Browsing by Author "Chen, K. Y."

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Criterion for optimizing high-power acousto-optically Q-switched self-Raman yellow lasers with repetition rates up to 500 kHz
(2020-04-01)
Chen, Y. F.
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Chen, K. Y.
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Liu, Y. C.
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Chen, C. M.
;
Tsou, C. H.
The criterion for optimizing the high-power acousto-optically Q-switched self-Raman yellow laser is originally explored for the repetition rate within 100-500 kHz. The minimum allowed value for the gate-open time is experimentally verified to be determined by the pulse buildup time. By using the minimum allowed gate-open time, the highest conversion efficiency can be achieved to raise the output power by approximately 20% in comparison with the conventional results. At a repetition rate of 200 kHz, the maximum output power at 588 nm can be up to 8.8 W at an incident pump power of 26 W. Furthermore, a practical formula is developed to accurately calculate the threshold pump power as a function of the gate-open time for a given repetition rate. (C) 2020 Optical Society of America
Microwave-induced DC currents in mesoscopic structures
(2010-02-01)
Li, L. C.
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Sung, Y. T.
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Chang, C. W.
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Suen, Y. W.
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Chen, K. Y.
We report the power (P) dependence of microwave (MW)-induced current (I(ph)) of a 1-mu m sized mesoscopic structure fabricated from two-dimensional electron gas in the GaAs/AlGaAs heterostructure at temperature of 1.4 K. MW signals were fed onto the sample through a loop antenna nearby and I(ph) is measured from a pair of ohmic contacts. We found that I(ph) is proportional to P at low-P limit; this dependence has been predicted for diffusion-limited electron transport in mesoscopic systems. By contrast, for large P. the dependence is extremely non-monotonous and complicated; even though its physical origin is still not clear so far, our data suggest it is related to the scattering processes from boundaries and impurities in the mesoscopic structure. We also investigated the symmetry properties against reversal of magnetic field (B) and found that the field-symmetric part of I(ph)(B) is consistent with the variation of magnetoresistance; there exists also an anti-symmetric part, which should be related to time-reversal-symmetry-breaking scattering mechanisms in the channel. (C) 2009 Elsevier B.V. All rights reserved.
Probing mobility gaps at resistivity minima in the integer quantum Hall effect
(2008)
Liang, C. -T.
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Chen, K. Y.
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Wu, Jau-Yang
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Lin, S. D.
;
Lin, Li-Hung
Magneto-transport measurements are performed on the AlGaAs/GaAs quantum Hall (QH) devices fabricated recently by our group. A series of Hall plateaus are observed with increasing the perpendicular magnetic field, and the mobility gaps resulting from localization effects are investigated at the minima in the longitudinal resistivity. Only the gap corresponding to the filling factor i=2 is close to the expected cyclotron energy, and our study supports that the low-field QH conductors may suffer problems due to insufficient localization. The anomalous change on the Hall slope is observed when the i=3 plateau is destroyed by the large current.
Resonant spin dipole induced by an in-plane potential gradient spin-orbit interaction
(2007-10-01)
Chen, K. Y.
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Chu, C. S.
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Mal'shukov, A. G.
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電子物理學系
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Department of Electrophysics
Spin-orbit interaction (SOI) arising from in-plane potential gradient is invoked for the generation of spin accumulation in a driven electric field. The SOI and a local in-plane potential pattern together bring about resonant spin dependent scatterings to electrons in a nonequilibrium distribution. In the vicinity of a ring-shaped potential barrier pattern, a spin dipole distribution with a resonant dipole strength characteristic is obtained. As the chemical potential mu is increased across one such resonant energy, the dipole strength manifests both sign reversal and large amplitude enhancement. The scattering resonance, thus, provides an additional knob for the manipulation of the spin accumulation.