Rydberg levels collisional

From these values, wavelength ranges to search for bound Rydberg series with field or collisional ionization or to search for autoionizing series converging to excited states of the ion were estimated for various parent levels that could be conveniently populated by one or two-step excitation. The threshold determinations reduced the search ranges for Rydberg levels to reasonable values. Scans were made from various parent levels until series were obtained. 

With two visible lasers, levels m) with excitation energies up to 6 eV can be reached. Optical frequency doubling of both lasers allows even the population of levels up to 12 eV. This makes the Rydberg levels of most atoms and molecules accessible to detailed investigations. The population of Rydberg levels of species M can be monitored either by their fluorescence or by detecting the ions or the electrons e that are produced by photoionization, field ionization, collisional ionization, or autoionization of the Rydberg levels. 

Purely optical excitation is possible for alkali and alkaline earth atoms. For most other atoms the transition from the ground state to any other level is at too short a wavelength to be useful. To produce Rydberg states of such atoms a combination of collisional and optical excitation is quite effective. A good example is the study of the Rydberg states of Xe by Stebbings et al.24 As shown in Fig. 3.5, a thermal beam of Xe atoms is excited by electron impact, and a reasonable fraction of the excited atoms is left in the metastable state. Downstream from the electron excitation the atoms in the metastable state are excited to a Rydberg state by pulsed dye laser excitation. 

Using a simple, three level model we can develop a feeling for the microwave powers required to observe radiatively assisted collisional energy transfer between Rydberg atoms.3 Consider the dipole-dipole atomic system shown in Fig. 15.1(a). In the Na ns + ns— np + (n - l)p resonant collisions described in the previous chapter the ns state corresponds to both s and s of Fig. 15.1(a) and the n — 1 and np states correspond to p and p of Fig. 15.1(a), respectively. The collisions occurs via the interaction... 

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