• The Magazine of the IEIE
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• v.30 no.5
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• pp.509-517
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• 2003

지금까지 GaN 계열 물질의 양자점 소자 관련 연구 동향을 양자점 구현 방식을 중점으로 하여 살펴보았다. GaN 계열 물질의 양자점을 구현하는 방법은 S-K 성장모드를 이용한 자발형성 양자점 구현법, anti-surfactaant를 이용하는 방법, selective epitaxy를 이용한 양자점 구현법 등이 시도되고 있다. 현재 GaN 계열 물질의 양자점 소자 연구는 아직 충분한 연구가 이루어지짖 않은 관계로 optical pumping을 통한 LD lasing 구현에 머무르고 있는 실정이다. 후 소자로의 응용을 위해서는 여러 가지 문제점이 해결되어야 한다. 우선 우수한 결정성을 지니는 양자점의 성장이 이루어져야 한다. 이외에도 각 구현 방법 별로 GaN 및 AlGaN 양자점 성장용 기판으로 많이 사용되는 높은 조성의 AlGaN 및 AlN의 doping 기술 개발, patterning 기술의 개선을 통한 미세 공정 개발 등의 여러 가지 과제들이 남아 있다. 그러나, 양자점이 지진 우수한 특성과 이를 이용한 높은 응용 가능성을 고려할 때 GaN 계열 양자점 소자의 전망은 밝다고 할 수 있다.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.257-258
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• 1996

1607 OH/IR stars associated with IRAS sources are assembled and the IRAS LRS spectra of 980 OH/IR stars are examined in this paper. The nature of the circumstellar dust for these sources is classified. The distributions of these subgroups of OH/IR stars in the IRAS color-color diagram and the period-color diagram are interpreted with their evolutionary status. The Galactic and the velocity distributions of these subgroups of OH/IR stars are also presented. The correlations among the expanding velocities of the envelopes, colors, periods and the pumping efficiencies for subgroups of OH/IR stars are investigated to outline the evolutionary status of OH/IR stars.

• Publications of The Korean Astronomical Society
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• v.7 no.1
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• pp.155-166
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• 1992

We observed a total of 14 Mira variables as well as 4 late type variable stars for their SiO ${\nu}= 1$, J = 2 - 1 maser lines from April 1989 to November 1990 with the 13.7 m radio telescope at Daeduk Radio Astronomy Observatory. The maser intensity variations were the prime objective of the observations which well covered the periods of the variations. The origion of the variations were studied by comparing wi th those previousely measured in optical and infrared(IR) wavelengths and we confirmed that the intensity variations were in good correlation with those in V magnitude and IR intensity as previousely found in former investigators in general. However, for a few sources, we could find the missing maxima. The intensities themselves also were in good correlation with SiO ${\nu}\;=\;1$, J = 1 - 0 maser intensities observed in Yebes as expected. The good correlations indicate that the pumping source of the SiO maser is likely to be the IR emission in the masing regions and the "missing maxima" that are apparent in two particular sources are considered to relate wi th the strength of shocks arising from the eruptive mass-loss from central stars.

• Korean Journal of Optics and Photonics
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• v.6 no.1
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• pp.16-20
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• 1995

We have studied the spectral narrowing characteristics of the tunable Ti:sapphire laser pumped by the second harmonic generation of Nd:YAG laser. Ti:sapphire laser has uniform excitation distribution by both-side end pumping. We have controlled the angle of grating linearly and achieved the continuous selection of wavelength in the broad range from 705 to 835 nm. The output energy of $380{\mu}J$ at 790 nm. the spectral linewidth of $0.13cm_{-1}$ and the beam divergence of 1.2 mrad have been obtained. The wavelength range with power more than 50% of maximum output was 730-825 nm.825 nm.

• Korean Journal of Optics and Photonics
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• v.4 no.3
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• pp.289-293
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• 1993

A Nd:YLF laser pumped by a CW GaAlAs laser diode(LD) at 792 nm has been designed and fabricated. The output power was investigated as a function of LD spectrum and pump power. A folded laser resonator was desinged to compensate for the astigmatism produced at the Brewster surface of Nd:YLF rod. We obtained output power of CW 1.1 Watt when the pumping power was 2.8 Watt and the output wavelength of LD was temperature tuned to the peak absorption line of Nd:YLF. The overall efficiency was 39 % and slope efficiency was 41 %.

• Korean Journal of Optics and Photonics
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• v.8 no.1
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• pp.52-57
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• 1997

We report an investigation of the statistical fluctuations of the two-mode laser output as the asymmetry parameter is varied. The above results relate to computer solutions of the coupled Langevin equations both with and without pumping fluctuations. We find that as the asymmetry parameter is changed positively, the mean intensity of one mode is increased because the normalized intensity auto-correlation is decreased so that the natural dwell time is lengthen. The laser output does respond to a sinusoidally injected asymmetry parameter for small pump parameter.

• Current Optics and Photonics
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• v.1 no.2
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• pp.113-117
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• 2017

With the increasing use of high-power laser diode bars (LDBs) and stacked LDBs, the issue of thermal control has become critical, as temperature is related to device efficiency and lifetime, as well as to beam quality. To improve the thermal resistance of an LDB set, we propose and analyze a bypass heat sink with a top canopy structure for an LDB set, instead of adopting a thick submount. The thermal bypassing in the top-canopy structure is efficient, as it avoids the cross-sectional thermal saturation that may exist in a thick submount. The efficient thickness range of the submount in a typical LDB set is guided by the thermal resistance as a function of thickness, and the simulated bypassing efficiency of a canopy is higher than a simple analytical prediction, especially for thinner canopies.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.10a
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• pp.349-352
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• 2001

The transient response in TDFA(Thulium-Doped Fiber Amplifier) is theoretically investigated. The TDFA has the spectral gain band in 1.47 ${\mu}{\textrm}{m}$. The transient model includes the transient buildup of the population inversion, the pump power, the signal power and their transient variation along the fiber amplifier. The results of numerical analysis can predict the gain saturation and recovery time at the fiber amplifier. It also shows the gain saturation and recovery effect depending on the pumping and saturation rate.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.140.1-140.1
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• 2012

We investigate properties of maser emission for 3373 O-rich AGB stars. We divide the sample stars into four different groups whether they were detected by OH, SiO and $H_2O$ maser emission or not. To understand the nature of the maser sources, we present various infrared two-color diagrams (2CDs) using IRAS, near infrared and AKARI data. For each group, we compare the positions on the various infrared 2CDs with theoretical models. We find that OH maser sources generally show higher color indices and larger dust optical depths than SiO or $H_2O$ maser sources. This could be due to differences of the mass-loss rates and/or variability which may influence the maser pumping mechanisms.

• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.204-208
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• 1997

We analyze the intensity characteristics of the output beams of the ring laser, in which only one mode is generated in each direction, within the neoclassical model by using the Maxwell-Bloch equation. Considering the Nd:YAG crystal as a gain medium, we investigate the stability and the modulation of the output beam intensity as the pumping rate, the relaxation or the decay rate, and the frequency detuning vary, upon taking into account the effect of the beam in one beam in one direction onto the beam in the other direction. In particular, we examine the variation of the output beam intensity and the stability condition through a computer simulation.