• Current Optics and Photonics
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• v.7 no.6
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• pp.738-744
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• 2023

Graphene-based saturable absorbers (SAs) are widely used as laser mode-lockers at various laser oscillators. In particular, transmission-type graphene-SAs with ultrabroad spectral coverage are typically manufactured on transparent substrates with low nonlinearity to minimize the effects on the oscillators. Here, we developed two types of transmitting graphene SAs based on CaF₂ and ZnSe. Using the graphene-SA based on CaF₂, a passively mode-locked mid-infrared Cr:ZnS laser delivers relatively long 540 fs pulses with a maximum output power of up to 760 mW. In the negative net cavity dispersion regime, the pulse width was not reduced further by inhomogeneous group delay dispersion (GDD) compensation. In the same laser cavity, we replaced only the graphene-SA based on CaF₂ with the SA based on ZnSe. Due to the additional self-phase modulation effect induced by the ZnSe substrate with high nonlinearity, the stably mode-locked Cr:ZnS laser produced Fourier transform-limited ~130 fs near 2,340 nm. In the stable single-pulse operation regime, average output powers up to 635 mW at 234 MHz repetition rates were achieved. To our knowledge, this is the first attempt to achieve shorter pulse widths from a polycrystalline Cr:ZnS laser by utilizing the graphene deposited on the substrate with high nonlinearity.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.40.2-40.2
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• 2021

The impact of AGN on star formation is one of the main questions in AGN-galaxy coevolution studies. However, direct evidence of AGN feedback is still rare. One of the main obstacles is that various star formation rate (SFR) indicators are contaminated by AGN contribution. We present IR-based SFR measurements of a sample of 52 local (z<0.3) AGNs, which were selected based on kinematical properties of ionized gas outflows, using SED analysis with JCMT/SCUBA-2 data. First, we will compare IR-based SFR with other SFR indicators to check the reliability of the SFR indicators. Second, we will discuss the contribution of Mid-IR emission from hot dust of AGN torus by comparing SED fitting results with and without including AGN dust component. Finally, we will report the correlation between specific SFR (sSFR) and AGN activity (e.g., outflow strength or Eddington ratio) as evidence of no instantaneous feedback and discuss the implications of these results

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.289-290
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• 2012

Feedback from accreting BH (AGN) is thought to be responsible for the co-evolution of BHs and galaxies. It is likely to be prominent in the most luminous dust-obscured quasars, particularly those containing radio sources too luminous to be powered by starbursts. In order to investigate the feedback mechanism in detail, we select a unique sample containing ~ 200 of the most luminous obscured QSOs by cross-matching the WISE catalog with the FIRST and NVSS radio surveys. We present overall statistics for the observed range of colors and radio/mid-IR flux density ratio. We also present our efforts to understand the physical and evolutionary nature of these extreme feedback candidates using various telescopes such as Magellan, SOAR, Herschel, and ALMA.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.97.2-97.2
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• 2013

달 및 행성탐사선에 탑재된 적외선 분광기는 태양계 행성들의 지표 및 대기 성분 관측을 위해 널리 활용되고 있다. 적외선 분광기 관측 영역 중 $3-5{\mu}m$ 파장 대에서는 행성의 지표 및 대기에 존재하는 물(얼음), 이산화탄소, 일산화탄소, 메탄, 중수와 같은 여러 성분의 분광선 관측이 가능하다. 이 파장대를 관측한 해외 탐사선 탑재체 사례로는 화성의 경우 Mars Express에 탑재된 OMEGA와 PFS, 소행성의 경우 ROSETTA에 탑재된 VIRTIS 등이 해당된다. $3-5{\mu}m$ 파장대의 분광기는 국내에서 개발 사례가 없으며 해외에서도 달 탐사선에 탑재된 바가 없어 달 얼음과 관련된 다른 파장대의 자료와 상호보완이 가능한 자료를 제공할 것으로 기대된다. 본 연구에서는 달 및 행성탐사를 위한 $3-5{\mu}m$ 파장 영역을 탐사하는 적외선 분광기의 요구사양을 그 과학임무에 비추어 제안하고자 한다.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.49-53
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• 2017

The point sources in the Bright Source Catalogue of the AKARI Far-Infrared Surveyor (FIS) were classified based on their FIR and mid-IR fluxes and colours into young stellar object (YSO) and extragalactic source types using a Quadratic Discriminant Analysis method (QDA) and Support Vector Machines (SVM). The reliability of the selection of YSO candidates is high, and the number of known YSO candidates were increased significantly, that we demonstrate in the case of the nearby open cluster IC348. Our results show that we can separate galactic and extragalactic AKARI point sources in the multidimensioal space of FIR fluxes and colours with high reliability, however, differentiating among the extragalactic sub-types needs further information.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1628-1628
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• 2001

Near infrared (NIR) spectroscopy is a powerful technique for non-destructive analysis that can be obtained in a wide range of environments. Recently, NIR measurements have been utilized as probe for quantitative analysis in agricultural, industrial, and medical sciences. In addition, it is also possible to make practical application on NIR for molecular structural analysis. In this work, Fourier transform near infrared (FT-NIR) measurements were carried out to utilize extensively in the relative amounts of different secondary structures were employed, such as Iysozyme, concanavalin A, silk fibroin and so on. Several broad NIR bands due to the protein absorption were observed between 4000 and $5000\;^{-1}$. In order to obtain more structural information from these featureless bands, second derivative and Fourier-self-deconvolution procedures were performed. Significant band separation was observed near the feature at $4610\;^{-1}$ ,. Particularly the peak intensity at $4525\;^{-1}$ shows a characteristic change with thermal denaturation of fibroin. The structural information can be also obtained by mid-IR and CD spectral. Correlation of NIR spectra with protein structure is discussed.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.56.1-56.1
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• 2016

A low-mass star-forming region, L1251B, is an excellent example of a small and nearby group of protostellar objects. L1251B has been mapped spectroscopically with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. IRS has provided mid-IR emission lines (e.g., [Fe II], [Ne II], and ro-vibrational H2) and absorption features of CO2 and H2O ice in studying the physical state of the ionized gas and the material residing in the circumstellar environments. We will present the distribution of outflows and ice components in L1251B.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.37.1-37.1
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• 2012

We present mid-IR (MIR) and near-UV (NUV) properties of red sequence galaxies defined by optical color-magnitude relation. We use the Wide-field Infrared Survey Explorer (WISE) preliminary released data matched with the SDSS DR7/GALEX GR6. The red sequence galaxies with little emission lines show a wide spread of MIR (3.4um-12um) colors, implying a variety of MIR excess emission. We focus on the properties of the red sequence galaxies with MIR excess, comparing the properties of post-starburst galaxies to trace how galaxies migrate to the red sequence.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.3
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• pp.124-133
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• 1995

A theoretical self-consistent thermoelectric model has been developed for optimal thermal design in the self-signal processing infraed detectors. The model is achived by employing the coupled thermoelectric equation which allows which allows the simultaneous investigation of the termal and electrical aspects of device behavior. The thermal limitation of detectivity and responsivity are determined by the enegy gap, carrier concentration, lifetime, and mobility as a function of the temperature. The calculated results indicate that the detectivity is decreased at bias fields above about 50 V/cm, because the performence is limiting by temperature when the bias voltage reached the level associated with Joule heating. It has been also found that the improvement in the mid-band modulation transfer function(MTF) may be restricted by increasing the bias fields. Further, the important paramerers in the thermal optimization of SPIR detector, such as temperature in the device, ambipolar velocity, element thickness and length, are also considered. The analytical study provides a mathematical basis for optimal design of such a photoconductive IR detector and the agreement between the experimental and theoretical results are seen to be good.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.3
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• pp.276-283
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• 2012

In this study, it was studies the utilization of LIT(lock-in infrared thermography) which can detect defects in welded parts of ship and offshore structures. Quantitative analysis was used through methods of filtering and texture measurement of image processing techniques to find the optimized experimental condition. We verified reliability in our methods by applying image processing techniques in order to normalize evaluations of comparative images that show phase difference. In addition, low to mid exposure showed good results whereas high exposure did not provide significant results in regards to intensity of light exposure on surface. Lock-in frequency was satisfactory around 0.1 Hz regardless of intensity of light source we had. In addition, having the integration time of thermography camera inversely proportional to intensity of exposed light source during the experiment allowed good outcome of results.