L.P.Yatsenko§, T.Halfmann*, B.W.Shore# and K.Bergmann*

* Fachbereich Physik der Universität Kaiserslautern, 67653 Kaiserlautern, Germany
§ Permanent Address: Institute of Physics, Ukrainian Academy of Sciences, prospekt Nauki 46, Kiev-22w, 252650
# Permanent Address: Lawrence Livermore National Laboratory, Livermore, CA 95440, USA

We report the observation of laser-induced structure (LICS) in the flat photoionization continuum 
of Helium out of the metastable 2s 1S0 state. The structure is a pronounced and spectrally sharp 
resonance, showing both enhanced and diminished ionization. The ionization suppression (as much 
as 70%) is due to population trapping associated with the LICS. Experimental and theoretical studies 
reveal the significant consequences of the dynamic Stark shifts on the laser-induced continuum structure.