Browsing by Author "Chang, C. C."

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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.
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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
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.
A robust certification service for highly dynamic MANET in emergency tasks
(2009-09-01)
Ge, M.
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Lam, K. Y.
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Gollmann, D.
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Chung, S. L.
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Chang, C. C.
In emergency tasks, cross-agency operations being carried out in disaster-hit areas require some supporting communication system for command and control. Mobile Ad hoc Network (MANET) is a very suitable way to meet such communication requirements since it can function without any pre-installed communication infrastructure. Owing to potential threats in the field environment and the unique features of MANET (e.g. the open nature of wireless links and the absence of security infrastructure), security of communications over MANET is a serious issue that is typically addressed by asymmetric cryptographic mechanisms. In this paper, we tackle issues critical to asymmetric key management in MANET, which almost invariably serves as a basis of security services in a network environment. To address the deficiencies of existing key management schemes, we propose the concept of mission-specific certificate to manage public keys in our scenario. For issuance and/or revocation of mission-specific certificate, a Mission-specific Certificate Authority (MCA), which consists of a collection of server nodes to operate the threshold cryptographic scheme, is proposed. Furthermore, to cater for the occurrence of network partitioning, which is common in highly dynamic MANET, we propose a partition-tolerant mechanism for MCA by introducing the notion of auxiliary server nodes. We discuss the security and performance of our scheme and show that our approach is a secure and partition-tolerant mechanism can effectively improve availability of the MCA. Copyright (C) 2009 John Wiley & Sons, Ltd.
Admittance spectroscopy of the electric properties of 1,4-bis[N-(1-naphthyl)-N '-phenylamino]-4,4 ' diamine doped with tungsten oxide
(2006)
Hsieh, M. T.
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Chang, C. C.
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Hu, C. A.
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Huang, Y. T.
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Yang, S. L.
We report an efficient p-type doping of NPB layer using WO(3) as a p-dopant. We find that increasing the WO(3) volume percentage can reduce the activation energy of the NPB layer and increase the hole concentration in NPB layer. As a result, the hole-injection can be improved via tunneling through a narrow depletion region due to the increasing band bending which corresponds to the difference of Fermi level position between the ITO and the NPB layer.
Assessment of autonomic nervous system by using empirical mode decomposition-based reflection wave analysis during non-stationary conditions
(2014-09-01)
Chang, C. C.
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Kao, S. C.
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Hsiao, T. C.
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Hsu, H. Y.
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分子醫學與生物工程研究所
Arterial blood pressure (ABP) is an important indicator of cardiovascular circulation and presents various intrinsic regulations. It has been found that the intrinsic characteristics of blood vessels can be assessed quantitatively by ABP analysis (called reflection wave analysis (RWA)), but conventional RWA is insufficient for assessment during non-stationary conditions, such as the Valsalva maneuver. Recently, a novel adaptive method called empirical mode decomposition (EMD) was proposed for non-stationary data analysis. This study proposed a RWA algorithm based on EMD (EMD-RWA). A total of 51 subjects participated in this study, including 39 healthy subjects and 12 patients with autonomic nervous system (ANS) dysfunction. The results showed that EMD-RWA provided a reliable estimation of reflection time in baseline and head-up tilt (HUT). Moreover, the estimated reflection time is able to assess the ANS function non-invasively, both in normal, healthy subjects and in the patients with ANS dysfunction. EMD-RWA provides a new approach for reflection time estimation in non-stationary conditions, and also helps with non-invasive ANS assessment.
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.
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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.
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.
Cryogenically monolithic self-Raman lasers: observation of single-longitudinal-mode operation
(2015-05-01)
Lee, C. Y.
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Chang, C. C.
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Tuan, P. H.
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Cho, C. Y.
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Huang, K. F.
A cryogenically monolithic Nd:YVO4 self-Raman laser is experimentally explored and theoretically analyzed. The variation of the stimulated Raman scattering (SRS) threshold on the temperature is found to be nonlinear because the reduction of thermal lensing enlarges the cavity mode size. In spite of the nonlinear variation of the SRS threshold on the temperature, the overall SRS output power can be efficiently increased from 0.78 to 1.36 W for temperature decreasing from 285 to 80 K at an absorbed power of 17.2 W. More interestingly, the single-longitudinal-mode operation is experimentally achieved when temperature is lower than 125 K. (C) 2015 Optical Society of America
Diode-end-pumped solid-state lasers with dual gain media for multi-wavelength emission
(2015-01-01)
Cho, C. Y.
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Chang, C. C.
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Chen, Y. F.
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電子物理學系
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Department of Electrophysics
We develop a theoretical model for designing a compact efficient multi-wavelength laser with dual gain media in a shared resonator. The developed model can be used to analyze the optimal output reflectivity for each wavelength to achieve maximum output power for multi-wavelength emission. We further demonstrate a dual-wavelength laser at 946 nm and 1064 nm with Nd: YAG and Nd: YVO4 crystals to confirm the numerical analysis. Under optimum conditions and at incident pump power of 17 W, output power at 946 nm and 1064 nm was up to 2.51 W and 2.81 W, respectively.
Effect of Laser Welding on Properties of Dissimilar Joint of Al-Mg-Si and Al-Mn Aluminum Alloys
(2010-03-01)
Chang, C. C.
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Chou, C. P.
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Hsu, S. N.
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Hsiung, G. Y.
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Chen, J. R.
This study discusses the welding properties for the components of an aluminum-alloy ultra-high vacuum chamber and beam position monitor (BPM). The welding parameters include the modes of laser output (pulsed wave and continuous wave), welding speed, shield gas flow, welding bead structure, and focusing distance. The results showed that the welding defect rate of the pulsed wave type was larger than that of the continuous wave type. The crack in the welding bead reduced with decreasing welding speed. The fusion penetration of the welding bead was higher when the focusing distance was long enough to deepen into the welding material. Weld morphology during the experimental process revealed the proper flow of shield gas. The adaptability design of the welding bead structure in the preceding processes had more effect on overall welding structure and morphology.
Efficient dual-wavelength laser at 946 and 1064 nm with compactly combined Nd:YAG and Nd:YVO4 crystals
(2013-04-01)
Cho, C. Y.
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Chang, C. C.
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Chen, Y. F.
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電子物理學系
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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%.
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.
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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.
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.
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.
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Liang, H. C.
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Chen, Y. F.
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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.
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.
Generation of terahertz optical beating from a simultaneously self-mode-locked Nd: YAG laser at 1064 and 1123 nm
(2017-01-15)
Sung, C. L.
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Lee, C. Y.
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Chang, C. C.
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Liang, H. C.
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Chen, Y. F.
The reflectivity of the output coupler is designed to achieve the synchronously self-mode-locked operation at 1064 and 1123 nm in a diode-end-pumped Nd:YAG laser. Numerical analyses are performed to confirm that the designed output coupler can lead the emission lines to be predominant at 1064 and 1123 nm. Moreover, the crossover of the threshold pump powers for the 1064 and 1123 nm emission lines can be exploited to obtain the single central wavelength of 1064 nm or the single central wavelength of 1123 nm or, simultaneously, dual-central-wavelength self-mode-locked operation by finely adjusting the cavity alignment. For the dual-central-wavelength mode-locked emissions, the pulse repetition rate and the pulse duration are 4.5 GHz and 50.8 ps, respectively. The maximum output power can be up to 2.47 W at a pump power of 7.5 W. The synchronization of the 1064 and 1123 nm mode-locked pulses generates the optical beating pulse trains with repetition rates up to 14.7 THz. (C) 2017 Optical Society of America
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
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.
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
Long Photon Lifetime from Microdisk Cavity Laser with Type II GaSb/GaAs Quantum Dots
(2013-01-01)
Hsu, K. S.
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Chang, C. C.
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Lin, W. H.
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Shih, M. H.
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Lin, S. Y.
Microdisk lasers with active region made of type II GaSb/GaAs quantum dots on the GaAs substrate have been demonstrated. Lasing wavelengths near 1 mu m was achieved and longer photon lifetime from type II structure also observed. (C) 2013 Optical Society of America