סמינר בחומר מעובה: Attosecond Science: tracking and manipulating electronic processes on their natural timescale
Avner Fleischer, Technion-Israel Institute of Technology
Atoms and Molecules subjected to intense infrared laser fields may ionize by one of the most fundamental quantum processes: tunnel ionization. Depending on the release time of the electron into the continuum, one of two scenarios might take place. In the first, the electron simply flies towards the detector. I will show that this electron carries significant fingerprints about the electronic orbital from which it was torn. By analyzing its properties (momentum, energy) in a COLTRIM (cold target recoil ion momentum) spectrometer, we essentially constructed a "laser-STM" – an analogue to the conventional STM - capable of studying electron dynamics with ultrafast temporal resolution. I will show how this machinery can be used to take femtosecond-resolution snapshots of an evolving electronic wavepacket density inside several atoms and molecules . This work paves the way towards imaging of more complex electronic processes, such as charge transfer in molecules and semiconductor devices. In the second scenario the electron might return to the vicinity of the ion and recollide with it- giving rise to the emission of high energy photons by high harmonic generation (HHG). I will present our recent solution to a problem which existed nearly 20 years in the field of HHG: how to control the polarization state of the emitted harmonics . I will show how attosecond sub-cycle synchronization of multiple recollision events, occuring from different hitting directions in a two-dimensional plane, can be used to obtain full polarization control of the HHG radiation. With this unique source at hand, the role of spin angular momentum in HHG was explored for the first time.
This work represents a critical advance towards the development of tabletop-systems for imaging of ultrafast magnetism  and other chiral media with very high spatial and temporal resolution.
 A. Fleischer, H. J. Wӧrner, L. Arissian, L. Liu, M. Meckel, A. Rippert, R. Dӧrner, D. M. Villeneuve, P. B. Corkum and A. Staudte, "Probing Angular Correlations In Sequential Double Ionization", Phys. Rev. Lett. 107 113003 (2011).
 A. Fleischer, O. Kfir, T. Diskin, P. Sidorenko and O. Cohen,"Spin angular momentum and tunable polarization in high-harmonic generation", Nature Photonics 8 543 (2014).
**see also News & Views by M. Ivanov and E. Pisanty, Nature Photonics 8 501 (2014).
 Ofer Kfir, Patrik Grychtol, Emrah Turgut, Ronny Knut, Dmitriy Zusin, Dimitar Popmintchev, Tenio Popmintchev, Hans Nembach, Justin M. Shaw, Avner Fleischer, Henry Kapteyn, Margaret Murnane and Oren Cohen, "Generation of phase-matched circularly-polarized extreme ultraviolet high harmonics for magnetic circular dichroism spectroscopy", arXiv 1401.4101 (2014), accepted to Nature Photonics.
מארגן הסמינר: פרופ' שמשון ברעד