  We have investigated photoionization of Ne$^+$ in the combined field of a
short infra-red laser pulse and a delayed ultra-short pulse of the infra-red
laser's 23$^r$$^d$ harmonic. We observe an ionization yield compatible with a
picture in which one electron gets excited into Rydberg states by the harmonic
laser field and is subsequently removed by the infra-red laser field.
Modulations are seen in the ionization yield as a function of time delay. These
modulations originate from the trapping of population in low members of the
Rydberg series with different states being populated at different ranges of
delay times. The calculations further demonstrate that single-threshold
calculations cannot reproduce the Ne$^+$ photoionization yields obtained in
multi-threshold calculations.
