Final state distributions of Li Rydberg atoms at high scaled microwave frequency

H. Maeda, Thomas F. Gallagher

J. H. Gurian, H. Maeda, Thomas F. Gallagher

Nami Takiguchi, A. Takamine, Yoshihiro MIZUGAI +1 more

We have measured state distribution of Rydberg Li atoms exposed to linearly polarized 17.5-GHz microwave pulses in the regime where microwave frequency is nearly equal to the classical Kepler frequency of Rydberg atom.The experimental results are analyzed using one-dimensional classical and quantum mechanical Floquet theory.

Michio Takami, H. Maeda, Yukari Matsuo +3 more

Christopher R. Mahon, James L. Dexter, P. Pillet +1 more

We have studied the ionization of Na ns and nd Rydberg atoms by \ensuremath{\sim}1-\ensuremath{\mu}s pulses of 10-MHz, 670-MHz, 2-GHz, and 4-GHz fields, bridging the gap between the previous measurements of ionization by \ensuremath{\sim}1-\ensuremath{\mu}s rise-time pulses and 8- and 15-GHz microwave fields. We have also studied the ionization of Li ns and nd Rydberg atoms by 4-, 8-, and 15-GHz fields, which, due to the smaller Li quantum defects, represents the high-frequency limit of nonhydrogenic microwave ionization. The Na measurements show that ionization at 10 MHz occurs without change in n at fields of 1/16${\mathit{n}}^{4}$ and 1/9${\mathit{n}}^{4}$. At 670 MHz \ensuremath{\Vert}m\ensuremath{\Vert}=0, 1, and 2 states are all ionized at fields between 1/3${\mathit{n}}^{5}$ and 1/9${\mathit{n}}^{4}$, indicating that transitions to higher-n states are occurring. As the frequency is raised further, to 2 and 4 GHz, the \ensuremath{\Vert}m\ensuremath{\Vert}=0 and 1 states exhibit an increasingly sharp threshold for ionization at E=1/3${\mathit{n}}^{5}$, but the \ensuremath{\Vert}m\ensuremath{\Vert}=2 states are unlikely to ionize at this field, with ionization occurring mostly at higher fields, 1/3${\mathit{n}}^{5}$E1/9${\mathit{n}}^{4}$, approaching the 15-GHz behavior of ionization at E=1/9${\mathit{n}}^{4}$. At 4 GHz, Li n=20 \ensuremath{\Vert}m\ensuremath{\Vert}=0 and 1 states ionize at E=1/3${\mathit{n}}^{5}$, but at n\ensuremath{\simeq}45, \ensuremath{\Vert}m\ensuremath{\Vert}=1 states ionize at E=1/9${\mathit{n}}^{4}$, and the \ensuremath{\Vert}m\ensuremath{\Vert}=0 states ionize at E>1/3${\mathit{n}}^{5}$. The \ensuremath{\Vert}m\ensuremath{\Vert}=2 states appear to ionize at E=1/9${\mathit{n}}^{4}$. As the frequency is raised to 8 and then to 15 GHz, the transition of \ensuremath{\Vert}m\ensuremath{\Vert}=0 and 1 states to ionization at E=1/9${\mathit{n}}^{4}$ occurs at lower n. When a small static field is applied, the Li ionization threshold fields drop from 1/9${\mathit{n}}^{4}$ to fields somewhat above 1/3${\mathit{n}}^{5}$. Together the Na and Li measurements show that microwave ionization depends on a rate-limiting step, which is a resonant multiphoton transition.

Thomas F. Gallagher