Final Defense

Ahmed Helal, UT-Austin

"Explosion Dynamics of Van der Walls Clusters Using 38 nm XUV Laser Pulses"

12:00pm, RLM 11.204

Abstract: The interaction of intense XUV laser pulses with matter and rare gas cluster has been the focus of the scientific community for decades. This focus has been sparked by the ongoing efforts to reach microscopy with atomic resolution, leading to a time resolved image on the scale of the atomic motion.

The interest in Van Der Waals clusters appears due to its similarity with the small bio-molecules, studying the behavior of these cluster will shed some light on how the biomolecules behavior under intense laser pulse.

We have conducted a major upgrade to the UT THOR laser system, that enables us to achieve 5 nJ of XUV energy, produced by high harmonic generation, which is used to conduct multiple cluster experiments.

We investigated the dynamics of rare-gas clusters produced by Ar and Xe gases, the ion time of flight, kinetic energy and electron energy have been measured, the generation of ion kinetic energy of two different temperatures (6 and 55 eV) due to hydrodynamic expansion was observed.

For Xe clusters, we observed the generation of unexplained high charge states up to Xe 10+, that could be due to the effect of continuum lowering and inner ionization of the giant resonance 4d-level.

We also investigated the dynamics of small molecule clusters. Stating with nitrogen clusters, we noticed a dependence of the ionization ratio between N 2 + and N + on the cluster size has been noticed. In addition to that nitrogen clusters shows the highest ion kinetic energy generated between all the clusters investigated in this dissertation.

The interaction of XUV laser pulses with Methane cluster is studied, we could not detect any high charges of methane fragments such as (CH 4 2+ ). However, we noticed that we generated multiple fragments by breaking C-H bonds (CH 3 + , CH 2 + , CH + ) in addition to bare carbon with high cluster sizes. The generation of CH 5 + , H + and H 2 + was also observed. Studying the partial yield of each of these reveals that the correlation between CH 5 + and H + is opposite to what is expected, which might be due to the change of the cluster properties (especially the phase) or the expansion dynamic itself (towards more hydrodynamics).