Browsing by Author "Jiang, Tsin Fu"

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Quantum control of atomic two-photon ionization by ultrashort light pulse effect
(2017-07-25)
Lee, Han Chieh
;
Da Jheng, Shih
;
Jiang, Tsin Fu
;
物理研究所
;
Institute of Physics
We demonstrate that the two-photon photoelectron spectrum can be manipulated by an ultra-short light pulse. We decompose a short pulse into a linear superposition of Fourier modes. The two-photon transition amplitude becomes a summation of all pathways. The contribution of each pathway was accurately calculated by using a second-order variational method. By properly choosing the carrier frequency and pulse duration according to the calculated two-photon absorption factor versus the absorbed first photon energy, the photoelectron spectrum can become single-or double-peaked. We use the hydrogen atom as a model and study both cases of linearly and circularly polarized light pulse.
Theory of infrared-dressed atomic photoionization by extremely ultraviolet attosecond pulse trains
(2012-03-01)
Lee, Han Chieh
;
Da Jheng, Shih
;
Jiang, Tsin Fu
;
物理研究所
;
Institute of Physics
We theoretically study the infrared (IR)-dressed photoionization of atoms excited by extreme ultraviolet attosecond pulse trains above ionization threshold. The initial state of atoms is treated perturbatively by the IR field, and the continuum states are considered as Coulomb-Volkov (CV) waves. CV waves can much reduce the gauge difference calculated with Volkov waves, and, in general, the contribution of ground-state perturbation to the photoelectron spectrum is negligible. Our calculations show qualitative agreement with the experimental results [Phys. Rev. Lett. 95, 013001 (2005)]. An evident dependence of the photoelectron spectrum on the delay phase between the IR field and the attosecond pulse train is exhibited in both helium and argon. The angular distribution of photoelectrons with various IR polarizations and the corresponding photoelectron spectra are presented. The linearly polarized IR fields are shown to have a higher controlling capability of the spectrum via IR delay phases than the circularly polarized fields. On the other hand, the circularly polarized IR fields have a fruitful angular dependence of photoelectrons with various IR delay phases. (C) 2012 Optical Society of America
Timing analysis of infrared-driven high-order harmonic generation with above-ionization attosecond pulses
(2013-05-01)
Lee, Han Chieh
;
Jiang, Tsin Fu
;
物理研究所
;
Institute of Physics
We theoretically study infrared (IR)-driven high-order harmonic generation (HHG) assisted by attosecond pulses with a central energy above the atomic ionization threshold. We provide a clear physical picture for controlling HHG using the time delay between the attosecond pulses and the IR laser reported by Faria et al. [Phys. Rev. A 74, 053416 (2006)]. This physical picture also indicates that the combined attosecond pulses and IR laser can help resolve the dynamics of ionized electrons from time-dependent harmonic spectra. We present the quantum effect on HHG as an example. While leaving parent ions, ionized electrons can still emit harmonics in the semi-classically forbidden situation. The two-color excitation provides a practical method to observe the quantum effect experimentally. Furthermore, in our work, attosecond pulses and an IR field are considered with a realistic pulse shape, which shows a quantitatively important effect in controlling harmonic spectra. Accordingly, a guide to optimize the control capability for HHG is presented, and a method to determine the IR carrier-envelope phase based on the pulse-shape effect on the HHG is also proposed. (C) 2013 Optical Society of America