Cross sections of Penning ionization for Rydberg atoms

Collisional ionization between two Rydberg atoms in relative motion is examined. A classical trajectory Monte Carlo method is used to determine the cross sections associated with Penning ionization. The dependence of the ionization cross section on the magnitude and the direction of orbital angular momentum of the electrons and the direction of the Laplace-Runge-Lenz vector of the electrons is studied. For a given magnitude of angular momentum, there can exist a difference of a factor of up to $\ensuremath{\sim}2.5$ in the ionization cross section between the orientations with the highest and the lowest ionization cross section. The case of exchange ionization is examined and its dependence on the magnitude of angular momentum is studied.Collisional ionization between two Rydberg atoms in relative motion is examined. A classical trajectory Monte Carlo method is used to determine the cross sections associated with Penning ionization. The dependence of the ionization cross section on the magnitude and the direction of orbital angular momentum of the electrons and the direction of the Laplace-Runge-Lenz vector of the electrons is studied. For a given magnitude of angular momentum, there can exist a difference of a factor of up to $\ensuremath{\sim}2.5$ in the ionization cross section between the orientations with the highest and the lowest ionization cross section. The case of exchange ionization is examined and its dependence on the magnitude of angular momentum is studied.

arXiv:2004.01390Physical Review ASep 24, 20203 citations

Studies of strongly interacting Rydberg systems

Robert Gavin Fields

Rydberg atoms are increasingly being used as a means of introducing long-range, tunable interactions into atomic systems through their strong dipole-dipole interactions. When creating such interactions, however, there are a variety of potential effects that can occur, such as state (n and/or L) changing or Penning ionization, which can complicate the dynamics of the system. In the following work, such interactions are investigated for Rydberg-Rydberg collisions using very high-n, n ~300, strontium Rydberg atoms in an atomic beam configuration. By exploiting Rydberg blockade and the inherent distribution of atomic velocities present in an atomic beam, it is possible to create a 1D array of moving Rydberg atoms which will naturally overtake each other over time. Measurements of both Penning ionization and state changing for such collisions are made and compared with classical trajectory Monte-Carlo (CTMC) simulations, with both indicating large collisional cross sections on the order of 1 x 10-6 cm2 for Penning ionization and nearly 8 x 10-5 cm2 for state changing interactions. In a second series of experiments, previous work involving doubly-excited Rydberg states is expanded upon by investigating autoionization with high-n, L > 3, Rydberg states. Past research involving autoionization has shown that the effect is strongly L-dependent, with high-L states having significantly smaller autoionizing rates. To create well-defined, L > 3 states, the use of microwave fields to drive various high-n, n ~ 150, n1F3 → (n+1)1G4, (n+2)1H5 transitions is investigated, with spectroscopic measurements of these transitions providing quantum defect values for n1G4 and n1H5 states. These measurements provide a basis for future studies into the L-dependence of high-n, n ~ 300, autoionizing Rydberg atoms, with the eventual goal of creating a long-lived, doubly-excited “planetary” Rydberg state.Rydberg atoms are increasingly being used as a means of introducing long-range, tunable interactions into atomic systems through their strong dipole-dipole interactions. When creating such interactions, however, there are a variety of potential effects that can occur, such as state (n and/or L) changing or Penning ionization, which can complicate the dynamics of the system. In the following work, such interactions are investigated for Rydberg-Rydberg collisions using very high-n, n ~300, strontium Rydberg atoms in an atomic beam configuration. By exploiting Rydberg blockade and the inherent distribution of atomic velocities present in an atomic beam, it is possible to create a 1D array of moving Rydberg atoms which will naturally overtake each other over time. Measurements of both Penning ionization and state changing for such collisions are made and compared with classical trajectory Monte-Carlo (CTMC) simulations, with both indicating large collisional cross sections on the order of 1 x 10-6 cm2 for Penning ionization and nearly 8 x 10-5 cm2 for state changing interactions. In a second series of experiments, previous work involving doubly-excited Rydberg states is expanded upon by investigating autoionization with high-n, L > 3, Rydberg states. Past research involving autoionization has shown that the effect is strongly L-dependent, with high-L states having significantly smaller autoionizing rates. To create well-defined, L > 3 states, the use of microwave fields to drive various high-n, n ~ 150, n1F3 → (n+1)1G4, (n+2)1H5 transitions is investigated, with spectroscopic measurements of these transitions providing quantum defect values for n1G4 and n1H5 states. These measurements provide a basis for future studies into the L-dependence of high-n, n ~ 300, autoionizing Rydberg atoms, with the eventual goal of creating a long-lived, doubly-excited “planetary” Rydberg state.

Apr 1, 20210 citations

Ionization experiments involving Na Rydberg atoms

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

pigJan 1, 19950 citations

Spectroscopic and ionization properties of atomic Rydberg states

S. Feneuille, P. Jacquinot

Springer eBooksJan 1, 19790 citations

Electron Impact Ionization of Sodium Rydberg Atoms below 2 eV

Kannadaguli Nagesha, Keith B. MacAdam

We have observed electron impact ionization of highly excited sodium Rydberg atoms in $ns$ and $nd$ states, $n=35--51$ , below $E=2\text{ }\text{ }\mathrm{e}\mathrm{V}$ electron kinetic energy with energy resolution 0.25 eV. Measured absolute cross sections near 0 eV range from ${\ensuremath{\sigma}}_{35d}\ensuremath{\approx}7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ to ${\ensuremath{\sigma}}_{50d}\ensuremath{\approx}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{2}$. The energy dependence is consistent with that of widely used binary encounter approximation cross sections, and ${\ensuremath{\sigma}}_{n}$ follows a power law in $n$ . The measured cross sections are 14 to 24 times larger than theoretically predicted values. This enhancement may signal the effect of large polarizabilities of high Rydberg states not yet accounted for in ionization theories.We have observed electron impact ionization of highly excited sodium Rydberg atoms in $ns$ and $nd$ states, $n=35--51$, below $E=2\text{ }\text{ }\mathrm{e}\mathrm{V}$ electron kinetic energy with energy resolution 0.25 eV. Measured absolute cross sections near 0 eV range from ${\ensuremath{\sigma}}_{35d}\ensuremath{\approx}7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ to ${\ensuremath{\sigma}}_{50d}\ensuremath{\approx}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{2}$. The energy dependence is consistent with that of widely used binary encounter approximation cross sections, and ${\ensuremath{\sigma}}_{n}$ follows a power law in $n$. The measured cross sections are 14 to 24 times larger than theoretically predicted values. This enhancement may signal the effect of large polarizabilities of high Rydberg states not yet accounted for in ionization theories.

Physical Review LettersSep 12, 200318 citations

We have observed electron impact ionization of highly excited sodium Rydberg atoms in

ns

and

nd

states,

n=35--51

, below

E=2\text{ }\text{ }\mathrm{e}\mathrm{V}

electron kinetic energy with energy resolution 0.25 eV. Measured absolute cross sections near 0 eV range from ${\ensuremath{\sigma}}_{35d}\ensuremath{\approx}7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ to ${\ensuremath{\sigma}}_{50d}\ensuremath{\approx}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{2}$. The energy dependence is consistent with that of widely used binary encounter approximation cross sections, and ${\ensuremath{\sigma}}_{n}$ follows a power law in

n

. The measured cross sections are 14 to 24 times larger than theoretically predicted values. This enhancement may signal the effect of large polarizabilities of high Rydberg states not yet accounted for in ionization theories.