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International audience; Manganese arsenide layers epitaxially grown on GaAs(001) are known to feature a temperature dependent self-assembled microstructure of ordered stripes, alternating the ferromagnetic α and paramagnetic β phases. The surface dipolar fields generated by the α/β stripes have been used for achieving temperature controlled magnetization switching of a ferromagnetic overlayer. For this kind of application, it is advantageous to minimize the MnAs layer thickness. In this work we investigate, using x-ray scattering techniques, the presence of the ordered microstructure as a function of the MnAs layer thickness and we identify a minimum value of ~40 nm for the formation of ordered α/β stripes in MnAs/GaAs(001). These results have an impact for envisaging magnetization-switching applications that rely on the control of the temperature-or laser-driven surface dipolar fields in MnAs-based devices.

Synopsis We report recent results of photoelectron angular distributions (PADs) for photoionization (PI) of atomic and molecular targets, resolved in the time domain at the attosecond scale, combining electron-ion coincidence momentum spectroscopy and the RABBITT scheme. We propose a unified formalism synthetizing the PAD(θ, τ) results in terms of a reduced set of coefficients.

Single-photon laser enabled Auger decay (spLEAD) is an electronic de-excitation process which was recently predicted and observed in Ne. We have investigated it using bichromatic phase-locked free electron laser radiation and extensive angle-resolved photoelectron measurements, supported by a detailed theoretical model. We first used separately the fundamental wavelength resonant with the Ne+ 2s–2p transition, 46.17 nm, and its second harmonic, 23.08 nm, then their phase-locked bichromatic combination. In the latter case the phase difference between the two wavelengths was scanned, and interference effects were observed, confirming that the spLEAD process was occurring. The detailed theoretical model we developed qualitatively predicts all observations: branching ratios between the final Auger states, their amplitudes of oscillation as a function of phase, the phase lag between the oscillations of different final states, and partial cancellation of the oscillations under certain conditions.

The FERMI@Elettra project is a seeded free electron laser (FEL) source, based on the High Gain Harmonic Generation (HGHG) scheme. It is designed to supply photons in a spectral range from 65 to 20 nm with the first undulator line (FEL-1) and from 20 nm to 4 nm with the second undulator line (FEL-2). After a first period of commissioning of the electron beam up to 100 MeV at low charge, started in August 2009, several phases of installations and beam commissioning periods have been alternated through the 2010. On December 2010 the first FEL light in the FEL-1 line was obtained at 65 nm and 43 nm by adopting as an initial seed the third harmonic of a TiSa laser. The complete optimization and commissioning of the photo-injector has been carried on in parallel with the Linac and FEL commissioning, from a conservative set-up to the final designed configuration. This paper reports the electron beam characterization in the injector area, the comparison with the theoretical expectations and the experimental process which resulted in a high brightness electron beam. This beam was optimized to be compressed and then transported through the undulators of FEL-1 where intense photons ranging from 65 nm to 20 nm were generated [1,2].