Browsing by Author "Chen, SW"

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Compact efficient intracavity optical parametric oscillator with a passively Q-switched Nd : YVO4/Cr4+: YAG laser in a hemispherical cavity
(2003-10-01)
Chen, YF
;
Chen, SW
;
Chen, YC
;
Lan, YP
;
Tsai, SW
A compact eye-safe optical parametric oscillator (OPO) using a noncritically phase-matched KTP crystal intracavity pumped by a passively Q-switched Nd: YVO4 laser is experimentally demonstrated. To enhance the performance of passive Q-switching, a Cr4+: YAG saturable absorber crystal is coated as an OPO output coupler in a nearly hemispherical cavity. With an incident pump power of 2.5 W, the compact intracavity OPO cavity, operating at 62.5 kHz, produces average powers at 1573 nm up to 255 mW and peak powers higher than 1 kW.
Cyclic behaviour of unreinforced and rib-reinforced moment connections
(2005-01-01)
Chen, CC
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Chen, SW
;
Chung, MD
;
Lin, MC
;
土木工程學系
This study investigates the cyclic behaviour of the beam-to-column welded moment connections used in steel moment-resisting frames. Two unreinforced welded connections were tested initially to elucidate the behaviour and failure mode. Test results showed that both specimens failed by the brittle fracture of the beam flange, initiated from the root of the weld access hole. Nonlinear finite element analysis was used to identify the causes of the failure. The stress concentration in the weld access hole region has the potential to cause the beam flange to fracture. Analytical results also demonstrated that reinforcing the connection with a single rib can reduce the concentration of stresses at the root of the weld access hole. Further tests of two specimens whose beam flanges were each reinforced by a single rib revealed that the single rib effectively prevents beam flange fracture in the weld access hole region. (C) 2004 Elsevier Ltd. All rights reserved.
Direct COSi2 thin-film formation with homogeneous nanograin-size distribution by oxide-mediated silicidation
(2004-09-01)
Chang, JJ
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Liu, CP
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Chen, SW
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Chang, CC
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Hsieh, TE
By annealing at 460 degreesC for 120 s followed by 600 degreesC 120 s, nanocrystalline CoSi2 thin film with an average grain size of 5 nm can be directly formed from a Co/SiOx/Si multilayer with the SiOx, as a mediated layer. It is found that annealing at 460 degreesC for enough time is crucial for generating enough diffusion channels within the SiOx, layer. After these channels are created, subsequent annealing at 600 degreesC keeps these channels open and is responsible for rapid grain growth. In other words, by using two-step annealing, nucleation and growth processes can be effectively controlled and, hence, the resulting microstructure. The homogeneous nanograin-size distribution is important for ultralarge-scale integration technology below 90 nm to prevent resistance degradation induced by CoSi2, agglomeration. (C) 2004 American Vacuum Society.
Efficient sub-nanosecond intracavity optical parametric oscillator pumped with a passively Q-switched Nd : GdVO4 laser
(2004-11-01)
Chen, YF
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Chen, SW
;
Tsai, LY
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Chen, YC
;
Chien, CH
An efficient diode-pumped passively Q-switched Nd:GdVO4/Cr4+:YAG laser was employed to generate a high-repetition-rate, high-peak-power eye-safe laser beam with an intracavity optical parametric oscillator (OPO) based on a KTP crystal. The conversion efficiency for the average power is 8.3% from pump diode input to OPO signal output and the slope efficiency is up to 10%. At an incident pump power of 14.5 W, the compact intracavity OPO cavity, operating at 46 kHz, produces average powers at 1571 nm up to 1.2 W with a pulse width as short as 700 ps.
Formation of pyramid-like nanostructures during cobalt film growth by magnetron sputtering
(2005-04-01)
Liu, CP
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Chang, JJ
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Chen, SW
;
Chung, HC
;
Wang, YL
Cobalt pyramid-like nanostructures with sharp tips were formed on the surfaces of cobalt thin films grown by magnetron sputtering only when a negative bias was applied. There are two types of pyramids, which grew on top of a columnar grain structure directly from Si(001) substrates. The formation of pyramid-like nanostructures is only selective to a epsilon-Co (hcp) thin film but not a alpha-Co (fcc) thin film, where the basal plane is 10 (1) over bar0 with several well-defined low-energy faceted planes. When grown on Si(111) substrates, the shape of the basal plane changes to a pentagon or other polygon. The island nucleation seems to depend on adatom energy, sputtering rate and the interface stress between the Co thin film and the substrate, but growth is significantly determined by the minimum surface configuration of the structure.
High-power efficient diode-pumped passively Q-switched Nd : YVO4/KTP/Cr4+ : YAG eye-safe laser
(2004-04-15)
Chen, YF
;
Chen, YC
;
Chen, SW
;
Lan, YP
;
電子物理學系
A high-power efficient eye-safe laser is experimentally realized by using an intracavity optical parametric oscillators of a diode-pumped passively Q-switched Nd:YVO4/Cr4+ :YAG laser. Considering the thermal lensing effects, the cavity length was designed to allow mode matching with the pump beam and to provide the proper spot size in the saturable absorber. With an incident pump power of 14.5 W, the compact intracavity OPO cavity, operating at 58.5 kHz, produces average powers at 1573 nm up to 1.56 W and peak powers higher than 5 kW. (C) 2004 Elsevier B.V. All rights reserved.
High-repetition-rate eye-safe optical parametric oscillator intracavity pumped by a diode-pumped Q-switched Nd : YVO4 laser
(2003-03-01)
Chen, YF
;
Chen, SW
;
Tsai, SW
;
Lan, YP
;
電子物理學系
A high-repetition-rate eye-safe optical parametric oscillator (OPO), using a non-critically phase-matched KTP crystal intracavity pumped by an acousto-optically (AO) Q-switched Nd:YVO4 laser, is experimentally demonstrated. It is found that the average OPO signal power at 1573 nm can be efficiently increased by increasing the pulse repetition rate. Moreover, the intracavity OPO process effectively shortens the pulse width so that it is in the range 5 similar to 8 ns for pulse repetition rates of 10 to 80 kHz. As a result of the relatively short pulse, the peak power at 1573 nm is higher than 2 kW at a pulse repetition rate of 80 kHz.
Impact of nitrogen and/or fluorine implantation on deep-submicron Co-salicide process
(2002-08-01)
Chang, TY
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Lei, TF
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Chao, TS
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Chen, SW
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Kao, LM
In our previous study, using NF3 annealed poly-Si to improve gate oxide integrity for Co-silicide process has been proposed [SSDM, 1998, p. 164]. It is very interesting and important to know the mechanism of both F and N incorporation in the SiO2 and Co-salicide. In this study, F and/or N will be implanted into poly-Si with/without Co-salicide process, to identify the interaction of N and F in the SiO2 and Co-salicide process. In our work, we will describe the optimized structure and F/N incorporation for Co-silicide process. (C) 2002 Elsevier Science Ltd. All rights reserved.
Output optimization of a high-repetition-rate diode-pumped Q-switched intracavity optical parametric oscillator at 1.57 mu m
(2003-10-01)
Chen, YF
;
Chen, SW
;
Tsai, SW
;
Lan, YP
;
電子物理學系
The output optimization of a high-repetition-rate diode-pumped Q-switched intracavity optical parametric oscillator at 1573 nm with a type-II non-critically phase-matched x-cut KTP is experimentally and theoretically studied. The optimum output reflectivity is found to be 85%-90% for the maximum average power. The average conversion efficiency from diode-laser input power to OPO signal output power is up to 15% at a pulse repetition of 80 kHz. However, the optimum output reflectivity for the maximum peak power is found to be 60%-70%; the overall peak power amounts to 3-4 kW at a pulse repetition of 80 kHz.
Stabilization and elimination of transient unstable mixed convective vortex flow of air in a bottom heated horizontal flat duct by top plate heating
(2004-09-01)
Chen, SW
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Chang, CY
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Lir, JT
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Lin, TF
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機械工程學系
An experiment combining flow visualization and temperature measurement is carried out here to study the possible stabilization and elimination of the buoyancy driven unstable longitudinal, transverse and mixed vortex flow in mixed convection of air in a bottom heated horizontal flat duct by the top plate heating. The top plate temperature is varied systematically to examine its effects on the spatial and temporal flow structures in the duct. How the top plate temperature and the Reynolds and Rayleigh numbers of the flow affect the vortex flow characteristics is investigated in detail. Specifically the experiment is conducted for the Reynolds number varying from 1 to 50, Rayleigh number from 4000 to 8000 and the non-dimensional top plate temperature from 0 to 1 at an interval of 1/8, covering a wide range of the buoyancy-to-inertia ratio. The results indicate that the top plate heating substantially stabilizes and for some cases even eliminates the longitudinal, transverse, mixed longitudinal and transverse, and irregular vortex flows induced by the buoyancy associated with the heated bottom plate of the duct. At the high top plate temperature even the entire irregular vortex flow can be eliminated and the flow becomes unidirectional in the duct. Obviously the transient velocity and temperature oscillations in the flow are completely suppressed. (C) 2004 Published by Elsevier Ltd.