MICROWAVE IONIZATION OF NA-ATOMS IN WEAK-TO-STRONG STATIC ELECTRIC-FIELDS

We report measurements of the microwave ionization of Rydberg atoms as a function of static electric field, for static fields from zero to the classical ionization limit. The microwave-ionization threshold field shows clear structure as a function of the static field, in some static field regimes actually increasing as the static field is increased. The dependence of the microwave field can be understood by considering the dynamics of the levels in a temporally varying field.