Mechanism of single shot damage of Ru thin films irradiated by femtosecond extreme UV free electron laser

Ruthenium is a perspective material to be used for XUV mirrors at free electron laser facilities. Yet, it is still poorly studied in the context of ultrafast laser matter interaction. In this work, we present single shot damage studies of thin Ru films irradiated by femtosecond XUV free electron laser pulses at FLASH. Ex situ analysis of the damaged spots, performed by different types of microscopy, shows that the weakest detected damage is surface roughening. For higher fluences we observe ablation of Ru. Combined simulations using Monte Carlo code XCASCADE 3D and the two temperature model reveal that the damage mechanism is photomechanical spallation, similar to the case of irradiating the target with optical lasers. The analogy with the optical damage studies enables us to explain the observed damage morphologie

TTF2 ACC5 Gradient Measurement

The maximum, measured energy-contribution of ACC5 at TTF2 is 26.5 + 0.7 MV/m over 7 cavities, each 1.035 m long. For ACC5 gradient measurements, a comparison was made between the beam energy with ACC4 and 5 off and the beam energy with ACC4 detuned and ACC5 cavities 1-7 tuned. The maximum gradient was determined by increasing the amplitude of the RF until the cavity quenched. ACC5 cavities 1-7 were tuned to maximum gradient such that the RF pulse-shape had a flat top. The phase of the RF was, however, 30 + 10 degrees different from the beam phase for 6 of 7 cavities, producing 12.1 + 1.5 % less beam energy than on-crest operation would’ve produced. The beam energy was determined with a beam image on a screen in the dispersive region of the bypass-dogleg and the strength of the upstream dipole

Grazing-incidence spectrometer for the monitoring of the VUVFEL beam at DESY

A stigmatic spectrometer for the 2.5-40 nm EUV region has been realized. The design consists of a grazing-incidence spherical variable-line-spaced grating with flat-field properties and of a spherical mirror mounted in the Kirkpatrick-Baez configuration that compensates for the astigmatism. The spectrum is acquired on a fluorescent screen and intensified CCD detector, that can be moved along the spectral focal curve to select the spectral region to be acquired. The spectral and spatial resolution of the system have been characterized by using the emission from an hollow-cathode lamp and a laser-produced plasma. At present, the instrument is installed at the VUV-FEL at DESY for the spectral monitoring of the FEL beam in the 20-45 nm region

Grazing incidence spectrometer for the monitoring of the EUV FEL beam at DESY

A stigmatic spectrometer for the 2.5–40 nm extreme-ultraviolet (EUV) region has been realized. The design consists of a grazing-incidence spherical varied-line-spaced grating with flat-field properties and of a spherical mirror mounted in the Kirkpatrick–Baez configuration that compensates for the astigmatism. The spectrum is acquired on a fluorescent screen and intensified CCD detector that can be moved along the spectral focal curve to select the spectral region to be acquired. This stigmatic design has also spectral and spatial resolution capability for extended sources. The spectral and spatial resolution of the system has been characterized by using the emission from a hollow-cathode lamp or a laser-produced plasma. At present, the instrument is installed at the vacuum–ultraviolet free-electron-laser (VUV FEL) at DESY for the spectral monitoring of the FEL beam in the 20–40 nm region