This thesis investigates laser-assisted photoemission (LAPE) on metals using ultrashort extreme ultra-violet (XUV) laser pulses to release photoemitted electrons from solid samples. These electrons interact with a second ultrashort 800nm infrared (IR) laser pulse, generating replicas of the original photoemission line, known as sidebands. This technique, established in gas phase physics, allows for the exploration of ultrafast electronic processes and serves as a precise method for determining the temporal properties of radiation sources. The transition to solid-state applications is significant, as it enables characterization of radiation sources with lower photon density and the study of surface dynamics. Time-resolved X-ray photoelectron spectroscopy (trPES) measurements were conducted at the Free Electron Laser in Hamburg (FLASH) to analyze the 4f core levels of Pt(111) and W(110) and their corresponding sidebands from the LAPE process. Results for platinum aligned with theoretical predictions in both temporal distribution and intensity, while tungsten showed a temporal domain separation of the sideband signal, suggesting a dependence on the electron's origin—surface or bulk. Additionally, variations in sideband intensity indicated a need to adjust the IR field strength in the theoretical model. The technique also proved effective for characterizing higher harmonic FEL radiation, providing insights into the temporal distri
