Phase delay characterization of multilayer coatings for FEL applications

The phase delay induced by multilayer (ML) mirrors is an important feature in many fields such as attosecond pulses compression, photolithography or in pump and probe experiments performed with Free Electron Laser (FEL) pulses. The experimental characterization of the ML phase delay can be obtained by the standing wave distribution measurement (by using Total Electron Yield (TEY) signal) combined to reflectance measurement. In this work, a ML structure with aperiodic capping-layers was designed and deposited for FEL applications and their reflectance and phase delay was characterized. The method adopted allows to retrieve the ML phase delay by using the TEY signals taken at different working configurations and it doesn't require the comparison with a bulk reference sample. The results obtained are presented and discussed.