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Structural ordering transition and repulsion of the giant LO-TO splitting in polycrystalline BaSr1-xTiO3
(2001-12-01)
Kuo, SY
;
Liao, WY
;
Hsieh, WF
;
光電工程研究所
;
Institute of EO Enginerring
We report Raman and x-ray diffraction studies of polycrystalline BaxSr1-xTiO3 (BST) prepared by the sol-gel technique in the range of x = 0 to 1.0. Other than a tetragonal to cubic phase transition at composition x approximate to0.75 of the BST powders detected by x-ray diffraction and Raman spectroscopy, a new structural ordering transition around x approximate to0.4-0.5 is observed due to the atomic arrangement. By taking the anharmonic coupling between the three A(1) (TO) modes into account, the observed repulsion of the giant LO-TO splitting is a result of decreasing cell dimension and strengthening the electron-phonon coupling. The results help us to explain the weakening of the ferroelectricity in the BST tetragonal phase as x decreases. The anomalous inconsistency in our experimental results and theoretical prediction are attributed to the lack of detailed information of dynamical effective charges in the BaxSr1-xTiO3 compounds.
Lattice dynamics of perovskite PbxCa1-xTiO3
(2004-05-01)
Kuo, SY
;
Li, CT
;
Hsieh, WF
;
光電工程研究所
;
Institute of EO Enginerring
Investigation of the structural and vibrational properties of the PbxCa1-xTiO3 (PCT) system exhibits two phase transitions in the range of x=0-1 by using x-ray powder diffraction and Raman spectroscopy. The first transition occurring at xsimilar to0.65 corresponds to the tetragonal-to-cubic phase and the second one occurs near x=0.35 is attributed to the orthorhombic-to-cubic phase. The absence of the intermediate tetragonal phase between orthorhombic and cubic phases (0
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.
The preferable resonators for Kerr-lens mode-locking determined by stability factors of their iterative maps
(1998-10-15)
Wei, MD
;
Hsieh, WF
;
Sung, CC
;
光電工程研究所
;
Institute of EO Enginerring
The generalized stability factor of a general resonator was obtained from its iterative map based on the linear stability analysis. Since a physical system tends to stay with high stability, the preferred resonator for Kerr-lens mode-locking (KLM) is determined by the relative stability between KLM and CW operations. With this criterion the preferable KLM regions agree with the previous experimental self-starting regions when the Ken medium is located around the center of the resonator. (C) 1998 Elsevier Science B.V. All rights reserved.
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.
Lasing spectral blue shifts of fluorescent saturable absorbing dye in microdroplets
(1998-06-01)
Yu, IJ
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We report blue shifts of emission spectra of microdroplet lasers containing fluorescent saturable absorbing dye as compared with those of conventional dye lasers. The results cannot be simply explained by matching the lasing peaks to the minima of threshold condition without taking into account cavity enhancement. We find that the microdroplet lasers have quality factors of 10(4) with a 3X cavity enhancement and their lasing peaks at fixed concentration are independent of the incident pump power.
Fabrication and raman analysis of ZnSe quantum dots in glass matrix thin films by pulsed laser evaporation
(1998-07-01)
Yin, SB
;
Chen, L
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We have successfully fabricated ZnSe-microcrystal-doped silica-glass thin films by pulsed laser evaporation from ZnSe powder embedded in sol-gel glass targets and demonstrated that the spatial cell-elation model call be used to analyze the LO Raman mode of ZnSe semiconductor doped glass thin films. The obtained correlation lengths differ from the real sizes of the particulates observed by scanning electron microscopy which may bz due to the fact that the particulates art polycrystalline, with different orientations separated by grain boundaries, and the correlation length just provides a measure of the separated average grain dimension. The photoluminescence spectrum indicates that the carriers may tunnel through the grain walls in the polycrystalline particulates. Low temperature annealing only causes aggregate of particulates without merging the grain boundaries.
The preferable resonators for Kerr-lens mode-locking determined by stability factors of their iterative maps
(1998-10-15)
Wei, MD
;
Hsieh, WF
;
Sung, CC
;
光電工程學系
;
Department of Photonics
The generalized stability factor of a general resonator was obtained from its iterative map based on the linear stability analysis. Since a physical system tends to stay with high stability, the preferred resonator for Kerr-lens mode-locking (KLM) is determined by the relative stability between KLM and CW operations. With this criterion the preferable KLM regions agree with the previous experimental self-starting regions when the Ken medium is located around the center of the resonator. (C) 1998 Elsevier Science B.V. All rights reserved.
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.
Nanomachining of (110)-oriented silicon by scanning probe lithography and anisotropic wet etching
(1999-10-18)
Chien, FSS
;
Wu, CL
;
Chou, YC
;
Chen, TT
;
Gwo, S
We have demonstrated that silicon nanostructures with high aspect ratios, having similar to 400 nm structural height and similar to 55 nm lateral dimension, may be fabricated by scanning probe lithography and aqueous KOH orientation-dependent etching on the H-passivated (110) Si wafer. The high spatial resolution of fabricated features is achieved by using the atomic force microscope based nano-oxidation process in ambient. Due to the large (110)/(111) anisotropic ratio of etch rate and the large Si/SiO2 etch selectivity at a relatively low etching temperature and an optimal KOH concentration, high-aspect-ratio gratings with (111)-oriented structural sidewalls as well as hexagonal etch pit structures determined by the terminal etch geometry can be obtained. (C) 1999 American Institute of Physics. [S0003-6951(99)03242-8].

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