D 'nics of Excited Atoms (unclassified)

16. SUPPLEMENTARY NOTATION 17 COSATI CO0'ES- ~ SUB3JEC.T TERMS (Continue on reverse it necessary and identity by block number) FIELD GROUP SUB-GROUP>\laser, microwave, multiphoton, collisions), '9. RACT (Continue on reverse of necessary and identity by block number) I ' We have stu.died processes in excited atoms driven by strong microwave radiation fields to gain a quantitative understanding of what are usually thought of as highly nonlinear processes. We have discovered that circularly polarized microwave fields produce ionization only at fields above 1/16n4, the much higher field required for static field ionization1. We have also observed above threshold ionization at microwave frequencies and shown that in the microwave regime it is easily described by a classical theory, which ties together above threshold ionization and ponderomotive energy shifts. Finally, we have made significan