Thursday, October 26, 20172:00 PM - 3:00 PMCNLS Conference Room (TA-3, Bldg 1690)|
High-order harmonic generation: from gases to solids
The recent development of femtosecond laser technology has opened new avenues to explore ultrafast processes in nature. The auger decay in atoms, real-time observation of the oscillating infrared laser field and tomography reconstruction of molecular orbitals are some examples of those ultrafast phenomena which are nowadays investigated thanks to the generation of attosecond (10-18 s) and femtosecond (10-15 s) light sources.
So far, high-order harmonic generation, HHG, in gases has been used to produce and control attosecond pulses. A key feature of the HHG in gases is that the ionized electron recombines with its parent atom while in solids, the electron would recombine with any other atom in the lattice. This "delocalization" is poorly understood, yet believed to be important for attosecond pulse generation and thereby real-time imaging of the electronic density in a solid.
In this talk, we will review the HHG process in gases, its main mechanism and how it has been extended to solids, i.e. semiconductor crystals. Our main motivation will be to address the basic question of what it is the "localization" role of the HHG process in a semiconductor compared to the gas phase. By using localized Wannier basis in the valence band and a delocalized description in the conduction band, i.e. Bloch states, one that separates the contributions of neighboring lattice sites to each harmonic and hence determines the localization in the harmonic emission.
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Host: Chris Neale