• Title/Summary/Keyword: Laser threshold

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Lasing Modes of LD-Pumped Fiber Grating Lasers

  • Park, Dong-Wook;Hwang, Joon-Hwan
    • Journal of the Optical Society of Korea
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    • v.6 no.3
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    • pp.108-116
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    • 2002
  • Lasing modes of laser-diode-pumped fiber grating lasers are analyzed by coupled-mode theory. First, a power series solution of the coupled-mode equations is derived under the assumption of an exponentially-decreasing longitudinal modal gain profile for a laser-diode-pumped grating section, followed by determination of the transfer matrix for such a section. Based on these results, an eigenvalue equation for oscillation is then derived and solved numerically for the lasing modes of uniform and phase-shifted fiber grating lasers. Comparisons made with the uniform-gain results indicate that, surprisingly, the lasing mode characteristics are not as significantly altered as might be expected in most cases, even for a highly nonuniform gain profile. In the case of a phase-shifted grating, the phase-shift position appears to have a much greater impact on determining the threshold gain, the modal field distribution, and the front-to-back output power ratio.

Effects of electrical stress on low temperature p-channel poly-Si TFT′s (저온에서 제작된 p-채널 poly-Si TFT의 전기적 스트레스 효과)

  • 백희원;임동규;임석범;정주용;이진민;김영호
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2000.07a
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    • pp.324-327
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    • 2000
  • In this paper, the effects of negative and positive bias stress on p-channel poly-Si TFT's fabricated by excimer laser annealing have been investigated After positive and negative bias stress, transcon-ductance(g$_{m}$) is increased because of a reduction of the effective channel length due to the injected electron in the gate oxide. In the positive bias stress, the injection of hole is appeared after stress time of 3600sec and g$_{m}$ is decreased. On the other hand, the gate voltage at the maximum g$_{m}$, S-swing and threshold voltage(V$_{th}$) are decreased because of the interface state generation due to the injection of electrons into the gate oxide.e.ide.e.

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Stabilization of ionization in an intense laser field (초강력 레이저에 의한 원자의 이온화의 안정화)

  • 권덕희;이해웅;이용주
    • Proceedings of the Optical Society of Korea Conference
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    • 2002.07a
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    • pp.10-11
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    • 2002
  • 최근 수년간 원자의 쿨롱(Coulomb) 인력을 능가하는 전기장을 발생하는 강력한 레이저(I>$10^{16}$ W/$\textrm{cm}^2$)와 상호작용하는 원자계에서 보여지는 많은 흥미로운 비선형 현상들, 예를 들면 다중광자 이온화(multiphoton ionization), 임계 이상의 이온화(above-threshold ionization), 고차조화파 발생(high-harmonic generation)등에 대한 연구가 활발히 진행되어왔다. 또 하나의 비선형 현상으로 원자의 이온화의 안정화(stabilization)가 있고, 이 현상은 레이저의 세기가 증가하면서 이온화율이 포화되거나 감소하는 것을 의미한다. (중략)

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Low-coherence non-scanning michelson interferometry using visible broadband light source (가시광 영역의 저간섭성 광원을 이용한 마이겔슨 간섭계)

  • 송민호;이병호
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.33A no.10
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    • pp.160-167
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    • 1996
  • A new pathlength deviation detection technique which is composed of michelson interferometer is described and verified experimentally. The technique uses a sub-threshold biased visible laser diode of 20$\mu$m coherence length as a low-coherent light source. And for zeroth-order fringe(which is the largest among fringes) identification we used a piezoelectric transducer with a large modulation smplitude, which enables without the need of constant velocity scanning, to distinguish reflection surfaces separated by more than 10$\mu$m with a resolution of less than half-wavelength.

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Modelling the Mode Behavior of Circular Vertical-Cavity Surface-Emitting Laser

  • Ho, Kwang-Chun
    • International Journal of Internet, Broadcasting and Communication
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    • v.4 no.2
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    • pp.22-27
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    • 2012
  • The design characteristics of circular vertical-cavity surface-emitting lasers are studied by using a newly developed equivalent network. Optical parameters, such as the stop-band or the reflectivity of periodic mirrors and the resonance wavelength, are explored for the design of these structures. To evaluate the differential quantum efficiency and the threshold current density, a transverse resonance condition of modal transmission-line theory is also utilized. This approach dramatically reduces the computational time as well as gives an explicit insight to explore the optical characteristics of circular vertical-cavity surface-emitting lasers (VCSELs).

Lasing Characteristics of Dye-Doped Cholesteric Liquid Crystal

  • Porov, Preeti;Chandel, Vishal Singh;Manohar, Rajiv
    • Transactions on Electrical and Electronic Materials
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    • v.16 no.3
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    • pp.117-123
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    • 2015
  • Cholesteric liquid crystals are one dimensional photonic band-gap materials due to their birefringence and periodic structure. Dye doped cholesteric liquid crystals are self-assembling, mirror-less, low threshold laser structures that exhibit distributed feedback. In this review paper, we have presented the development in the field of lasing characteristics of dye doped cholesteric liquid crystals.

Design of the nonlinearly chirped grating for broadly tunable semiconductor lasers (넓은 파장 가변영역을 가지는 반도체 레이저를 위한 Nonlinearly Chirped Grating의 설계)

  • 김덕봉;최안식;윤태훈;김재창;김선호
    • Korean Journal of Optics and Photonics
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    • v.7 no.4
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    • pp.370-374
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    • 1996
  • A Superstructure Grating(SSG) Distributed-Bragg-Reflector(DBR) laser has a broad tuning range with a good mode suppression ratio. However, gaps of channel are observed in the wavelength-tuning characteristics of an SSGDBR laser which employs linearly-chirped DBR mirrors. We found by numerical simulation that the gaps may be attributed to the nonuniform reflection-peak heights of a linearly-chirped DBR mirrors. We propose a nonlinearly chirped grating DBR mirror structure that makes reflection-peak heights almost uniform. Therefore a nonlinearly chirped grating structure can be employed in an extended tuning range semiconductor laser to achieve gap-free tuning and low threshold current operation simultaneously.

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Characteristics of Er-Doped Fiber Laser on Resonator Reflectivities and Pump Power (공진기 반사율과 펌프 파워에 따른 어븀 광섬유 레이저의 특성)

  • 박서연;이학규;김경헌;이동한
    • Korean Journal of Optics and Photonics
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    • v.5 no.2
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    • pp.286-290
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    • 1994
  • Lasing characteristics of an Er-doped fiber laser have been investigated at various conditions of resonator reflectivities and pump powers. Variation of the laser wavelength with various mirror reflectivities has been compared with the theoretical analysis based on absorption, gain spectra, and resonator parameters. The maximum slope efficiency of 38% was obtained with the resonator's mirror reflectivities of 100% and 4% on both sides, and the threshold powers were varied from 7.8 mW to 5.6 mW, and lasing wavelengths were varied $1.532\mum to 1.563\mum and 1.558 \mum to 1.570 \mum$ for 6 and 15.8 mlong Er-doped fiber, respectively, as the resonator reflectivities were changed from 0.0016 to 0.9.to 0.9.

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Numerical Investigation on Nonequilibrium Energy Transfer in Thin Metal Film Structures during the Irradiation of Femtosecond Pulse Laser (펨토초 레이저가 조사되는 동안의 금속 박막내의 비평형 에너지 전달 현상에 대한 수치해석 연구)

  • Sim, Hyung-Sub;Lee, Seong-Hyuk
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.56 no.2
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    • pp.367-373
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    • 2007
  • The present study investigates numerically nonequilibrium energy transfer between electrons and phonons in metal thin films irradiated by ultrashort pulse lasers and it also provides the temporal and spatial variations of electron and phonon temperatures using the well-established two-temperature model(TTM) on the basis of the Boltzmann transport equation(BTE). This article predicts the crater shapes in gold film structures, and compares the results by using two-dimensional energy transport equation. From the results, it is found that nonequilibrium energy transfer between electrons and phonons takes place, and the equilibrium time increases with the increase of laser fluence. On the other hand, above threshold fluence the ablation time doesn't change nearly with increasing fluences. Compared with one-dimensional TTM, it also reveals that the temporal distributions of electron and phonon temperatures at the top surface estimated by using two-dimensional TTM have a similar tendency. The results show that two-dimensional TTM can simulate the crater shape of metals during the irradiation of femtosecond pulse lasers and the absorbed energy is propagated to z-direction faster than to r-direction.