• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.873-877
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• 2005

The burr of micro drilling and micro cutting on thin metal film is a major obstacle to mass production for micro PCB boards in micro technologies of personal computing and telecom explosion. As the burr affects on the assembling process, it is necessary to study continuously on control or elimination of the burr. In order to get higher valued products, it is also needed to competitive techniques with the high resolution. In this paper, we studied experimentally the burr generation that when it is processed on the copper foil by laser in micro-hole machining. Unlike mechanical machining the burr produced on substrate is a resultants of melt and re-solidification of a melten metal which was heated and treated by laser. And higher laser energy increases the size of burr. Therefor in micro-drilling with laser, it is difficult to reduce the effects of burr for very thin metal sheets. We investigated the stale of the burr and analyzed the laser ablation Cu micro machining with respect to laser intensity and processing time.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.1
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• pp.90-94
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• 2022

Metal 3D-printing technology enables the manufacture of complex features or internal structures, which is not possible in fabrication by conventional cutting methods. The most successful types of metal 3D printing have been powder bed diffusion and directed energy deposition, which use laser heads exploiting high-power laser sintering metal powder. In this study, a cost-effective optical design was proposed for a 2-kW-level fiber laser head. Only two commercial lenses, a beamsplitter and a window, are used in the laser head, satisfying the technological requirements. According to the optical design, the spot size was 2.54 mm, and the stand-off distance from the laser head was 295 mm. The intensity distribution was Gaussian. Thus, smooth power sintering was possible without any laser spot marks. Monte Carlo analysis was employed to verify the consistency of the optical performance under conventional assembly tolerance.

• Journal of the Optical Society of Korea
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• v.7 no.3
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• pp.139-144
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• 2003

We have characterized the optical parametric chirped-pulse amplification of femtosecond Ti:sapphire laser pulses by using a BBO crystal. It is numerically verified that a high gain and a broad gain bandwidth can be obtained with a 532-nm pump laser. The dependence of the gain profile of OPA on phase matching angles, pump intensity, and crystal length is numerically investigated. Experimental results shows that the temporal fluctuation of a pump laser causes the modulation of an amplified spectrum in OPCPA.

• Korea-Australia Rheology Journal
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• v.19 no.2
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• pp.61-66
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• 2007

The aggregation characteristics of red blood cells (RBCs) are known as important factors in the microvascular flow system, and increased RBC aggregation has been observed in various pathological diseases, such as thrombosis and myocardial infarction. This paper describes a simple microfluidic device for measuring the RBC aggregation by integrating a microfluidic slit rheometry and laser-backscattering technique. While a decreasing-pressure mechanism was applied to the microfluidic rheometry, a syllectogram (the light intensity versus time) showed an initial increase and a peak caused by the high shear stress-induced disaggregation, immediately followed by a decrease in the light intensity due to RBC aggregation. The critical shear stress (CST) corresponding to the peak intensity was examined as a new index of the RBC aggregation characteristics. The CST of RBCs increased with increasing aggregation-dominating protein (fibrinogen) in the blood plasma. The essential feature of this design was the combination of the rheometric-optic characterization of RBC aggregation with a microfluidic chip, which may potentially allow cell aggregation measurements to be easily carried out in a clinical setting.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.652-655
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• 2001

In this paper, I have studied minimization of the kerf-width and surface burning which are occurred after the singulation process of multi layer $\mu$-BGA( thickness 1.1 mm, 0.9 mm) with a pulsed Nd:YAG( = 532 nm, repetition rate = 10 Hz) laser. The thermal energy of a pulsed Nd:YAG laser is used to cut the copper layer. I have studied are minimization of the surface burning and kerf-width using a photo resist, $N_2$blowing and polyester double sided tape as a cutting parameter. The $N_2$blowing reduces a laser energy loss by debris and suppresses a surface carbonization. Also, I have studied characters of cutting with a choice of side of laser beam incidence. The SEM(Scanning Electron Microscope), non-contact 3D inspector and high-resolution microscope are used to measure kerf width and surface state. The optimum value of 1.1 mm $\mu$-BGA singulation is 524 $\mu$m that is reduced kerf width of 60 % with $N_2$blowing. And I obtained reduction of carbonization of 68 % with a polyester double side tape in 0.9 mm $\mu$-BGA. I used laser intensity of 1.91$\times$10$^{6}$ / $\textrm{cm}^2$ in this study.

• IEMEK Journal of Embedded Systems and Applications
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• v.11 no.6
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• pp.379-392
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• 2016

This paper presents the design and simulation of a laser power beaming (LPB) system for an electric vehicle that establishes an optimal power transmission path based on the received signal strength. The LPB system is possible to transfer power from multiple transmitters to a single receiver according to the characteristics of the laser and the solar panel. When the laser beams of multiple transmitters aim at a solar panel at the same time, the received power is the sum of all energy at a solar panel. Our proposed LPB system consists of multiple transmitters and multiple receivers. The transmitter sends its power characteristics as optically coded pulses with a class 1 laser beam and powers as a high-intensity laser beam. By using the attenuated power level, the receiver can estimate the maximum receivable powers from the transmitters and select optimal transmitters. Throughout the simulation, we verified the possibility that different LPB receivers were achieved their required power by the optimal allocation of the transmitter among the various transmitters.

• Journal of the Korean Society of Marine Environment & Safety
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• v.3 no.2
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• pp.23-31
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• 1997

The results of high speed photography, acoustic emission detection and plasma UV radiation intensity measurement during CO2 laser welding of stainless steel 304 are presented. Video images with high spatial and temporal resolution allowed to observe the melt dynamics and keyhole evolution. The existence of a high speed melt flow which originated from the part of weld pool and flowed along the sides wall of keyhole was confirmed by the slag motion on the weld pool. the characteristic frequencies of flow instability and keyhole fluctuations at different welding speed were measured and compared with the results of Fourier analyses of temporal acoustic emission (AE) and light emission (LE) spectra. The experimental results were compared with the newly developed numerical model of keyhole dynamics. (The model is based on the assumption that the propagation of front part of keyhole into material is due to the melt ejection driven by laser induced surface evaporation.) The calculations predict that a high speed melt flow is induced at the front part of keyhole when the sample travel speed exceeds several 10mm/s. The numerical analysis also shows the hump formation on the front keyhole wall surface. Experimentally observed melt behavior and transformation of the AE and LE spectra with variation of welding speed are qualitatively in good agreement with the model predictions.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.11
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• pp.51-57
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• 2001

A light beam reflected from a machined surface generally containes information concerning about its surface roughness. This study examines and proposes a surface roughness measurement technique for on-machine measurement of machined surfaces. The technique is based on the measurement of a reflected laser beam pattern and the statistical analysis of its light intensity distribution. The surface roughness was found to be closely related to the standard deviation of the light intensity on the primary axis of the reflected pattern. An image acquisition device is made up of a laser diode, a half mirror, a screen, and a CCD camera. The exact image with the primary and secondary axes of a reflected laser beam pattern is calculated through such image processing algorithm as thresholding, edge detection, image rotation, segmentation, etc. A median filter and a surrounding light correction algorithm are improve the image quality and reduce the measuring error. Using the developed measuring device the effect of screen materials and workpiece and workpiece materials was investigated. Experimental results regarding to relatively high-quality surfaces machined by grinding, polishing, lapping processes have shown the measurement error is within 10% in the range of $0.1{mu}m~0.8{\mu}m R_q.$Therefore, the proposed method is thought to be effectively used when quick measurements is needed with workpieces fixed on the machine.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1571-1573
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• 1994

In order to substitute for the conventional measuring system which could bring about technical inconveiences, measuring techniques for the fast transient high voltage upto 100 kV and small signals less than 1 V are developed by use of Laser Source with Packets cell. for the former, capacitive voltage divider was specially designed for reducing the impulse voltage less than the half-wave voltage of pockets cell. For the tatter, interferometer type was employed as a mean to removing the fluctuation of Laser output intensity. And also the main beam through the Pockels cell and the reference beam from the Laser source are seperated before being detected respectively by photo diodes. And then, these two signals are amplified and compared for detecting only the small signals applied across the Pockels cell. Throughout this work, Laser-based measuring system is likely to enable us, at this moment, to detect correctly lightning impulse voltage upto 100 kV and the small signals less than 1 V upto the 2 MHz. Such a system could be employed as a possible diagnostic measuring system at the substation.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.5
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• pp.459-462
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• 1999

Recent advances in NLO Borate Crystals for UV Generation are reviewed with the particular emphasis on the technique to improve the life time of UV optics. The laser-damage resistance of CLBO and fused silica surfaces was successfully improved after removing polishing compound by ion beam etching. The polishing compound embedded in the CLBO and fused silica surfaces were to a depth of less than 100nm. We were able to remove polishing compound without degrading the surface condition when the applied ion beam voltage was less than 200 V. The laser-induced surface damage threshold of CLBO was improved up to 15J/$\textrm{cm}^2$(wavelength: 355 nm, pulse width: 0.85 ns)as compared with that of the as-polished surface (11 J/$\textrm{cm}^2$). The laser-induced surface damage of fused silica also increased from 7.5J/$\textrm{cm}^2$ to 15J/$\textrm{cm}^2$. For the irradiation of a 266 nm high-intensity and high-repetition laser light, the surface lifetime of CLBO and fused silica could be more doubled compared with that of the as-polished surface.