The successful implementation of the baseline instruments at the European XFEL has triggered a second phase of instrument developments aiming to extend the portfolio of available techniques. At the soft X-ray undulator (SASE 3), the Soft X-ray Port (SXP) instrument is currently under construction. Conceived as an open port, it focuses primarily on femtosecond time-resolved X-ray photoelectron spectroscopy (TR-XPES), which has proven to be a powerful tool to understand the properties of materials and the interaction between their internal degrees of freedom. The extension of this technique to the soft X-ray energy range is only possible at MHz free electron lasers (FELs) due to space-charge effects which limit the maximum photon flux per pulse on the sample. In this contribution, the SXP instrument at the European XFEL and the implementation of TR-XPES using a momentum microscope are presented. The photon energy range available at SASE 3, 0.25 keV to 3.5 keV, and the variable polarization will allow for the simultaneous characterization of the electronic, magnetic, chemical and structural properties of materials with femtosecond time resolution. To this end, a wide range of laser excitation wavelengths, ranging from the XUV to the THz region, will be available.

This contribution presents the laser infrastructure concept of the Soft X-ray Port (SXP) instrument at the European X-ray Free Electron Laser (XFEL) for day one operation. This scientific platform is conceived as an open port complementing the scientific scope of the other two, already operating baseline instruments at the SASE 3 soft x-ray undulator focusing on atomic, molecular and non-linear optical (SQS) as well as condensed matter physics (SCS). The main driving force behind SXP originates from the time-resolved X-ray photo-electron spectroscopy community contemplating key questions in the dynamics of materials science at interfaces. Nonetheless, proposals to investigate high-valent metal intermediates in biological and inorganic catalysts for chemical bond activation by means of fluorescence spectroscopy as well as research on highly charged ions in the light of astrophysics are also pursued. The outstanding capabilities of the European XFEL pave the way for ultrafast pump-probe investigations at the SXP instrument combining intense and tunable soft X-rays with versatile optical laser capabilities, which are provided by two synchronized femtosecond laser systems, whose wavelength ranges can be extended into the infrared as well as extreme ultraviolet region.