Browsing by Author "Yu, Y. T."

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A cryogenically cooled Nd:YAG monolithic laser for efficient dual-wavelength operation at 1061 and 1064 nm
(2013-04-01)
Cho, C. Y.
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Tuan, P. H.
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Yu, Y. T.
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Huang, K. F.
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Chen, Y. F.
We experimentally explore the fluorescence spectra of the Nd:YAG (YAG: yttrium aluminum garnet) crystal at cryogenic temperatures to confirm the feasibility of dual-wavelength operation at 1061 and 1064 nm. Furthermore, a cryogenically cooled Nd:YAG crystal with coating to form a monolithic cavity is employed to investigate the performance of the dual-wavelength operation. At an incident pump power of 20 W, the output powers for each wavelength can simultaneously reach 6.0 W at the optimally balanced temperature of 152 K. The optimal temperature for balancing the output powers of the two wavelengths is experimentally determined as a function of the incident pump power intensity.
A Superconducting Magnetization System With Hybrid Superconducting Wire for the Study and Application of Superconductivity
(2012-06-01)
Chen, S. D.
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Yu, Y. T.
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Jan, J. C.
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Lin, F. Y.
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Hwang, C. S.
For the study of high-temperature superconductors and for the application of superconductivity, a superconducting high-field magnetization system with a hybrid superconducting coil was designed. This coil is composed of superconducting wires of three kinds-HTS YBCO 2G-wire, high-field and low-field NbTi wires. Three principal purposes of building this system are to inspect the characteristics of disk-shape bulk YBCO, to develop a HTS-bulk undulator, and to magnetize a portable HTS-bulk high-field magnet for application to a resonant X-ray scattering experiment. With four steps of temperature decrease, a two-stage GM-type cryocooler and liquid nitrogen provide cooling for the magnetization system. The hybrid superconducting coil, two cryogenic systems for the magnetization system and the portable HTS-bulk magnet, and the control and monitor systems that were designed are discussed.
Characterizing classical periodic orbits from quantum Green's functions in two-dimensional integrable systems: Harmonic oscillators and quantum billiards
(2017-01-30)
Chen, Y. F.
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Tung, J. C.
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Tuan, P. H.
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Yu, Y. T.
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Liang, H. C.
A general method is developed to characterize the family of classical periodic orbits from the quantum Green's function for the two-dimensional (2D) integrable systems. A decomposing formula related to the beta function is derived to link the quantum Green's function with the individual classical periodic orbits. The practicality of the developed formula is demonstrated by numerically analyzing the 2D commensurate harmonic oscillators and integrable quantum billiards. Numerical analyses reveal that the emergence of the classical features in quantum Green's functions principally comes from the superposition of the degenerate states for 2D harmonic oscillators. On the other hand, the damping factor in quantum Green's functions plays a critical role to display the classical features in mesoscopic regime for integrable quantum billiards, where the physical function of the damping factor is to lead to the coherent superposition of the nearly degenerate eigenstates.
Design of a HTS Magnet for Application to Resonant X-Ray Scattering
(2011-06-01)
Chen, S. D.
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Yu, Y. T.
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Huang, Z. W.
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Jan, J. C.
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Hwang, C. S.
In material research, the characteristics of novel materials vary greatly with the environment. A magnet with a strong field will be developed for an experimental station for resonant X-ray scattering to investigate the magnetic properties of materials. This magnet will be developed with high-temperature superconductor (HTS) bulk YBa(2)Cu(3)O(7) and magnetized with a HTS coil magnet wound with 2G HTS wire. HTS (RE) BCO will be selected to construct the coil of this magnet. Both the bulk and coil magnets will be assembled on the same movable system. The bulk HTS magnet will provide flux density greater than 4 T with a gap 34 mm that can accommodate the sample holder of the experimental station. The bulk magnet will be cooled with cryocoolers to 29 K and the coil magnet to 4.2 K; the coil magnet is separable from the bulk magnet after the field is trapped. We describe the concept of the magnetic-field calculation, the overall design of these magnets, and the cooling algorithm for the bulk HTS magnet system.
Efficient continuous-wave self-Raman Yb:KGW laser with a shift of 89 cm(-1)
(2013-10-21)
Chang, M. T.
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Zhuang, W. Z.
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Su, K. W.
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Yu, Y. T.
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Chen, Y. F.
We demonstrated a continuous-wave (CW) self-Raman laser with high conversion efficiency by using Yb:KGW as the Raman crystal. The first Stokes line of wavelength centered at 1095.2 nm with spectral bandwidth of 8 nm and the cascaded Raman conversion wavelength at 1109.5 nm with spectral bandwidth of 3.4 nm were observed with a Raman shift of 89 cm(-1) with respect to the fundamental laser wavelength at 1085.0 nm with spectral bandwidth of 10 nm. The CW Raman output power of 1.7 W was attained under the diode pump power of 7.8 W which corresponds to the slope efficiency and the diode-to-Stokes optical conversion efficiency of 26.6% and 21.8%, respectively. (C)2013 Optical Society of America
Exploiting broad-area surface emitting lasers to manifest the path-length distributions of finite-potential quantum billiards
(2016-01-11)
Yu, Y. T.
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Tuan, P. H.
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Chang, K. C.
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Hsieh, Y. H.
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Huang, K. F.
Broad-area vertical-cavity surface-emitting lasers (VCSELs) with different cavity sizes are experimentally exploited to manifest the influence of the finite confinement strength on the path-length distribution of quantum billiards. The subthreshold emission spectra of VCSELs are measured to obtain the path-length distributions by using the Fourier transform. It is verified that the number of the resonant peaks in the path-length distribution decreases with decreasing the confinement strength. Theoretical analyses for finite-potential quantum billiards are numerically performed to confirm that the mesoscopic phenomena of quantum billiards with finite confinement strength can be analogously revealed by using broad-area VCSELs. (C) 2016 Optical Society of America
Exploration of water jet generated by Q-switched laser induced water breakdown with different depths beneath a flat free surface
(2013-01-14)
Chen, Ross C. C.
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Yu, Y. T.
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Su, K. W.
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Chen, J. F.
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Chen, Y. F.
The dynamics of a water jet on a flat free surface are investigated using a nanosecond pulsed laser for creating an oscillating bubble with different depths beneath the free surface. A thin jet is shown to deform a crater surface resulted from surface depression and cause a circular ring-shaped crater on the connection surface between the crater of surface depression and the thin jet. The collapse of this circular ring-shaped crater is proposed to the crown-like formation around a thick jet. The evolution of the bubble depth suggests a classification of four distinctive ranges of the bubble depths: non-crown formation when the parameter of bubble depth over the maximum bubble radius gamma <= 0.5, unstable crown formation when 0.5 <= gamma <= 0.6, crown-like structure with a complete crown wall when 0.6 <= gamma <= 1.1, and non-crown formation when 1.1 <= gamma. Furthermore, the orientation of the crown wall gradually turns counterclockwise to vertical direction with increasing gamma from 0.5 to 1.1, implying a high correlation between the orientation of the crown wall and the depth of the bubble. This correlation is explained and discussed by the directional change of the jet eruption from the collapse of circular ring-shaped crater. (C)2013 Optical Society of America
Exploring lasing modes and polarization characteristics in broad-area square-shaped vertical-cavity surface emitting lasers with frequency detuning
(2014-11-01)
Yu, Y. T.
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Tuan, P. H.
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Wen, C. P.
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Huang, K. F.
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Chen, Y. F.
We experimentally explore the polarization characteristics of broad-area square-shaped vertical-cavity surface emitting lasers with the cryogenic cooling to achieve a wide range of frequency detuning. At room temperature the lasing modes are subject to thermal effects and exhibit the phenomenon of polarization switching. For operating temperatures below 260 K, the transverse modes are confirmed to be mainly controlled by the lateral oxide boundary and usually do not display polarization switching. Near the maximum frequency detuning, the lasing modes are well localized on the ray trajectories and display a remarkable frequency-locking phenomenon from single-frequency to multi-frequency operation for the injected current changing from near to far above lasing threshold.
Exploring morphological variations of a laser-induced water jet in temporal evolution: formation of an air bubble enclosing a water drop
(2013-11-01)
Chen, Ross C. C.
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Yu, Y. T.
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Su, K. W.
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Chen, Y. F.
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電子物理學系
We explore the spatio-temporal dynamics of a water jet that is generated by laser-induced water breakdown beneath a flat free surface. We find that morphological variations in the temporal evolution can be divided into three categories depending on the depth parameter gamma, which is the ratio of the water-breakdown depth to the maximum bubble radius. For a depth parameter in the range 0.8 <= gamma <= 1.03, we observe an intriguing pattern formation in which an air bubble perfectly encloses a water drop through the process of the Plateau-Rayleigh instability.
Exploring the distinction between experimental resonant modes and theoretical eigenmodes: From vibrating plates to laser cavities
(2014-02-12)
Tuan, P. H.
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Wen, C. P.
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Yu, Y. T.
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Liang, H. C.
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Huang, K. F.
Experimentally resonant modes are commonly presumed to correspond to eigenmodes in the same bounded domain. However, the one-to-one correspondence between theoretical eigenmodes and experimental observations is never reached. Theoretically, eigenmodes in numerous classical and quantum systems are the solutions of the homogeneous Helmholtz equation, whereas resonant modes should be solved from the inhomogeneous Helmholtz equation. In the present paper we employ the eigenmode expansion method to derive the wave functions for manifesting the distinction between eigenmodes and resonant modes. The derived wave functions are successfully used to reconstruct a variety of experimental results including Chladni figures generated from the vibrating plate, resonant patterns excited from microwave cavities, and lasing modes emitted from the vertical cavity.
Exploring the formation of thermally detuned transverse patterns in a broad-area square VCSEL
(2019-06-15)
Tuan, P. H.
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Yu, Y. T.
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Huang, K. F.
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Chen, Y. F.
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電子物理學系
The formation of thermally detuned transverse patterns of a broad-area square-aperture vertical-cavity surface-emitting laser (VCSEL) via cryogenic cooling is explored. It is found that the transverse wave vector gradually rotates from the horizontal or vertical direction to the diagonal direction of the square boundary as the transverse mode order increases. A model based on the quantum billiards with a finite potential well is developed to emulate the transition behavior of lasing modes. Combining the effective modal gain analysis with the response wave function of driven finite potential billiards, all experimental lasing patterns under different operation temperatures are well recon- structed. (C) 2019 Optical Society of America
Exploring the influence of boundary shapes on emission angular distributions and polarization states of broad-area vertical-cavity surface-emitting lasers
(2014-11-03)
Yu, Y. T.
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Tuan, P. H.
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Huang, K. F.
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Chen, Y. F.
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電子物理學系
We design the stadium-shaped and rectangular vertical-cavity surface-emitting lasers (VCSELs) to investigate the influence of boundary shapes on the emission angular distributions and polarization states. For the stadium-shaped VCSELs, the emission angular distribution prefers to be almost omnidirectional because the lasing mode with purely scarred structure is seldom to be excited. On the contrary, the rectangular VCSELs usually generate dominant lasing modes with the morphology of quasi-periodic linear ridges, which can make emission angular distribution to be concentrated on the certain direction. From the polarization-resolved light-current curves, the stadium-shaped VCSEL is quite prone to exhibit numerous abrupt changes (kinks) associated with polarization switching with increasing current, whereas for rectangular VCSEL there is no conspicuous kink to be seen during a wide range of current changing from near to far above lasing threshold. (C) 2014 Optical Society of America
Exploring the origin of the directional emission from a microcavity with a large-aperture surface-emitting laser
(2009-06-15)
Chen, Ross C. C.
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Yu, Y. T.
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Huang, Y. J.
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Chen, C. C.
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Chen, Y. F.
The origin of the direction emission from a microcavity is investigated with a large-aperture surface-emitting laser with an equilateral-triangular shape. Experimental results reveal that a wide-spread eigen-mode and a localized superscar mode can display quite similar far-field directional emissions. This experimental finding is theoretically confirmed with the quantum-billiard wave function and the approximation of the paraxial propagation. (C) 2009 Optical Society of America
Exploring the resonant vibration of thin plates: Reconstruction of Chladni patterns and determination of resonant wave numbers
(2015-04-01)
Tuan, P. H.
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Wen, C. P.
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Chiang, P. Y.
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Yu, Y. T.
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Liang, H. C.
The Chladni nodal line patterns and resonant frequencies for a thin plate excited by an electronically controlled mechanical oscillator are experimentally measured. Experimental results reveal that the resonant frequencies can be fairly obtained by means of probing the variation of the effective impedance of the exciter with and without the thin plate. The influence of the extra mass from the central exciter is confirmed to be insignificant in measuring the resonant frequencies of the present system. In the theoretical aspect, the inhomogeneous Helmholtz equation is exploited to derive the response function as a function of the driving wave number for reconstructing experimental Chladni patterns. The resonant wave numbers are theoretically identified with the maximum coupling efficiency as well as the maximum entropy principle. Substituting the theoretical resonant wave numbers into the derived response function, all experimental Chladni patterns can be excellently reconstructed. More importantly, the dispersion relationship for the flexural wave of the vibrating plate can be determined with the experimental resonant frequencies and the theoretical resonant wave numbers. The determined dispersion relationship is confirmed to agree very well with the formula of the Kirchhoff-Love plate theory. (c) 2015 Acoustical Society of America.
Extracting trajectory equations of classical periodic orbits from the quantum eigenmodes in two-dimensional integrable billiards
(2017-02-21)
Hsieh, Y. H.
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Yu, Y. T.
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Tuan, P. H.
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Tung, J. C.
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Huang, K. F.
The trajectory equations for classical periodic orbits in the equilateral-triangular and circular billiards are systematically extracted from quantum stationary coherent states. The relationship between the phase factors of quantum stationary coherent states and the initial positions of classical periodic orbits is analytically derived. In addition, the stationary coherent states with noncoprime parametric numbers are shown to correspond to the multiple periodic orbits, which cannot be explicable in the one-particle picture. The stationary coherent states are further verified to be linked to the resonant modes that are generally observed in the experimental wave system excited by a localized and unidirectional source. The excellent agreement between the resonant modes and the stationary coherent states not only manifests the importance of classical features in experimental systems but also paves the way to manipulate the mesoscopic wave functions localized on the periodic orbits for applications.
Integral-based parallel algorithm for the fast generation of the Zernike polynomials
(2020-01-20)
Hsieh, Y. H.
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Yu, Y. T.
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Lai, Y. H.
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Hsieh, M. X.
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Chen, Y. F.
The integral representation of the Zernike radial functions is well approximated by applying the Riemann sums with a surprisingly rapid convergence. The errors of the Riemann sums are found to averagely be not exceed 3 x 10(-14), 3.3 x 10(-14), and 1.8 x 10(-13) for the radial order up to 30, 50, and 100, respectively. Moreover, a parallel algorithm based on the Riemann sums is proposed to directly generate a set of radial functions. With the aid of the graphics processing units (GPUs), the algorithm shows an acceleration ratio up to 200-fold over the traditional CPU computation. The fast generation for a set of Zernike radial polynomials is expected to be valuable in further applications, such as the aberration analysis and the pattern recognition. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Level statistics and eigenfunctions of square torus billiards: Manifesting the transition from regular to chaotic behaviors
(2012-02-02)
Tuan, P. H.
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Yu, Y. T.
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Chiang, P. Y.
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Liang, H. C.
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Huang, K. F.
We thoroughly analyze the level statistics and eigenfunctions in concentric as well as nonconcentric square torus billiards. We confirm the characteristics of quantum and classical correspondence and the existence of scarred and superscarred modes in concentric square torus billiards. Furthermore, we not only verify that the transition from regular to chaotic behaviors can be manifested in nonconcentric square torus billiards, but also develop an analytical distribution to excellently fit the numerical level statistics. Finally, we intriguingly observe that numerous eigenstates commonly exhibit the wave patterns to be an ensemble of classical diamond trajectories, as the effective wavelengths are considerably shorter than the size of internal hole.
Manifestation of quantum-billiard eigenvalue statistics from subthreshold emission of vertical-cavity surface-emitting lasers
(2011-01-11)
Chen, Y. F.
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Yu, Y. T.
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Chiang, P. Y.
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Tuan, P. H.
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Huang, Y. J.
We report that the subthreshold emission spectra of vertical-cavity surface-emitting lasers (VCSELs) can be analogously used to manifest the quantum-billiard energy spectra. The Fourier-transformed distributions of the subthreshold emission spectra are demonstrated to display various peak structures that are in good agreement with the results of the quantum-billiard model. We also verify that the statistical analyses of the nearest-neighbor eigenvalue spacing distributions obey a Poisson distribution for an equilateral-triangular device and a Wigner distribution for a stadium-shaped device.
Non-paraxial contributions to the far-field pattern of surface-emitting lasers: a manifestation of the momentum-space wavefunctions of quantum billiards
(2011-07-01)
Yu, Y. T.
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Huang, Y. J.
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Chiang, P. Y.
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Lin, Y. C.
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Huang, K. F.
We investigated experimentally non-paraxial contributions to the high-order far-field pattern of large-area vertical-cavity surface-emitting lasers in order to explore by analogy the momentum-space wave distributions of quantum billiards. Our results reveal that non-paraxial contributions significantly influence the morphology of the high-order far-field pattern. A fast reliable method is developed for transforming the experimental far-field patterns to the correct Fourier transform of the corresponding near-field lasing modes. In this way we visualize the momentum-space (p-q) wavefunctions of quantum billiards.
Observation of disordered wave functions with conical second-harmonic generation and verification of transition from extended to prelocalized states in weak localization
(2013-01-18)
Lin, Y. C.
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Tuan, P. H.
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Yu, Y. T.
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Liang, H. C.
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Su, K. W.
We experimentally acquire the disordered wave functions from the conical second-harmonic generation to explore the variation of weak localization from extended to prelocalized states. We numerically verify that the experimental density distributions with different extents of weak localization can be excellently analyzed with a reduced version of the nonlinear sigma model (RV-NLS model). Moreover, we demonstrate that the chi-square distributions with fractional degrees of freedom are practically equivalent to the density distributions of the RV-NLS model. Our finding indicates that the concept of fractional degrees of freedom can be applied to the statistical properties of disordered wave functions. DOI: 10.1103/PhysRevB.87.045117