Pressure Shifts of Highly Excited States of Atoms

Daniel Kleppner

M. G. Payne, W. R. Garrett, Roger C. Hart +1 more

When three-photon atomic excitation is produced by two laser beams of angular frequencies ${\mathrm{\ensuremath{\omega}}}_{\mathit{L}1}$ and ${\mathrm{\ensuremath{\omega}}}_{\mathit{L}2}$, which are crossed at an angle \ensuremath{\theta}, large cooperative pressure-dependent shifts can be produced in the peak position of the excitation line shape. Such shifts occur when the transition between states is dipole allowed in both one and three photons. When \ensuremath{\theta} or ${\mathrm{\ensuremath{\omega}}}_{\mathit{L}2}$/${\mathrm{\ensuremath{\omega}}}_{\mathit{L}1}$ is small, these shifts are very large compared to the pressure broadened width of the line. Our analysis shows that for small \ensuremath{\theta} or small ${\mathrm{\ensuremath{\omega}}}_{\mathit{L}2}$/${\mathrm{\ensuremath{\omega}}}_{\mathit{L}1}$, where the shift is large, the excitation is suppressed near the unperturbed resonance due to a destructive interference between the three-photon excitation by the laser and one-photon excitation due to the four-wave-mixing field, whereas the shifted resonance appears at the position where the atoms interact through ``resonant'' four-wave-mixing photons that are phase matched with the laser field. By studying an experimental situation in xenon we show that the theoretical predictions are in precise agreement with experiment for several angles and a wide range of pressures.

K -D Heber, P. J. West, Eckart Matthias

Pressure shift and broadening measurements of 5snd 1 D 2 and 5snd 3 D 2 Rydberg states of Sr I due to Xe have been performed in the range 8<or=n<or=35 by means of Doppler-free two-photon excitation, combined with thermionic detection and the use of a molecular frequency standard. The data show striking differences between pressure shifts and broadenings of singlet and triplet states, which up to now have not been predicted by theory.

Boris Michailovich Smirnov

M. G. Payne, W. R. Garrett

We show that when three-photon excitation of a dipole-allowed transition is mediated by two laser beams at angular frequencies ${\mathrm{\ensuremath{\omega}}}_{\mathit{L}1}$ and ${\mathrm{\ensuremath{\omega}}}_{\mathit{L}2}$ that are crossed at an angle \ensuremath{\theta}, large cooperative pressure-dependent shifts occur in the line shape for resonant excitation. When excitation of the state is by a 2${\mathrm{\ensuremath{\omega}}}_{\mathit{L}1}$\ifmmode\pm\else\textpm\fi{}${\mathrm{\ensuremath{\omega}}}_{\mathit{L}2}$ process and either \ensuremath{\theta}\ensuremath{\ll}1 or ${\mathrm{\ensuremath{\omega}}}_{\mathit{L}1}$\ensuremath{\gg}${\mathrm{\ensuremath{\omega}}}_{\mathit{L}2}$, the cooperative shift is large compared with the pressure-induced width of the line. For the 2${\mathrm{\ensuremath{\omega}}}_{\mathit{L}1}$+${\mathrm{\ensuremath{\omega}}}_{\mathit{L}2}$ case the shift is toward higher excitation energy, while for 2${\mathrm{\ensuremath{\omega}}}_{\mathit{L}1}$-${\mathrm{\ensuremath{\omega}}}_{\mathit{L}2}$ the shift is to lower excitation energies. In cases where the resonance can be reached by more than one pathway, differing only in the directions of propagation of the photons involved in the excitation, multiple peaks are predicted in the excitation line shape.

Karl Taylor Compton