• Journal of the Optical Society of Korea
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• v.17 no.1
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• pp.5-9
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• 2013

We report on high-power continuous-wave operations of an Er:YAG ceramic laser in-band pumped by a cladding-pumped Er,Yb fiber laser at 1532 nm. With an output coupler of 10% transmission, the ceramic laser yielded 16.7 W of continuous-wave output at 1645 nm for 28.8 W of incident pump power, corresponding to a slope efficiency of 61.0% with respect to the incident pump power. The lasing wavelength switched to 1617 nm when output couplers of > 20% transmission were used. Up to 16.2 W of 1617 nm output was generated for 33.0 W of incident pump power, corresponding to a slope efficiency of 51.8%. Graphene Q-switched operation of Er:YAG cermic laser at 1645 nm was also demonstrated with stable pulses of 30-74 kHz repetition rates and 1.5-6.4 ${\mu}s$ pulse widths.

• The Journal of the Acoustical Society of Korea
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• v.28 no.2
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• pp.127-134
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• 2009

In this study, possibility of the laser eavesdropping is investigated on the window glasses with various thicknesses, Glass windows are excited by maximum length sequency (MLS) signal and the vibration sound is detected by a laser doppler vibrometer. From the detected sound, speech intelligibility is objectively estimated. Speech transmission index (STI), which is based on the modulation transfer function (MTF). is calculated for the estimation. Finally, disturbing wave effect on the speech intelligibility is analysed by using an outside speaker and a window shaker attached on the glass window. The purpose of the study is to estimate the possibility of remote eavesdropping by the laser sensor and to evaluate the performance of the homemade window shaker to protect from the remote eavesdropping.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.169-175
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• 2002

World demand for natural gas has generated the need for many new land transmission pipelines to be installed in the next decade or so. Although mechanized gas metal arc welding is well developed, there are opportunities for cost savings by using alternative welding processes. Hybrid Nd:YAG laser - gas metal arc welding enables fibre optic delivery of the laser energy to a robotic welding head to be combined with the addition of extra energy and a consumable to produce good quality, deep penetration welds in a single pass. The present paper describes initial procedure development to optimize the laser and gas metal arc welding parameters for making joints in pipeline steel. Satisfactory joint quality was obtained and it is intended to develop the process to prototype field trials.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.2
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• pp.289-293
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• 1996

The basic study on laser triggered lightning was carried out for the active protection of lightning in power transmission system. The lengths of generated plasma channels were simulated numerically for variations of energy and pulse width of CO$_{2}$ laser by Runge-Kutta-Gill method. As results, the effective lengths of plasma channels were 2.3m, 2.67m and 3.4m respectively for energy of 45J, 60J and 100J of CO$_{2}$ laser pulse with pulse width of 50nsec using focusing mirror with focal length of 10m. And also the effects of pulse width of first pulse and tail pulse of CO$_{2}$ laser on the length of plasma channel were examined.

• Laser Solutions
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• v.5 no.2
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• pp.31-38
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• 2002

This paper describes the process of nanoparticle synthesis by laser ablation of consolidated microparticles. We have generated nanoparticles by high-power pulsed laser ablation of Al, Cu and Ag microparticles using a Q-switched Nd:YAG laser (wavelength 355 nm, FWHM 5 ㎱, fluence 0.8∼2.0 J/㎠). Microparticles of mean diameter 18∼80 ㎛ are ablated in the ambient air The generated nanoparticles are collected on a glass substrate and the size distribution and morphology are examined using a scanning electron microscope and a transmission electron microscope. The effect of laser fluence and collector position on the distribution of particle size is investigated. The dynamics of ablation plume and shock wave is analyzed by monitoring the photoacoustic probe-beam deflection signal. Nanosecond time-resolved images of the ablation process are also obtained by laser flash shadowgraphy. Based on the experimental results, discussions are made on the dynamics of ablation plume.

• Proceedings of the KIEE Conference
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• 1993.11a
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• pp.275-277
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• 1993

It is practically required to develop an optical transmission system, for the diagnosis of electric power apparatus, which enables to distinguish the right signals related to the partial discharge taken place inside the apparatus. These partial discharges are transformed into ultra sonic signals by the sensor and then used for the voltage application to pokels cell. Afterwards, the modulated laser beam is transmitted through the optical fiber. Throughout this work, a laser-beam based detecting system is developed and permits us to reproduce the transmitted signals indirectly without electromagnetic interference. For this purpose the characteristics of this system is well analyzed by means of different type of signals from function generator.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.551-556
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• 2008

Possibility of the remote eavesdropping through window glass is investigated using a laser sensor. Various thicknesses and types of glass windows are excited by maximum length sequency (MLS) signal and the vibration sound is detected by a laser doppler vibrometer. Intelligibility of the detected sound is evaluated using the speech transmission index (STI), which is based on the modulation transfer function (MTF). In order to identify the disturbing effect, different level of disturbing wave is generated by an outside speaker and a window shaker attached on the glass window. On the different thickness of glass windows, decrease effect of the speech intelligibility is analysed.

• Journal of the Optical Society of Korea
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• v.18 no.5
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• pp.485-494
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• 2014

A novel antenna with ellipsoid-paraboloid surfaces configuration is designed for matching the incident radial radiation fiber laser distribution for maximum transmission efficiency. The on-axial and off-axial defocus effects on the optical antenna system, resulting in energy loss, are analyzed in detail. Knowledge of the effects of those defocuses on beam divergence, aberration and antenna transmission efficiency is of great importance to the long range communication systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.12 s.91
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• pp.1207-1215
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• 2004

A Gigabit Ethernet upstream transmission over a WDM-PON employing remotely wavelength-locked Fabry-Perot lasers has been demonstrated. We have successfully demonstrated a WDM transmission of four Gigabit Ethernet channels with 100 GHz channel spacing over 30 km conventional single mode fiber. The measured f-factor was larger than 17.1 dB. We have also investigated the beating noise characteristics of a wavelength-locked Fabry-Perot laser and showed the remotely wavelength-locked Fabry-Perot laser suppresses the intensity noise of the incoherent light injected, which cause a 6.3 dB SNR improvement compared with that of the conventional spectrum-sliced light source.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.745-753
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• 2002

It is required to evaluate nondestructively the crack depth of surface-breaking cracks for the assurance of safety of structure. Optical generation of ultrasound produces well defined pulses with a repeatable frequency content, that are free of any mechanical resonances; they are broad band and are ideal for the measurement of attenuation and scattering over a wide frequency range. Self-calibrating surface signal transmission measurement is very sensitive and practical tool for surface-breaking crack depth. In this paper, the self-calibrating technique by laser-based ultrasound is used to evaluate the depth of surface-breaking crack of material. It is suggested that the relationship between the signal transmission and crack depth can be used as a practical model for predicting the surface-breaking crack depths from the signal transmission measured in structure.