简介: |
In the microscopic world, the timescale of electron motion ranges from a few hundred attoseconds (10-18 s) to several femtoseconds (10-15 s), and is driven by electron-electron and electron-nuclear correlations. Previously, static measurements mainly provided time averaged information in the spectral domain, without shedding new light on the temporal dynamics of electrons and their correlation with other degrees of freedom in complex systems. This restricts our understanding and control of intermediate steps in chemical reactions and phase transitions. In my presentation, two examples will show that electron dynamics can now be observed and controlled in the time domain via novel ultrafast X-ray sources. In the first example, we combined isolated attosecond XUV pulses generated from the double optical gating (DOG) technique with a few-cycle NIR dressing field to control the electron autoionization process in argon [1, 2]. This experiment demonstrates the possibilities of controlling chemical reactions using strong laser fields. In the second example, angular resolved photoemission spectroscopy (ARPES) was integrated with single harmonic XUV sources. By using a UV laser as the driving field, we were able to generate a high flux (1013 photon/s) single harmonic source with a narrow band (<50 meV), and a high repetition rate (50 kHz) without using a complicated monochromator [3]. Through NIR-pump/XUV-probe spectroscopy, complex degrees of freedom, such as electron-phonon and electron-electron correlations, can be accessed directly in the time domain, which provides insight into the properties of strongly correlated materials such as high Tc superconductors. These techniques offer new paths to observing and controlling electron dynamics in complex systems.
[1] X. Feng, et al., Phys. Rev. Lett., 103, 183901 (2009)
[2] H. Wang, et al., Phys. Rev. Lett., 105, 143002 (2010)
[3] H. Wang, et al., Conference on Lasers and Electro-Optics (CLEO), QF1C2, San Jose, CA (2013)
个人简介：
He Wang received his B.S. degree from University of Science and Technology of China (USTC) in 2005 and Ph.D. from Kansas State University in 2010. He is currently a postdoctoral fellow at the Lawrence Berkeley National Laboratory (LBNL) studying ultrafast electron dynamics in strongly correlated materials.
His research interests include ultrafast solid laser development, ultrafast XUV/X-ray source development, attosecond and femtosecond electron dynamics. His main achievements include: (1) By using liquid crystal based adaptive phase modulator, he successfully generated 5-fs pulse with mJ level pulse energy and coherently control the spectrum of high harmonic generation (HHG). (2) Generation and application of single attosecond pulses: using the single attosecond pulse generated by double optical gating (DOG) technique, he was able to control the ultrafast autoionization process of argon in the temporal domain and observe the sub-cycle dynamics of AC stark shift in helium. (3) At LBNL, he has successfully developing the high repetition femtosecond, single harmonic source with flux comparable to the synchrotron beam line. Now he is integrating such powerful light source with a state-of-the-art angle resolved photoemission spectroscopy (ARPES) end station, which is a powerful tool for pump-probe experiments on strongly correlated materials.
Dr. Wang is a member of the Optical Society of America and the American Physical Society. |
