heat input is introduced to consider the influence of power and cutting speed of laser on the kerfwidth together. From the results of experiments, the allowable cutting region and the relationship between the effective heat input and kerfwidth fur the case of cutting of CSP 1N sheet using high power CW Nd:YAG laser have been obtained to improve the dimensionalaccuracyofthecutarea.

• Korean Journal of Optics and Photonics
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• v.18 no.3
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• pp.208-215
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• 2007

A fiber-coupled laser-diode pumped ceramic Nd:YAG laser for compensating the thermal tensing effect was developed. The thermal tensing effect was compensated using a convex lens, which was 25 mm away from the laser rod, with a focal length of 30 mm and an effective clear aperture of 22 mm. Without a compensator, the laser output power decreased suddenly above a pump power of 6 W. Using a compensator, the laser output power increased linearly according to the pump power. The beam propagation factor $M^{2}$ was 2.4 under a pump power of 12 W.