  When atoms are exposed to intense laser or microwave pulses ~10% of the atoms
are found in Rydberg states subsequent to the pulse, even if it is far more
intense than required for static field ionization. The optical spectra of the
surviving Li atoms in the presence of a 38 GHz microwave field suggest how
atoms survive an intense pulse. The spectra exhibit a periodic train of peaks
38 GHz apart. One peak is just below the limit, and with a 90 V/cm field
amplitude the train extends from 300 GHz above the limit to 3000 GHz below it.
The spectra and quantum mechanical calculations imply that the atoms survive in
quasi stable states in which the Rydberg electron is in a weakly bound orbit
infrequently returning to the ionic core during the intense pulse.
