Seminars Archive

Quantum dynamics and control on the 1-fs time scale, using several optical and XUV fields tuned in intensity and time

Abstract
The motion of electrons in superpositions of excited states can proceed extremely quickly, and determines the outcome (final products) of chemical reactions. Extremely short flashes of light have, for quite some time now, allowed insights into these very fast processes, and to steer electron dynamics either by directly driving them with the electric field of intense laser pulses, or via interference of few-/multi-photon absorption processes. Yet, even the most simple atomic and molecular systems are difficult to understand, starting from as few as three particles (He or H2+), and in particular when we expose these systems to laser light of just moderate intensities. Here I will present our experimental approach to understanding and steering fundamental quantum dynamics directly in the time domain. We aim at detecting the full range of observables, electrons, ions, and light, if possible in coincidence, for systems interacting with weak to intense laser light of optical and extreme ultraviolet frequencies. A particular focus of our research is the role and evolution of (quasi-)bound excited states in strong laser fields, as these are the interesting transition states for neutral-state chemistry. We use the tuning of relative time delays of laser pulses, and their intensity, to uncover dynamical mechanisms and to pave the road towards novel multidimensional spectroscopies. These approaches result in a way to quantify intense light–matter interaction by analyzing spectral line shapes, which applies generally for gas-phase atoms all the way to complex molecules in solution. Examples include the control of two-electron wavefunctions excited by attosecond-pulsed extreme ultraviolet (XUV) light, as well as the strong driving of a double excitation in the intense XUV fields of the Free-electron-LASer at Hamburg (FLASH). For the latter, we directly observed Stark shifts of excited states in intense XUV FEL light.