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Now showing 1 - 10 of 25

A gasket-type standard leak element using femtosecond laser micromachining
(2020-10-01)
Chan, C. K.
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Tu, C. Y.
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Yeh, S. D.
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Chang, C. C.
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Lin, T. C.
A gasket-type standard leak element with a microfluidic channel was developed and measured. The microfluidic channel with a diameter of several micrometers and a length of one hundred micrometers was fabricated by using femtosecond laser micromachining. The conductances (<1 x 10(-6) L s(-1)) of the micmfluidic channel for various non-condensable gases - H-2, He, CH4, N-2 and CO2 were determined by a measuring system based on conductance modulation (CM) method. The experimental results show that the flow characteristics of our devices exhibit molecular flow at a pressure up to 100 mbar and the conductance values of H-2, He, CH4, N-2 and CO2 are inversely proportional to the square root of their molecular mass.
24-W cryogenically cooled Nd:YAG monolithic 946-nm laser with a slope efficiency > 70%
(2015-04-20)
Cho, C. Y.
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Lee, C. Y.
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Chang, C. C.
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Tuan, P. H.
;
Huang, K. F.
A high-power efficient monolithic Nd: YAG 946-nm laser is demonstrated at the cryogenic temperature. By exploring the absorption and the fluorescence spectra of the Nd: YAG crystal, it reveals the fact that the absorption bandwidth at 808 nm is narrowing and the fluorescence intensity at 1061 nm is significant enhanced when the temperature is decreased. The temperature dependence of the lasing threshold at 946 nm is found to display a minimum value near a temperature of 170 K. At an incident pump power of 34.5 W, the local heating leads the optimum temperature to be approximately 120 K and the maximum output power can reach 24.4 W with the conversion efficiency of 71% as well as the slope efficiency up to 75%. (C)2015 Optical Society of America
Exploiting concave-convex linear resonators to design end-pumped solid-state lasers with flexible cavity lengths: application for exploring the self-mode-locked operation
(2016-11-14)
Tuan, P. H.
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Chang, C. C.
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Lee, C. Y.
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Cho, C. Y.
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Liang, H. C.
The characteristics of a convex-concave linear resonator under the thermal lensing effect are theoretically analyzed to find an analytical model for designing end-pumped solid-state lasers with flexible cavity lengths. By exploiting the design model, the power scaling for continuous-wave operation under strong thermal lensing can be easily achieved in the proposed resonator with different cavity lengths. Furthermore, the proposed resonator is applied to explore the exclusive influence of cavity length on the self-mode-locked (SML) operation. It is discovered that the lasing longitudinal modes will split into multiple groups in optical spectrum to lead to a multi-pulse mode-locked temporal state when the cavity length increases. Finally, a theoretical model is derived to reconstruct the experimental results of SML operation to deduce a simple relationship between the group number of lasing modes and the cavity length. (C) 2016 Optical Society of America.
Structural distortion and electronic states of Rb doped WO3 by X-ray absorption spectroscopy
(2016-01-01)
Wang, Y. C.
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Hsu, C. H.
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Hsu, Y. Y.
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Chang, C. C.
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Dong, C. L.
Rubidium tungsten bronzes (RbxWO3) have recently attracted much attention due to their intriguing phenomena, such as complex structural phase transitions, strong electron-phonon coupling, and superconducting properties. This study investigates the local atomic and electronic structures of RbxWO3 (0.17 <= x <= 0.33). X-ray powder diffraction patterns showed a hexagonal tungsten bronze (HTB) phase. X-ray absorption spectra (XAS) at the W L-3-edge and Rb K-edge of RbxWO3 were carried out. The XAS analysis indicated a local distorted WO6 octahedron which leads to a splitting of e(g) and t(2g) energy states in the tungsten 5d orbital and this splitting of energy levels exhibited an asymmetrical behavior at x = 0.23 and 0.27. Overall analysis revealed a distortion of local atomic structure of the WO6 octahedra by rubidium doping, leading to the modification of the electronic structures of e(g) and t(2g) states in the tungsten 5d orbital, thereby accounting for the property changes in CDW formation and superconducting transition temperature of these materials.
Intracavity continuous-wave multiple stimulated-Raman-scattering emissions in a KTP crystal pumped by a Nd:YVO4 laser
(2015-08-24)
Lee, C. Y.
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Chang, C. C.
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Sung, C. L.
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Chen, Y. F.
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電子物理學系
Intracavity continuous-wave (CW) multiple stimulated-Raman-scattering emissions have been successfully demonstrated in a KTP crystal pumped by a Nd:YVO4 1064-nm laser for the first time. Three different output couplers (OCs) with high-reflection (HR) coating in the range of 1-1.1, 1-1.13, and 1-1.15 mu m are employed in the experiment to generate lasing wavelengths at 1095 (the first-Stokes emission of the 266 cm(-1) Raman shift), 1095 + 1128 (the first-and second-Stokes emission of the 266 cm-1 Raman shift), and 1095 + 1128 + 1149 nm (the first two Stokes emissions of the 266 cm-1 Raman shift and the first-Stokes emission of the 694 cm-1 Raman shift), separately. This Raman laser paves a way to produce more-closely spaced set of CW emission in the green-yellow region. (C) 2015 Optical Society of America
Modelling end-pumped passively Q-switched Nd-doped crystal lasers: manifestation by a Nd:YVO4/Cr4+:YAG system with a concave-convex resonator
(2017-02-06)
Tuan, P. H.
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Chang, C. C.
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Chang, F. L.
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Lee, C. Y.
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Sung, C. L.
A theoretical model for the passively Q-switched (PQS) operation which includes the spatial overlapping between the pump and lasing modes under the thermal lensing effect is developed to give a transcendental equation that can directly determine the critical parameters such as pulse energy, pulse repetition rate, and pulse width for the PQS performance. More importantly, an analytical function which gives the approximate solution for the transcendental equation as well as a specific critical criterion for good PQS operation are derived for practical analyses and design. A Nd: YVO4/Cr4+: YAG system with a concave-convex resonator which can achieve fairly stable PQS pulse trains even at a high pump level is further exploited to manifest the proposed spatially dependent model. The good agreement between the experimental results and the theoretical predictions is verified to show the feasibility of the proposed model for designing high-power PQS lasers with high accuracy. (C) 2017 Optical Society of America
Influence of Passivation Layers on Characteristics of High Mobility Amorphous Indium-Zinc-Tin-Oxide Thin-Film Transistors
(2016-01-01)
Liu, P. T.
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Chang, C. H.
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Zheng, G. T.
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Chang, C. C.
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電子工程學系及電子研究所
We investigated the influence of passivation-layer deposition on the characteristics of a-InZnSnO thin-film transistors (TFTs). The threshold voltage (Vth) of the TFTs shifted markedly as a result of the ion bombardment induced by the passivation layers above. By adjusting the post annealing temperature, the performance of the TFTs can be modulated. The a-InZnSnO TFTs after passivation exhibited good performance with a field-effect mobility of 21.34 cm(2)/Vs, a threshold voltage of -5.03V, and a subthreshold slope of 0.52 V/decade.
Generating high-peak-power structured lights in selectively pumped passively Q-switched lasers with astigmatic mode transformations
(2017-12-01)
Chang, C. C.
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Hsieh, Y. H.
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Lee, C. Y.
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Sung, C. L.
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Tuan, P. H.
Various high-order Hermite-Gaussian (HG) modes with high repetition rates and high peak powers are systematically generated by designing the cavity configuration to satisfy the criterion of the passive Q-switching. For the HG(m,0) modes with the order m = 1-9, the pulse repetition rate can exceed 100 kHz with peak power higher than 0.3 kW. For the HG(m,m) modes with the order m = 1-10, the pulse repetition rate can be up to 37 kHz with peak power higher than 0.35 kW. Furthermore, the high-order HG beams is transformed by using an astigmatic mode converter to generate various structured lights with optical vortices. Experimental patterns of the transformed high-order HG beams in the propagation are theoretically analyzed and the phase structures are numerically manifested.
Characterizing the propagation evolution of wave patterns and vortex structures in astigmatic transformations of Hermite-Gaussian beams
(2018-01-01)
Chen, Y. F.
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Chang, C. C.
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Lee, C. Y.
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Tung, J. C.
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Liang, H. C.
Theoretical wave functions are analytically derived to characterize the propagation evolution of the Hermite-Gaussian (HG) beams transformed by a single-lens astigmatic mode converter with arbitrary angle. The derived wave functions are related to the combination of the rotation transform and the antisymmetric fractional Fourier transform. The derived formula is systematically validated by using an off-axis diode-pumped solid-state laser to generate various high-order HG beams for mode conversions. In addition to validation, the creation and evolution of vortex structures in the transformed HG beams are numerically manifested. The present theoretical analyses can be used not only to characterize the evolution of the transformed beams but to design the optical vortex beams with various forms.
High-peak-power large-angular-momentum beams generated from passively Q-switched geometric modes with astigmatic transformation
(2017-12-01)
Chen, Y. F.
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Chang, C. C.
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Lee, C. Y.
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Sung, C. L.
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Tung, J. C.
The criterion of achieving efficient passive Q-switching is analyzed to design an off-axis pumped Nd:YVO4/Cr4+ : YAG laser with a degenerate cavity. Experimental results reveal that pure high-order HG(0,m) or HG(m,0) eigenmodes with the order m between 0 and 14 can be generated, depending on the off-axis displacement along the y axis or the x axis. On the other hand, lasing modes naturally turn into planar geometric modes when the off- axis displacement is larger than the value for exciting the HG(0,m) or HG(m,0) eigenmodes with m > 14. The overall peak powers for high- order eigenmodes or geometric modes can exceed 140 W. Furthermore, the high- order eigenmodes and geometric modes are employed to generate vortex beams with large orbital angular momentum by using an external cylindrical mode converter. Theoretical analyses are performed to confirm experimental results and to manifest the phase structures of the generated vortex beams. (C) 2017 Chinese Laser Press

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