Raum: Seminar Room V, O1.109 Gastgeber: Angel Rubio

Matteo Lucchini - Attosecond dynamics in polycrystalline diamond

MPSD Seminar
The possibility to manipulate the electrical properties of matter with very short opticalpulses is a fascinating field of research with possible far reaching applications inmany relevant technological fields. The first step towards the realization of this goal is to understand the ultrafast dynamics at the basis of light-matter interaction. Short and intense pulses allowed us to investigate a very interesting regime where the photon energy becomes comparable to the cycle-averaged kinetic energy of the electrons in the field. As the optical response of the material transitions from a classical to quantum-mechanical description many intriguing effects co-exist in this regime and the importance of inter- versus intra-band transitions is still debated. We used attosecond transient absorption spectroscopy (ATAS) to study the optical response of polycrystalline diamond driven by few-femtosecond, intense (IIR ~1012 W/cm2) infrared (IR) pulses. We monitored the system response by looking at the induced change in the absorbance with a 250-as pulse centred around 40 eV. We observed the appearance of oscillating features which modulate at twice the IR frequency, ωIR, and fully recover after the interaction. Simultaneous photoelectron acquisition from a gas nozzle placed in front of the diamond target allowed us to study the phase relation of the oscillating features and the pumping IR field. We found that the timing of the diamond response changes significantly with the probing energy and does not always follow the IR field adiabatically. Ab initio calculations performed by coupling time-dependent density functional theory (TDDFT) in real time with Maxwell’s equations reproduced the experimental observations. Further comparison with a numerical two-band model allowed us to conclude that intra-band motion dominates over inter-band transitions, thus identifying the dynamical Franz- Keldysh effect as the dominant mechanism in this regime. Our analysis constitutes an important step towards a full understanding of the optical properties of dielectrics in the Petahertz regime. [mehr]

Quantum control and dynamics with x-rays

MPSD Seminar
More than fifty years ago, it was the invention of the laser that revolutionized atomic physics and laid the foundations for quantum optics and coherent control. With only optical frequencies available, the interaction of coherent light with matter was for a long time mainly restricted to atomic transitions. Only recently have novelhigh-frequency light sources rendered x-ray quantum optics possible. In this higher frequency regime, atomic nuclei rise as natural candidates for the interaction with coherent light creating a new bridge between atomic physics, quantum optics and nuclear condensed matter physics. Nuclei are very clean quantum systems, well isolated from the environment and benefiting from long coherence times. Combining the advantages of x-rays and nuclei, a prominent incentive is to exploit x-rays as the future quantum information carriers or for novel probing technologies based on quantum effects. Furthermore, the control of nuclear transitions would open the possibility to use long-lived nuclear excited states as a compact and clean energy storage solution. The lecture will follow the developments on the emerging field of x-ray quantum optics and focus on the mutual control of coherent x-ray radiation and nuclear transitions in this new regime of laser-matter interactions. [mehr]
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