ULAD

Ultrafast Lasers and Attosecond Dynamics

 Partecipanti

Mappa

 Word cloud

Esplora la "nuvola delle parole (Word Cloud) per avere un'idea di massima del progetto.

 Obiettivo del progetto (Objective)

'Attosecond technology realizes the century-old dream of direct measurement of electron dynamics at the atomic scale. The ensuing experimental cornucopia, with many publications in Nature and Science, underscores the need for better analytic tools to explain the data, as a step towards a better physical foundation for a truly multi-disciplinary science. Current theoretical technique must be substantially improved to properly address some recent experimental controversies, such as measurements of quantum tunneling time. In particular, high harmonic generation (HHG), crucial to many experiments in attosecond science, requires a clearer 'physical picture' than semi-classical models allow. A major goal of this proposal is to provide a theoretical framework for the experiments performed by Prof. Keller's group (ETH, Zurich) and others, and thereby to bring light to current debates. The research will develop analytic techniques to calculate quantum tunneling time in HHG, and better explain other steps of the HHG process, in particular the generation of attosecond pulses via quantum path interference and the interaction of the continuum electron with the laser pulse. The analysis will address both quantum and classical regimes of HHG: e.g., the quantum tunneling calculation will use a path integral approach, the interaction of the continuum electron with the laser field will employ plasma physics techniques, etc. Both of these approaches match well with the Fellow's background: the path integral approach was previously used to study escape from a potential well, and the Fellow's dissertation focuses on the interaction of charged particles with E&M fields. The project offers a possibility of close collaboration with the Fellow's graduate institution of Princeton University and other major research centers.'

Introduzione (Teaser)

EU-funded scientists have introduced new theoretical concepts to support experimental measurements of electrons exiting a quantum system even though they appeared trapped within it.

Descrizione progetto (Article)

According to the laws of quantum physics, electrons bound to atoms can penetrate through a potential wall confining their location like a wave. The wave may reach the other side of the potential without climbing over it. The question of how long it takes an electron to pass through the barrier has been the subject of theoretical debate since the early days of quantum physics.

In 2008, researchers at the Swiss Federal Institute of Technology in Zurich (ETHZ) manipulated helium atoms with a laser pulse to lower the barrier to ionisation. This helped one of the electrons to tunnel out easily, and they could for the first time measure the tunnelling time. They proposed the 'Ultrafast lasers and attosecond dynamics' (ULAD) project to develop a solid theoretical framework for their experiments.

During the course of the ULAD project, scientists compared predictions of the main competing theories and applied a new approach to calculating tunnelling times. Specifically, the probability distribution of tunnelling times was estimated with the use of Feynman's path integrals. This approach led to results that are in good agreement with the experimental data.

ULAD scientists applied adiabatic and non-adiabatic models to calculate the tunnelling time from experimental measurements. They delved deep into the incompatibility of the theoretically derived tunnelling times with experimental measurements. This allowed them to gain a deeper theoretical understanding of the physical process behind electrons traversing across a potential barrier.

The results of the ULAD project have been described in six scientific papers published in eminent peer-reviewed journals: three Physical Review Letters, Optica, J. Phys. B (recognized as J. Phys. B Highlight of 2013) and New Journal of Physics (recognised as a highlight of 2013 across all IOP journals). The research work also received significant attention at international conferences where it was presented. Already, further experiments have been planned at ETHZ to validate the ULAD project's findings.

Resolving questions arising from experimental results will give physicists deeper insight into the structure of atoms as well as the ionisation process itself.