Interferometric long-term stabilization of a delay line:: a tool for pump-probe photoelectron-photoion-coincidence spectroscopy on the attosecond time scale

We report a new long-term interferometric stabilization scheme for a delay line to be used for pump-probe spectroscopy on the attosecond time scale. A separate interferometer with a He-Ne laser beam is used to stabilize the delay line with respect to a slow drift in the optical delay induced mainly by ambient temperature changes in the laboratory. The power of the stabilization scheme is demonstrated with the characterization of an attosecond pulse train in the extreme ultraviolet formed through high order harmonic generation of Ti:sapphire laser radiation. We use the RABBITT technique for the attosecond pulse-train characterization in a reaction microscope employed here for photoelectron-photoion-coincidence spectroscopy.