• Journal of the Optical Society of Korea
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• 제13권1호
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• pp.80-85
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• 2009

An experimental study of energy absorption and x-ray emission from ultrashort laser pulse irradiation of in-situ produced solid clusters has been performed. Silver clusters produced by a 30 mJ, 300 ps laser pulse were irradiated up to an intensity of $3{\times}10^{17}\;W/cm^2$ by a 70 mJ, 45 fs compressed laser pulse from the same Ti:sapphire laser. Absorption of the laser light exceeding 70% was observed, resulting in an x-ray yield (>1 keV) of ${\sim}60{\mu}J$ pulse. This may constitute a much simpler means of intense x-ray generation using ultrashort laser pulses as compared to the irradiation of structured / pre-deposited cluster targets, and it offers higher x-ray conversion efficiency than that from gas clusters and planar solid targets.

• Nuclear Engineering and Technology
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• 제37권3호
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• pp.279-286
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• 2005

A prototype of a relativistic proton generation system, based on laser-induced plasma interaction, has been designed and fabricated. The system is composed of three major parts: a fs TW laser; a target chamber, including targets and controls; and a diagnostic system for charged particles and lasers. An Offner-type pulse stretcher for chirped pulse amplification (CPA) and eight pass pre-amplifier are installed. The main amplifier will be integrated with a new pumping laser. The design values of the laser at the first stage are 1 TW in power and 50 fs in pulse duration. We expect to generate protons with their maximum energy of approximately 3 MeV and the flux of at least $10^6$ per pulse using a 10 $\mu$m Al target. A prototype target chamber with eight 8-inch flanges, including target mounts, has been designed and fabricated. For laser diagnostics, an adaptive optics based on the Shack-Hartmann type, beam monitoring, and alignment system are all under development. For a charged particle, CR-39 detectors, a Thomson parabola spectrometer, and Si charged-particle detectors will be used for the density profile and energy spectrum. In this paper, we present the preliminary design for laser-induced proton generation. We also present plans for future work, as well as theoretical simulations.

• Journal of Periodontal and Implant Science
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• 제41권5호
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• pp.234-241
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• 2011

Purpose: One of the most frequent complications related to dental implants is peri-implantitis, and the characteristics of implant surfaces are closely related to the progression and resolution of inflammation. Therefore, a technical modality that can effectively detoxify the implant surface without modification to the surface is needed. The purpose of this study was to evaluate the effect of erbium-doped: yttrium, aluminium and garnet (Er:YAG) laser irradiation on the microstructural changes in double acid-etched implant surfaces according to the laser energy and the application duration. Methods: The implant surface was irradiated using an Er:YAG laser with different application energy levels (100 mJ/pulse, 140 mJ/pulse, and 180 mJ/pulse) and time periods (1 minute, 1.5 minutes, and 2 minutes). We then examined the change in surface roughness value and microstructure. Results: In a scanning electron microscopy evaluation, the double acid-etched implant surface was not altered by Er:YAG laser irradiation under the condition of 100 mJ/pulse at 10 Hz for any of the irradiation times. However, we investigated the reduced sharpness of the specific ridge microstructure that resulted under the 140 mJ/pulse and 180 mJ/pulse conditions. The reduction in sharpness became more severe as laser energy and application duration increased. In the roughness measurement, the double acid-etched implants showed a low roughness value on the valley area before the laser irradiation. Under all experimental conditions, Er:YAG laser irradiation led to a minor decrease in surface roughness, which was not statistically significant. Conclusions: The recommended application settings for Er:YAG laser irradiation on double acid-etched implant surface is less than a 100 mJ/pulse at 10 Hz, and for less than two minutes in order to detoxify the implant surface without causing surface modification.

• 한국광학회지
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• 제26권6호
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• pp.318-321
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• 2015

We demonstrate a frequency-resolved optical grating (FROG) device for measuring the intensity and phase versus time of several-tens-of-picoseconds laser pulses, using a thick nonlinear optical crystal. The huge pulse-front tilt generated by a holographic grating increases the temporal range of the device, which can make a single-shot measurement of laser pulses less than 100 ps in duration. To verify the measurement technique, we generate double pulses using a Michelson interferometer. The measured duration of a single pulse is about 300 fs and the measured maximum delay of two pulses is 60 ps, which implies that the proposed FROG device can measure laser pulses with maximum pulse width of about 120 ps.

• Journal of the Optical Society of Korea
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• 제19권2호
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• pp.130-135
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• 2015

Based on the extended nonlinear Schr$\ddot{o}$dinger equation, the influences of the filter effect on pulse splitting in a passively mode-locked erbium-doped fiber laser with positive dispersion cavity are investigated theoretically. Numerical results show that, as the bandwidth of the spectral filter decreases, the nonlinear chirp appended to the pulse increases under the combined action of the filter effect of the super-Gaussian spectral filter and the self-phase modulation effect. On further decreasing the bandwidth, the wave breaking of the pulse takes place. In addition, by varying the pump power of the laser or the profile of the spectral filter, the influences of the filter effect on pulse splitting also change accordingly.

• 한국광학회지
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• 제20권1호
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• pp.34-40
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• 2009

$MgF_2$, $SiO_2$ 및 ZnS 박막을 물리 증기 증착하는 동안 펄스 레이저(Nd-YAG, 제2고조파 532 nm)로 Annealing 하여 표면 거칠기 특성을 개선하였다. 펄스 반복율이 10 Hz, 펄스폭 5 ns, 파장 532 nm인 펄스레이저로 Annealing한 유리 기판에 증착된 $MgF_2$와 $SiO_2$ 시료들은 레이저 에너지가 $140\;mJ/cm^2$ 경우에 산란 총량 값이 최소가 되었지만, ZnS 박막의 경우에는 Annealing 레이저광 에너지가 $62\;mJ/cm^2$일 때 산란 총량이 최소값을 나타냈다. AFM을 사용하여 박막시료의 표면 거칠기에 대한 펄스 레이저 Annealing 효과를 측정 하였다. 그 결과는 TIS 측정치와 유사 하여 표면 거칠기는 Annealing 하기위해 조사된 레이저 에너지에 의존 하여 감소하였다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권5호
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• pp.190-197
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• 2005

A reliable and compact pulse power supply using a thyratron and a magnetic pulse compression (MPC) circuit was developed for a metal vapor laser. The life time of the pulse power supply is expected to be much longer than that of a conventional thyratron-discharge type pulse power supply. A thyratron generated a long pulse of its conduction pulse width 500 ns and then it was compressed to less than 80 ns of its output voltage rise time by a three stage MPC circuit. This pulse power supply was applied to a laser plasma tube of 30 mm inner diameter and 1.5 m discharge length. It was operated several hundreds hours without any troubles.

• 한국정밀공학회지
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• 제27권11호
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• pp.17-23
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• 2010

Titanium alloy is one of the hard processing materials made by the traditional manufacturing method because of the excellent mechanical strength. Ablation of titanium alloy is investigated by using a femtosecond laser which is a regenerative amplified Ti:sapphire laser with 1kHz repetition rate, 184fs pulse duration time and 785nm wavelength. Experiments are carried out under various ablation conditions with different pulse overlap ratios for the rectangular shape and micro hole. Test results show that the ablation characteristic according to pulse overlap ratio of titanium alloy seems to be as non-linear type at the different zone of energy fluence. The optimal condition of rectangular shape processing is obtained at the laser peak power 1.3mW, pulse overlap ratio of 90%, beam gap of $1\;{\mu}m$. The micro hole has a good quality from the pulse overlap ratio of 99% at the same laser peak power. With the optimal processing condition, the fine rectangular shape and micro hole without burr and thermal damage are achieved.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권9호
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• pp.541-545
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• 2000

We propose a pulsed $CO_2$laser below 30W by the AC(60Hz) switching control of leakage transformer primary which has some advantages of cost and size compared to a typical pulsed power supply. Pulse repetition rate is adjusted from 5 Hz to 60 to Hz control laser output. In this laser a low voltage open loop control for high voltage pulse discharge circuit is employed to aviod the Hv sampling or switching and high voltage leakage transformer is used to convert low voltage pulse rectified from AC to high voltage one. A ZCS(Zero Crossing Switch) circuit and a PIC(programble one-chip microprocessor are used to control gate signal of SCR precisely. The pulse repetition rate is limited by 60Hz due to the frequency of AC line and a high leadkage inductance. The maximum laser output was about 23 W at pulse repetition rate of 60Hz total gas mixture of $CO_2$ : $N_2$ : He=1: 9: 15 and total pressure of 18 Torr

• Journal of the Optical Society of Korea
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• 제7권3호
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• pp.135-138
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• 2003

A chirped-pulse amplification femtosecond Ti:sapphire laser operating at 1 KHz has been developed. The laser system consisted of a long-cavity femtosecond oscillator, a four-pass grating pulse stretcher, two multi-pass amplifiers and a double-pass grating pulse compressor. Thermal lensing at the amplifiers was reduced by cooling Ti:sapphire crystals using Peltier coolers. Gain narrowing and residual phase errors were compensated for by the use of an acousto-optic pulse shaper. The final laser output had an energy per pulse of 2.0 mJ and a pulse duration of 19.5 fs, reaching 0.1 TW at 1 KHz.