• Proceedings of the KWS Conference
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• 2002.10a
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• pp.561-569
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• 2002

Laser has been called a "Quantum Machine" because of its mechanism of generation since the development on July 7,1960.by T.H.Maiman. We can now use this machine as a tool for manufacturing in industries. At present, 45kW CO2 laser, 10kW Nd:YAG laser, 6kW LD pumped YAG laser and 4kW direct diode laser facilities are available for welding a heavy steel plate of 40mm in thickness and for cutting metals at high speed of 140m/min. Laser Materials Processing is no longer a scientific curiosity but a modern tool in industries. Lasers in manufacturing sector are currently used in welding, cutting, drilling, cladding, marking, cleaning, micro-machining and forming. Recently, high power laser diode, 10kW LD pumped YAG laser, 700W fiber laser and excimer laser have been developed in the industrialized countries. As a result of large numbers of research and developments, the modem laser materials processing has been realized and used in all kinds of industries now. In the present paper, metallurgical studies on laser materials processing such as porosity formation, hot cracking and the joint performances of steels and aluminum alloys and dissimilar joint are discussed after the introduction of laser facilities and laser applications in industries such as automotive industry, electronics industry, and steel making industry. The wave towards the use of laser materials processing and its penetration into many industries has started in many countries now. Especially, development of high power/quality diode laser will be accelerate the introduction of this magnificent tool, because of the high efficiency of about 50%, long life time and compact.

• Korean Journal of Optics and Photonics
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• v.10 no.4
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• pp.311-317
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• 1999

Unidirectional single-mode operation of a diode-pumped Nd:YAG laser with a planar semimonolithic ring cavity has been demostrated at 1064 nm. The semimonolithic cavity consists of a laser active medium placed in a magnetic field, a crystal quartz plate, and an output coupling mirror. They form an optical diode by acting each part as a Faraday rotator, a reciprocal polarization rotator and a partial polarizer, respectively. An eigenpolarization theory for the cavity configuration was presented and losses for the eigenmodes were calculated. A pump-limited single-mode output power of 155 mW and a slope efficiency of 17% were obtained when the laser was pumped by a 1.2 W, 809 nm diode-laser. A laser linewidth of less than 100 kHz is inferred from a beat note frequency spectrum between two identical laser systems and continous single-mode tuning range was more than 2 GHz.

• Current Optics and Photonics
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• v.2 no.6
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• pp.582-588
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• 2018

A $Nd:YVO_4$ laser dual-end-pumped by a wavelength-locked 878.6 nm laser diode is presented. At the repetition rate of 500 KHz, the absorbed pump power of 58 W, an output power of 26.1 W at 1064 nm is obtained, corresponding to an optical-optical efficiency of 45%. The pulse width is 44.2 ns. Meanwhile, the effects of traditional 808 nm pumping and 878.6 nm dual-end-pumping on the output laser beam quality and pulse width are compared and analyzed in an experiment.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.365-368
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• 2001

입사면에서 발생하는 열을 효율적으로 제거하기 위하여 Yb:YAG 결정의 표면에 sapphire 창을 부착하여 레이저를 발진 시켰다. Yb:YAG 결정에서 발생하는 열이 sapphire 창을 통하여 구리판으로 전달되는 경우 와 Yb:YAG 결정의 측면에서 냉각하는 경우의 레이저 출력을 측정하여 각각의 레이저 발진 특성을 비교하여 보았다. 여기면을 sapphire 창으로 냉각하는 micro-chip Yb:YAG 레이저의 레이저 에너지 전환 효율은 38%였으며 레이저 발진 문턱값은 4 kw/mm$^2$, slope efficiency는 56%로 측정되었다. Sapphire 창을 사용하는 경우 표면에서의 열전달도는 10 W/mm$^2$이상으로 관측되었다. Yb:YAG의 도핑율, 출력경의 반사율 등을 레이저 변수를 최적화할 경우 같은 구조에서 50 W급 레이저도 발진 가능할 것으로 예상된다.

• Current Optics and Photonics
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• v.4 no.1
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• pp.63-68
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• 2020

We built an optical parametric oscillator (OPO) generating orthogonally polarized signals at different wavelengths simultaneously, based on a periodically poled lithium niobate (PPLN) crystal. The OPO was pumped by ns-pulses at 1.064 ㎛ from a diode-pumped solid-state laser, where we found the type-0 and the type-1 quasi-phase matching conditions were satisfied simultaneously in the PPLN crystal. This enabled us to create a coherent light source which can emit dual signals which could be accessed easily by rotating a polarizer.

• The Optical Journal
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• s.100
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• pp.26-29
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• 2005

레이저 가공기 세계시장은 2010년에 약 70억 달러 이상의 규모가 예상되고 고출력 CW 고체 레이저 시장은 2010년까지 매년 약 30%의 성장이, 펄스레이저 시스템 및 레이저마킹기 시장는 연간 10% 이상의 성장을 예상하고 있다. 반면, 세계 레이저 발진기의 시장에서 CO2 레이저의 경우 시장의 규모가 작아져서 2004년에 약 4억 달러의 규모가 2010년에는 약 2.3억 달러 수준으로 하향할 것으로 예상되고 있다. 고체 레이저에서 특기할 사항은 2010년에 Lamp Pumped CW Nd;YAG 레이저의 경우 약 74백만 달러로 규모가 축소됨에 비해 고출력 DPSSL(Diode Pumped Solid State laser) 시장규모는 약 17억 달러로 급성장하며 레이저 마킹 및 미세 정밀 가공용 저출력 DPSSL의 시장 규모가 약 13억 달러로 고속 성장할 것으로 예측이 된다.

• Journal of the Optical Society of Korea
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• v.11 no.1
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• pp.34-39
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• 2007

Laser-induced breakdown of colloidal suspensions, such as polystyrene, $ZrO_2$, and $SiO_2$ particles in diameters of 100-400 nm in water is investigated by nanosecond flash-pumped Nd:YAG laser pulses operating at a wavelength ${\lambda}$= 532 nm. The breakdown threshold intensity is examined in terms of breakdown probability as a function of laser pulse energy. The threshold intensity for $SiO_2$ particles ($1.27{\times}10^{11}\;W/cm^2$) with a size of 100 nm is higher than those for polystyrene and $ZrO_2$ particles with the same size, namely $5.7{\times}10^{10}$ and $5.5{\times}10^{10}\;W/cm^2$, respectively. Results indicate that the absorption of five photons is required to induce ionization of $SiO_2$ particles, whereas the other particles necessitate four-photon absorption. These breakdown thresholds are compared with those measured by nanosecond pulses from a diode-pumped Nd:YAG laser having a different focusing geometry.

• Korean Journal of Optics and Photonics
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• v.4 no.3
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• pp.289-293
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• 1993

A Nd:YLF laser pumped by a CW GaAlAs laser diode(LD) at 792 nm has been designed and fabricated. The output power was investigated as a function of LD spectrum and pump power. A folded laser resonator was desinged to compensate for the astigmatism produced at the Brewster surface of Nd:YLF rod. We obtained output power of CW 1.1 Watt when the pumping power was 2.8 Watt and the output wavelength of LD was temperature tuned to the peak absorption line of Nd:YLF. The overall efficiency was 39 % and slope efficiency was 41 %.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.312-320
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• 2003

The basic mechanistic aspects of the interaction and practical considerations related to polymer ablation were briefly reviewed. Photochemical and photothermal effects, which highly depend on laser wavelength have close correlation with each other. In this study, multi-scanning laser ablation processing of polymer with a DPSS (Diode Pumped Solid State) 3rd harmonic Nd:YVO$_4$ laser (355 nm) was developed to fabricate a three-dimensional micro shape. Polymer fabrication using DPSSL has some advantages compared with the conventional polymer ablation process using KrF and ArF laser with 248 nm and 193 nm wavelength. These advantages include pumping efficiency and low maintenance cost. And this method also makes it possible to fabricate 2D patterns or 3D shapes rapidly and cheaply because CAD/CAM software and precision stages are used without complex projection mask techniques. Photomachinability of polymer is highly influenced by laser wavelength and by the polymer's own chemical structure. So the optical characteristics of polymers for a 355 nm laser source is investigated experimentally and theoretically. The photophysical and photochemical parameters such as laser fluence, focusing position, and ambient gas were considered to reduce the plume effect which re-deposits debris on the surface of substrate. These phenomena affect the surface roughness and even induce delamination around the ablation site. Thus, the process parameters were tuned to optimize for gaining precision surface shape and quality. This maskless direct photomachining technology using DPSSL could be expected to manufacture tile prototype of micro devices and molds for the laser-LIGA process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.197-197
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• 2009

We have investigated the holographic grating formation on Ag-doped amorphous chalcogenide AsGeSeS thin films with Ag thickness. Holographic gratings have been formed using Diode Pumped Solid State laser (DPSS, 532.0nm) under [P:P] polarized the intensity polarization holography. The diffraction efficiency was obtained by +1st order intensity.