  Attosecond noncollinear four wave mixing spectroscopy with one attosecond
extreme ultraviolet (XUV) pulse and two few-cycle near-infrared (NIR) pulses
was used to measure the autoionization decay lifetimes of inner valence
electronic excitations in neon atoms. After a 43-48 eV XUV photon excites a 2s
electron into the 2s2p6[np] Rydberg series, broadband NIR pulses couple the
2s2p6[3p] XUV-bright state to neighboring 2s2p6[3s] and 2s2p6[3d] XUV-dark
states. Controllable delays of one or both NIR pulses with respect to the
attosecond XUV pulse reveal the temporal evolution of either the dark or bright
states, respectively. Experimental lifetimes for the 3s, 3p, and 3d states are
measured to be 7 +/- 2 fs, 48 +/- 8 fs, and 427 +/- 40 fs, respectively, with
95% confidence. Accompanying calculations with two independent ab initio
theoretical methods, NewStock and ASTRA, verify the findings. The results
support the expected trend that the autoionization lifetime should be longer
for states that have a smaller penetration in the radial region of the 2s core
hole, which in this case is for the higher angular momentum Rydberg orbitals.
The underlying theory thus links the lifetime results to electron correlation
and provides an assessment of the direct and exchange terms in the
autoionization process.
