• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.2
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• pp.139-147
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• 2003

In this paper we proposed system parameter values of M-ary PPM/TH(Pulse Position Modulation/Time Hopping) ultra-wideband systems having data rate of 100 Mbps for the frequency band, which is allocated by Federal Communications Commission(FCC). We also analyzed performance of the proposed system in the AWGN channels. According to the results of performance analysis, It is observed that available pulse duration is very limitative for this system. In case of constant data rate, if M and the pulse repetition numbers are increased, then the system performance is improved and the user number is decreased.

• Journal of Welding and Joining
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• v.15 no.6
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• pp.85-95
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• 1997

This study is to investigate the optimum conditions of Nd:YAG laser beam welding for Zircaloy-4 end cap closure by optical fiber transmission. Laser welding parameters which affect the penetration depth and bead width were experimentally examined using the various beam radius by the beam quality analyzer, joint geometries of end cap and the laser parameters which mean pulse width, repetition rate and pulse energy. Also, an optimum welding speed and the effect of assistant gas with varying the flow rate of He were investigated. We found that the laser average power for the end cap welding will be 230W and rotation speed must not exceed 8 RPM, the best position of focus using optical fiber with 600.mu.m will be 2 to 3mm below the surface of the material.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1781-1783
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• 2004

Flue gas from fossil fuel combustion is the main source of air pollution. It is recognized that $SO_2$ and $NO_x$, (sum of NO and $NO_2$) react with $H_2O$ and $O_2$ in atmosphere and convert precursors of acid rain. Streamer corona process using pulse power is one of the effective methods to remove these gases from stack. For this, pulse generator with 160 kV of output peak voltage, 0.3 ${\mu}s$ of pulse width and 120Hz of pulse repetition rate is developed. This paper shows the pulse compression characteristics to obtain optimum parameters for basic system design.

• Proceedings of the KIEE Conference
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• 2001.04a
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• pp.215-217
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• 2001

This paper describes an all solid-state switch pulse generator for various applications where square pulse voltage is required. The pulse generator produces various voltage pulses: voltage $5{\sim}100kV$. current $10{\sim}200A$, pulse width $1{\sim}10{\mu}sec$, repetition rate up to 500Hz. The output power is the combination of these parameters up to 10kW. It consists of a DC-DC converter and several pulse generating modules which are connected in series to obtain higher pulse voltage. Each module contains semiconductor switches (IGBT's), energy storage capacitors and control units to trigger switches. The structure and operational principle are described and the protection circuit for reliable operation is suggested. Experimental results show that the pulse generator can be used for applications with nonlinear loads.

• Proceedings of the Optical Society of Korea Conference
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• 2004.02a
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• pp.90-91
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• 2004

• Proceedings of the Korean Vacuum Society Conference
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• 2005.08a
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• pp.110-110
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• 2005

• Journal of the Korea Computer Industry Society
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• v.2 no.3
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• pp.357-362
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• 2001

For general laser power supply to control the laser power density, the secondary of the power transformer is connected to the rectifier and filter capacitor. The output of a rectifier is applied to a switching element in the secondary of the transformer. So power supply is complicated and the loss of switching is considerably. In addition, according to increasing pulse repetition rate, charged energy of energy-storage capacitor bank is not transferred sufficiently to flashlamp, and laser output efficiency decreases. In this study, we have proposed the power supply in which the SCR was turned on at the zero point of input AC voltage by the method of zero cross control(ZCC). As a result of that, The new power supply employed ZCC are simple and compact in design. And laser output efficiency increased by the 3.5$\%$ other than conventional power supply (SCADC), when a repetition rate was increased by the 10pps. In 60pps, efficiency was increased by about 20$\%$.

• Laser Solutions
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• v.14 no.4
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• pp.14-20
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• 2011

The advantage of using lasers for through silicon via (TSV) drilling is that they allow higher flexibility during manufacturing because vacuums, lithography, and masks are not required; furthermore, the lasers can be applied to metal and dielectric layers other than silicon. However, conventional nanosecond lasers have disadvantages including that they can cause heat affection around the target area. In contrast, the use of a picosecond laser enables the precise generation of TSVs with a smaller heat affected zone. In this study, a comparison of the thermal and crystallographic defect around laser-drilled holes when using a picosecond laser beam with varing a fluence and repetition rate was conducted. Notably, the higher fluence and repetition rate picosecond laser process increased the experimentally recast layer, surface debris, and dislocation around the hole better than the high fluence and repetition rate. These findings suggest that even the picosecond laser has a heat accumulation effect under high fluence and short pulse interval conditions. To eliminate these defects under the high speed process, the CDE (chemical downstream etching) process was employed and it can prove the possibility to applicate to the TSV industry.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.82-85
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• 2000

We introduce pulsed $CO_2$ laser power supply excited by half-wave rectified 60Hz AC discharge some advantage of cost and size compared to a typical pulsed power supply. AC frequency is adjusted from 10Hz to 60Hz to control laser output. In this laser, a low voltage open loop control for high voltage AC discharge circuits is employed to avoid the HV sampling or switching. The control is achieved by using a ZCS circuit and a PIC one-chip microprocessor that control the gate signal of SCR precisely. The pulse repetition rate is limited by 60Hz due to a high leakage inductance. The maximum laser output was obtained about 20W at the condition of total pressure, 18Torr and pulse repetition rate,60Hz.

• Current Optics and Photonics
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• v.4 no.3
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• pp.238-246
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• 2020

The heat distribution in crystals in a 2-㎛ acousto-optic Q-switched Tm:LuAG laser pumped by pulsed-laser-diode (pulsed-LD) intermittent-pumping technology was analyzed using COMSOL software. The thermal lensing effect of the Tm:LuAG crystal can be mitigated by pulsed-LD intermittent-pumping techniques. An experimental setup using this kind of approach achieved maximum output energy of 8.31 mJ, minimum pulse width of 101.9 ns, and highest peak power of 81.55 kW, reached at a Q-switched repetition rate of 200 Hz. It offers significant improvement of performance of the output laser beam, compared to pulsed-LD double-ended pumping technology at the same repetition rate.