• Journal of the Korean Ceramic Society
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• v.31 no.3
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• pp.312-320
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• 1994

Effect of the laser shot number on the particulates density of the pulsed laser deposited YBa2Cu3O7-x thin films and the laser irradiated surface morphology of the YBa2Cu3O7-x bulk target have been investigated. Until 100 laser shots of cumulative irradiation, the films has the particulates density of ~103 mm-2. However, after 100 laser shots, the density was increased more than 10 times. This results has been explained by the change of particulate ejection path with the development of conical structure at the target surface.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.496-496
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• 2007

Low level laser has various therapy effects. This paper performed the basic study for fabricating the low level laser therapy apparatus, and one of the goals of this paper was to make this apparatus used handily. The apparatus has been fabricated using the laser diode and microprocessor unit. The apparatus used a 660nm Laser diode for blood stream improvement and was designed for a pulse width modulation type to increase stimulation effects. In result, we could get the light power of 660nm wavelength and the 1~10Hz irradiation frequency could be controlled stably.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.4
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• pp.683-693
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• 2001

The purpose of this study was to evaluate the effects of Er:YAG laser on cutting efficacy and its histologic findings. Dentin specimens of human premolars and molars were used and irradiated by Er:YAG laser with noncontact handpiece type delivery system under different treatment condition of irradiation time. Cavity pattern and volume were evaluated to determine the cutting efficacy and following results were obtained. 1. Cutting volume of sound dentin was getting larger with time immersed in water increase 2. With the condition of irradiation (150mJ, 10Hz, 30sec), surface irregularity was more increased in sound dentin comparing to carious dentin. For the light microscopic examination, dentinal tubules were opened and ash flecks and cracks were noted with inconsistence of dentinal tubules. 3. In case of 30 sec. irradiation in carious dentin, dark zone was limited to small focus whereas 1 min. irradiation, more wider, and cracks were noted in the perpendicular to direction of dentinal tubules. For the 2 min. irradiation, cavity was the widest and more cracks were found.

• Clinical and Experimental Reproductive Medicine
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• v.26 no.2
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• pp.185-192
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• 1999

The present study was performed to investigate the efficacy and safety of laser assisted hatching (AH) on mouse embryos. Non-contact $1.48{\mu}m$ diode laser system used to create a precise hole on zona pellucida. 2-cell embryos were collected from the mice (ICR) that had the coitus vaginal plug confirmed at 48 hours after hCG injection. Collected 2-cell embryos were cultured in the HTF medium supplemented with 0.4% BSA. For experiments, embryos at 8-cell stage were used after 18-22 hours in culture. After assisted hatching, the embryos were further cultured in HTF medium containing 0.1% PVP (anti-hatching system) for 3 days. For evaluate efficiency of laser on mouse embryo hatching, the effect of AH methods (acidic tyrode, pronase and laser), the number of artificial holes (1, 2 and 3 hole) and the irradiation time of laser (2, 4, 6, 8 and 10 ms) were examined. Hatching rates of laser AH group (95.2%) was significantly higher than that of control group (50.8%), but there was no differences among the laser (95.2%), acidic tyrode (100%) and pronase (98.5%) groups. Hatching rates of the number of zona pellucida opening by laser, there were no differences among the 1 hole (87.5%),2 hole (92.1%) and 3 hole (85.9%) groups. Developmental and hatching rates of embryos according to laser irradiation time were similar in the treatment groups. Therefore, these results suggest that laser AH using non-contact $1.48{\mu}m$ diode laser is a simple and accurate and effective procedure for AH. Based on these results, laser AH could be use safely for human ART program.

• Journal of the korean academy of Pediatric Dentistry
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• v.23 no.3
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• pp.640-658
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• 1996

The purpose of this study was to examine the mechanism of improving acid resistance of Nd-YAG laser irradiated tooth enamel and determine the most effective energy density for improving acid resistance. The bovine tooth enamel were lased with a pulsed Nd-YAG laser. The energy densities of exposed laser beam were varied from 10 to $70\;J/cm^2$. To investigate the degree of improving acid resistance by irradiation, all the samples were submerged to demineralize in 0.5 N $HClO_4$ solution for 1 minute. After 1 minute, 0.05 % $LaCl_3$ was added to the solution for interrupting the demineralization reaction. The amounts of dissolved calcium and phosphate in the solution were measured by using an atomic absorption spectrophotometer and the UV/VIS spectrophotometer, respectively. To examine the mechanism of improving acid resistance, X-ray diffraction analysis, infrared spectroscopy, and scanning electron microscopy were taken. The X-ray diffraction pattern of the samples were obtained in the $10^{\circ}{\sim}80^{\circ}2{\theta}$ range with $Cu-K{\alpha}$ radiation using M18HF(Mac Science Co.) with X-ray diffractometer operating at 40 KV and 300 mA. The infra-red spectra of the ground samples in 300 mg KBr pellets 10 mm diameter were obtained in the $4000cm^{-1}\;to\;400cm^{-1}$ range using JASCO 300E spectrophotometer. The scanning electron microscopy was carried out using JSM6400(JEOL Co.) with $500{\sim}2000$ times magnification. The results were as follow 1. The concentration of calcium dissolved from laser irradiated enamel with $50J/cm^2$ was significantly lesser than that of unlased control group (p<0.05) 2. From the result of the X-ray diffraction analysis, $\beta$-TCP, which increases acid solubility, was identified in lased enamel but the diffraction peaks of (002) and (004) became sharp with increasing energy density of laser irradiation. This means that the crystals in lased samples were grown through the c-axis and subsequently, the acid solubility of enamel decreased. 3. The a-axis parameter was slightly increased by laser irradiation, whereas the c-axis parameter was almost constant except for a little decrease at $50J/cm^2$. 4. In the infra-red spectra of lased enamels, phosphate bands ($600{\sim}500cm^{-1}$), B-carbonate bands (870, $1415{\sim}1455cm^{-1}$), and A-carbonate band ($1545cm^{-1}$) were observed. The amounts of phosphate bands and the B-carbonate bands were reduced, on the other hand, the amount of the A-carbonate band was increased by increase the energy density. 5. The SEM experiments reveal that the surface melting and recrystallization were appeared at $30J/cm^2$ and the cracks were observed at $70J/cm^2$. From above results, It may be suggested that the most effective energy density for improving acid resistance of tooth enamel with the irradiation of Nd-YAG laser was $50J/cm^2$. The mechanism of improving acid resistance were reduction of permeability due to surface melting and recrystallization of lased enamel and reduction of acid solubility of enamel due to decrease of carbonate content and growth of crystal.

• Biomedical Science Letters
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• v.15 no.1
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• pp.87-91
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• 2009

In photodynamic therapy (PDT), oxygen plays important role. Because of singlet oxygen which is produced by activated photosensitizer after laser irradiation of specific wavelength. The aim of this study is to find how oxygen concentration affects anticancer effect in PDT. Groups were divided into PDT with oxygen applied group and only PDT applied group. PDT with oxygen applied group supplied oxygen for 15 minute before laser irradiation. In vitro, CT-26 cell was incubated with various concentration of photofrin $(50.0{\sim}0.05{\mu}g/ml)$ and was irradiated with 632nm diode laser 6hr after application of photofrin. The cell viability of two groups was assessed by MTT assay. In vivo, CT-26 cell line was transplanted into the subcutaneous tissue of BALB/c mouse. The anticancer effect of two groups was measured by tumor volume change. In vitro study, the cell viability was significantly decreased at $1.56{\sim}3.13{\mu}g/ml$ in PDT with oxygen applied group. In vivo study, the PDT with oxygen applied group significantly higher reduction rate of tumor volume 7 days after PDT compared to PDT only group. The high oxygen concentration might enhance the anticancer effect of the photodynamic therapy.

• Korean Journal of Optics and Photonics
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• v.1 no.2
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• pp.210-216
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• 1990

This study was performed to obtain fundamental data on temperature increases in the dental tissues irradiated by IO.opm laser radiation. For this purpose a experimental facility was established. which was composed of a CO2 laser. a shutter unit and a temperature sensing device. The temperature changes in the pulp chamber of extracted molars. during and after the laser irradiation. were measured as function of laser power. the time of irradration and the thickness of the sample. An empirical formula for the maximum temperature increases, $\DeltaT_m$ was derived from the measured data as follows; $\DeltaT_m=\alphaP\Delta\tauexp(-\betad)$$ where P. $\Delta\tau$ and d are the laser power(W). irradiation time{sec) and the thickness(mm) between pulp chamber and occlusal surface. respectively. Also a theoretical calculation model based on simplified assumptions were established and the results from the calculation were compared with the measured temperature data. A fairly good agreement was obtained.obtained.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2001.07a
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• pp.104-109
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• 2001

A 355 nm (3.5 eV) neodymium:yttrium aluminum gamet laser, produced by a harmonic generator, was used to create silver metallic particles as seeds for nucleation in photosensitive glass containing Ag+ and Ce3+ ions. The pulse width and frequency of the laser were 8 ns and 10 Hz, respectively. Heat treatment was conducted at 570 C for 1 h, following laser irradiation, to produce crystalline growth, after which a LiAlSi3O8 crystal phase appeared in the laser-irradiated Li2O A1203 SiO2 glass. For the Present study, we compared the effect of laser-induced crystallization on glass crystallization with that of spontaneous crystallization by heat treatment.

• Transactions of Materials Processing
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• v.13 no.3
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• pp.268-272
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• 2004

Transparent materials such as fused silica are widely utilized in optical and optoelectronics field because of its outstanding properties, such as transparency in a wide wavelength range, strong damage resistance for laser irradiation, and high thermal and chemical stability. In this study, we made a few micro patterns on the surface of fused silica plate using laser induced wet etching. KrF excimer laser was used as a light source. There were no burrs and micro cracks on the etched surface of fused silica and the flatness of the etched surface was fairly good. We investigated the influence of etchant upon the etch rate and quality in laser induced wet etching. Pyrene-acetone solution and toluene were used as etchant. In the side of etch rate, toluene solution was better than pyrene-acetone solution. But we made in wider range of energy density using pyrene-acetone solution. But pyrene-acetone solution gave us wider window of energy density for successful micro patterning.

• International Journal of Contents
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• v.5 no.2
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• pp.16-19
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• 2009

In this paper, we concern about the distribution characteristics of surface temperature by the increment of time, diffusivity and heat flux on irradiating of a laser. The penetration depth corresponding to the induced constant heat flux or irradiated laser, is simulated by a computer algorithm. The distribution of temperature versus penetration depth for the variation of time and diffusivity is characterized at the constant heat flux and on irradiating of a laser. The temperature of constant heat flux at the fixed diffusivity or time, is decreased by the pattern of exponential function as the time t or diffusivity a is increased (a=10, 100, 1000). The temperature of constant heat flux is not changed but exponentially fixed with the increasing diffusivity and the fixed time. On the other hand, the temperature of laser at the fixed diffusivity or time is decreased linearly. Our results show that the characteristics of the simulated surface temperature in a semi-infinite solid are similar to the graphs on theoretical consideration.