Browsing by Author "Jiang, T. F."

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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.
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物理研究所
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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.
Analysis of angular dependence of strong-field tunneling ionization for CO(2)
(2009-11-01)
Zhao, Song-Feng
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Jin, Cheng
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Le, Anh-Thu
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Jiang, T. F.
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Lin, C. D.
We analyzed the discrepancy of the angular dependence of strong-field ionization for CO(2) among the different theoretical calculations and experiments. Using a more accurate ground-state wave function of CO(2) in the asymptotic region, we showed that the accuracy in the earlier tunneling ionization theory of Tong [Phys. Rev. A 66, 033402 (2002)] is much improved. We also concluded that the angular dependence deduced from the experiment of Paviccicacute [Phys. Rev. Lett. 98, 243001 (2007)] appears to be too narrowly distributed.
Analysis of angular dependence of strong-field tunneling ionization for CO2
(2009-11-01)
Zhao, Song-Feng
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Jin, Cheng
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Le, Anh-Thu
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Jiang, T. F.
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Lin, C. D.
We analyzed the discrepancy of the angular dependence of strong-field ionization for CO2 among the different theoretical calculations and experiments. Using a more accurate ground-state wave function of CO2 in the asymptotic region, we showed that the accuracy in the earlier tunneling ionization theory of Tong [Phys. Rev. A 66, 033402 (2002)] is much improved. We also concluded that the angular dependence deduced from the experiment of Paviccicacute [Phys. Rev. Lett. 98, 243001 (2007)] appears to be too narrowly distributed.
Analytic theory for betatron radiation from relativistic electrons in ion plasma channels with magnetic field
(2010-11-01)
Lee, H. C.
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Jiang, T. F.
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物理研究所
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Institute of Physics
We analytically solve the relativistic equation of motion for an electron in ion plasma channels and calculate the corresponding trajectory as well as the synchrotron radiation The relativistic effect on a trajectory is strong, i e, many high-order harmonic terms in the trajectory, when the ratio of the initial transverse velocity (v(x0)) to the longitudinal velocity (v(z0)) of the electron injected to ion plasma channels is high Interestingly, these high-order harmonic terms result in a quite broad and intense radiation spectrum, especially at an oblique angle, in contrast to an earlier understanding As the initial velocity ratio (v(x0) v(z0)) decreases, the relativistic effect becomes weak, only the first and second harmonic terms remain in the transverse and longitudinal trajectories, respectively, which coincides with the result of Esarey et al [Phys Rev E 65, 056505 (2002)] Our formalism also allows the description of electron's trajectory in the presence of an applied magnetic field Critical magnetic fields for cyclotron motions are figured out and compared with semiclassical results The cyclotron motion leads to more high-order harmonic terms than the trajectory without magnetic fields and causes an immensely broad spectrum with vastly large radiation amplitude for high initial velocity ratios (v(x0) v(z0)) The radiation from hard x-ray to gamma-ray regions can be generated with a broad radiation angle, thus available for applications 0 2010 American Institute of Physics [doi 10 1063/1 3496983]
Band structures of a slowly rotating dipolar Bose-Einstein condensate with a quantized vortex along a one-dimensional optical lattice
(2010-06-01)
Lee, H. C.
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Jiang, T. F.
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物理研究所
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Institute of Physics
We derive the effective Gross-Pitaevskii equation for a slowly rotating dipolar Bose-Einstein condensate (BEC) with a quantized vortex along a one-dimensional optical lattice and calculate its band structures. The band structure of a slowly rotating BEC in a lattice becomes interesting when dipole-dipole interaction (DDI) is involved. Under rotation, a dipolar rotating term emerges from the DDI potential. The dipolar rotating term makes a BEC with an attractive DDI more stable than one with a repulsive DDI. The dipolar rotating term changes and generalizes the definition for the type of BEC, which cannot be simply determined by an s-wave scattering length or an effective contact interaction term. The dipolar rotating term also makes the band structure fascinating and tunable. A so-called swallowtail band structure, i.e., a multi-valued solution due to nonlinear interaction, can either elongate or shrink as the band index increases, in contrast to a non-rotating dipolar BEC system with a monotonic dependence. With the dipolar rotating term, various band structures as well as an attractive BEC without collapse can be easily achieved. We demonstrate that a rotating dipolar BEC system subject to an optical lattice combines features of a crystal and a superfluid and promises wide applications.
Calculation of atomic hydrogen and its photoelectron spectra in momentum space
(2008-04-15)
Jiang, T. F.
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物理研究所
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Institute of Physics
An essential modification to the kernel in the numerical calculation of hydrogenic momentum wave functions, is presented in this paper. Using only 256 grid points, the calculated eigenvalues, eigenfunctions and the oscillator strengths are shown to be in excellent agreement with the exact analytic results. The reliable pseudocomplete set of momentum space eigenfunctions is then applied to the time-dependent calculation of intense laser pulse on the hydrogen atom. With the advantage of having no boundary reflection during the time evolution, like that inherent in the coordinate space method, the photoelectron spectra of above-threshold-ionization (ATI) are elucidated for four cases. Some of which are not feasible or very difficult to solve with the coordinate space method. Generalization of the method to single-active electron systems is straightforward. Due to the good accuracy with a reasonably small-sized basis set, applications to the currently interested intense case of laser pulse on atom or molecule are expected. (c) 2007 Elsevier B.V. All rights reserved.
Control mechanism of atomic ionization and high-order harmonic generation assisted by attosecond pulses
(2012-12-01)
Lee, H. C.
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Jiang, T. F.
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物理研究所
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Institute of Physics
Attosecond pulses combined with infrared laser constitute a powerful tool for controlling atomic photoionization and high-order harmonic generation (HHG). We apply the intense-field many-body S-matrix theory to solve such two-pulse excitation problems. The theory can give a clear explanation for the oscillation of ionization probability as a function of time delay between infrared field and attosecond pulses with central frequency lying below ionization threshold at moderate infrared intensities. The HHG assisted by such attosecond pulses is also interpreted. In addition to a known dramatic enhancement of HHG, a harmonic emission from rapid oscillation of bound-state population caused by the counter-rotating wave is presented.
Determination of structure parameters in strong-field tunneling ionization theory of molecules
(2010-03-01)
Zhao, Song-Feng
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Jin, Cheng
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Le, Anh-Thu
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Jiang, T. F.
;
Lin, C. D.
In the strong field molecular tunneling ionization theory of Tong et al. [Phys. Rev. A 66, 033402 (2002)], the ionization rate depends on the asymptotic wave function of the molecular orbital from which the electron is removed. The orbital wave functions obtained from standard quantum chemistry packages in general are not good enough in the asymptotic region. Here we construct a one-electron model potential for several linear molecules using density functional theory. We show that the asymptotic wave function can be improved with an iteration method and after one iteration accurate asymptotic wave functions and structure parameters are determined. With the new parameters we examine the alignment-dependent tunneling ionization probabilities for several molecules and compare with other calculations and with recent measurements, including ionization from inner molecular orbitals.
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
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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.
Ground state of the dipolar Bose-Einstein condensate
(2006-12-01)
Jiang, T. F.
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Su, W. C.
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土木工程學系
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物理研究所
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Department of Civil Engineering
We present a variational method to study the ground state of the newly realized Cr-52 dipolar Bose-Einstein condensate. Besides the usual contact potential term in the mean-field equation, there is an additional long-range and anisotropic dipole-dipole interaction potential. We develop an efficient Newton-Raphson's scheme to solve the condensate state. The solution shows a double-peak feature in the loosely confined dimension. Compared to the existing single-peak calculations, the double-peak solution has lower energy and reflects the distinct property of the dipole-dipole interaction. Our method is easy and efficient to use for future investigations of the dipolar systems.
Instabilities of Bose-Einstein condensates in optical lattices
(2007-04-01)
Kuan, W. H.
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Jiang, T. F.
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Cheng, Szu-Cheng
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物理研究所
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Institute of Physics
We study the instabilities, Landau and dynamical instabilities, that are two mechanisms responsible for the breakdown of superfluidity in Bose-Einstein condensates interacting with a one-dimensional optical lattice. An effective-mass Gross-Pitaevskii equation was used to calculate the excitation spectrum and the condensate density of Bose-Einstein condensates in a weak periodic potential. After the condensate velocities greater than the speed of sound, we observe a decreasing of the condensate density, which is the onset of Landau instability. The condensate is dissipated, but not completely, from colliding with the thermal atom cloud. For even higher velocities of the condensate, we find a fast decreasing of the condensate density until full removal of the condensate. The regime of totally removing of the condensate is happened at the inverse effective mass of the condensate becoming zero or negative, where the condensate is on the dynamical instability.
Momentum-time flux conservation method for one-dimensional wave equations
(2010-03-01)
Huang, Zhen-Ting
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Hsu, Huan-Chun
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Chang, Chau-Lyan
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Wu, Chin-Tien
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Jiang, T. F.
We present a conservation element and solution element method in time and momentum space. Several paradigmatic wave problems including simple wave equation, convection-diffusion equation, driven harmonic oscillating charge and nonlinear Korteweg-cle Vries (KdV) equation are solved with this method and calibrated with known solutions to demonstrate its use. With this method, time marching scheme is explicit, and the nonreflecting boundary condition is automatically fulfilled. Compared to other solution methods in coordinate space, this method preserves the complete information of the wave during time evolution which is an useful feature especially for scattering problems. (C) 2009 Elsevier B.V. All rights reserved.
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.
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Cheng, Szu-Cheng
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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
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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.
Theory of probing attosecond electron wave packets via two-path interference of angle-resolved photoelectrons
(2010-07-15)
Choi, N. N.
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Jiang, T. F.
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Morishita, T.
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Lee, M. -H.
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Lin, C. D.
We study theoretically the electron wave packet generated by an attosecond pulse train (APT) which is probed with a time-delayed infrared (IR) laser pulse. The APT creates an excited state and a continuum electron wave packet. By ionizing the excited state with an IR, a delayed new continuum electron wave packet is created. The interference of the wave packets from the two paths, as reflected in angle-resolved photoelectron spectra, is analyzed analytically. Using the analytical expressions, we examine the possibility of retrieving information on the electron wave packet generated by the APT.
Transition temperature of the interacting dipolar Bose gas
(2007-03-01)
Kao, Yee-Mou
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Jiang, T. F.
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物理研究所
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Institute of Physics
We investigate the effects of long-ranged dipole-dipole potential on the transition temperature of a weakly interacting Bose gas. We apply the two-fluid model to derive the energy spectra of the thermal and the condensate parts. From the interaction modified spectra of the system, the formula for the shift of transition temperature was derived. Compared to the conventional weakly interacting Bose system with contact potential only where thermal effect is larger, we find that the condensate effect is about two times that of the thermal part in the dipolar system. Due to the relative smallness of dipole-dipole interaction with respect to the contact interaction in current dipolar Bose-Einstein condensation, we suggest to measure the dipolar effect by tuning the scattering length to negligible small by the Feshbach resonance technique.
Transition temperatures of the trapped ideal spinor Bose gas
(2006-11-01)
Kao, Y. -M.
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Jiang, T. F.
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物理研究所
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Institute of Physics
The thermodynamic properties of the trapped ideal spinor Bose gas are studied in details with the constraints of fixed total number of atoms N, and magnetization M. The double transition temperatures, their corresponding corrections due to finite particle number, and the population of each component are investigated. The generalization to the ideal spinor Bose gas of hyperfine quantum number F is also discussed. We propose that the order and disorder parameters to describe the symmetry broken of condensation.