• Journal of Communications and Networks
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• 제10권1호
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• pp.1-4
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• 2008

This paper reports the design of a multiwavelength fiber laser source that utilizes a linear cavity of hybrid Brillouin/Erbium fiber laser (BEFL). The output power, threshold power and free running cavity modes were investigated against the pump powers. The structure exhibited low threshold operation of 4 mW at 2.3 mW injected Brillouin pump power. The optimization of Brillouin pump wavelength, power and Erbium gain led to a maximum possible number of channels generated. Simultaneous and stable operation of 21 channels with 10.88 GHz channels spacing were obtained from this architecture at 1 mW injected Brillouin pump power and 90 m W Erbium doped fiber pump power in the 1555 nm region.

• 분석과학
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• 제8권4호
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• pp.1101-1108
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• 1995

Acousto-optic tunable filter is a compact, all solid state electronic dispersive device. It is based on the acousto-optic interaction in an anisotropic crystal. Compared to conventional grating monochromators. the AOTF has no moving parts, wider spectral tuning range (from UV through visible and near-IR to IR), higher throughput, higher resolution, faster scanning (${\mu}s$) and random wavelength access. These features make it possible to use the filter to develop novel instruments which are not possible otherwise. The instrument development and unique advantages of such AOTF based instruments including the multidimensional fluorimeter, the multiwavelength thermal lens spectrometer, and the detectors for HPLC and flow injection analysis are described.

• 천문학회지
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• 제36권3호
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• pp.149-158
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• 2003

Deep surveys at mid-infared through submillimeter wavelengths indicate that a substantial fraction of the total luminosity output from galaxies at high redshift (z > 1) emerges at wavelengths 30 - 300${\mu}m$. In addition, much of the star formation and AGN activity associated with galaxy building at these epochs appears to reside in a class of luminous infrared galaxies (LIGs), often so heavily enshrouded in dust that they appear as 'blank-fields' in deep optical/UV surveys. Here we present an update on the state of our current knowledge of the cosmic evolution of LIGs from z = 0 to z $\~$ 4 based on the most recent data obtained from ongoing ground-based redshift surveys of sources detected in ISO and SCUBA deep fields. A scenario for the origin and evolution of LIGs in the local Universe (z < 0.3), based on results from multiwavelength observations of several large complete samples of luminous IRAS galaxies, is then discussed.

• 천문학회보
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• 제36권1호
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• pp.51.2-51.2
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• 2011

The Spitzer Public Legacy Survey of the UKIDSS Ultra Deep Survey (SpUDS) has been carried out with four IRAC bands and one MIPS band (24um). SpUDS surveys 1 square degree of the UDS field, that has been covered by one of the deepest near IR surveys and by various multiwavelength observations from X-ray to radio (XMM, GALEX, Subaru, SCUBA, VLA). We present a summary of the photometric data including number counts derived at 3.6-24 microns. In conjunction with extensive multiwavelengh data, we are able to show the multiwavelenght color distribution of MIR sources, and how different SED types contribute to the number counts.

• 한국광학회:학술대회논문집
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• 한국광학회 2000년도 하계학술발표회
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• pp.210-211
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• 2000

황사가 기상, 환경에 미치는 영향에 대한 사회적인 관심이 집중되면서 많은 연구들이 진행되고 있으며 특히 황사의 물리, 화학적 변화를 정확히 측정하려는 연구가 증대되고 있다. 이러한 이유에서 최근에는 황사의 형태, 크기 등을 복합적으로 측정할 수 있는 가장 효율적인 계측장비로 다파장 라이다가 개발되어 활용되고 있다. 본 논문에서는 개발된 다파장 에어로졸 라이다를 이용한 수원상공 황사의 계측과 이의 분석 결과에 대하여 보고한다. 다파장 에어로졸 라이다는 대기중의 에어로졸 후방산란비, 입자형태, 크기, 편광비를 광자계수방식 및 아날로그 방식으로 다양한 파장 영역에서 측정 할 수 있다. 이러한 파라메터들의 측정에는 주로 355, 532 nm 파장을 사용하였다. (중략)

• 천문학논총
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• 제10권1호
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• pp.79-90
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• 1995

The unique compact radio source, Sgr $A^*$, at the Galactic center show many observational signs that it is powered by supermassive black hole. Recent observations also imply that it is surrounded by winds from nearby IR sources. So we explore the model in which multiwavelength spectrum from Sgr $A^*$ is due to the spherical accretion of these winds onto the central supermassive black hole. Improving upon the previous work, we allowed the possibility that ions and electrons have different temperatures, included the Compton effects and pair processes. Electrons radiate via cyclosynchrotron and bresstrahlung with comptoniztion. We find that ion approaches the virial temperature ${\sim}10^{13}K$ while electron temperature saturates at ${\sim}10^{10}K$. However, decoupling between ion and electron does not greatly affect the shape of the emission spectrum. When the mass of the black hole is ${\sim}10^6M_{\odot}$, radio, IR, X-ray, $\gamma$-ray band spectrum is reasonably explained by the model. Yet Compton effect which is neglected in previous works produces significant emission in IR band, which is marginally compatible with observations. Pair production is negligible and annihilation lines cannot be observed.

• International Journal of Precision Engineering and Manufacturing
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• 제8권4호
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• pp.22-26
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• 2007

We describe a new way of implementing absolute displacement measurements by exploiting the optical comb of a femtosecond pulse laser as a wavelength ruler, The optical comb is stabilized by locking both the repetition rate and the carrier offset frequency to an Rb clock of frequency standard. Multiwavelength interferometry is then performed using the quasi-monochromatic beams of well-defined generated wavelengths by tuning an external cavity laser diode consecutively to preselected light modes of the optical comb. This scheme of wavelength synthesizing allows the measurement of absolute distances with a high precision that is traceable to the definition of time. The achievable wavelength uncertainty is $1.9{\times}10^{-10}$, which allows the absolute heights of gauge blocks to be determined with an overall calibration uncertainty of 15 nm (k = 1). These results demonstrate a successful industrial application of an optical frequency synthesis employing a femtosecond laser, a technique that offers many possibilities for performing precision length metrology that is traceable to the well-defined international definition of time.

• 조명전기설비학회논문지
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• 제27권12호
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• pp.10-15
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• 2013

In this paper, we propose a Lyot-type optical fiber comb filter based on a polarization-diversity loop structure (PDLS), which has flat-top pass bands and multiwavelength switching capability. Generally, the PDLS can remove the dependency of the filter on input polarization. The proposed filter is composed of a polarization beam splitter, two half-wave plates (HWPs), and two polarization-maintaining fiber loops concatenated with a $60^{\circ}$ offset between their principal axes. By controlling two HWPs, it can operate in a flat-top band mode or a lossy flat-top band mode with an inherent insertion loss of ~3.49dB. In particular, flat-top bands can be interleaved in both modes, which cannot be realized in a Lyot-Sagnac comb filter based on a fiber coupler. Compared with Solc-type high-order comb filters with the same order, the proposed filter shows sharper transition between pass and stop bands.

• 천문학회보
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• 제35권1호
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• pp.74.2-74.2
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• 2010

We present a multi-wavelength study of a supercluster in the NEP region at z=0.087, using AKARI (Infrared space telescope) NEP-Wide (5.8 deg2) survey which has obtained an unique IR imaging dataset with contiguous wavelength coverage from 2 to $24{\mu}m$, overcoming the Spitzer limitation of imaging capability at $10-20{\mu}m$. The NEP-Wide survey is also covered in other wavelength such as X-ray, Radio, GALEX UV in the archive, optical (BRI from Maidanak 1.5m and CFHT's MegaPrime), and NIR imaging data (JH from KPNO 2.1m), with nearly 1900 optical spectra, mostly obtained by our group using MMT/Hectospec and WIYN/Hydra. Armed with the multiwavelength datasets, we investigate the connection between IR properties of galaxies and their environments as a tool to understand the evolution of galaxies in a supercluster environment. Specific attention will be given to MIR emission which can trace star formation activities and passive phases right after post-starbursts, and its relation to other wavelength data.

• 천문학회보
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• 제42권1호
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• pp.55.3-55.3
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• 2017

The L1641 cloud in Orion is an active site of star formation. We mapped a square region of 60 arcmin by 60 arcmin in the continuum emission from 0.89 mm to 2.0 mm wavelength using MUSIC mounted on the Caltech Submillimeter Observatory 10.4 m telescope. Eight sources were detected in at least two wavelength bands, and all the detected emission comes from thermal dust continuum radiation of dense cloud cores. Their spectral energy distributions were characterized. The dust emissivity spectral index is beta = 1.3 on average, within the range of typical cores in nearby star-forming regions. Two cores, V380 Ori NE and HH 34 MMS, have unusually low emissivity index of beta = 0.3. These cores may contain millimeter-sized dust grains, which suggests that the lifetime of some dense cores can be much longer than the free-fall timescale.