Effects of dc Electric Fields on Multiphoton Ionization Spectra in Cesium
The three-photon (one frequency) ionization of cesium atoms is greatly enhanced when the second photon is resonant with a Rydberg nd level. Enhancement by the ns levels is comparatively small. Three-photon ionization is also observed when the first photon excites a quadrupole transition to 5d. This occurs when either (a) the first photon is resonant with one of the 5d spinorbit states, or (b) when the second photon is resonant with the 7f state.
A dc electric field introduces a number of new features: (a) high Rydberg states can be field-ionized, (b) the photoionization cross sections of the ns levels are greatly enhanced, (c) two-photon access to the np and nf series is induced, and (d) two-photon access to 7g (via a virtual quadrupole transition to 5d) is observed.
These effects have been quantified, the role of laser polarization documented, and a useful scaling law (as a function of the effective principle quantum number) has been demonstrated.
KeywordsPhotoionization Cross Section Quadrupole Transition Cesium Atom High Rydberg State Principle Quantum Number
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- 1.C E. Klots and R. N. Compton (to be published).Google Scholar