Attosecond time-resolved measurements of electron and photon beams with a variable polarization X-band RF deflector at an X-ray free-electron laser

X-ray free-electron lasers (FELs) are modern research instruments utilized in multiple scientific fields capable of analyzing matter with unprecedented time and spatial resolutions. Time-resolved measurements of electron and photon beams are essential in X-ray FELs. RF transverse deflector structures (TDSs) with a fixed streaking direction are standard diagnostics to measure the temporal properties of the electron beams. If placed after the undulator of the FEL facility, TDSs can also be employed to reconstruct the power profile of the FEL pulses. In this contribution we will present measurements of an X-band RF TDS system with variable polarization with a resolution below one femtosecond. We will show FEL power profile measurements with associated rms pulse durations as short as 300 attoseconds. The measurements have been carried out at the soft X-ray beamline of SwissFEL. Measurements with variable polarization and attosecond resolution are essential to characterize and optimize the electron beams in all its dimensions for all type of X-ray FEL experiments, in particular for ultrafast X-ray applications.