• Smart Structures and Systems
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• v.22 no.2
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• pp.223-230
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• 2018

This study examines a non-contact laser scanning-based ultrasound system, called an angular scan pulse-echo ultrasonic propagation imager (A-PE-UPI), that uses coincided laser beams for ultrasonic sensing and generation. A laser Doppler vibrometer is used for sensing, while a diode pumped solid state (DPSS) Q-switched laser is used for generation of thermoelastic waves. A high-speed raster scanning of up to 10-kHz is achieved using a galvano-motorized mirror scanner that allows for coincided sensing and for the generation beam to perform two-dimensional scanning without causing any harm to the surface under inspection. This process allows for the visualization of longitudinal wave propagation through-the-thickness. A pulse-echo ultrasonic wave propagation imaging algorithm (PE-UWPI) is used for on-the-fly damage visualization of the structure. The presented system is very effective for high-speed, localized, non-contact, and non-destructive inspection of aerospace structures. The system is tested on an aluminum honeycomb sandwich with disbonds and a carbon fiber-reinforced plastic (CFRP) honeycomb sandwich with a layer overlap. Inspection is performed at a 10-kHz scanning speed that takes 16 seconds to scan a $100{\times}100mm^2$ area with a scan interval of 0.25 mm. Finally, a comparison is presented between angular-scanning and a linear-scanning-based pulse-echo UPI system. The results show that the proposed system can successfully visualize defects in the inspected specimens.

• Journal of Power System Engineering
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• v.18 no.5
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• pp.94-99
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• 2014

In this study, AISI M2 powder was selected primarily through various literature in order to improve the hardness and wear resistance. Among the laser metal deposition parameters, laser power was studied to improve the deposition efficiency in the laser metal deposition using a diode pumped disk laser. SKD61 hot work steel plate and AISI M2 powder were used as a substrate and powder for laser metal deposition, respectively. Fixed parameters are CTWD, focal position, travel speed, powder feed rate, etc. Experiments for the laser metal deposition were carried out by changing laser power. Through optical micrographs analysis of cross-section in LMD track, effect of the major parameters were predicted by track pitch. As the track pitch increased, so the reheated zone width, the overlap width and the minimum thickness was decreased. The hardness was decreased in the HAZ area, the hardness in the reheated HAZ area was decreased significantly and regularly in particular.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.5
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• pp.104-109
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• 2007

Photochemical patterning of self-assembled mono layers (SAMs) has been performed by diode pumped solid state (DPSS) 3rd harmonic Nd:$YVO_4$ laser with wavelength of 355 nm. SAMs patternings of parallel lines have subsequently been used either to generate compositional chemical patterns or fabricate microstructures by a wet etching. This paper describes a selective etching process with patterned SAMs of alkanetiolate molecules on the surface of gold. SAMs formed by the adsorption of alkanethiols onto gold substrate employs as very thin photoresists. In this paper, the influence of the interaction between the functional group of SAMs and the etching solution is studied with optimal laser irradiation conditions. The results show that hydrophobic functional groups of SAMs are more effective for selective chemical etching than the hydrophilic ones.

• Korean Journal of Optics and Photonics
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• v.26 no.6
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• pp.312-317
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• 2015

We investigate the effect of laser-resonator mode size on the output of a Yb:YAG laser that is mode-locked by a semiconductor saturable absorber mirror (SESAM). We demonstrate that the smaller the product of the mode sizes at a SESAM and at a Yb:YAG crystal, the more stable the mode-locked output is. Also, we found numerically that there is a resonator length at which the mode-locked output occurs, regardless of the thermal lens effect of a Yb:YAG.

• Journal of the Semiconductor & Display Technology
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• v.18 no.3
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• pp.72-76
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• 2019

A Q-switched diode-pumped neodymium-doped yttrium vanadate (YVO₄, λ =1064nm) laser was used for the direct patterning of indium tin oxide (ITO) films on glass substrate. During the laser direct patterning, the laser beam was incident on the two different directions of glass substrate and the laser ablated patterns were compared and analyzed. At a low scanning speed of laser beam, the larger laser etched lines were obtained by laser beam incident in reverse side of glass substrate. On the contrary, at a higher scanning speed, the larger etched pattern sizes were found in case of the beam incidence from front side of glass substrate. Furthermore, it was impossible to find no ablated patterns in some laser beam conditions for the laser beam from reverse side at a much higher scanning speed and repetition rate of laser beam. The laser beam is expected to be transferred and scattered through the glass substrate and the laser beam energy is thought to be also dispersed and much more influenced by the overlapping of each laser beam spot.

• Korean Journal of Optics and Photonics
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• v.26 no.1
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• pp.38-43
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• 2015

We propose a linearly polarized long-cavity Yb:YAG laser with a variable-reflectivity output coupler and investigate its output characteristics. The variable output coupler consists of a polarized beam splitter and a quarter-wave plate. The linearly polarized laser has a long cavity length of about 3.7 m. The slope efficiency of the proposed laser is 19%, and the beam quality ($M^2$) is about 1.2.

• Transactions on Electrical and Electronic Materials
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• v.14 no.2
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• pp.59-62
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• 2013

At an infra-red (IR) wavelength of 1,064 nm, a diode-pumped Q-switched $Nd:YVO_4$ laser was used for the direct patterning of various transparent conductive oxide (TCO) thin films on glass substrate. With various laser beam conditions, the laser ablation results showed that the indium tin oxide (ITO) film was removed completely. In contrast, zinc oxide (ZnO) film was not etched for any laser beam conditions and indium gallium zinc oxide (IGZO) was only ablated with a low scanning speed. The difference in laser ablation is thought to be due to the crystal structures and the coefficient of thermal expansion (CTE) of ITO, IGZO, and ZnO. The width of the laser-patterned grooves was dependent on the film materials, the repetition rate, and the scanning speed of the laser beam.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.222-223
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• 2000

지금까지 gold-coated 반사체, cusp-shaped 반사체, 복합 포물 반사체(CPC), 난반사 공동체 등 다양한 형태의 반사체가 횡펌핑을 이용한 Nd:YAG 레이저의 개발을 위하여 고안되어졌다. 횡여기되는 Nd:YAG 레이저의 광학적 효율은 반사체의 형태, 다이오드 레이저의 파장, Nd:YAG 결정의 지름, Nd$^3$의 도핑농도에 따라 영향을 받는다.$^{(1)}$ 본 연구에서는 고출력의 횡여기 Nd:YAG 레이저를 개발할 목적으로 광여기 공동으로 사용된 난반사 공동체의 내부지름과 레이저 매질인 Nd:YAG 결정의 흡수계수 등 매개변수를 변화시켜 흡수분포와 출력을 계산하였으며, 이러한 매개변수들이 기울기 효율에 미치는 영향을 수치 해석적으로 연구해 보았다. 광선추적법에서 사용한 매개변수 중에서 다이오드 레이저의 파장은 808 nm이고, 반사율은 90%이며, 여기 다이오드 출력은 1080 W이다. 난반사 공동체$^{(2)}$ 의 반사율은 95.7%이고, 결정의 투과율은 90%이며, 결정의 반지름은 2.5 mm이다. 사용된 여기 구조도는 그림 1과 같다. 여기헤드는 Nd:YAG 결정, 난반사 공동체, 그리고 3개의 360 W급 다이오드 어레이들로 구성되어 있다. (중략)

• Journal of the Semiconductor & Display Technology
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• v.18 no.4
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• pp.6-11
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• 2019

For a wider application of laser direct patterning, selective laser ablation of indium tin oxide (ITO) film on transparent oxide semiconductor (TOS) thin film was carried out using a diode-pumped Q-switched Nd:YVO₄ laser at a wavelength of 1064 nm. In case of the laser ablation of ITO on indium gallium zinc oxide (IGZO) film, both of ITO and IGZO films were fully etched for all the conditions of the laser beams even though IGZO monolayer was not ablated at the same laser beam condition. On the contrary, in case of the laser ablation of ITO on zinc oxide (ZnO) film, it was possible to etch ITO selectively with a slight damage on ZnO layer. The selective laser ablation is expected to be due to the different coefficient of thermal expansion (CTE) between ITO and ZnO.

• Current Optics and Photonics
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• v.5 no.1
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• pp.59-65
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• 2021

This paper reports a tunable diode-pumped folded intracavity Q-switched singly resonant optical parametric oscillator based on multi-period MgO:PPLN. A wide tuning mid-infrared parametric light from 2.78 ㎛ to 4.17 ㎛ was obtained in real time by changing the poled periods and temperatures. The maximum output power of 1.89 W at 3.2 ㎛, 1.53 W at 3.5 ㎛, 0.87 W at 3.8 ㎛ and 0.486 W at 4.1 ㎛ were achieved. The highest optical-optical conversion efficiency was 7.89%. During experiments, a range tunable output of 2.78-4.17 ㎛ in the mid-infrared range was achieved.