Two colour photoionization with the ultrafast EUV laser 'FLASH'. Free electron laser in Hamburg: Progress report

The Free Electron Laser at Hamburg (FLASH) emits pulses of up to 150 μJ with durations in the 10-30 fs range in the Extreme-UV (EUV), 6-60 nm, at repetition rates of (currently) 5-300 Hz. The system opens up new research pathways in few photon-few electron processes and photoionization processes with ultra-low cross sections and/or ultra-dilute targets. In combination with an ultrafast optical laser synchronised to FLASH, two colour photoionization experiments, where both fields are of comparably high intensity but orders of magnitude different in photon energy, have become possible. We focus here on coherent photoionization processes in intense superposed EUV and optical fields. Apart from fundamental interest it provides a mechanism to measure EUV-Optical field jitter in femtotime. (author)