Secondary Electron Emission Effects in Selective Field Ionization of Na Rydberg Atoms

M. Allegrini, F. Fuso, F. Giammanco +2 more

Thomas F. Gallagher, William E. Cooke

Using selective field ionization (SFI) of Na Rydberg atoms we have detected the 300 °K blackbody radiation which induces the Na transitions 17s→17p, 18s→18p, 17d→18p, and 17d→18f frequencies of 27.3, 22.8, 7.4, and 41.6 cm−1, respectively. Investigation of the probable collisional effects show that they are negligible at 300 °K and allow us to project temperatures of <25 °K for Rydberg-atom long-wave detectors.

康弘 岸本

Vincent C. Gregoric, Jason J. Bennett, Bianca R. Gualtieri +5 more

The electron signals from the field ionization of two closely spaced Rydberg states of rubidium-85 are separated using quantum control. In selective field ionization, the state distribution of a collection of Rydberg atoms is measured by ionizing the atoms with a ramped electric field. Generally, atoms in higher energy states ionize at lower fields, so ionized electrons which are detected earlier in time can be correlated with higher energy Rydberg states. However, the resolution of this technique is limited by the Stark effect. As the electric field is increased, the electron encounters numerous avoided Stark level crossings which split the amplitude among many states, thus broadening the time-resolved ionization signal. Previously, a genetic algorithm has been used to control the signal shape of a single Rydberg state. The present work extends this technique to separate the signals from the $34s$ and $33p$ states of rubidium-85, which are overlapped when using a simple field ramp as in selective field ionization.

G. M. Lankhuijzen, Marcel Drabbels, F. Robicheaux +1 more

Transitions from bound atomic Rydberg Stark states in a static electric field to autoionizing Rydberg states above the electric-field-induced ionization threshold are studied using a broadband, tunable free-electron laser (photon energy 160--1400 ${\mathrm{cm}}^{\ensuremath{-}1}$, pulse duration $\ensuremath{\sim}1$ ps) and compared with multichannel quantum defect theory calculations. An atomic streak camera is used to record the time-resolved electron emission transients of the autoionizing atoms. For Stark states located on the downfield side of the potential, the far-infrared ionization spectrum is found to be smooth and the electron emission prompt $(<2$ ps), whereas for Stark states located on the upfield side, the far-infrared spectrum has sharp resonances, and the lifetime of the quasicontinuum states is considerably longer. The electron-emission transients from optical ionization of ground-state atoms are compared to transients from far-infrared ionization of Rydberg atoms, showing that the angular motion of the wave packet is responsible for the ionization dynamics for both cases, but different coherent superpositions of angular momentum states are excited depending on the initial state. Finally, we discuss the feasability of using Rydberg atoms as an ultrafast far-infrared detector, starting from a downfield state, or as a wavelength-selective detector, starting from an upfield state.

D. Tong, S. M. Farooqi, S. Krishnan +7 more