Transcript Observing real-time electron motion with attosecond soft x-ray

Department of Chemistry
Seminar Announcement
Date/Time/Venue
Title/Speaker
17 Mar (Thu)
11am – 12nn
Observing real-time electron motion with
attosecond soft x-ray spectroscopy
@ S8 Level 3
Executive
Classroom
Dr Loh Zhi Heng
Nanyang Technological University
Host : Asst Prof Chan Yin Thai
About the Speaker
Dr Loh Zhi Heng was born and raised in Singapore. He received his
S.B. in chemistry from the Massachusetts Institute of Technology in
2003 and his Ph.D. in physical chemistry from the University of
California, Berkeley, in 2008. He remained in Berkeley as a postdoctoral
researcher before joining NTU as an Assistant Professor in December
2010. During his Ph.D. and postdoctoral studies, both performed under
the tutelage of Professor Stephen Leone, he extended transient
absorption spectroscopy into the soft x-ray and attosecond time
domain; the latter was achieved in collaboration with Professor Ferenc
Krausz at the Max-Planck-Institut für Quantenoptik, Germany. His research interests are in
employing attosecond to femtosecond time-resolved core-level spectroscopies to study
coherent quantum dynamics and strong-field phenomena in atoms, molecules, and
nanomaterials.
Abstract
The wave-like nature of matter is one of the basic tenets of the intriguing world of
quantum mechanics. The synchrony of these wave-like states with a definite phase
relationship yields a quantum coherence that encodes the motion of quantum mechanical
entities. In the case of electrons, the time scale for their ultrarapid motion resides in the
attosecond domain, where one attosecond is one billion-billionth of a second. The direct
observation of electron dynamics in the time domain has remained only a dream until very
recently. In this talk, I shall describe my previous work in applying soft x-ray pulses of
femtosecond to attosecond time durations to study ultrafast quantum dynamics. In the
femtosecond regime, time-resolved soft x-ray transient absorption spectroscopy reveals
the electronic quantum state distribution of ions [1] and time scales for dissociative
photoionization [2] following the interaction of intense laser pulses with atoms and
molecules. A recent experiment with attosecond soft x-ray pulses allowed the first realtime observation of valence electron motion [3]. In the experiment, valence electron
motion that is driven by the spin-orbit superposition of the Kr+ 2P3/2 and 2P1/2 states is
observed after ionizing Kr atoms with an intense, few-cycle near-infrared laser pulse.
Retrieval of the entire ion density matrix from the experimental data enables visualization
of the Kr 4p valence shell electron motion in real time. If time permits, I will discuss some of
the experiments that will be pursued at NTU.
[1] Z.-H. Loh, M. Khalil, R.E. Correa, R. Santra, C. Buth, and S.R. Leone, “Quantum state-resolved probing of strong-fieldionized xenon atoms using femtosecond high-order harmonic transient absorption spectroscopy,” Phys. Rev. Lett.
98,143601 (2007).
[2] Z.-H. Loh and S.R. Leone, “Ultrafast strong-field dissociative ionization dynamics of CH2Br2 probed by femtosecond soft
x-ray transient absorption spectroscopy,” J. Chem. Phys. 128, 204302 (2008).
[3] E. Goulielmakis,* Z.-H. Loh,* A. Wirth, R. Santra, N. Rohringer, V.S. Yakovlev, S. Zherebtsov, T. Pfeifer, A.M. Azzeer, M.F.
Kling, S.R. Leone, and F. Krausz, "Real-time observation of valence electron motion" Nature 466, 739 (2010).
All are Welcome