Browsing by Author "Chen, YF"

Now showing 1 - 20 of 117

A diode-pumped high power Q-switched and self-mode-locked Nd : YVO4 laser with a LiF : F-2(-) saturable absorber
(2001-08-01)
Chen, YF
;
Tsai, SW
;
Wang, SC
;
Chen, J
;
電子物理學系
Simultaneous mode-locking and Q-switching has been accomplished in a diode-pumped Nd:YVO4/LiF:F-2(-) laser. At an absorbed pump power of 23.6 W, the average output power was 6.0W and the repetition rate of the Q-switched pulse was 260 kHz. A depth of mode-locking of 100% was obtained and there was no satellite pulse between mode-locked pulse trains. The mode-locked pulse inside the Q-switched pulse had a repetition rate of approximately 148 MHz and its average duration was estimated to be around 75 ps.
An evolutionary approach with pharmacophore-based scoring functions for virtual database screening
(2004)
Yang, JM
;
Shen, TW
;
Chen, YF
;
Chiu, YY
;
生物科技學系
We have developed a new tool for virtual database screening. This tool, referred to as the Generic Evolutionary Method for molecular DOCKing (GEMDOCK), combines an evolutionary approach and a new pharmacophore-based scoring function. The former integrates discrete and continuous global search strategies with local search strategies to speed up convergence. The latter simultaneously serves as the scoring function of both molecular docking and post-docking analysis to improve the number of the true positives. We accessed the accuracy of our approach on HSV-1 thymidine kinase using a ligand database on which competing tools were evaluated. The accuracies of our predictions were 0.54 for the GH score and 1.62% for the false positive rate when the true positive rate was 100%. We found that our pharmacophore-based scoring function indeed is able to reduce the number of the false positives. These results suggest that GEMDOCK is robust and can be a useful tool for virtual database screening.
Analysis of passively Q-switched lasers with simultaneous modelocking
(2002-03-01)
Chen, YF
;
Lee, JL
;
Hsieh, HD
;
Tsai, SW
;
電子物理學系
Simultaneous Q-switching and modelocking in a diode-pumped Nd: YAG/Cr4+ : YAG laser is experimentally demonstrated. A general recurrence is derived for the analysis of the temporal shape of a single Q-switched envelope with modelocked pulse trains. With the developed model, the mode-locked pulse energy and the total Q-switched pulse energy can be calculated. Excellent agreement was found between the present results and detailed theoretical computations.
Analytical functions for the optimization of second-harmonic generation and parametric generation by focused Gaussian beams
(2003-06-01)
Chen, YF
;
Chen, YC
;
電子物理學系
;
Department of Electrophysics
An analytical function involving four parameters is proposed to express the second-harmonic generation efficiency as well as the parametric generation gain coefficient in the Boyd-Kleinman theory. The analytical function clearly reveals the dependence of conversion efficiency on the focusing parameter and the walk-off parameter. Moreover, the optimum focusing parameter and its corresponding maximum efficiency are explicitly given in the analytical function, leading to a straightforward evaluation of a given crystal performance.
Analytical model for design criteria of passively Q-switched laser
(2001-03-01)
Chen, YF
;
Lan, YP
;
Chang, HL
;
電子物理學系
;
光電工程學系
A general and straightforward model was developed for the design of passively Q-switched lasers. With the second-threshold criterion and using a numerically fitting procedure, the output pulse energy was expressed as an analytical function of the initial transmission of the saturable absorber and the reflectivity of the output coupler. An analytical expression for the optimal output reflectivity was also obtained for maximizing the output pulse energy of a passively Q-switched laser with a given initial transmission of the saturable absorber. Excellent agreement was studied between the present results and detailed theoretical computations. A Nd:YAG laser with Cr4+:YAG as a saturable absorber was performed to illustrate the use of the present model.
Comment on "Formation of repetitively nanosecond spatial solitons in a saturable absorber Q-switched laser" - Reply
(2005-06-24)
Chen, YF
;
Huang, KF
;
電子物理學系
;
Department of Electrophysics
Compact efficient all-solid-state eye-safe laser with self-frequency Raman conversion in a Nd : YVO4 crystal
(2004-09-15)
Chen, YF
;
電子物理學系
;
Department of Electrophysics
An efficient compact eye-safe laser at 1525 nm is presented by use of self-frequency Raman conversion in a diode-pumped actively Q-switched Nd:YVO4 1342-nm laser. At an incident pump power of 13.5 W, the self-stimulated Raman laser produces 1.2 W of 1525-nm average output power at a repetition rate of 20 kHz. The corresponding peak power at 1525 nm is generally greater than 10 kW for repetition rates from 5 to 20 kHz. (C) 2004 Optical Society of America.
Compact efficient diode-pumped Nd : YVO4 Q-switched blue laser with intracavity frequency tripling
(2005-08-01)
Chen, YF
;
Chen, YS
;
Ou, TH
;
Su, KW
;
電子物理學系
We demonstrate a compact efficient diode-pumped acousto-optically Q-switched intracavity-frequency-tripled Nd:YVO4 blue laser. The optimum polarization state is experimentally investigated to optimize the output performance. Greater than 280 mW of 447-nm average power at a repetition rate of 25 kHz was generated with a 15-W diode pump power. At 25 kHz, the pulse width is shorter than 15 ns and the peak power is higher than 800 W.
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.
Compact efficient passively Q-switched Nd : GdVO4/PPLN/Cr4+: YAG tunable intracavity optical parametric oscillator
(2005-11-14)
Tsai, LY
;
Chen, YF
;
Lin, ST
;
Lin, YY
;
Huang, YC
We report on a compact efficient diode pumped passively Q-switched Nd:GdVO4/ Cr4+:YAG/ PPLN intracavity optical parametric oscillator (OPO) with a shared-resonator configuration. Experimental results reveal that the amplitude stability of the shared-resonator configuration is substantially superior to that of the conventional coupled-resonator configuration. At a diode pump power of 15 W, the compact intracavity OPO cavity produces the average power greater than 900 mW with a pulse repetition rate of 36 kHz. The output pulses noticeably display the mode-locking phenomenon that leads to the maximum peak power to be higher than 20 kW. (c) 2005 Optical Society of America.
Compact efficient self-frequency Raman conversion in diode-pumped passively Q-switched Nd : GdVO4 laser
(2004-04-01)
Chen, YF
;
電子物理學系
;
Department of Electrophysics
I report the first demonstration of the generation of efficient sub-nanosecond self-stimulated Raman pulses by a diode-pumped passively Q-switched Nd:GdVO4/Cr4+:YAG laser. The conversion efficiency for the average power is 7% from pump diode input to self-Raman output and the slope efficiency is up to 14%. At an incident pump power of 2.0 W, the pulse duration, pulse energy, and peak power for the Stokes wavelength of 1175.6 nm were found to be 750 ps, 6.3 muJ, and 8.4 kW, respectively, with a pulse-repetition rate of 22 kHz.
Comparative studies on field emission properties of carbon-based materials
(2000-04-01)
Chen, KH
;
Wu, JJ
;
Chen, LC
;
Wen, CY
;
Kichambare, PD
Comparative studies on field emission properties of various carbon-related materials including diamond, amorphous carbon, SiCN films, SiCN nanorods, and carbon nanotubes are presented. While diamond is well known for its potential use in cold cathodes, the emission current of a hydrogen-treated diamond film is relatively small compared to that of amorphous carbon or diamond-like-carbon film. Meanwhile, carbon nanotubes have demonstrated large emission currents at much lower threshold voltages, showing their potential for applications. However, the emission from carbon nanotubes is subjected to significant decay under long-term operation. The emission current and long-term stability can be improved using a new SiCN compound with nanorod morphology. The effective barrier height and the held enhancement factor derived from the Fowler-Nordheim equation are discussed in this paper. (C) 2000 Elsevier Science S.A. All rights reserved.
Comparison between c-cut and A-cut Nd : YVO4 lasers passively Q-switched with a Cr4+: YAG saturable absorber
(2002-04-01)
Chen, YF
;
Lan, YP
;
電子物理學系
;
光電工程學系
;
Department of Electrophysics
Comparison between c-cut and a-cut Nd:YVO4 microchip lasers passively Q-switched with a Cr4+:YAG saturable absorber is experimentally made. The lower emission cross section of the c-cut Nd:YVO4 crystal can enhance the passive Q-switching effect to produce a peak power 10 times higher than that obtained with the a-cut crystal. The experimental result further reveals that a c-cut Nd:YVO4 crystal is a very convenient material for short-pulse (sub-nanosecond) and high-peak-power (> 10 kW) lasers.
Comparison between shared and coupled resonators for passively Q-switched Nd : GdVO4 intracavity optical parametric oscillators
(2006-03-01)
Chen, YF
;
Tsai, LY
;
電子物理學系
;
Department of Electrophysics
Comparison between the shared and coupled resonators for the intracavity optical parametric oscillators pumped by passively Q-switched Nd:GdVO4 lasers is experimentally made. The shared and coupled resonators are found to be complementary in the performances of the pulse repetition rate, pulse duration and pulse energy. It is also found that the output signal pulses of the shared cavity explicitly display the mode-locking phenomenon. On the whole, the amplitude stability of the shared cavity configuration is substantially superior to that of the coupled cavity configuration.
Consensus scoring criteria for improving enrichment in virtual screening
(2005-07-01)
Yang, JM
;
Chen, YF
;
Shen, TW
;
Kristal, BS
;
Hsu, DF
Virtual screening of molecular compound libraries is a potentially powerful and inexpensive method for the discovery of novel lead compounds for drug development. The major weakness of virtual screening-the inability to consistently identify true positives (leads)-is likely due to our incomplete understanding of the chemistry involved in ligand binding and the subsequently imprecise scoring algorithms. It has been demonstrated that combining multiple scoring functions (consensus scoring) improves the enrichment of true positives. Previous efforts at consensus scoring have largely focused on empirical results, but they have yet to provide a theoretical analysis that gives insight into real features of combinations and data fusion for virtual screening. Results: We demonstrate that combining multiple scoring functions improves the enrichment of true positives only if (a) each of the individual scoring functions has relatively high performance and (b) the individual scoring functions are distinctive. Notably, these two prediction variables are previously established criteria for the performance of data fusion approaches using either rank or score combinations. This work, thus, establishes a potential theoretical basis for the probable success of data fusion approaches to improve yields in in silico screening experiments. Furthermore, it is similarly established that the second criterion (b) can, in at least some cases, be functionally defined as the area between the rank versus score plots generated by the two (or more) algorithms. Because rank-score plots are independent of the performance of the individual scoring function, this establishes a second theoretically defined approach to determining the likely success of combining data from different predictive algorithms. This approach is, thus, useful in practical settings in the virtual screening process when the performance of at least two individual scoring functions (such as in criterion a) can be estimated as having a high likelihood of having high performance, even if no training sets are available. We provide initial validation of this theoretical approach using data from five scoring systems with two evolutionary docking algorithms on four targets, thymidine kinase, human dihydrofolate reductase, and estrogen receptors of antagonists and agonists. Our procedure is computationally efficient, able to adapt to different situations, and scalable to a large number of compounds as well as to a greater number of combinations. Results of the experiment show a fairly significant improvement (vs single algorithms) in several measures of scoring quality, specifically "goodness-of-hit" scores, false positive rates, and "enrichment". This approach (available online at http://gemdock.life. nctu.edu.tw/dock/download.php) has practical utility for cases where the basic tools are known or believed to be generally applicable, but where specific training sets are absent.
Construction of a near-field spectrum analysis system using bent tapered fiber probes
(2001-01-01)
Chen, SH
;
Chen, YF
;
電子物理學系
;
Department of Electrophysics
We take advantage of a combination of laser heating and pulling and electric arc bending to fabricate bent tapered fiber probes. The bent angles can be varied from 30 degrees to 70 degrees and tip diameters fall within a few tens of nanometers. These bent fiber probes can easily be adapted into any dynamic mode atomic force microscope. By proper manipulation of the bent angles, a spatial resolution of up to 60 nm is achievable. After coating the bent fiber probes with a thin layer of Pt/Pd film by ion sputtering, the transmission efficiency is measured to be around 10(-5), which is applicable for near-field spectrum analysis experiment. (C) 2001 American Institute of Physics.
Continuous-wave high-power (320 mW) single mode operation of electronic vertically coupled InAs/GaAs quantum dot narrow-ridge-waveguide lasers
(2005-12-01)
Wang, JS
;
Lin, G
;
Hsiao, RS
;
Yang, CS
;
Lai, CM
High-power 3 mu m-wide narrow-ridge-waveguide lasers with ten stacks of electronic vertically coupled InAs/GaAs quantum dots in the active region were demonstrated. Unlike that from conventional uncoupled InAs quantum dot lasers, a narrow lasing spectrum was observed because the carriers tunneled in the vertical direction. Continuous-wave operation in single lateral mode yielded a kink-free output power of 320 mW with an efficiency of 0.46 W/A , and a sensitivity of lasing wavelength to temperature of 0.28 nm/K.
cw dual-wavelength operation of a diode-end-pumped Nd : YVO4 laser
(2000-04-01)
Chen, YF
;
電子物理學系
;
Department of Electrophysics
A dual-wavelength continuous wave (cw) diode-end-pumped Nd:YVO4 laser that generates simultaneous laser action at the wavelengths 1064 nm and 1342 nm is demonstrated. The optimum oscillation condition for the simultaneous dual-wavelength operation in a diode-end-pumped solid-state laser has been derived. The relationship between the laser cavity and the output stability is also studied. Experimental results show that the stability of the output power at the two wavelengths could be enhanced by use of a three-mirror cavity.
Design of efficient high-gower diode-end-pumped TEMoo Nd : YVO4 laser
(2000)
Chen, YF
;
Liao, CC
;
Lan, YP
;
Wang, SC
;
電子物理學系
A systematic investigation on a series of Nd:YVO4 crystals with different dopant concentrations is conducted to scale the diode-end-pumped laser performance to higher powers. The analysis reveals that lowering the dopant concentration linearly extends the fracture-limited pump power and the thermal shock parameter plays an important role in the estimation of the fracture-limited pump power: The thermal shock parameter in Nd:YVO4 crystals has been determined from the laser experiments, Based onthe analysis, we demonstrate a compact and efficient diode-end-pumped TEMoo laser with output power of 25.2-W for 52-W of incident pump power by use of a single YVO4 crystal with a Nd concentration of 0.3 at.%. In Q-switched operation 2 I-W of average power at a pulse repetition rate of 100 kHz and similar to 1.1-m pulse energy at a pulse repetition rate of 10 kHz were produced.
Determination of the Auger upconversion rate in fiber-coupled diode end-pumped Nd : YAG and Nd : YVO4 crystals
(2000-04-01)
Chen, YF
;
Liao, CC
;
Lan, YP
;
Wang, SC
;
電子物理學系
An analytical model is developed to study the influence of the Auger upconversion process on the thermal loading under lasing and nonlasing conditions. With the developed model, Auger upconversion rates can be determined by comparing theoretical calculations with experimental results for the ratio of the thermal loading under lasing and nonlasing conditions. The upconversion rates obtained with the present method are compared with the results measured from the fluorescence decay experiment.