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Chu, Shih-I

Publications and source records attributed to Chu, Shih-I.

3 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Atomic and Molecular Physics in Strong Fields

In this project, we have investigated a broad range of atomic, molecular, and optical (AMO) processes of current significance in strong-field and ultrafast science and technology. The main goals are to develop new theoretical formalisms and accurate computational methods for ab initio and in-depth non-perturbative study of time-resolved multiphoton quantum dynamics and spectroscopy, very-high-order harmonic generation, optimal control of ultrafast attosecond pulse generation, and resonance-enhanced below threshold harmonics in intense ultrashort laser fields. We have worked on the following projects and we have published 20 top 15 % SCI journal articles during the last 3.5 years (Jan. 1, 2016 to June 30, 2019), including one article in top raking Physical Review Letters, and 3 articles in top ranking (Nature) Scientific Reports, and one Physical Review A article was chosen as Editors’ suggestion paper, etc. (a) Development of new time-dependent methods for accurate and efficient solution of multi-dimensional time-dependent Schrödinger equation and time-dependent density functional theory. (b) Non-perturbative treatment of very-high order (1000th – 5000th order) harmonic generation and broadband supercontinuum spectra from XUV to soft x-ray regime. (c) Development of synchrosqueezing transform (SST) for precision time-frequency analysis of electron multi-rescattering dynamics. (d) Exploration of the dynamical origin of resonance-enhanced near- and below-threshold harmonics. (e) Probing the high-order harmonics generation in disordered semiconductor. (f) Multiphoton ionization of one-electron relativistic diatomic quasi-molecules in strong laser fields. and, (g) New development of non-adiabatic density functional theory. The theoretical and simulation projects we have pursued are closely related to the ongoing experimental researches in several leading laboratories in the US and Europe, etc. It is expected that the outcome of this project will provide timely and significant new information and insight for the advancement of strong-field atomic and molecular physics and ultrafast science and technology.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

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 H 2 + molecule in bichromatic (ω 0 , 2ω 0 ) counter-rotating circular polarized laser fields where we adopt wavelengths (790 and 395 nm) and intensities (2×10 14 W/cm2) 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, ω 0 and 2ω 0 . These time delayed circularly polarized driving pulses are applied to H atoms and H 2 + molecules, and in both atomic and molecular cases we conclude a zero time delay corresponds to the highest HHG intensity for short pulses. Finally, 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.

74 ATOMIC AND MOLECULAR PHYSICS↗