Browsing by Author "Jheng, Shih-Da"

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A theoretical study on the strong-field ionization of the lithium atom
(2013-06-14)
Jheng, Shih-Da
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Jiang, T. F.
;
物理研究所
;
Institute of Physics
We apply a recently developed momentum space method (Jiang et al 2012 Phys. Rev. E 86 066702) to investigate the experimental results of strong-field ionization of the lithium atom (Schuricke et al 2011 Phys. Rev. A 83 023413). By splitting the photoelectron into groups of even and odd angular momenta and by using the states' population history, we can analyse the ionization mechanism in further detail. The lower energy double-peak structure, shown experimentally, of the photoelectron is attributed to the three-level Lambda-coupling effect. The spectral difference of 10 and 30 fs pulses at a typical intensity is demonstrated. We explain why the strong-field ionization fluctuates at intensities of 6 and 10 fs, but not for a 30 fs pulse. The change of fan-like photoelectron angular distribution with intensity in direction parallel to polarization is explained. Use of the Keldysh parameter to classify the tunnelling and multiphoton ionization is not meaningful for the lithium atom, because the ground state is mostly depleted before reaching peak intensity.
Dark solitons in a spinor microcavity-polariton condensate
(2016-10)
Chen, Ting-Wei
;
Jheng, Shih-Da
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Hsieh, Wen-Feng
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Cheng, Szu-Cheng
;
物理研究所
Dark solitons of a two-component condensate occurring in nonresonantly-pumped microcavity polaritons (spinor MPCs) with integer vorticities, referred to as integer dark solitons (IDSs), can be excited by a laser beam with tunable polarization and power. We investigate the physical properties of stationary IDSs in a pure spinor MPCs without defects. From the excitations of a IDS, we show that the soliton is stable when the pump power is higher than a critical value. When the pump polarization is in favor of one component, we find that the critical pump power for the stabilization becomes higher. The stable IDS exists below a critical pump polarization. A stable phase diagram of IDSs in terms of the pump condition, i.e., pump polarization and power, is thus obtained. (C) 2016 Elsevier Ltd. All rights reserved.
Drag and critical velocities in a nonresonantly pumped trapped polariton condensate with a rotating defect
(2016-01-19)
Cheng, Szu-Cheng
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Chen, Ting-Wei
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Jheng, Shih-Da
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Hsieh, Wen-Feng
;
物理研究所
We model the superfluid properties of a trapped exciton-polariton condensate under non-resonant excitation subjected to a rotating defect. With increasing the linear velocity of rotating defect, the density modulation can be classified into superfluid-like regime, parabolic-like regime, Cherenkov regime and over-Cherenkov regime. The threshold-like behavior of drag force and the onset of turbulent fringes can define the critical velocity for the superfluidity. Based on the perturbative drag force in the Bogoliubov-type analysis, the rigid modes with gapped excitation spectrum have higher critical velocity than that of the soft modes. (C) 2015 Elsevier Ltd. All rights reserved.
Effect of bound electron wave packet displacement on the multiphoton ionization of a lithium atom
(2017-10-14)
Jheng, Shih-Da
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Jiang, T. F.
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物理研究所
;
Institute of Physics
We study numerically the strong-field single ionization of a Li atom over a wide range of wavelengths (400 nm-1600 nm) in the multiphoton regime. By observing the behavior of the ionization probabilities and the occupation of excited states, we found that the occupied 2p state in different wavelength regimes exhibit different bound electron wave packet motion. The motion is in phase in the long-wavelength regime, out of phase in the short-wavelength regime and lagged when the wavelength is close to resonance with the 2p state. We then demonstrate how these different motions of the bound electron wave packet affect the ionization probability.
Lande subtraction method with finite integration limits and application to strong-field problems
(2012-12-11)
Jiang, Tsin-Fu
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Jheng, Shih-Da
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Lee, Yun-Min
;
Su, Zheng-Yao
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物理研究所
The Lande subtraction method has been widely used in Coulomb problems, but the momentum coordinate p is an element of (0,infinity) is assumed. In past applications, a very large range of p was used for accuracy. We derive the supplementary formulation with p is an element of (0, p(max)) at reasonably small p(max) for practical calculations. With the recipe, accuracy of the hydrogenic eigenspectrum is dramatically improved compared to the ordinary Lande formula by the same momentum grids. We apply the present formulation to strong-field atomic above-threshold ionization and high-order harmonic generations. We demonstrate that the proposed momentum space method can be another practical theoretical tool for atomic strong-field problems in addition to the existing methods. DOI:10.1103/PhysRevE.86.066702
Magnetic quantum number dependence of hydrogen photoelectron spectra under circularly polarized pulse in barrier suppression ionization regime
(2018-08-01)
Jheng, Shih-Da
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Jiang, Tsin-Fu
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Chen, Jen-Hao
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Liu, Jinn-Liang
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物理研究所
Photoelectron spectra and transition mechanisms of a hydrogen atom in the n = 2 state under circularly polarized pulses in the barrier suppression ionization (BSI) regime, found by solving the time-dependent Schrodinger equation, are presented in detail. The photoelectron peak emerges from low-energy, in contrast to being centered at higher energy in the case of ionization from the ground state. We show that the magnetic quantum number dependence of photoelectron angular distributions on initial states yields 3- and 2-band structures for 2p(-) and 2p(0) in zenith angle, respectively, and 1-band structures for both 2p(+) and 2s. The intermediate transition pathways from these initial states to the corresponding final states are also revealed.
Nonequilibrium and nonlinear defect states in microcavity-polariton condensates
(2016-05-18)
Chen, Ting-Wei
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Jheng, Shih-Da
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Hsieh, Wen-Feng
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Cheng, Szu-Cheng
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物理研究所
The nonequilibrium and nonlinear defect modes (NNDMs), localized by a defect in a nonequilibrium microcavity-polariton condensate (MPC), are studied. There are three analytic solutions of NNDMs in a point defect: the bright NNDM, a bound state with two dark solitons for an attractive potential, and a gray soliton bound by a defect for a repulsive potential. We find that the stable NNDMs in a nonequilibrium MPC are the bright NNDM and gray soliton bound by a defect. The bright NNDM, which has the hyperbolic cotangent form, is a bright localized state existing in a uniform MPC. The bright NNDM is a unique state occurring in a nonequilibrium MPC that has pump-dissipation and repulsive-nonlinearity characters. No such state can exist in an equilibrium system with repulsive nonlinearity.
Physical Realization of von Neumann Lattices in Rotating Bose Gases with Dipole Interatomic Interactions
(2016-08-22)
Cheng, Szu-Cheng
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Jheng, Shih-Da
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物理研究所
;
Institute of Physics
This paper reports a novel type of vortex lattice, referred to as a bubble crystal, which was discovered in rapidly rotating Bose gases with long-range interactions. Bubble crystals differ from vortex lattices which possess a single quantum flux per unit cell, while atoms in bubble crystals are clustered periodically and surrounded by vortices. No existing model is able to describe the vortex structure of bubble crystals; however, we identified a mathematical lattice, which is a subset of coherent states and exists periodically in the physical space. This lattice is called a von Neumann lattice, and when it possesses a single vortex per unit cell, it presents the same geometrical structure as an Abrikosov lattice. In this report, we extend the von Neumann lattice to one with an integral number of flux quanta per unit cell and demonstrate that von Neumann lattices well reproduce the translational properties of bubble crystals. Numerical simulations confirm that, as a generalized vortex, a von Neumann lattice can be physically realized using vortex lattices in rapidly rotating Bose gases with dipole interatomic interactions.
Quantum fluctuations and stability of vortex lattices in a nonresonantly pumped exciton-polariton condensate
(2017-03-01)
Chen, Ting-Wei
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Jheng, Shih-Da
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Jiang, T. F.
;
Cheng, Szu-Cheng
;
物理研究所
The dynamics of an exciton-polariton condensate (EPC) subject to harmonic confinement can cause spontaneously formed vortices to arrange into a triangular vortex lattice. The stability of such a spontaneously formed vortex lattice is still unknown. We investigate the quantum fluctuations of vortex lattices in a rapidly rotating EPC with a rotation frequency close to the harmonic trap. In such a large condensate, we find that a vortex lattice with a triangular structure is stable, whereas one with a square structure becomes unstable. This result indicates that a driven-dissipative vortex array with strong quantum fluctuations can occur in an EPC.
Roton instabilities and correlated Wigner crystals of rotating dipolar fermions in the fractional quantum Hall regime
(2013-11-04)
Jheng, Shih-Da
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Jiang, T. F.
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Cheng, Szu-Cheng
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物理研究所
;
Institute of Physics
We point out that the Wigner crystal (WC) state of rotating dipolar fermions in the lowest Landau level is strongly correlated. From intra-Landau-level excitations of the fractional quantum Hall effect (FQHE) liquid, we find that the roton minimum of the excitation spectrum at. nu = 1/7 becomes negative, indicating an absence of the FQHE state, which is supposed to be the ground state of the system. Therefore, we show that the Hartree-Fock theory of the WC does not predict the correct ground-state energy in the lowest Landau level. There exists a strong correlation effect on the Wigner crystallization of rotating dipolar gases.
Study of the circular dichroism of He+ ion
(2019-12-01)
Chen, Jen-Hao
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Liu, Jinn-Liang
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Jheng, Shih-Da
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Cheng, Szu-Cheng
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Jiang, Tsin-Fu
We study the mechanism of circular dichroism (CD) in He+ under XUV and NIR pulses in the experimental condition presented by Ilchen et al. [Phys. Rev. Lett. 118, 013002 (2017)] and in a range of pulse intensities and durations by solving the time-dependent Schrodinger equation (TDSE) in momentum space. The method enables investigation of the ionization and intermediate transition probabilities of He+ in detail. We show that the lowest-order perturbation theory (LOPT) is qualitatively sufficient to describe experimental results and find that ionization favors co- and counter-rotating pulses for NIR intensities in and beyond LOPT regimes, respectively. In the experimental pulse duration, we show that a sub-peak along the first above-threshold ionization peak exists in the counter-rotating case due to one-photon absorption from excited states, which cannot be obtained by solving TDSE with a short duration of 22 fs, since the energy band width is too wide to resolve this substructure. We present the variation of CD values with NIR intensities. (C) 2019 Optical Society of America
The synchronization and stability of spinor polariton condensates
(2016-04)
Chen, Ting-Wei
;
Jheng, Shih-Da
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Hsieh, Wen-Feng
;
Cheng, Szu-Cheng
;
物理研究所
By taking account of the spin degree of freedom with varying the Zeeman splitting, we explore the possible synchronized states of spinor polariton condensates formed in a semiconductor microcavity. The interplay among nonlinear interactions, spin-flipping rates and energy splitting is theoretically investigated. Besides a minimum transverse field induced spin-flipping rate required to form the synchronized state, we find that the interaction effect between polaritons is the dominant factor. Therefore, with the manipulation of the energy splitting between the two spin states, the spinor condensate initially synchronized with "elliptical" polarization may become two separated desynchronized and "circularly" polarized condensates. Moreover, the region and stability of synchronized states are discussed for various asymmetric pumping configurations. (C) 2016 Elsevier Ltd. All rights reserved.