Shih-I Chu
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Previous Organizations / Institutes
The organizations / institutes from the scholar's other articles in the past ten years
Research Subjects
Shih-I Chu has a total of 64 co-authors. Here are the top co-authors by number of shared publications:
- Dmitry Telnov
Department of Physics, St. Petersburg State University, St. Petersburg, Russia
37 shared publications - Peng-Cheng Li
Shantou University
16 shared publications - John Heslar
Department of Physics, Center for Quantum Science and Engineering, Center for Advanced Study in Theoretical Sciences, National Taiwan University, Taipei 10617, Taiwan
12 shared publications - Siyuan Han
Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA
11 shared publications - Tak-San Ho
Princeton University
7 shared publications Cecil Laughlin
School of Mathematical Science, University of Nottingham, Nottingham NG7 2RD, England
6 shared publications
Latest Publications
- 26 August 2021
- Published by American Physical Society (APS) in Physical Review A
- Vol. 104 (2) , 023111
Relativistic ionization probabilities and photoelectron distributions of hydrogenlike ions in superstrong electromagnetic fields
The ionization probabilities and photoelectron distributions of the hydrogen atom and hydrogenlike ions and in superstrong electromagnetic fields are obtained by solving the time-dependent Dirac equation with the help of the generalized pseudospectral method in spherical coordinates. A simple transformation of the original radial Dirac Hamiltonian is suggested that removes the spurious states. The ionization probabilities are calculated both within and beyond the dipole approximation for two pulse durations and various peak field strengths scaled with respect to the nuclear charge for each target. Performance of two analytic parameters previously suggested to estimate the nondipole effects is assessed against the numerical data obtained in this study. The photoelectron energy and angular distributions exhibit the above-threshold ionization peaks as well as the low-energy structure. In the superstrong field regime, the low-energy structure builds up with increasing field strength while the above-threshold ionization peaks decrease. The nondipole effects in the photoelectron distributions are also revealed and analyzed.- 26 August 2021
- Published by American Physical Society (APS) in Physical Review A
- Vol. 104 (2) , 023111
Relativistic ionization probabilities and photoelectron distributions of hydrogenlike ions in superstrong electromagnetic fields
The ionization probabilities and photoelectron distributions of the hydrogen atom and hydrogenlike ions and in superstrong electromagnetic fields are obtained by solving the time-dependent Dirac equation with the help of the generalized pseudospectral method in spherical coordinates. A simple transformation of the original radial Dirac Hamiltonian is suggested that removes the spurious states. The ionization probabilities are calculated both within and beyond the dipole approximation for two pulse durations and various peak field strengths scaled with respect to the nuclear charge for each target. Performance of two analytic parameters previously suggested to estimate the nondipole effects is assessed against the numerical data obtained in this study. The photoelectron energy and angular distributions exhibit the above-threshold ionization peaks as well as the low-energy structure. In the superstrong field regime, the low-energy structure builds up with increasing field strength while the above-threshold ionization peaks decrease. The nondipole effects in the photoelectron distributions are also revealed and analyzed.- 11 December 2020
- Published by American Physical Society (APS) in Physical Review A
- Vol. 102 (6) , 063109
Relativistic ionization dynamics of hydrogenlike ions in strong electromagnetic fields: Generalized pseudospectral method for the time-dependent Dirac equation
We perform a theoretical and computational study of relativistic hydrogenlike ions subject to linearly polarized strong electromagnetic fields. The time-dependent Dirac equation is solved with the help of the generalized pseudospectral method in spherical coordinates. When solving the Dirac equation numerically with basis-set methods, spurious eigenstates usually show up. We suggest a simple transformation of the original discretized Dirac Hamiltonian that removes such states and keeps highly accurate true eigenstates. We calculate the ionization probabilities of the hydrogen atom and hydrogenlike ions and for various peak field strengths and pulse durations scaled with respect to the nuclear charge of the target. Calculations are performed both within and beyond the dipole approximation. We analyze the nondipole effects and find the region of the Lorentz deflection parameter where the dipole approximation is still applicable.- 11 December 2020
- Published by American Physical Society (APS) in Physical Review A
- Vol. 102 (6) , 063109
Relativistic ionization dynamics of hydrogenlike ions in strong electromagnetic fields: Generalized pseudospectral method for the time-dependent Dirac equation
We perform a theoretical and computational study of relativistic hydrogenlike ions subject to linearly polarized strong electromagnetic fields. The time-dependent Dirac equation is solved with the help of the generalized pseudospectral method in spherical coordinates. When solving the Dirac equation numerically with basis-set methods, spurious eigenstates usually show up. We suggest a simple transformation of the original discretized Dirac Hamiltonian that removes such states and keeps highly accurate true eigenstates. We calculate the ionization probabilities of the hydrogen atom and hydrogenlike ions and for various peak field strengths and pulse durations scaled with respect to the nuclear charge of the target. Calculations are performed both within and beyond the dipole approximation. We analyze the nondipole effects and find the region of the Lorentz deflection parameter where the dipole approximation is still applicable.- 7 January 2020
- Published by American Physical Society (APS) in Physical Review A
- Vol. 101 (1) , 011401
Role of nuclear symmetry in below-threshold harmonic generation of molecules
Below-threshold harmonic generation (BTHG) is one of few potential methods for the generation of novel vacuum-ultraviolet (VUV) light sources. However, most previous studies have focused on the atomic BTHG; a comprehensive understanding of the molecular BTHG is valuable for the advancement of this field. Here, we present an ab initio study of the role of nuclear symmetry on BTHG of both homonuclear and heteronuclear diatomic molecules. We reveal very distinctive electronic dynamical behaviors in molecular BTHG by identifying subtle multiple-channel contributions. In particular, it is found that the channels associated with the electron-nuclear coupling from light nuclear core to heavy nuclear core of the asymmetric molecules play an important role in the constructive interference of the harmonic emission, leading to a significant enhancement of the BTHG. Our results suggest that asymmetric molecular systems can be used for substantial improvement of the molecular BTHG-based VUV light sources.
- 7 January 2020
- Published by American Physical Society (APS) in Physical Review A
- Vol. 101 (1) , 011401
Role of nuclear symmetry in below-threshold harmonic generation of molecules
Below-threshold harmonic generation (BTHG) is one of few potential methods for the generation of novel vacuum-ultraviolet (VUV) light sources. However, most previous studies have focused on the atomic BTHG; a comprehensive understanding of the molecular BTHG is valuable for the advancement of this field. Here, we present an ab initio study of the role of nuclear symmetry on BTHG of both homonuclear and heteronuclear diatomic molecules. We reveal very distinctive electronic dynamical behaviors in molecular BTHG by identifying subtle multiple-channel contributions. In particular, it is found that the channels associated with the electron-nuclear coupling from light nuclear core to heavy nuclear core of the asymmetric molecules play an important role in the constructive interference of the harmonic emission, leading to a significant enhancement of the BTHG. Our results suggest that asymmetric molecular systems can be used for substantial improvement of the molecular BTHG-based VUV light sources.
- 1 January 2020
- Published by Optica Publishing Group
- p. Tu4A.41
Role of the bound states in below-threshold harmonic generation of Cs atom
We present an ab initio investigation of below-threshold harmonic generation (BTHG) of Cs atom in intense mid-infrared laser fields by accurately solving the time-dependent Schrödinger equation. We find that the spectra yield in BTHG of Cs atom dependents on the light intensity in the multiphoton ionization regime, and the bound states play an important role in the channel selection process for BTHG. Combining with wavelet time-frequency transform, semiclassical trajectories simulation, and quantum channel analysis, the dynamical origin of the BTHG is uncovered.
- 1 January 2020
- Published by Optica Publishing Group
- p. Tu4A.41
Role of the bound states in below-threshold harmonic generation of Cs atom
We present an ab initio investigation of below-threshold harmonic generation (BTHG) of Cs atom in intense mid-infrared laser fields by accurately solving the time-dependent Schrödinger equation. We find that the spectra yield in BTHG of Cs atom dependents on the light intensity in the multiphoton ionization regime, and the bound states play an important role in the channel selection process for BTHG. Combining with wavelet time-frequency transform, semiclassical trajectories simulation, and quantum channel analysis, the dynamical origin of the BTHG is uncovered.
- 1 January 2020
- Published by Optica Publishing Group
- p. Tu4B.46
Probing spectral and temporal fine structures of high-order harmonic generation in laser-driven electron-rescattering
We present an ab initio precision investigation of the subtle details of the spectral and temporal fine structures of high-order harmonic generation (HHG) in laser-driven electron-rescattering by using a new synchrosqueezing transform method (SST). The SST time-frequency analysis allows us to explore the in depth dynamics and contributions of the quantum trajectories in HHG associated with the electron-rescattering. Particularly it uncovers the subtle details of the spectral and temporal fine structures of the HHG and provides novel insights regarding the dynamical origin of the HHG in below-threshold harmonic regimes.
- 1 January 2020
- Published by Optica Publishing Group
- p. Tu4B.46
Probing spectral and temporal fine structures of high-order harmonic generation in laser-driven electron-rescattering
We present an ab initio precision investigation of the subtle details of the spectral and temporal fine structures of high-order harmonic generation (HHG) in laser-driven electron-rescattering by using a new synchrosqueezing transform method (SST). The SST time-frequency analysis allows us to explore the in depth dynamics and contributions of the quantum trajectories in HHG associated with the electron-rescattering. Particularly it uncovers the subtle details of the spectral and temporal fine structures of the HHG and provides novel insights regarding the dynamical origin of the HHG in below-threshold harmonic regimes.
- 1 January 2020
- Published by Optica Publishing Group
- p. JTu2A.5
Below-threshold harmonic generation of homonuclear and heteronuclear diatomic molecules
We present an ab initio quantum study of the roles of the nuclear symmetry on below-threshold harmonic generation (BTHG) from homonuclear and heteronuclear diatomic molecules. We discover the intuitive electronic dynamical behaviors in molecular BTHG.
- 1 January 2020
- Published by Optica Publishing Group
- p. JTu2A.5
Below-threshold harmonic generation of homonuclear and heteronuclear diatomic molecules
We present an ab initio quantum study of the roles of the nuclear symmetry on below-threshold harmonic generation (BTHG) from homonuclear and heteronuclear diatomic molecules. We discover the intuitive electronic dynamical behaviors in molecular BTHG.
- 30 October 2019
- Published by American Physical Society (APS) in Physical Review A
- Vol. 100 (4) , 043423
Minima in low-energy above-threshold-ionization spectra induced by electronic structure
A structure with local minima is found in the low-energy part of the above-threshold-ionization electron spectrum for several one-electron atomic and molecular targets initially in excited electronic states. The ionization regime is neither tunneling nor pure multiphoton with the Keldysh parameter slightly larger than unity. The effect is nonperturbative and depends on the frequency and intensity of the driving field. Although the ionization process is generally nonresonant, our analysis reveals an important role of intermediate bound states in formation of the structure.
- 30 October 2019
- Published by American Physical Society (APS) in Physical Review A
- Vol. 100 (4) , 043423
Minima in low-energy above-threshold-ionization spectra induced by electronic structure
A structure with local minima is found in the low-energy part of the above-threshold-ionization electron spectrum for several one-electron atomic and molecular targets initially in excited electronic states. The ionization regime is neither tunneling nor pure multiphoton with the Keldysh parameter slightly larger than unity. The effect is nonperturbative and depends on the frequency and intensity of the driving field. Although the ionization process is generally nonresonant, our analysis reveals an important role of intermediate bound states in formation of the structure.
- 15 February 2019
- Published by American Physical Society (APS) in Physical Review A
- Vol. 99 (2) , 023419
Conditions for perfect circular polarization of high-order harmonics driven by bichromatic counter-rotating laser fields
Recently, studies of high-order harmonic generation (HHG) from atoms driven by bichromatic counter-rotating circularly polarized laser fields have received considerable attention for this process could be a potential source of coherent circularly polarized extreme ultraviolet (XUV) and soft-x-ray beams in a tabletop-scale setup. In this paper, we address the problem with molecular targets and perform a detailed quantum study of the molecule in bichromatic () counter-rotating circular polarized laser fields where we adopt wavelengths (790 and 395 nm) and intensities () reported in a recent experiment [K. M. Dorney et al., Phys. Rev. Lett. 119, 063201 (2017)]. Here, we demonstrate appropriate conditions to produce perfectly circular polarized harmonics. The calculated radiation spectrum contains doublets of left and right circularly polarized harmonics which display perfect circular polarization with use of the trapezoidal pulse shape, and substantial deviations from perfect circular polarization with use of the sine-squared pulse shape. We also study in detail short- and long-cycle counter-rotating circularly polarized driving pulses with a time delay between the two driving fields, and . These time delayed circularly polarized driving pulses are applied to H atoms and molecules, and in both atomic and molecular cases we conclude a zero time delay corresponds to the highest HHG intensity for short pulses. For longer pulses there are no distinct differences in HHG intensities between the zero and nonzero time delays if the latter are within a few optical cycles of the fundamental frequency.- 15 February 2019
- Published by American Physical Society (APS) in Physical Review A
- Vol. 99 (2) , 023419
Conditions for perfect circular polarization of high-order harmonics driven by bichromatic counter-rotating laser fields
Recently, studies of high-order harmonic generation (HHG) from atoms driven by bichromatic counter-rotating circularly polarized laser fields have received considerable attention for this process could be a potential source of coherent circularly polarized extreme ultraviolet (XUV) and soft-x-ray beams in a tabletop-scale setup. In this paper, we address the problem with molecular targets and perform a detailed quantum study of the molecule in bichromatic () counter-rotating circular polarized laser fields where we adopt wavelengths (790 and 395 nm) and intensities () reported in a recent experiment [K. M. Dorney et al., Phys. Rev. Lett. 119, 063201 (2017)]. Here, we demonstrate appropriate conditions to produce perfectly circular polarized harmonics. The calculated radiation spectrum contains doublets of left and right circularly polarized harmonics which display perfect circular polarization with use of the trapezoidal pulse shape, and substantial deviations from perfect circular polarization with use of the sine-squared pulse shape. We also study in detail short- and long-cycle counter-rotating circularly polarized driving pulses with a time delay between the two driving fields, and . These time delayed circularly polarized driving pulses are applied to H atoms and molecules, and in both atomic and molecular cases we conclude a zero time delay corresponds to the highest HHG intensity for short pulses. For longer pulses there are no distinct differences in HHG intensities between the zero and nonzero time delays if the latter are within a few optical cycles of the fundamental frequency.- 1 January 2019
- Published by Optica Publishing Group
- p. NTu4A.46
Controlling electron quantum paths for generation of circularly polarized high-order harmonics by H 2 + subject to tailored (ω, 2ω) counter-rotating laser fields
We demonstrate the feasibility to control electron recollisions giving three returns per fundamental frequency cycle for generating circularly polarized (CP) attosecond pulse using tailored bichromatic (ω, 2ω) counter-rotating CP laser fields with molecular target.
- 1 January 2019
- Published by Optica Publishing Group
- p. NTu4A.46
Controlling electron quantum paths for generation of circularly polarized high-order harmonics by H 2 + subject to tailored (ω, 2ω) counter-rotating laser fields
We demonstrate the feasibility to control electron recollisions giving three returns per fundamental frequency cycle for generating circularly polarized (CP) attosecond pulse using tailored bichromatic (ω, 2ω) counter-rotating CP laser fields with molecular target.
- 1 January 2019
- Published by Optica Publishing Group
- p. JTh2A.1
Controlling electron quantum paths for generation of circularly polarized high-order harmonics by H 2 + subject to tailored (ω, 2ω) counter-rotating laser fields
We demonstrate the ability to control the electron recollisions giving three returns per one cycle of the fundamental frequency ω using tailored bichromatic (ω, 2ω) counter-rotating circularly polarized laser fields with a molecular target.
- 1 January 2019
- Published by Optica Publishing Group
- p. JTh2A.1
Controlling electron quantum paths for generation of circularly polarized high-order harmonics by H 2 + subject to tailored (ω, 2ω) counter-rotating laser fields
We demonstrate the ability to control the electron recollisions giving three returns per one cycle of the fundamental frequency ω using tailored bichromatic (ω, 2ω) counter-rotating circularly polarized laser fields with a molecular target.