  We study photoionization of various noble gas atoms by attosecond pulses
produced in High Harmonic Generation (HHG). We use a pump-probe experiment to
measure the time delays of electrons photoionized from Neon, Argon, and Krypton
relative to those photoionized from Helium atoms. The Attosecond Pulse Train
(APT) is characterized and the relative delay in photoionization of various
noble gases is measured. The photoionization delay of Ne, Ar, and Kr is
determined using previously calculated values for the He atomic delay and the
delay associated with the probe process.
