• 한국연소학회:학술대회논문집
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• 2007.05a
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• pp.27-30
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• 2007

We have been setting up experiments on propagation of shock waves generated by the pulsed laser ablation. One side of a thin metal foil is subjected to laser ablation as a shock wave is generated from a localized spot of high intensity energy source. The resulting reactive shock wave, which penetrates through the foil is reflected by an acoustic impedance which causes the metal foil to high-strain rate deform. This short time physics is captured on an ICCD camera. The focus of our research is generating reactive shock wave and high strain rate deforming of thin metal foil for accelerating micro-particles to a very high speed on the orders of several thousand meter per second. Somce innovative applications of this device will be discussed.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1334-1336
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• 2001

In this study, laser ablation atomic fluorescence (LAAF) spectroscopy has been applied for a nanometer-scale surface analysis of Na-doped polymethyl methacrylate (PMMA). LAAF spectroscopy is a new sensitive element detection technique which involves atomizing of a sample by the laser ablation and detection of ablated plume by laser-induced fluorescence (LIF) spectroscopy. Using this technique in the detection of Na atoms with Na-doped PMMA, a detection limit is obtained as 36 fg for single laser shot. Further, the depth distribution in the sample is measured with a very high spatial resolution using a two-layer PMMA sample by observing the shot-by-shot LIF intensity from the Na atoms.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.260-263
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• 2003

Lasers are used as the source of the interferometers in the industrial field. These lasers need 2 requirements. The first is the narrow linewidth of laser for the long coherence length. The second is the stabilized frequency of laser for the precision measurement. Now HeNe lasers are mostly used and the frequency stability is about 10$^{-9}$ . In this paper, we construct the HeNe laser systems of frequency stabilization using typical 2 method, the beat frequency stabilization method and the intensity difference method. So, we get the frequency stabilities of 2.01$\times$10$^{-9}$ (0.1s), 3.4$\times$10$^{-9}$ (0.1s).

• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.86-88
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• 2007

In the semiconductor manufacturing industry, the heterodyne laser interferometer plays as an ultra-precise measurement system. However, the heterodyne laser interferometer has some unwanted nonlinearity error which is caused from frequency-mixing. This is an obstacle to improve the measurement accuracy in nanometer scale. In this paper we propose a compensation algorithm based on RLS(recursive least square) method and artificial intelligence method, which reduce the nonlinearity error in the heterodyne laser interferometer. With the capacitance displacement sensor we get a reference signal which can be transformed into the intensity domain. Using the back-propagation Neural Network method, we train the network to track the reference signal. Through some experiments, we demonstrate the effectiveness of the proposed algorithm in measurement accuracy.

• Vacuum Magazine
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• v.2 no.1
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• pp.17-20
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• 2015

In this article, a historical and scientific review on the development of an ultrafast electron microscope is supplied, and the challenges in further improvement of time resolution under sub-picosecond or even sub-femtosecond scale is reviewed. By combining conventional scanning electron microscope and femtosecond laser technique, an ultrafast electron microscope was invented. To overcome its temporal resolution limit which originates from chromatic aberration and Coulomb repulsion between individual electrons, a generation of electron pulse via strong-field photoemission has been investigated thoroughly. Recent studies reveal that the field enhancement and field accumulation associated with the near-field formation at sharply etched metal nanoprobe enabled such field emission by ordinary femtosecond laser irradiation. Moreover, a considerable acceleration reaching 20 eV with near-infrared laser and up to 300 eV acceleration with mid-infrared laser was observed, and the possibility to control the amount of acceleration by varying the incident laser pulse intensity and wavelength. Such findings are noteworthy because of the possibility of realizing a sub-femtosecond, few nanometer imaging of nanostructured sample.in silicon as thermoelectric materials.

• Korean Journal of Optics and Photonics
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• v.26 no.6
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• pp.318-321
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• 2015

We demonstrate a frequency-resolved optical grating (FROG) device for measuring the intensity and phase versus time of several-tens-of-picoseconds laser pulses, using a thick nonlinear optical crystal. The huge pulse-front tilt generated by a holographic grating increases the temporal range of the device, which can make a single-shot measurement of laser pulses less than 100 ps in duration. To verify the measurement technique, we generate double pulses using a Michelson interferometer. The measured duration of a single pulse is about 300 fs and the measured maximum delay of two pulses is 60 ps, which implies that the proposed FROG device can measure laser pulses with maximum pulse width of about 120 ps.

• Journal of the Optical Society of Korea
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• v.12 no.3
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• pp.186-191
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• 2008

A phase retrieval method using an error reduction algorithm is developed for reconstructing a wavefront aberration of an 100-TW Ti:sapphire laser pulse from the measurement of a focal spot. The phase retrieval method can successfully reconstruct a wavefront aberration of a 100-TW Ti:sapphire laser pulse, and the reconstructed wavefront aberration shows a good agreement with the wavefront aberration measured with a wavefront sensor. The effect of the dynamic range and the intensity noise on the reconstruction is also investigated in reconstructing a wavefront aberration of an 100-TW Ti:sapphire laser pulse.

• Journal of the Korea Institute of Military Science and Technology
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• v.15 no.5
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• pp.705-711
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• 2012

The purpose of this study is to develop the model to estimate the penetration rate of metal under a high power continuous wave laser irradiation. To estimate it, an empirical modeling is more practical when the penetration phenomena of metal by laser irradiation is too complex to be analyzed by the numerical simulation. When several methods published earlier were applied to our results, we found out that their methods were not appropriate as the model. Therefore, we suggested the new empirical method considering effective intensity as a key variable. As a result, we confirmed that the new method was effective to model the penetration rate of SUS304 metal and expected that it could be available to other metals.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.6
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• pp.260-264
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• 2002

We developed LD Pumped Nd:$VVO_4$ microchip laser with the cavity length of 1mm. The microchip laser output was 87.5㎽ at the wavelength of 1063.9nm with the input power of 241㎽ at the wavelength of 809nm. The slope efficiency was 40.7% and the threshold input power was 31.1㎽. We have also defined input power limit for the single longitudinal mode operation theoretically. It was 2.5 times larger than that of threshold input intensity. According to the results of simulation, the Nd:YVO$_4$ microchip laser can be operated with the maximum output of 15㎽ for the single longitudinal mode up to the input power of 77.75㎽.

• Transactions of the Society of Information Storage Systems
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• v.7 no.1
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• pp.36-41
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• 2011

The micro laser module was designed and prepared to deliver the light to the HAMR head. It consists of laser diode, photo diode and actuator to realize stable light delivery even though the head is fluctuated during the disk rotation. The optical evaluation was carried out with the actual distance between the light source and HAMR head with a range of reflectivity and it was found that the incident angle could be controlled within ${\pm}0.125^{\circ}$ to maintain same intensity into the HAMR head. It was also confirmed that the designed micro laser module is thermally stable without any severe effect on the magnetic head.