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OSA Student Chapter Meeting

SPEAKER: Peter Zhokhov
TITLE: Field-cycle-resolved anisotropic ioninzation of solids.
I'd like to give more expanded version of the talk from the meeting with Dr. Corkum, including some latest results. The Keldysh theory of photoionization in a solid dielectric is generalized to the case of ultrashort driving pulses. We derive a closed-form solution for the nonadiabatic ionization rate in a transparent solid with a periodic dispersion relation, which reveals ultrafast ionization dynamics within the field cycle and recovers the key results of the Keldysh theory in the appropriate limiting regimes. The anisotropic behavior of ionization current in the solids with simplest lattice structure is analysed.

SPEAKER: Sasha Zhdanova
TITLE: X-ray two-photon absorption competing against single and sequential multiphoton processes
The success of X-ray free-electron lasers (XFELs) has extended the frontier of nonlinear optics into the hard X-ray region. Recently, sum-frequency generation has been reported, as well as parametric downconversion. These are of the lowest (second) order, and higher-order processes remain unexplored. I will be presenting on the work of Kenji Tamasaku, et. Al. In their paper, they report the first observation of a third-order process: two-photon absorption of a 5.6 keV XFEL beam by germanium. They find that two-photon absorption competes with single and sequential multiphoton processes, but they successfully determine the intrinsic cross-section by analysing the pulse-energy dependence. They also discuss the two-photon absorption cross-section by comparing a new mechanism unique to X-rays with the conventional mechanism and show that the latter is consistent with the present result. The experimental determination and understanding of the cross-section would allow two-photon absorption spectroscopy. Their result indicates that X-ray analogues of other third-order nonlinear optical processes, such as nonlinear Raman and optical Kerr effects, are available for XFEL applications in spectroscopy, imaging and beam control. Tamasaku, Kenji, et al. "X-ray two-photon absorption competing against single and sequential multiphoton processes."Nature Photonics (2014), doi:10.1038/nphoton.2014.10.

Friday, February 07, 2014
IQSE 578, 11:30 noon
Mitchell Physics Building

Department of Physics and Astronomy
Institute for Quantum Science and Engineering
Texas A&M University

(Pizza lunch as usual. Newcomers welcome!)

Host: Ellie Figueroa