著者

Wang Xiaowei Chini Michael Cheng Yan Wu Yi Tong Xiao-Min Chang Zenghu

出版者

The American Physical Society

雑誌

Physical review A (ISSN:10502947)

巻号頁・発行日

vol.87, no.6, pp.063413, 2013-06

被引用文献数

49 7

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The dynamics of an atom in a strong infrared laser field (1013 W/cm2) result in substantial changes to the field-free electronic energy levels, which can be probed on time scales shorter than the laser cycle using isolated attosecond pulses. Here, we measure the transient absorption of an isolated attosecond pulse by laser-dressed bound states of neon near the first ionization threshold. The observed subcycle changes in the absorption spectrum result from both laser-induced ac Stark shifts and from quantum interferences between different multiphoton excitation pathways. We further demonstrate the ability to experimentally turn off the quantum interference mechanism by eliminating one of the interfering pathways.

著者

Sandhu A.S. Tong Xiao-Min

出版者

IEEE

雑誌

IEEE journal of selected topics in quantum electronics (ISSN:1077260X)

巻号頁・発行日

vol.18, no.1, pp.351-362, 2012

被引用文献数

1 2

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Attosecond-duration, fully coherent, extreme-ultraviolet (XUV) photon bursts obtained through laser high-harmonic generation have opened up new possibilities in the study of atomic and molecular dynamics. We discuss experiments elucidating some of the interesting energy redistribution mechanisms that follow the interaction of a high-energy photon with a molecule. The crucial role of synchronized, strong-field, near-IR laser pulses in XUV pump-probe spectroscopy is highlighted. We demonstrate that near-IR pulses can in fact be used to modify the atomic structure and control the electronic dynamics on attosecond timescales. Our measurements show that the Gouy phase slip in the interaction region plays a significant role in these attosecond experiments. We perform precision measurement of interferences between strong field-induced Floquet channels to extract the intensity and phase dependence of photoionization dynamics. Applications of emerging table-top ultrafast XUV sources in the study of core electron dynamics are also discussed.

著者

Shivaram Niranjan Timmers Henry Tong Xiao-Min Sandhu Arvinder

出版者

Elsevier B.V.

雑誌

Chemical physics (ISSN:03010104)

巻号頁・発行日

vol.414, pp.139-148, 2013-03

被引用文献数

7

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We present experimental results and a theoretical framework for understanding the ionization dynamics in atoms exposed to XUV attosecond pulse trains and strong multi-cycle infrared (IR) fields. We invoke the Floquet formalism to model dressed atomic states as a manifold of Fourier components spaced by the laser frequency. In XUV-IR pump–probe measurements, we observe that the ionization yield oscillates due to quantum interference between photo-excitation paths to a Floquet state. We show that the intensity-dependent shifts of atomic structure modify the ionization channels and the associated interference phase. We extract this phase variation and compare it with simulations. These results provide a comprehensive description of the two-color ionization process and enable new schemes for control of attosecond ionization and fragmentation dynamics.

著者

Jin Ying-Jun Tong Xiao-Min Toshima Nobuyuki

出版者

The American Physical Society

雑誌

Physical review A (ISSN:10502947)

巻号頁・発行日

vol.86, no.5, pp.053418, 2012-11

被引用文献数

6 1

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We studied the high-harmonic generation of H2+ ions in an intense laser field by solving the time-dependent Schrödinger equation in prolate spheroidal coordinates. By analyzing the power spectra of the harmonics with the electric field polarized along the molecular axis, we found that the yield of the third-order harmonic drops by several orders of magnitude at a specified aligned angle between the laser polarization direction and the molecular axis. The laser polarization angle of the minimum depends on the internuclear distance and it disappears both in the separated- and united-atom limits. This infers that the minimum is associated with the molecular symmetry. By decomposing individual contributions of the σ and π states, we identified that the minimum is attributed to the cancellation of the induced dipole moments of the σ and π states, like a dynamical Cooper minimum, but the position of the minimum can be tuned by the laser intensity for a given internuclear distance.