AMO Seminar - Speaker Giulio Vampa (University of Ottawa, Canada) - Tuesday, May 31st

[Shipley, Dameyon]

Please join us for a special AMO seminar.

Speaker:               Giulio Vampa (University of Ottawa, Canada)
Date:                     Tuesday, May 31, 2016
Time:                     2:00 PM
Place:                    Room 4138, Physics Research Building
Title:                      High-harmonic spectroscopy in condensed media

Abstract: When intense laser pulses interact with a medium, high order harmonics of the fundamental laser frequency can be created. Traditionally, the medium is an atomic or molecular gas but, recently, high harmonics have been generated from bulk semiconductors as well [1]. In experiments performed in ZnO [2] and Si crystals, we find that high harmonics are generated by recollisions between accelerated electrons and their correlated holes upon their birth through tunneling across the forbidden gap. The analogous mechanism is responsible for atomic high harmonic generation, and is the cornerstone of attosecond atomic science.  Thanks to the link we establish between atomic and solid harmonics, it will be possible to extend attosecond spectroscopy to solids. We also foresee solids becoming an important medium for attosecond technology.

Finally, using the high harmonics we develop an all-optical method to reconstruct the crystal's momentum-dependent band gap [3]. This method can be applied when photoelectrons are not accessible, such as for materials under high pressures or high magnetic fields.

[1] S. Ghimire et al., Nature Physics 7, 138-141 (2011).
[2] G. Vampa et al., Nature 522, 462-464 (2015).
[3] G. Vampa et al., PRL 115, 193603 (2015).





Abstract: Millijoule-level ultrashort pulses in the 1.5-2.5 micron spectral region are ideal for extending the cutoff in high-order harmonic generation. I will present several strands of recent work towards using such pulses to  measure attosecond dynamics. Systematic studies of high-order harmonic spectra in benzene and its halogen and methyl substituted derivatives shed light on the roles played by strong-field ionization and the beating of multiple cation states. Spectral shearing interferometry of few-cycle 1.8 micron pulses after spectral broadening and compression in an argon-filled capillary reveals a clean spatio-temporal profile and an ultrabroadband 0.64-2.6 micron supercontinuum. I will also outline our plans for boosting the energy of the few-cycle source as part of the MURI collaboration with the ultrafast group at OSU.
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