Browsing by Author "Hsieh, WF"

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Analytical spatio-temporal design of Kerr lens mode-locked laser resonators
(1996-08-01)
Lin, KH
;
Hsieh, WF
;
光電工程研究所
;
Institute of EO Enginerring
An analytical method of spatio-temporal design for a Kerr lens mode-locked Ti:sapphire laser is presented. Various spatial and temporal effects are considered to derive simple quadratic equations of the pulse width for both standing- and traveling-wave cavities. By solving the quadratic equation, we obtain the relations between pulse width and other cavity parameters for a given system for optimal design of a Kerr lens mode-locked cavity and to generate the shortest laser pulses. Our theoretical results agree well with the experimental results, and the computation time of this analytic approach for cavity parameters is reduced drastically as compared with an iteratively numerical approach. (C) 1996 Optical Society of America.
Analytical spatio-temporal design of Kerr lens mode-locked laser resonators
(1996-08-01)
Lin, KH
;
Hsieh, WF
;
交大名義發表
;
光電工程學系
;
National Chiao Tung University
An analytical method of spatio-temporal design for a Kerr lens mode-locked Ti:sapphire laser is presented. Various spatial and temporal effects are considered to derive simple quadratic equations of the pulse width for both standing- and traveling-wave cavities. By solving the quadratic equation, we obtain the relations between pulse width and other cavity parameters for a given system for optimal design of a Kerr lens mode-locked cavity and to generate the shortest laser pulses. Our theoretical results agree well with the experimental results, and the computation time of this analytic approach for cavity parameters is reduced drastically as compared with an iteratively numerical approach. (C) 1996 Optical Society of America.
Band gap engineering and spatial confinement of optical phonon in ZnO quantum dots
(2006-06-26)
Lin, KF
;
Cheng, HM
;
Hsu, HC
;
Hsieh, WF
;
光電工程學系
Both band gap engineering and spatial confinement of optical phonon were observed depending upon the size of ZnO quantum dots at room temperature. Size-dependent blueshifts of photoluminescence and absorption spectra reveal the quantum confinement effect. The measured Raman spectral shift and asymmetry for the E-2(high) mode caused by localization of optical phonons agree well with that calculated by using the modified spatial correlation model. (c) 2006 American Institute of Physics.
Band gap variation of size-controlled ZnO quantum dots synthesized by sol-gel method
(2005-06-30)
Lin, KF
;
Cheng, HM
;
Hsu, HC
;
Lin, LJ
;
Hsieh, WF
ZnO quantum dots were synthesized successfully via a simple sol-gel method. The average size of quantum dots can be tailored using well-controlled concentration of zinc precursor. Size-dependent blue shifts of photoluminescence and absorption spectra revealed the quantum confinement effect. The band gap enlargement is in agreement with the theoretical calculation based on the effective mass model. Furthermore, as the particle size decreases, we observed an increase in the size-dependent Stokes shift of the photoluminescence peak relative to the absorption onset. (c) 2005 Elsevier B.V. All rights reserved.
Beam-propagation-dominant instability in an axially pumped solid-state laser near degenerate resonator configurations
(2001-08-01)
Chen, CH
;
Wei, MD
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
Propagation-dominant instabilities and chaos were found under so-called good-cavity conditions in an axially pumped solid-state laser operated near the 1/3-degenerate cavity configuration that had not previously been studied numerically. By using the generalized Huygens integral together with rate equations, we obtained a V-shaped configuration that depends on a quasi-periodic threshold. We call the propagation dominant because the laser behaves as a conservative system governed by beam propagation. Although it had previously been predicted that chaos would be impossible under nearly degenerate conditions, we have recognized that the laser is transformed into chaos as a result of the interplay of beam propagation and gain dynamics as the cavity is tuned close to degeneracy. (C) 2001 Optical Society of America.
Bifurcation of fundamental Gaussian modes in Kerr-lens mode-locked lasers
(1999-09-01)
Wei, MD
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We propose that more than one spatial fundamental Gaussian mode may occur in concentric and confocal resonators under persisting nonlinear effect. Extensively studying the influence of the resonator's parameters in a Kerr-lens mode-locked resonator, pitchfork bifurcation results in more symmetrical configurations, and saddle-node bifurcation appears as the symmetry being broken. From the properties of bifurcation, we suggest that the equal-arm and near-confocal resonator is suitable for the emergence of bistability in Kerr-lens mode-locked lasers. (C) 1999 Elsevier Science B.V. All rights reserved.
Bottle beam from a bare laser for single-beam trapping
(2004-11-10)
Chen, CH
;
Tai, PT
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We demonstrate that a laser beam converging from a specific transverse mode is a bottle beam, as described in J. Opt. Soc. Am. B 20, 1220 (2003). To our knowledge, this is the first time that a bottle beam has been generated directly from a laser. By calculating the radiation forces on a dielectric Rayleigh sphere in the bottle beam, we show that the single beam can trap high-refractive-index particles at the multiple axial sites of intensity maxima, and it can confine low-index particles on a transverse plane within the bottle regions. Such a novel laser beam may have other applications. (C) 2004 Optical Society of America.
Catalyst-free GaN nanorods grown by metalorganic molecular beam epitaxy
(2006-05-01)
Kuo, SY
;
Kei, CC
;
Hsiao, CN
;
Chao, CK
;
Lai, FI
High-density GaN nanorods with outstanding crystal quality were grown on c-sapphire substrates by radio-frequency plasma-assisted metalorganic molecular beam epitaxy under catalyst- and template-free growth condition. Morphological and structural characterization of the GaN nanorods was employed by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy (HRTEM). These results indicate that the rod number density can reach 1 x 10(10) cm(-2) and the nanorods are well-aligned with preferentially oriented in the c-axis direction. Meanwhile, no metallic (Ga) droplet was observed at the end of the rods, which is the intrinsic feature of vapor-liquid-solid method. Nanorods with no traces of any extended defects, as confirmed by TEM, were obtained as well. In addition, optical investigation was carried out by temperature- and power-dependent micro-photoluminescence (mu-PL). The PL peak energies are red-shifted with increasing excitation power, which is attributed to many-body effects of free carriers under high excitation intensity. The growth mechanism is discussed on the basis of the experimental results. Catalyst-free GaN nanorods presented here might have a high potential for applications in nanoscale photonic devices.
Cavity configurations for soft-aperture Kerr-lens mode locking and multiple-period bifurcations in Ti : sapphire lasers
(2001-08-01)
Lin, JH
;
Wei, MD
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We find that soft-aperture Kerr-lens mode locking (SAKLM) in a Ti:sapphire laser always takes place around certain discrete cavity configurations accompanied by peculiar beam patterns. By correlating the superposition of proper transverse modes to the observed beam patterns and fitting the beat frequencies to the resonance equation, we discovered that the patterns for SAKLM are formed by phase locking of the fundamental mode with specific degenerate transverse modes that occur near different degenerate cavity configurations. As predicted by the stability analysis, period-3 and period-2 SAKLM does occur around the 1/3- and 1/4-degenerate cavity configurations, which cannot be fully explained in terms of total mode locking of TEM00 and TEM01 modes. (C) 2001 Optical Society of America.
Cavity-configuration-dependent instability in a tightly focused end-pumped solid-state laser
(2004-11-01)
Chen, CH
;
Tai, PT
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We experimentally studied the cavity-configuration-dependent instability in an end-pumped Nd:YVO4 laser in the vicinity of the degenerate resonator configuration Of g(1)g(2) = 1/4 with small pump size. We found that the laser instability occurs in a narrow range of cavity tuning on each side of the degeneracy, which shows periodic, period-doubling, and chaotic time evolutions. By using Collin's integral together with rate equations and taking into account the thermal lens effect, we show that the simulation is consistent with the experiments. The observed instabilities are new and, as far as we know, this is the first report that discusses the relationship between the instability and the thermal lens effect. (C) 2004 Elsevier B.V. All rights reserved.
Cavity-configuration-dependent nonlinear dynamics in Kerr-lens mode-locked lasers
(2000-08-01)
Wei, MD
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We determined theoretically that the nonlinear dynamics of a Gaussian beam is configuration dependent in a general cavity. This prediction was confirmed by numerical simulation in a Kerr-lens mode-locked cavity for which the self-focusing effect is considered the nonlinear source in both the spatial and the temporal domains. Period doubling, tripling, and quadrupling can occur in these configurations with the products of generalized cavity G parameters equal to 1/2, 1/4 (or 3/4), and (2 +/- root 2)/4, respectively. The dynamic behavior of the cavity beam will become irregular if the nonlinear effect is further increased. (C) 2000 Optical Society of America [S0740-3224(00)00708-6] OCIS codes: 140.3410, 140.4050, 260.5950, 140.1540.
Characterization of prototype silicon pitch artifacts fabricated by scanning probe lithography and anisotropic wet etching
(2005-01-01)
Chien, FSS
;
Hsieh, WF
;
Gwo, S
;
Jun, J
;
Silver, RM
Scanning probe lithography (SPL) and anisotropic tetra-methyl ammonium hydroxide (TMAH) etching (SPL+TMAH) were used to fabricate a series of one-dimensional prototype pitch structures on (110)-oriented silicon substrates. Overall lateral dimensions of the test structure are 20 mum x 80 mum. Line scales, consisting of 10-mum-long, 100-nm-tall, and 40-nm-wide lines, are observable by optical and scanning electron microscopy (SEM). Etched features were produced with pitches varying from 100 nm to 8 mum. Large-scale pattern placement errors of the SPL tool have been evaluated by analysis of optical image data obtained with a calibrated optical metrology instrument. Small-scale errors were analyzed in the range of 100 nm to 2 mum using SEM. Sources of placement error are discussed and possible methods for minimizing them are presented. The SPL+TMAH process in conjunction with a closed-loop scan control has the precision necessary for repeatable device prototyping in the nanoscale regime. (C) 2005 American Vacuum Society.
Comparison of visible fluorescence properties between sol-gel derived Er3+-Yb3+ and Er3+-Y3+ co-doped TiO2 films
(2003-06-23)
Chen, SY
;
Ting, CC
;
Hsieh, WF
;
材料科學與工程學系
;
光電工程學系
Both Er3+-Yb3+ and Er3+-Y3+ co-doped TiO2 films were prepared on fused silica by sol-gel processes. The effect of doping concentration upon the up-conversion fluorescence of Yb3+-Er3+ and Er3+-Y3+ co-doped TiO2 systems will be focused in this investigation. Although the influence of Yb3+ and Y3+ ions on the structural of Er3+-TiO2 host material is almost the same, different up-conversion emissions are observed. Both Er3+-doped and Er3+-Y3+ co-doped TiO2 films exhibit the up-conversion emission with green and red light. However, much stronger intensity of red light relative to green light is observed for the Er3+-Y3+ co-doped TiO2 system. For Er3+ (5 mol%)-Y3+ co-doped TiO2 samples, the relative intensity ratio (I-R/I-G) rapidly decreases with the increase of Y3+ concentration above 10 mol%. On the contrary, the relative intensity ratio (I-R/I-G) increases with increasing Yb3+ concentration for Er3+(5 mol%)-Yb3+ co-doped TiO2 samples. The up-conversion emission in the Er3+-Y3+ co-doped TiO2 system belongs to a two-photon absorption up-conversion process. However, the overall up-conversion efficiency in the Er3+-Yb3+ co-doped TiO2 system could be contributed from the complicated mechanisms. (C) 2003 Elsevier Science B.V. All rights reserved.
Construction of a wavelength-tunable self-starting Kerr lens mode-locked Ti:sapphire
(1996-04-01)
Lai, JG
;
Lin, KH
;
Juang, DG
;
Hsieh, WF
;
交大名義發表
We have successfully constructed a soft-aperturing, asymmetric cavity Kerr lens mode-locked (KLM) Ti:sapphire laser that is self-starting within 0.5 ms over 780-840 nm wavelength range without any additional starting devices or intracavity hard apertures. We believed that the soft-aperturing mechanism is essential in the self-starting KLM Ti:sapphire lasers and the round trip gain discrimination between CW and KLM modes of the Ti:sapphire laser is sufficient to support self-starting.
Decreasing giant splitting of longitudinal and transverse optical phonons in PbxSr1-xTiO3 due to Pb covalency
(2002-10-14)
Kuo, SY
;
Li, CT
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
In contrast to the increase of giant splitting of longitudinal optical (LO) and transverse optical (TO) phonons in polycrystalline BaxSr1-xTiO3 [Phys. Rev. B. 64, 224103-1 (2001)], a decreasing splitting of the softest A(1)(1TO) and the hardest A(1)(3LO) was observed in PbxSr1-xTiO3. A similar structure but anomalous discrepancies in lattice dynamics of ABO(3) perovskite are related to the diverse electronic states of Pb2+ and Ba2+ ions. In this article, Pb-O interaction is proposed to be more hybridized than Ba-O, and thus the change of effective charge to the LO-TO splitting may be the dominant mechanism in PbxSr1-xTiO3, while unit-cell volume change is in the BaxSr1-xTiO3 systems. (C) 2002 American Institute of Physics.
Dependence of luminescence efficiency on dopant concentration and sintering temperature in the erbium-doped Ba0.7Sr0.3TiO3 thin films
(2002-08-15)
Kuo, SY
;
Chen, CS
;
Tseng, TY
;
Chang, SC
;
Hsieh, WF
We found the dependence of luminescence efficiency on Er3+ concentration and sintering temperature in the Er-doped Ba0.7Sr0.3TiO3 (BST) thin films is governed by crystallinity and ion-ion interaction. X-ray diffraction and Raman studies of the sol-gel prepared samples show that the BST polycrystalline phase occurred when the sintering temperature reaches 700 degreesC, whereas, it becomes worse for temperature above 700 degreesC resulting from phase separation and the Er3+ concentration exceeding 3 mol % due to charge compensation mechanism. The observed green emission reaches maximum at sintering temperature 700 degreesC and 3 mol % Er3+ ions concentration. We also showed the Er dopant does not affect the dielectric property of BST thin films in C-V measurement and the Ba0.7Sr0.3TiO3 films doped with Er3+ ions may have potential use for electroluminescence devices. (C) 2002 American Institute of Physics.
Design and analyses of compact bent-tapered waveguides using guided-wave lens sets
(2004-08-20)
Chang, CW
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We propose compact bent-tapered waveguides using guided-wave lens sets, which are constructed by disposing lens-shaped waveguide regions in planar tapered waveguides. Two applications of the abruptly bent tapered waveguide and the Z-bend tapered waveguide demonstrate high transmittances of 91% and 86% with bent and tapered angles of 10degrees. (C) 2004 Wiley Periodicals, Inc.
Design of low-loss tapered waveguides using the telescope structure compensation
(2003-10-01)
Chang, CW
;
Wu, ML
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
A low-loss tapered waveguide is achieved by the telescope structure compensation. The configuration of this design is similar to the Galilean telescope based on the bulk geometrical optics. We numerically calculate the transmission efficiency in the use of the beam propagation method (BPM) and the finite-difference time-domain method. The BPM simulation results reveal that the normalized transmission efficiency is more than 95%, even if the tapered angle is as large as 10degrees.
Differential gain and buildup dynamics of self-starting Kerr lens mode-locked Ti:sapphire laser without an internal aperture
(1997-08-01)
Juang, DG
;
Chen, YC
;
Hsu, SH
;
Lin, KH
;
Hsieh, WF
The small-signal differential gain was calculated from the measured average cw and Kerr lens mode-locked (KLM) output powers over the least-misalignment-sensitive region of a completely soft-aperturing, self-starting KLM Ti:sapphire laser. The results indicate that the self-starting condition is reached with this laser operating near the center of the stable range. The simulated location of maximum differential gain and pulse buildup process show good agreement with the experimental results. (C) 1997 Optical Society of America.
Differential gain and buildup dynamics of self-starting Kerr lens mode-locked Ti:sapphire laser without an internal aperture
(1997-08-01)
Juang, DG
;
Chen, YC
;
Hsu, SH
;
Lin, KH
;
Hsieh, WF
The small-signal differential gain was calculated from the measured average cw and Kerr lens mode-locked (KLM) output powers over the least-misalignment-sensitive region of a completely soft-aperturing, self-starting KLM Ti:sapphire laser. The results indicate that the self-starting condition is reached with this laser operating near the center of the stable range. The simulated location of maximum differential gain and pulse buildup process show good agreement with the experimental results. (C) 1997 Optical Society of America.