• Laser Solutions
• /
• v.11 no.2
• /
• pp.33-38
• /
• 2008

Laser micromachining has increasingly been adopted in various advanced industries where the high-precision machining of large-area, high-density and multi-layered components is in a strong demand. To effectively meet the requirements, the laser micromachining process must be carefully monitored. In order to facilitate the development of a new laser micromachining process and/or a new system, we have fabricated a UV laser micromachining platform that is equipped with optical modules for monitoring the process online. They include a laser power stabilizing module, a module for laser-induced breakdown spectroscopy, and an auto-focusing module.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2003.11a
• /
• pp.200-200
• /
• 2003

Polycrystalline Si(polysilicon) TFTs have opened a way for the next generation of display devices, due to their higher mobility of charge carriers relative to a-Si TFTs. The polysilicon W applications extend from the current Liquid Crystal Displays to the next generation Organic Light Emitting Diodes (OLED) displays. In particular, the OLED devices require a stricter control of properties of gate oxide layer, polysilicon layer, and their interface. The polysilicon layer is generally obtained by annealing thin film a-Si layer using techniques such as solid phase crystallization and excimer laser annealing. Typically laser-crystallized Si films have grain sizes of less than 1 micron, and their electrical/dielectric properties are strongly affected by the presence of grain boundaries. Impedance spectroscopy allows the frequency-dependent measurement of impedance and can be applied to inteface-controlled materials, resolving the respective contributions of grain boundaries, interfaces, and/or surface. Impedance spectroscopy was applied to laser-annealed Si thin films, using the electrodes which are designed specially for thin films. In order to understand the effect of grain size on physical properties, the amorphous Si was exposed to different laser energy densities, thereby varying the grain size of the resulting films. The microstructural characterization was carried out to accompany the electrical/dielectric properties obtained using the impedance spectroscopy, The correlation will be made between Si grain size and the corresponding electrical/dielectric properties. The ramifications will be discussed in conjunction with active-matrix thin film transistors for Active Matrix OLED.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.39 no.5
• /
• pp.451-457
• /
• 2011

A short laser pulse irradiates a sample to create the highly energetic plasma that emits light of a specific wavelength peak according to the material. By identifying different peaks for the analyzed samples, its chemical composition can be rapidly determined. The LIBS (Laser-Induced Breakdown Spectroscopy) has great advantages as an elemental analyzer on board a space rover, namely real-time rapid analysis and stand-off detection. The LIBS signal intensity is remarkably increased by using double-pulse LIBS system for component analysis of lunar environments where the surrounding pressure is low. Also the angle of target is adjusted for replicating arbitrary shapes of the specimen.

• Current Optics and Photonics
• /
• v.1 no.4
• /
• pp.402-411
• /
• 2017

Combined LIBS-Raman spectroscopy has been widely studied, due to its complementary capabilities as an elemental analyzer that can acquire signals of atoms, ions, and molecules. In this study, the classification of polymorphs was performed by laser-induced breakdown spectroscopy (LIBS) to overcome the limitation in molecular analysis; the results were verified by Raman spectroscopy. LIBS signals of the $CaCO_3$ polymorphs calcite and aragonite, and $CaSO_4{\cdot}2H_2O$ (gypsum) and $CaSO_4$ (anhydrite), were acquired using a Nd:YAG laser (532 nm, 6 ns). While the molecular study was performed using Raman spectroscopy, LIBS could also provide sufficient key data for classifying samples containing different molecular densities and structures, using the peculiar signal ratio of $5s{\rightarrow}4p$ for the orbital transition of two polymorphs that contain Ca. The basic principle was analyzed by electronic motion in plasma and electronic transition in atoms or ions. The key factors for the classification of polymorphs were the different electron quantities in the unit-cell volume of each sample, and the selection rule in electric-dipole transitions. The present work has extended the capabilities of LIBS in molecular analysis, as well as in atomic and ionic analysis.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.10
• /
• pp.3355-3360
• /
• 1996

To provide standard data of temperature and species concentration in a flame for calibrating the laser based combustion diagnostics, we investigated combustion characteristics of a flat flame burner(Mckennar Product). For various stoichiometric ratios we measured temperature and concentration of OH in the premixed methane/air flame with Coherent anti-Stokes Raman spectroscopy and laser induced fluorescence technique, respectively. Assuming the chemical equilibrium condition at the measured temperature, the mole fraction of the OH radical in the flame was obtained and compared with numerical analysis.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.24 no.6
• /
• pp.625-631
• /
• 2015

The hardness of surface treated magnesium alloy was evaluated using laser induced breakdown spectroscopy. The surface of the specimen was hardened mechanically, and the hardness profiles were measured using a traditional measurement technique. A laser beam was irradiated to generate a plasma, and the peaks of the components of the specimen were analyzed. A wavelength of 333.66 nm and 293.65 nm were selected as the atomic and ionic peaks, respectively. The ratios of the ionic peak to the atomic peak were obtained so as to compare the hardness profile. As the depth increased, the ratio decreased. These results are in good agreement with the previous hardness measurement results. It can be considered that this technique could be applied for remote and time-efficient hardness measurement.

• Journal of the Korean Society for Heat Treatment
• /
• v.37 no.2
• /
• pp.73-78
• /
• 2024

This study presents a real-time method that uses Laser Absorption Spectroscopy (LAS) to measure exhaust gas temperatures in turbulent flow fields. It was possible to measure temperature by passing a laser beam through the exhaust gas in a grid pattern, and obtain a temperature distribution image through time series analysis at 0.1 second intervals. Temperature image resolution has been improved with CT reconstruction algorithms. Estimating maximum temperature values and locations enabled 2D temperature analysis, surpassing single-point methods like thermocouples. The accuracy of LAS measurements was evaluated by comparison with thermocouple measurements. This approach will contribute to automotive technology and environmental protection by providing reliable temperature data for interpreting turbulent temperature distributions.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.19 no.2
• /
• pp.9-17
• /
• 2020

In this study, the surface changes of titanium alloy using laser surface treatment and the surface analysis using laser-induced plasma spectroscopy were carried out. The laser surface treatment induced changes in surface roughness and the diffusion of atmospheric elements. Excessive melting or less melting caused roughness changes, but when moderate levels of energy were applied, a smoother surface could be obtained than the initial surface. In the process, the diffusion of atmospheric elements took place. To analyze the diffusion of atmospheric elements with respect to surface morphology, the surfaces were re-shaped with grinding. In this experimental conditions, the effect of plasma formation by surface roughness was identified. Compensated plasma signals for the material properties were obtained and analysed by removing the background plasma signal.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.2
• /
• pp.34-39
• /
• 2010

In order to achieve and maintain dimensional accuracy in laser micro-machining, dominant parameters such as laser power and laser focus position need to be monitored and controlled real time. Also, in order to selectively machine multi-layered materials, the material being presently machined need to be recognized. This paper presents an auto-focusing (AF) module to keep laser focus on a large-area surface; a real-time laser power stabilizing module based on optical attenuation; and a laser-induced breakdown spectroscopy (LIBS) module. With these monitoring modules, position error in laser focus on a 4" silicon wafer was kept below $4{\mu}m$, initially $51{\mu}m$, and laser power stability of a UV laser source was improved from 1.6% to 0.3%. Also, the material transition from polyimide to copper in machining of FCCL (flexible copper clad laminate) was successfully observed.

• Journal of the Optical Society of Korea
• /
• v.18 no.1
• /
• pp.50-54
• /
• 2014

In this paper we studied the laser-induced crater depth, mass, and emission spectra of laser-ablated high-density polyethylene (HDPE) polymer using the laser-induced plasma spectroscopy (LIPS) technique. This study was performed using a Nd:YAG laser with 100 mJ energy and 7 ns pulse width, focused normal to the surface of the sample. The nanoscale change in ablated depth versus number of laser pulses was studied. By using scanning electron microscope (SEM) images, the crater depth and ablated mass were estimated. The LIPS spectral intensities were observed for major and minor elements with depth. The comparison between the LIPS results and SEM images showed that LIPS could be used to estimate the crater depth, which is of interest for some applications such as thin-film lithography measurements and online measurements of thickness in film deposition techniques.