• Proceedings of the Korean Society of Laser Processing Conference
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• 2005.11a
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• pp.42-45
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• 2005

• Journal of the Korean Magnetics Society
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• v.15 no.6
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• pp.320-324
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• 2005

The core loss of $3\%$ SiFe is strongly dependent on silicon content, impurities, permeability, and domain structure of the SiFe. Domain refining has been proved to be very good method for reduction of core loss in high permeability grain oriented SiFe, and laser scribing is well-blown as an effective and industrially important method of domain refinement. In this work, magnetic domain refinement has been carried out by using a pulsed Nd : YAG laser, and the core losses have been measured and analyzed to and optimal parameters of the laser treatment. The laser hem was focused with a spot size of $100{\mu}m$ and pulse energy of 10${\~}$35mJ and the lines were scribed with a period of ${\~}$5mm. The core loss was improved up to $17\%$ with 30 ns-Nd : YAG laser beam in $3\%$ SiFe.

• 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 Oral Medicine and Pain
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• v.20 no.2
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• pp.327-334
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• 1995

In order to observe the influence of pulsed Nd:YAG laser at its out-of-contact with dentin on tooth temperature, we have applied pulsed Nd:YAG laser to 2mm thick dentin sample at a point of contact and from a distance of 1mm, 2mm, 3mm and 4mm with an energy of 0.3W, 0.5W, 0.8W, 1.5W and 2.0W. They were exposed to periods of 3 seconds, 6 seconds, 9 seconds and 15 seconds respectively and measured temperature changes. The results as follows : 1. When the time ad intensity of power were constant, the temperature changes on dentin of tooth depended on the distance. The temperature increased when the laser intensity increased bu two other conditions were contact. 2. At the point of contact, the temperature has risen over $5^{\circ}C$ regrdless of intensity of the power or the time. However, there was $5^{\circ}C$ fluctuation with 0.3 W for 3 seconds treatment. 3. The temperature change was less than $5^{\circ}C$ thermal change at the distance of 1mm and 2mm respectively when lased for 3 seconds, 6 seconds, 12 seconds and 15 seconds with 0.3 W. Similar results were observed at 3 and 6 seconds treatment with 0.5 W and at 3 seconds treatment with 0.8 and 1.0W respectively. 4. It showed less than 5(C thermal change when lased for 3 seconds, 6 seconds, 9 seconds, 12 seconds and 15 seconds with 0.3W at the distance of 3mm and 4mm. The same results were seen in 3 seconds, 6 seconds and 9 seconds treatment with 0.5W and in 3 seconds with 0.8W and 1.0W respectively. As we have seen the above, the results has indicated that pulsed Nd:YAG lasing at its off contact on dentin of 2mm thickness will not cause irreversible changes if lasing intensity, lasing distance and lasing time are appropriate.

• Restorative Dentistry and Endodontics
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• v.28 no.1
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• pp.50-56
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• 2003

The purpose of this study was to evaluate the effects of EDTA and pulsed Nd :YAG laser on apical leak-age of canal obturation. Forty-eight single-rooted teeth were used in this study. The teeth were instrumented up to a size 40 K-file and irrigated with 2.5% NaOCl between each fie size. And the teeth were divided into 4 groups. In group A, the root canals were irrigated with a final flush of 5ml 2.5% NaOCl as a control group. The teeth in group B were irrigated with a final flush of 5ml 17% EDTA. The teeth in group C and D were irradiated by pulsed Nd：YAG laser(laser parameters were set at 1W, 100mJ, 10Hz, and 2W, 100mJ, 20Hz respectively). The results were as follows : 1. Apical leakage was observed in 50% of samples in group A, 30% of samples in group B, 20% of samples in group C, and 10% of samples in group D. 2. The teeth in group B had less leakage than group A, but there was no statistically significant differences(p＞0.05). 3. The teeth in group C, D had less leakage than group A, and there was statistically significant differences(p＜0.05). 4. The teeth in group C, D had less leakage than group B, but there was no statistically significant differences(p＞0.05). 5. There was no significant differences in apical leakage between group C and group D(p＞0.05).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.652-655
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• 2001

In this paper, I have studied minimization of the kerf-width and surface burning which are occurred after the singulation process of multi layer $\mu$-BGA( thickness 1.1 mm, 0.9 mm) with a pulsed Nd:YAG( = 532 nm, repetition rate = 10 Hz) laser. The thermal energy of a pulsed Nd:YAG laser is used to cut the copper layer. I have studied are minimization of the surface burning and kerf-width using a photo resist, $N_2$blowing and polyester double sided tape as a cutting parameter. The $N_2$blowing reduces a laser energy loss by debris and suppresses a surface carbonization. Also, I have studied characters of cutting with a choice of side of laser beam incidence. The SEM(Scanning Electron Microscope), non-contact 3D inspector and high-resolution microscope are used to measure kerf width and surface state. The optimum value of 1.1 mm $\mu$-BGA singulation is 524 $\mu$m that is reduced kerf width of 60 % with $N_2$blowing. And I obtained reduction of carbonization of 68 % with a polyester double side tape in 0.9 mm $\mu$-BGA. I used laser intensity of 1.91$\times$10$^{6}$ / $\textrm{cm}^2$ in this study.

• Journal of Welding and Joining
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• v.20 no.4
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• pp.525-534
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• 2002

During laser spot welding of the braun tube electron gun, phenomena such as serious spattering and oxidative reaction, etc. were occurred. The spatter occurred from weld pool affects the braun tube, namely it blocks up a very small hole on the shadow mask and causes short circuit between two roles of the electron gun. We guessed that high power density and oxidative reaction are main sources of these problems. So, we studied to prevent and to reduce spatter occurring in spot welding of the braun tube electron gun using pulsed Nd:YAG laser. The characteristics of laser output power was estimated, and the loss of laser energy by optical parameter and spatter was measured by powermeter. The effects of welding parameters, laser defocused distance and incident angle, were investigated on the shape and penetration depth of the laser welded bead in flare and flange joints. From these results, the laser peak power was a major factor to control penetration depth and to occur spatter. It was found that the losses of laser energy by optic parameter and sticked spatter affect seriously laser weldability of thin sheets. The deepest penetration depth is gotten on focal position, and a "bead transition" occurred with a slight displacement of focal position relative to the workpiece surface and the absorption rate of the laser energy is affected by the shape factor of the workpiece. When we changed the incident angle of laser beam, the penetration depth was decreased a little with increasing of the incident angle, and the bead width was increased. The spattering was prevented by considering laser beam energy and incident angle.ent angle.

• Journal of Electrical Engineering and Technology
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• v.6 no.2
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• pp.275-279
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• 2011

Sterilization of Escherichia coli (E. coli) is examined using a unique pulsed ultra-violet (UV) elliptical reactor based on Nd:YAG laser resonator, UV radiation from a pulsed xenon flashlamp. The light from the discharge has a broadband emission spectrum extending from the UV to the infrared region with a rich UV contained. Sterilization method by using the UV light is fast, environment-friendly and it does not cause secondary pollution. A Nd:YAG laser resonator having elliptical shape has advantage of concentrating the radiation of the UV light at two foci as the quart sleeve filled with E. coli. The primary objective of this research is to determine the important parameters such as pulse per second (pps), the applied voltage for sterilizing E. coli by using an UV elliptical reactor. From the experiment result, the sterilization effect of UV elliptical reactor is better than that of UV cylindrical reactor, and it can be 99.9% of sterilization at 800V regardless of the pps within 10 minutes.

• Journal of Oral Medicine and Pain
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• v.25 no.4
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• pp.403-411
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• 2000

The authors experienced a non-painful, elevated, dome-shaped lesion on lower lip in Korean male of 22-year-old and a non-painful, elevated, dome-shape lesion on left side of mouth floor in Korean female of 36-year-old. And diagnosed the lesions as a mucocele and a ranula respectively, based on the comprehensive evaluation of data obtained from history taking, clinical and radiologic examination and histopathological findings. In these cases, the authors removed mucocele and ranula using the pulsed Nd:YAG laser with advantage of good hemostatic effect, and so we could minimize improper tissue destruction during operation. The excisional wounds of lower lip and mouth floor had a good healing process without any symptom of pain and any signs of bleeding and infection.

• Korean Journal of Optics and Photonics
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• v.13 no.1
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• pp.70-72
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• 2002

Amplified pulsed laser beam with narrow linewidth was generated from CW laser beam with narrow linewidth by using frequency doubled Nd:YAG laser beam and Bethune cell. The degree of the frequency chirping of the amplified pulse laser was measured by using the heterodyne method and obtained by calculating instantaneous phase change from heterodyne beating signals. The frequency chirping of amplified pulsed laser beam from CW laser beam with sub-MHz linewidth by 10 ns pulse was 80 MHz so that pulsed laser beam with very narrow linewidth was obtained.