Exploring particle-induced excitations in the time domain
The impact of an energetic particle onto a solid surface generates a strongly perturbed and extremely localized non-equilibrium state, which relaxes on extremely fast time scales. In order to facilitate a time-resolved observation of the relaxation dynamics using established ultrafast pump-probe techniques, it is necessary to pinpoint the projectile impact in time with sufficient accuracy. In this project, we will develop a novel ion source which generates ion pulses of (sub-) pikosecond duration to access the ultrafast dynamics for the first time with an experimental technique.
Detailed ion trajectory simulations (for details see New J. Phys. 21 (2019) 053017 ) show that single ion pulses of sub-picosecond duration can be generated via femtosecond photoionization of rare gas atoms entrained in a supersonic jet. The photoion cloud can be generated with a standard table-top laser system. We could show that Arq+ ions with q = 1–5 can be generated, which are then accelerated to energies in the keV range over a very short distance and bunched to impinge onto the target surface in a time-focused manner. Charge state broadening is insignificant for pulses containing up to 10–20 ions and starts to increase the pulse width only above ~50 ions/pulse.
The realization of the corresponding experimental set-up is currently underway ...