Multiphoton classification of prethreshold structures in measured microwave ionization curves of hydrogen Rydberg atoms

Abstract

We present a complete multiphoton classification of prethreshold structures in measured microwave ionization data of hydrogen Rydberg atoms. We show that fourth-order quasienergy perturbation theory reproduces the locations of prethreshold structures, thus proving that prethreshold structures are a perturbative effect. Additional prethreshold structures are predicted to occur at field and frequency values, to our knowledge, not yet explored experimentally.