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Now showing 1 - 10 of 11

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.
;
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.
;
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.
;
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.
;
Chen, Y. F.
;
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
Frequency comb expansion in a monolithic self-mode-locked laser concurrent with stimulated Raman scattering
(2014-09-01)
Lee, C. Y.
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Chang, C. C.
;
Liang, H. C.
;
Chen, Y. F.
;
交大名義發表
The discovery of a novel phase-locked frequency comb generated from a monolithic laser with the concurrent processes of self-mode locking (SML) and stimulated Raman scattering (SRS) is reported. It is experimentally shown that the width of the Raman gain can be exploited to considerably expand the frequency comb of a monolithic SML crystal laser via the SRS process. At a pump power of 6.5 W, an output power of 140 mW in the Stokes wave with a pulse width as narrow as 2.9 ps at a pulse repetition rate of 6.615 GHz is obtained. The present finding not only provides useful insights into the monolithic intracavity SRS process but also paves the way for generating mode-locked pulses based on monolithic self-Raman crystals.
Efficient dual-wavelength laser at 946 and 1064 nm with compactly combined Nd:YAG and Nd:YVO4 crystals
(2013-04-01)
Cho, C. Y.
;
Chang, C. C.
;
Chen, Y. F.
;
電子物理學系
;
Department of Electrophysics
We originally employ a compact combination of a Nd:YAG crystal and a Nd:YVO4 crystal to develop an efficient dual-wavelength laser operating at 946 and 1064 nm. We exploit a short Nd:YAG crystal to generate 946 nm laser by reducing the reabsorption loss and a follow-up Nd:YVO4 crystal to generate a 1064 nm laser by absorbing the residual pump light. The output power ratio between the 946 and 1064 nm emissions can be flexibly adjusted from 0.3 to 0.9 by varying the separation between the two output couplers. At an incident pump power of 17 W, the total output power is generally higher than 5.2 W, with an overall optical-to-optical efficiency greater than 30%.
Characterization of Hot Cracking Due to Welding of High-Strength Aluminum Alloys
(2012)
Chang, C. C.
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Chen, C. L.
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Wen, J. Y.
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Cheng, C. M.
;
Chou, C. P.
The "Spot-Varestraint Test'' was applied to assess the sensitivity of three aluminum alloys-A2024-T351, A2219-T87, and A7050-T6 to hot cracking from welding. The results indicate that the number of cracks increases with increasing augmented strain. This phenomenon occurs in both the fusion and the heat-affected zones. The number of thermal cycles also has a significant influence on the heat-affected zone; the number of hot cracks increases, especially in the heat-affected zone of the metal weld, with increasing number of thermal cycles. The compositions of these three alloys show that A2024 and A7050 have similar tendencies to be subject to hot cracking, greater than A2219. With increasing number of thermal cycles, the hot cracks show the same tendency, A2024 > A7050 > 2219.
Spectroscopic study of bio-functionalized nanodiamonds
(2006-04-01)
Chung, P. -H.
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Perevedentseva, E.
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Tu, J. -S.
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Chang, C. C.
;
Cheng, C. -L.
Nano-scale materials with attached biomolecules on the surface can be used as bioprobes in cell and tissue analysis. The conjugation of these nanoparticles with biomolecules is one of the key steps in the development of bioprobes. In this work nanometer-sized diamonds (5 and 100 nm) are functionalized and conjugated with protein lysozyme via physical adsorption. The process of creating functional groups on the nanodiamond surface is studied using Fourier Transform Infrared-spectroscopy (FTIR). The conjugation of nanodiamonds with biontolecules and nanodiamond-biomolecule interaction are analyzed with UV/VIS and FTIR spectroscopy. (c) 2005 Elsevier B.V. All rights reserved.
Employing pipelined thinning architecture for real-tire fingerprint verifier
(2006-09-01)
Hsiao, P. Y.
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Chen, X. Z.
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Lin, C. C.
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Hua, C. H.
;
Chang, C. C.
Thinning is a very important operation in the pre-processing stage of fingerprint recognition. With the availability of fast thinning hardware, real-time image processing applications can be achieved. The authors introduce a detailed hardware architecture design of a thinning processor used in an embedded fingerprint recognition system. The proposed thinning algorithm has a parallel-pipelining structure suited to hardware realisation, which is implemented and verified using FPGA. Equipped with a modification unit array, a designated operating schedule, and an address generator based on systolic counter, this thinning processor is able to perform a thinning operation within 0.07 s at 40 MHz for a 512 x 512 picture, which is at least 40 times faster than software execution. Consequently, the proposed thinning processor was successfully integrated into a real-time fingerprint recognition system.

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