Microwave Excitation of Helium Rydberg Atoms
Abstract
The microwave field amplitude dependence of the excitation probability of highly excited n^3S helium atoms in a linearly polarized microwave field is studied. The helium Rydberg atomic structure in the field free, static and oscillating electric field environments is discussed and Floquet maps of the quasi -energy level structure as a function of the microwave field amplitude are constructed. For principle quantum numbers nin{26-32} and several different microwave field frequencies, the results of excitation experiments are explained quantitatively using a theory of multiphoton resonances. The physics is shown to be analogous to that of slow atomic collisions with the field switching transients causing coherent evolution (Landau-Zener dynamics) along the Floquet "potential surfaces.". The quantum phase interference effect known in the context of collision theory as Stueckelberg oscillations was experimentally observed in the microwave excitation of 28 ^3S helium Rydberg atoms at frequencies near 29 GHz. The measured visibility and separation of the oscillations are shown to depend sensitively on the Floquet structure, the atomic beam velocity and particularly on additive noise, which both smears and broadens the pattern. Two frequency microwave excitation experiments were also performed in which a distinct second pattern of interferences was observed. The dependence of the new oscillatory structure on the amplitude and frequency of the second field and the influence of additive noise were studied. Two frequency Floquet calculations show the new interferences arise as a consequence of degeneracy lifting of Floquet level crossings by the second field.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- January 1992
- Bibcode:
- 1992PhDT........84Y
- Keywords:
-
- FLOQUET STRUCTURE;
- Physics: Atomic