Desorption, ablation, and plasma formation have been studied for a large variety of materials (insulators, semiconductors, and metals). Damaged surfaces have been investigated using light, electron, and atomic force microscopy. Short-wavelength ablation was very efficient and clean when proper irradiation conditions were chosen. The edges of craters were sharp, and the area around the craters was clean. A distinct difference in the behavior of conducting materials and insulators was observed. In the case of insulators the morphology of the irradiated surface and the crater depth hardly depended on the beam intensity. In contrast, the irradiated silicon surface becomes very rough when the intensity exceeds the damage threshold. At high intensities multiple charged ions were registered. Kinetic energy of the ions increases with charge state and reaches keV range for highly-charged ions. Again, a clear difference between insulators and conducting material was observed. High charge states and energetic ions were typical for conductors and semiconductors. Only single ions states and low energetic ions (~50 eV) were detected for insulators for all irradiation conditions.

Longitudinal plasma oscillations are becoming a subject of great interest for XFEL physics in connection with LSC microbunching instability [1] and certain pump-probe synchronization schemes [2]. In the present paper we developed the first exact analytical treatment for longitudinal oscillations within an axis-symmetric, (relativistic) electron beam, which can be used as a primary standard for benchmarking space-charge simulation codes. Also, this result is per se of obvious theoretical relevance as it constitutes one of the few exact solutions for the evolution of charged particles under the action of self-interactions.

During the design of X-FELs, space-charge codes are required to simulate the evolution of longitudinal plasma oscillation within an electron beam in connection with LSC microbunching instability [1] and certain pump-probe synchronization schemes [2]. In the paper [3] we presented an analytical solution to the initial value problem for longitudinal plasma oscillation in an electron beam. Such a result, besides its theoretical importance, allows one to benchmark space-charge simulation programs against a self-consistent solution of the evolution problem. In this paper we present a comparison between our results [3] and the outcomes of the simulation code ASTRA.