Attosecond Ionization Dynamics and Time Delays
The basic motivation is to understand and ultimately control how matter functions at the electronic, atomic and molecular level. Initially our focus is on the question how quanta of energy and charge are transported on an atomic spatial and attosecond time scale. In principle, time dependent-processes in quantum mechanics are described by the time-dependent Schrödinger Equation (TDSE). The challenge is that the TDSE in most cases cannot be solved without approximations and that time is not an operator and therefore not a direct observable. Very common approximations could not be tested fully but with attosecond time resolution we can isolate purely electronic dynamics on short time scales with atomic resolution. At the same time recent progress in ultrafast lasers, nonlinear frequency conversion and XFELs give access to synchronized pulses ranging from the THz to the hard X-ray. We have now reached a point where not only do we have the time resolution to probe the motion of atoms within assemblies (molecules, solids, liquids, proteins) but also that of the electrons, which are the main actors in the formation and breaking of bonds. We can therefore study time-dependent electronic and atomic structure for the first time. Semi-classical models seem to explain suprisingly well many current attosecond measurement which have advanced rapidly with reproducable and high-quality data, allowing for very fundamental tests for our current understanding and models in time-dependent quantum mechanics. This talk will give a general introduction, motivation and use as an example the recent progress in attosecond ionization dynamics and time delays in tunnel ionization. Following the peak of an electron wavepacket (i.e. the group delay) for determining time delays can be tricky and often misleading. We will discuss why in tunnel ionization regime the group delay (or the related Wigner delay) gives the wrong explanation for the measured delay, whereas in the single-photon ionization regime we can show experimentally that the Wigner time delay can explain the general trend correctly.
Prof. Dr. Ursula Keller is the Director of the National Center of Competence in Research for Molecular Ultrafast Science and Technology (MUST) (1) and heads Research Group at ETH Zurich (2). She was a co-founder of two high-tech companies: Time-Bandwidth Products (acquired by JDSU in 2014) and GigaTera, a venture capital funded telecom company (acquired by Time-Bandwidth). Previously she was a Member of Technical Staff at AT&T Bell Laboratories, and a visiting professor at the University of California, Berkeley and the Lund Institute of Technologies. In 1992, she invented and demonstrated the first passively mode-locked diode-pumped solid-state laser and solved a 25-year-old challenge. Her research interests are exploring and pushing the frontiers in ultrafast science and technology, including attosecond science. She received her Physics Diplom from ETH Zurich and PhD in Applied Physics from Stanford University. In 2013, the Laser Institute of America gave Prof. Keller the Arthur L. Schawlow Award, which recognizes individuals who have made distinguished contributions to applications of lasers in science, industry, or education and in 2015 she received the OSA Charles H. Townes Award and the Geoffey Frew Fellowship from the Australian Academy of Science which also supports this public presentation.
(1) http://www.nccr-must.ch (2) http://www.ulp.ethz.ch