• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.3
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• pp.246-254
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• 2007

The scanning laser source (SLS) technique is a promising new laser ultrasonic tool for the detection of small surface-breaking defects. The SLS approach is based on monitoring the changes in laser-generated ultrasound as a laser source is scanned over a defect. Changes in amplitude and frequency content are observed for ultrasound generated by the laser over uniform and defective areas. The SLS technique uses a point or a short line-focused high-power laser beam which is swept across the test specimen surface and passes over surface-breaking or subsurface flaws. The ultrasonic signal that arrives at the Rayleigh wave speed is monitored as the SLS is scanned. It is found that the amplitude and frequency of the measured ultrasonic signal have specific variations when the laser source approaches, passes over and moves behind the defect. In this paper, the setup for SLS experiments with full B-scan capability is described and SLS signatures from small surface-breaking and subsurface flaws are discussed using a point or short line focused laser source.

• Transactions of Materials Processing
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• v.19 no.8
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• pp.517-522
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• 2010

Selective laser melting (SLM) is emerged as a new manufacturing technique to directly fabricate precise parts using metallic materials. The final characteristics of a component fabricated through the SLM process are strongly dependent upon various parameters such as laser power, scan rate and pulse duration, etc. This paper, therefore, focuses on the dimensional characteristics of melted $20{\mu}m$ Fe-Cr-Ni powder by fiber laser for the selective laser melting process. With energy density decrease, the height and depth were decreased. Although the conditions are of the same energy density, the shape is different by laser power and scan rate. The shapes at various laser parameters were divided into 3 groups based on depth over height. The smooth regular shape is obtained under the conditions of $50{\mu}m$ of powder height and $15-20{\mu}s$ of pulse duration. And the laser power influenced the variation of shape more significantly than the scan rate.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.5
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• pp.377-380
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• 2012

Laser direct patterning of indium tin oxide(ITO) is one of new methods of direct etching process to replace the conventional photolithography. A diode pumped Q-switched Nd:$YVO_4$ (${\lambda}$= 1,064 nm) laser was used to produce ITO electrode on various transparent oxide semiconductor films such as zinc oxide(ZnO). The laser direct etched ITO patterns on ZnO were compared with those on glass substrate and were considered in terms of the overlapping rate of laser beam. In case of the laser etching on double-layer, it was possible to obtain the higher overlapping rate of laser beam.

• The Journal of Internal Korean Medicine
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• v.31 no.3
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• pp.612-619
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• 2010

Background : Low level laser therapy may be an effective method to protect tissue damage in acute stroke. Recently, series of clinical studies on the basis of animal experiments report efficacy and safety of laser therapy at early stages of acute stroke. Laser promotes mitochondrial ATP synthesis to reduce cell death by ischemic infarction. Objectives : To report possibility of non-invasive laser therapy for acute stroke by reviewing literature about its effectiveness, safety and mechanism. Methods : We searched papers using PubMed and 'Web of Knowledge' of Thomson ISI, using the keywords "Laser Therapy, Low-Level" and "Stroke". Limitations were last 10 years of publications and only in English. Search range includes RCTs, clinical reports, reviews and animal experiments. Papers not matched with inclusion criteria were excluded. Results : A total 223 studies were found, 203 excluded during title and extract screening. After scanning 20 papers the final 2 serial RCTs were selected and analyzed. They reported that transcranial laser therapy led in neuroprotective effect for acute stroke patents. Clinical evaluation factors showed favorable trend and initial safety. Conclusions : Non-invasive laser secured safety of clinical application. It may be a favorable choice for the acute stage of stroke.

• Journal of Biomedical Engineering Research
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• v.16 no.1
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• pp.67-76
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• 1995

Explosive evaporative removal process of biological tissue by absorption of a CW laser has been simulated by using gelatin and a multimode Nd: YAG laser. Because the point of maximun temperature of laser-irradiated gelatin exists below the surface due to surface cooling, evaporation at the boiling temperature is made explosively from below the surface. The important parameters of this process are the conduction loss to laser power absorption (defined as the conduction-to-laser power parameter, Nk), the convection heat transfer at the surface to conduction loss (defined as Bi), dimensionless extinction coefficient (defined as BrJ, and dimensionless irradiation time (defined as Fo). Dependence of Fo on Nk and Bi has been observed by experiment, and the results have been compared with the numerical results obtained by solving a 2-dimensional conduction equation. Fo and explosion depth (from the surface to the point of maximun temperature) are increased when Nk and Bi are increased. To find out the minimum laser power for explosive evaporative removal process, steady state analysis has been also made. The limit of Nk to induce evaporative removal, which is proportional to the inverse of the laser power, has been obtained.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.1080-1083
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• 2002

In this paper, we have studied with regard to the use of lasers for modifying the surface properties of silicon in order to improve it's wettability and adhesion characteristics. Using an Nd:YAG pulse laser, the wettability and adhesion characteristics of silicon surface have been developed by an Nd:YAG pulse laser. It was found that the laser treatment of silicon surfaces modified the surface energy. In the result of wetting experiments, by the sessile drop technique using the distilled water, wetting characteristic of silicon after the laser irradiation shows a decreased value of the contact angle. In case of the laser treated silicon surface, laser direct writing of copper lines has been achieved by pyrolytic decomposition of copper formate films$(Cu(HCOO)_2{\cdot}4H_2Q)$, using a focused $Ar^+$ laser beam$(\lambda=514.5nm)$ on the silicon substrates. The deposited patterns were measured by energy dispersive X-ray(EDX), Scanning Electron Microscopy(SEM) and surface profiler($\alpha$-step) to examine the cross section of deposited copper lines and linewidth.

• Journal of Welding and Joining
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• v.22 no.6
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• pp.19-24
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• 2004

The laser welding and its analysis of thin-sheet carbon steels were carried out with high power $CO_{2}$ laser. The main factor of weld quality of laser welding is gap and edge quality. This work was preformed to focus on the gap tolerance problem during laser welding. First, bead on plate welding of thin sheet was examined to investigate the effect of laser welding variables, and to obtain optimum welding condition. Butt welding was also carried out to show the effect of gap on the laser weldability of thin sheet. In order to investigate the effect of gap on formability of welded thin sheet, LDH test was caried out. At high welding speed, the partial penetration was obtained by low heat input. Otherwise, porosity was formed in the bead at low weld speed because of too much heat input. The optimum welding condition of welding was derived from bead width, penetration and hardness property. The maximum gap tolerance on laser welding was observed to be about 0.2mm. This gap size has good relationship with beam size of laser spot(about 0.3mm). The formability of welded sheet was about $80{\%}$ value of base metal and the gap size has not affected on the formability, although weld quality is dependent on the gap size.

• Journal of Welding and Joining
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• v.34 no.5
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• pp.54-60
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• 2016

In order to quantitatively evaluate the solidification cracking susceptibility in laser welds of three types of austenitic stainless steels (type 310: A mode, type 316-A: AF mode, type 316-B: FA mode solidifications), the laser beam welding (LBW) transverse-Varestraint tests consisted of multi-mode fiber laser, welding robot and hydraulic pressure system were performed. As the welding speed increased from 1.67 to 40.0 mm/s, the solidification brittle temperature range (BTR) of laser welds for type 316 stainless steels enlarged (316-A: from 37 to 46 K, 316-B: from 14 to 40 K), while the BTR for type 310 stainless steel reduced from 146 to 120 K. In other words, it founds that solidification cracking susceptibility could not be simply mitigated through application of LBW process, and the BTR variation behavior is quite different upon solidification mode of austenitic stainless steels.

• Laser Solutions
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• v.11 no.1
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• pp.1-6
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• 2008

We proposed new light guide panel (LGP) fabrication method exploiting laser-processed inner scatterers and surface pattern. The proposed method has achieved LGP performance improvement in both brightness and uniformity. The inner scatterers and surface pattern of grid type were fabricated with a 2nd harmonic Nd:YAG pulse laser engraving system and a $CO_2$ laser scanning system, respectively. In the implementation of LGP, inner scatterers was arranged in accordance with linear or curved pattern with changing density and surface pattern was engraved on the surface of an inner-scatterers embedded LGP. The increase of scatterers' density and the use of surface patterns in both linear and curved pattern provided high luminance and uniformity enhancement. While thecurved pattern incorporated with increased scatterers' density and surface patterns yielded brightness improvement with preserving good uniformity, the linear pattern showed highly localized brightness near the light entrance of the LGP. We can also observe that the uniformity was mainly determined by pattern of inner scatterers, and the brightness was improved by the higher density and the utilization of surface patterns. From the results, the use of laser-processed inner and surface patterns can be a potential alternative for efficient and simple LGP fabrication method.

• Korean Journal of Optics and Photonics
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• v.15 no.3
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• pp.263-267
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• 2004

We have investigated the characteristics of a Nd:YAG laser pumped by a cw Ti:sapphire laser. When the pumping power of the Ti:sapphire laser was 850 ㎽, the maximum output power of the Nd:YAG laser was 450 ㎽. As a result, the slope efficiency for the output power of the Nd:YAG laser was measured to be 56%. We have also investigated the characteristics of a passively Q-switched Nd:YAG laser by using a Cr$^{4+}$:YAG as saturable absorber with initial transmission of 90%. The maximum average output power of 200 ㎽ was obtained with repetition rate of 23.8 KHz and pulse width of 17.0 ns.