Ultrafast sub-cycling dynamics of autoionizing states of Xe embedded in ionization continuum by isolated attosecond pulses

In study of electron dynamics in attosecond time scale, it is naturally assumed that electrons take instantaneous response to the external field. However, it still needs to be addressed whether bound electrons embedded in ionization continuum are able to rearrange themselves on sub-laser cycle time scales. To examine the sub-cycle oscillation by counter rotating term(CRT) of a bound state embedded in ionization continuum, we examine the ultrafast dynamics of autoionizing states 4d^-16p and 4d^-17p in Xe neutral atom using isolated attosecond pulses in an attosecond transient absorption spectroscopy.

We experimentally for the first time observed the sub-cycle oscillation of autoionizing states 4d^-16p and 4d^-17p of Xenon along with asymmetric Autler-Townes splitting. This observation is in good agreement with time dependent configuration interaction singles (TDCIS) calculations which confirms that the sub cycle oscillation is due to the CRT, which has been neglected in the rotating wave approximation.