• Title, Summary, Keyword: Laser Power

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Development of a pulsed Nd:YAG laser materials processing system (정밀 용접용 펄스형 Nd:YAG 레이저 가공기 개발)

  • 김덕현;정진만;김철중;이종민
    • Journal of Welding and Joining
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    • v.9 no.1
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    • pp.32-39
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    • 1991
  • A 200W pulsed Nd: YAG laser for fine welding was developed. The important laser parameters such as laser peak power, average power, pulse width, and pulse energy for welding were studied. In order to obtain the sufficient laser power density for welding, thermal lensing effects were analyzed and a laser resonator with laser beam divergence was designed. The power supply unit was designed to support up to 7kW input. The pulse control unit was developed using a GTO thyristor and could control over 100kW input power to obtain 3.5kW peak power laser. Also due to the GTO thyristor the pulse width could be varied continuously from 0.1 to 20 msec and maximum repetition rate was as high as 300pps.

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Effects of laser power on hardness and microstructure of the surface melting hardened SKD61 hot die steel using Yb:YAG disk laser (Yb:YAG 디스크로 레이저 표면 용융 경화된 SKD61 열간금형강의 경도와 미세조직에 미치는 레이저 출력의 영향)

  • Lee, Kwang-Hyeon;Choi, Seong-Won;Kang, Chung-Yun
    • Journal of Welding and Joining
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    • v.33 no.3
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    • pp.54-61
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    • 2015
  • In this study, effect of laser power on hardness and microstructure of SKD61 Hot Die steel of which surface was melted and hardened with Yb:YAG disk laser was investigated. Beam speed was fixed at 70 mm/sec and distance between them was 0.8 mm about Laser surface melting. The only thing that was changed laser power. Laser powers were 2.0, 2.4 and 2.8 kW. No defect was found under all conditions. As the laser power increased, the penetration depth were deepened and the bead width was also widened. There was no hardness deviation of fusion zone at same laser power and it was higher than that of heat affected zone. In addition, the more laser power increased, the more hardness in fusion zone decreased. Fusion zone was macroscopically dendrite structure. However, core matric in dendrite was lath martensite of 100 nm size. There were $M_{23}C_6$ of 500 nm and the VC and $Mo_2C$ of a nano meters on boundary of dendrite.

Development of CO Laser-Arc Hybrid Welding Process

  • Lee, Se-Hwan
    • Journal of Korean Society of Laser Processing
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    • v.5 no.3
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    • pp.15-20
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    • 2002
  • The principal obstacle to selection of a laser processing method in production is its relatively high equipment cost and the natural unwillingness of production supervision to try something new until it is thoroughly proven. The major objective of this work is focused on the combined features of gas tungsten arc and a low-power cold laser beam. In this work, the laser beam from a 7 watts carbon monoxide laser was combined with electrical discharges from a short-pulsed capacitive discharge GTA welding power supply. When the low power CO laser beam passes through a special composition shielding gas, the CO molecules in the gas absorbs the radiation, and ionizes through a process blown as non-equilibrium, vibration-vibration pumping. The resulting laser-induced plasma(LIP) was positioned between various configurations of electrodes. The high-voltage impulse applied to the electrodes forced rapid electrical breakdown between the electrodes. Electrical discharges between tungsten electrodes and aluminum sheet specimens followed the ionized path provided by LIP. The result was well-focused melted spots.

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A Unified Analysis of Low-Power and High-Power Density Laser Welding Processes with Evolution of Free Surface (자유표면변형을 고려한 저에너지밀도 및 고에너지밀도 레이저 용접공정 통합 해석)

  • Ha Eung-Ji;Kim Woo-Seung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.10
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    • pp.1111-1118
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    • 2005
  • In this study, a unified numerical investigation has been performed on the evolution of weld pool and key-hole geometry during low-power and high-power density laser welding. Unsteady phase-change heat transfer and fluid flow with the surface tension are examined. The one-dimensional vaporization model is introduced to model the overheated surface temperature and recoil pressure during high-power density laser welding. It is shown that Marangoni convection in the weld pool is dominant at low-power density laser welding, and the keyhole with thin liquid layer and the hump are visible at high-power density laser welding. It is also shown that the transition from conduction welding to penetration welding fur iron plate exists when the laser power density is about $10^6W/Cm^2$.

A Study on the Output Stabilization of the Nd:YAG Laser by the Monitoring of Capacitor Charging Voltage

  • Noh, Ki-Kyong;Song, Kum-Young;Park, Jin-Young;Hong, Jung-Hwan;Park, Sung-Joon;Kim, Hee-Je
    • KIEE International Transactions on Electrophysics and Applications
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    • v.4C no.3
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    • pp.96-100
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    • 2004
  • The Nd: YAG laser is commonly used throughout many fields such as accurate material processing, IC marking, semiconductor annealing, medical operation devices, etc., due to the fact that it has good thermal and mechanical properties and is easy to maintain. In materials processing, it is essential to vary the laser power density for specific materials. The laser power density can be mainly controlled by the current pulse width and pulse repetition rate. It is important to control the laser energy in those fields using a pulsed laser. In this paper we propose the constant-frequency current resonant half-bridge converter and monitoring of capacitor charging voltage. This laser power supply is designed and fabricated to have less switching loss, compact size, isolation with primary and secondary transformers, and detection of capacitor charging voltage. Also, the output stabilization characteristics of this Nd: YAG laser system are investigated. The test results are described as a function of laser output energy and flashlamp arc discharging constant. At the energy storage capacitor charges constant voltage, the laser output power is 2.3% error range in 600[V].

Pulse Laser Power Stabilization Using PID Control Method (PID 제어기법을 이용한 펄스 레이저 출력 안정화에 관한 연구)

  • Ryoo, Hoon-Chul;Kwak, Seung-Woo;Kang, Dong-Won;Kim, Kyoung-Sik;Hahn, Jae-Won
    • Journal of Korean Society of Laser Processing
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    • v.9 no.2
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    • pp.17-22
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    • 2006
  • In this study, PID control method was applied to decrease the power fluctuation of the pulse laser which is one of the major processing variables in laser machining process. To stabilize the power fluctuation of the pulse laser, we averaged 10 pulse outputs of Nd:YAG laser operating in 10Hz using boxcar averager, and with taking this averaged output as an input signal, we conducted PID control using optical attenuator which is consisted of half wave plate attached on the stepping motor and polarizer. When PID control was not enabled, the power fluctuation was 4.71% and with PID control, the power fluctuation was 1.86% for 2 hours and 1 hour respectively. As a result, we stabilized the power fluctuation of the pulse laser by 60.5%

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Pulse Laser Power Stabilization Using PID Control Method (PID 제어기법을 이용한 펄스 레이저 출력 안정화에 관한 연구)

  • Ryu, Hoon-Chul;Kwak, Seung-Woo;Kang, Dong-Won;Kim, Kyoung-Sik;Hahn, Jae-Won
    • Proceedings of the Korean Society of Laser Processing Conference
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    • pp.89-96
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    • 2006
  • In this study, PID control method was applied to decrease the power fluctuation of the pulse laser which is one of the major processing variables in laser machining process. To stabilize the power fluctuation of the pulse laser, we averaged 10 pulse outputs of Nd:YAG laser operating in 10Hz using boxcar averager, and with taking this averaged output as an input signal, we conducted PID control using optical attenuator which is consisted of half wave plate attached on the stepping motor and polarizer. When PID control was not enabled, the power fluctuation was 4.71% and with PID control, the power fluctuation was 1.86% for 2 hours and 1 hour respectively. As a result, we stabilized the power fluctuation of the pulse laser by 60.5%

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Optimization of Diode-pumped Cesium Vapor Laser Using Frequency Locked Pump Laser

  • Hong, Seongjin;Kong, Byungjoo;Lee, Yong Soo;Oh, Kyunghwan
    • Current Optics and Photonics
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    • v.2 no.5
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    • pp.443-447
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    • 2018
  • We propose a diode-pumped cesium laser using frequency locking of a pump laser that can effectively increase the maximum output power of the cesium laser. We simultaneously monitored the absorption spectrum of cesium and the laser output power, and the frequency of pump laser was locked at the center of the $D_2$ absorption line of the cesium atom to obtain an effective gain enhancement. Using this scheme, we have achieved output power increase of ~0.1 W compared to when frequency locking was not applied. Furthermore, by optimizing the temperature of the cesium cell and the reflectivity of the output coupler, we successfully achieved an output power of 1.4 W using the pump power of 2.9 W, providing a slope efficiency of 61.5% and optical-to-optical efficiency of 49%.

Optimization of a Passively Q-switched Yb:YAG Laser Ignitor Pumped by a Laser Diode with Low Power and Long Pulse Width

  • Kim, Jisoo;Moon, Soomin;Park, Youngin;Kim, Hyun Su
    • Current Optics and Photonics
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    • v.4 no.2
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    • pp.127-133
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    • 2020
  • We successfully constructed a passively Q-switched Yb:YAG laser ignitor pumped by a diode laser with low power and long pulse width. To the best of our knowledge, this is the first study to achieve a quasi-MW output power from an optimized Q-switch Yb:YAG laser ignitor by using a pumping diode laser module emitting at under a power of 23 W. The output pulse energy of our optimized laser is 0.98 mJ enclosed in a 1.06 ns pulse width, corresponding to a peak power of 0.92 MW.

All-fiber Tm-Ho Codoped Laser Operating at 1700 nm

  • Park, Jaedeok;Ryu, Siheon;Yeom, Dong-Il
    • Current Optics and Photonics
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    • v.2 no.4
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    • pp.356-360
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    • 2018
  • We demonstrate continuous-wave operation of an all-fiber thulium-holmium codoped laser operating at a wavelength of 1706.3 nm. To realize laser operation in the short-wavelength region of the emission-band edge of thulium in silica fiber, we employ fiber Bragg gratings having resonant reflection at a wavelength around 1700 nm as a wavelength-selective mirror in an all-fiber cavity scheme. We first examine the performance of the laser by adjusting the central wavelength of the in-band pump source. Although a pump source possessing a longer wavelength is observed to provide reduced laser threshold power and increased slope efficiency, because of the characteristics of spectral response in the gain fiber, we find that the optimal pump wavelength is 1565 nm to obtain maximum laser output power for a given system. We further explore the properties of the laser by varying the fiber gain length from 1 m to 1.4 m, for the purpose of power scaling. It is revealed that the laser shows optimal performance in terms of output power and slope efficiency at a gain length of 1.3 m, where we obtain a maximum output power of 249 mW for an applied pump power of 2.1 W. A maximum slope efficiency is also estimated to be 23% under these conditions.