Figure 5. Facility-wide synchronization characterized by THz streaking.

In a, the kinetic energy of the Ne 2p photoemission peak is plotted as the relative timing between the ionizing FEL pulse and the streaking THz pulse is scanned. Each data point corresponds to a distinct single-shot measurement. The final measured kinetic energy of the photoelectrons depends on the exact arrival time of the FEL pulse. Thus, by evaluating the position of the peak in the single-shot streaked photoelectron spectrum, the arrival time can be determined. Furthermore, the width of the streaked spectrum can be used to simultaneously determine the pulse duration. The arrival time distribution of 600 consecutive FEL pulses recorded at the zero-crossing of the streaking field is shown in b. The jitter is observed to be (28±2) fs r.m.s., with the error given by the numerical fit. The average pulse duration over these 600 consecutive shots was ~90 fs FWHM, with the corresponding distribution shown in c. The FWHM of the single-shot pulse duration was determined with an average measurement precision of 7 fs.