Commissioning of a photoelectron spectrometer for soft X ray photon diagnostics at the European XFEL

Commissioning and first operation of an angle-resolved photoelectron spectrometer for non-invasive shot-to-shot diagnostics at the European XFEL soft X-ray beamline are described. The objective with the instrument is to provide the users and operators with reliable pulse-resolved information regarding photon energy and polarization that opens up a variety of applications for novel experiments but also hardware optimization

Direct observation of confined states in metallic single-walled carbon nanotubes

We investigated the local density of states (LDOS) of extended individual metallic single-walled carbon nanotubes using low-temperature scanning tunneling spectroscopy. We observed that the LDOS oscillates with energy close to the Fermi level. The oscillation period of about 50 meV varies with position on the nanotube. Maps of the LDOS reveal that the peaks in the oscillation are related to confined states. The widths of the peaks increase with increasing distance from the Fermi level.BN/BionanoscienceApplied Science

Measurements and simulations of seeded electron microbunches with collective effects

Measurements of the longitudinal phase-space distributions of electron bunches seeded with an external laser were done in order to study the impact of collective effects on seeded microbunches in free-electron lasers. When the collective effects of Coulomb forces in a drift space and coherent synchrotron radiation in a chicane are considered, velocity bunching of a seeded microbunch appears to be a viable alternative to compression with a magnetic chicane under high-gain harmonic generation seeding conditions. Measurements of these effects on seeded electron microbunches were performed with a rf deflecting structure and a dipole magnet which streak out the electron bunch for single-shot images of the longitudinal phase-space distribution. Particle tracking simulations in 3D predicted the compression dynamics of the seeded microbunches with collective effects