• Korean Journal of Optics and Photonics
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• v.15 no.3
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• pp.263-267
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• 2004

We have investigated the characteristics of a Nd:YAG laser pumped by a cw Ti:sapphire laser. When the pumping power of the Ti:sapphire laser was 850 ㎽, the maximum output power of the Nd:YAG laser was 450 ㎽. As a result, the slope efficiency for the output power of the Nd:YAG laser was measured to be 56%. We have also investigated the characteristics of a passively Q-switched Nd:YAG laser by using a Cr$^{4+}$:YAG as saturable absorber with initial transmission of 90%. The maximum average output power of 200 ㎽ was obtained with repetition rate of 23.8 KHz and pulse width of 17.0 ns.

• Journal of the korean academy of Pediatric Dentistry
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• v.23 no.4
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• pp.954-967
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• 1996

Laser application to modify healthy permanent dentin to improve microhardness and caries resistence has been previously reported but the physical modification and ablation thresholds of carious and sclerotic dentin has yet to be identified. This study determined the energy density required by modify (physical modification threshold, PMT) and remove (ablation threshold, AT) infected carious, affected and selerotic dentin compared to healthy permanent dentin. $1{\pm}0.25mm$ thick dentin sections(n=272) from extracted human teeth were used. Smear layer was removed 0.5M EDTA for 2 minutes. Utilizing three pulsed fiberopitc delivered contact lasers with different emission wavelengths($1.06{\mu}m$=Nd : YAG, $2.10{\mu}m$=Ho : YAG and $2.94{\mu}mEr$ : YAG). The energy density($J/cm^2$) was incrementally increased and the resulting tissue interaction classified on a scale from 0-6. A minimum of 5 repetitions/energy density were completed. Light microscopy(10-25X) was used to verify the physical modification(scale=3) and ablation thresholds(scale=4) of the various forms of dentin and the data were analyzed by logistic regression at the 95 % confidence interval. PMT and AT by the laser and the dentin types were: PMT and AT was lower in infected dentin than in sound dentin for all lasers. PMT and AT induced by Nd : YAG>Ho : YAG>Er : YAG for all forms of dentin. Microhardness was increased in sound dentin at PMT. Morphology of crater examined by light microscopy showed Nd : YAG was safe and effective for removing carious dentin and Er: YAG was effective for removing sound dentin. The PMT and AT for YAG lasers are different as a function of dentin type which may be utilized for selective modification and removal of dentin.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.186-186
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• 2010

The crack behavior in the ceramic Nd:YAG at a laser-diode end-pumped Nd:YAG ceramic laser was investigated. The fracture critical temperature difference of the ceramic Nd:YAG is about $355^{\circ}C$. The fracture of the 2 at% and the 4 at.% ceramic Nd:YAG occurred more than 14.9 W and 6.9 W pump powers, respectively, under lasing conditions.

• Journal of the Korean Ceramic Society
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• v.37 no.8
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• pp.739-744
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• 2000

YAG(Y3Al5O12) as host material of YAG:Tb3+ was studied via hydrothermal synthesis of metal hydroxides. We changed the kind of mineralizer, the concentrations and process conditions in hydrothermal synthesis. As a result, we found, acicular YAG powders were obtained by the use of KOH as a mineralizer, the concentration of KOH affected the shape and size of YAG powder. Fine grained YAG were perpared by the use of NH4OH as a mineralizer and the concentration of NH4OH affected crystal phases but did not affect particle size. We could finally get the spherical looking YAG powder at 8 M NH4OH and at 35$0^{\circ}C$ for 12h. The average particle size was about 0.2${\mu}{\textrm}{m}$.

• Korean Journal of Optics and Photonics
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• v.9 no.4
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• pp.231-235
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• 1998

Passively Q-switched, laser diode(LD) end-pumped Nd:YAG laser was demonstrated by using $Cr^{4+}$:YAG as a saturable absorber. In addition , we could calculate an excitation efficiency, which is an important parameter to evaluate the pumping geometry, directly by measuring the absorbed power in Nd:YAG at threshold condition. We found that output parameters such as average power, pulse duration, and repetition rate strongly depended on the low intensity transmission of $Cr^{4+}$:YAG and driving current of lase diode. The maximum Q-switched output power of 1 W was obtained with 40 kHz repetition rate. The pulse duration was varied from 50 ns to 200 ns.

• Resources Recycling
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• v.17 no.5
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• pp.52-59
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• 2008

Sol-gel process applied in this study was carried out by chelation of metal ions and citric acid. From the results of thermal gravimetric analysis and XRD analysis of gel powder obtained through sol-gel and heat treatment, gel powders are mostly amorphous, and crystallize completely at $900^{\circ}C$, and the crystalline structure of YAG increases with increasing calcinations temperature. Since YAG prepared by sol-gel & calcinations process was porous, and the sape and size was irregular and nonuniform, the shape and size of YAG powder had to be controlled. Therefore the effects of organic materials such as ethylene glycol and surfactant on the crystalline structure of YAG powder were investigated. Polyesterification of ethylene glycol and citric acid separated reaction area of metal ions in the solution and decreased the size of YAG primary particles. The addition of Igepal 630 as surfactant formed the droplet in the solution, and increased the size of primary particles which forms the aggregate of YAG In order to obtain monodispersed YAG particles of uniform size, gel powder prepared with organic materials had to be milled before calcination. And milling process was very important for obtaining YAG of uniform size.

• Proceedings of the Optical Society of Korea Conference
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• 1998.08a
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• pp.82-83
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• 1998

• The korean journal of orthodontics
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• v.27 no.1
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• pp.141-155
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• 1997

The purpose of this study was to evaluate the effectiveness of the Nd:YAG laser and the Er:YAAG laser on etching enamel for direct bonding of orthodontic bracket. The advantages of laser etching rather than conventional acid etching are to reduce the subsurface demineralization rate, to inhibit the spillage of acid onto uninvolved ""its of enamel, and to save the clinical manipulation time involving drying, trashing and drying again. 189 freshly extracted human premolars were prepared for this research. 165 out of them were divided into 11 groups of 15 teeth. One group was acid etching and the rest groups were irradiated with Nd:YAG laser by four different energy levels(100mj 10pps, 100mj 20pps, 150mj 20pps, 200mj 20pps) and with Er:YAG laser by six different energy levels(60mj 5pps, 60mj 10pps, 100mj 10pps. 200mj 10pps, 200mj l5pps, 400mj 10pps). Shear bond strength was tested with Instron after 24 hours, one week, and three weeks. Twenty-four out of 189 teeth were divided into twelve groups untreated control, acid etching, and ten laser irradiation subgroups. And the ultrastructural enamel surfaces of each group were observed with scanning electron microscope. The results were as follows; 1. The means and the standard deviations of shear bond strength of Nd:YAG and Er:YAU laser irradiation by different energy levels were obtained. 2. Shear bond strengths of Er:YAG laser irradiation groups were higher than those of Nd:YAG laser irradiation groups at the identical energy level. 3. Maximum bond strengths was achieved at the energy of I50mj, 20pps in Nd:YAG laser irradiation groups or 60mj, 10pps in Er:YAG laser irradiation groups. 4. It was acceptible for direct bonding to irradiate lb0mj 20pps with Nd:YAG laser or to irradiate 60mj 10pps with Er:YAG laser considering the results of shear bond strength tests and SEM obsesvation.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.3
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• pp.439-447
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• 2003

This was performed to evaluate the inhibitory effect of laser on the growth of S. mutans. The bacterial pallets containing S. mutans KCTC 3065 were irradiated with Er:YAG laser and Nd :YAG laser by non-contact method at an intensity of 50mJ for 5 sec with the pulse repetition rates of 10Hz and 30Hz, respectively. The following results were obtained on colony count, acid producing ability, and the amount of insoluble extracellular polysaccharide synthesis. 1. The irradiation of Nd:YAG laser after photosensitization with Chinese ink inhibited the proliferation of S. mutans the most, and the irradiation of Er:YAG also inhibited the proliferation. However, the irradiation of Nd:YAG laser alone could not inhibited the proliferation of S. mutans. The pulse repetition rate did not affect significantly on the proliferation of bacteria in overall. 2. The irradiation of Nd:YAG laser after the photosensitization with Chinese ink inhibited the acid production of S. mutans the most for a certain period of time. Er:YAG laser also inhibited acid production. When Nd:YAG laser was used alone, the acid production of S. mutans was not been inhibited. The irradiation of Nd:YAG laser after photosensitization with Chinese ink inhibited the acid production ability of bacteria the most as the pulse repetition rate increased. 3. Laser irradiation did not inhibited the synthesis of insoluble extracellular polysaccharide of S. mutans. From these results, we conclude that the irradiation of Er:YAG laser and Nd:YAG laser after photosensitization with Chinese ink would inhibit the proliferation and acid production by S. mutans, which may prevent dental caries. However, this effect does not last long time so that the laser irradiation should be repeated frequently in order to obtain clinical effect; thus, this laser irradiation would not have a clinical usefulness in preventing dental caries when used solely.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.5
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• pp.212-217
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• 2021

The applicability of the white LED from the blue LED of the coating film as a binder for surface and curved coatings were confirmed. The particle size of YAG is D₅₀: 9~10 ㎛, and the crystal structure is garnet (Y₃Al₅O₁₂), cubic. The coating film had no cracks, at the same time, the silica sol was uniformly coated with YAG phosphor, and the YAG content and thickness in the coating film showed a tendency to increase up to 40 ㎛ in proportion to the increase in the amount added. Furthermore, as the YAG content increased, the PL emission intensity increased and the color coordinate shift toward the end of the chromatic locus curve was confirmed.