Physical Review Letters

Ionization of Rydberg atoms by a circularly polarized microwave field

Panmimg Fu, T. J. Scholz, J. M. Hettema, Thomas F. Gallagher

Published Jan 29, 1990• 87 citations

Abstract

We report the first observation of the ionization of Rydberg atoms by a circularly polarized 8.5-GHz microwave field. The observed threshold field for ionization is E=1/16${\mathrm{n}}^{4}$, a value higher than that required for ionization by a linearly polarized microwave field. The origin of this threshold can be understood by transforming to a frame rotating at the microwave frequency. In the rotating frame no transitions occur, and level mixings alone are responsible for the ionization.

DOI: 10.1103/physrevlett.64.511

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Physical Review Letters

Ionization of Rydberg atoms by a circularly polarized microwave field

Panmimg Fu, T. J. Scholz, J. M. Hettema, Thomas F. Gallagher

Published Jan 29, 1990• 87 citations

Publisher

Abstract

We report the first observation of the ionization of Rydberg atoms by a circularly polarized 8.5-GHz microwave field. The observed threshold field for ionization is E=1/16

{\mathrm{n}}^{4}

, a value higher than that required for ionization by a linearly polarized microwave field. The origin of this threshold can be understood by transforming to a frame rotating at the microwave frequency. In the rotating frame no transitions occur, and level mixings alone are responsible for the ionization.

DOI: 10.1103/physrevlett.64.511

Related papers

IONIZATION OF RYDBERG ATOMS BY CIRCULARLY POLARIZED MICROWAVE FIELDS

Thomas F. Gallagher

In circularly polarized microwave fields of frequencies in the vicinity of 10 GHz ionization of Na Rydberg atoms occurs at a field E=1/16n4, up to principal quantum number n=50. This field is equal to the classical field for ionization and the static field required to ionize a Na atom. On the other hand, this field is far below the linearly polarized 10 GHz field required to ionize Na atoms, E=1/3n5. If the problem is transformed to a frame rotating with the microwave field, the field becomes a static field. In this case it is straightforward to calculate the ionization field classically. However, it is far lower than the experimentally observed field, a discrepancy which may be due to an angular momentum barrier.In circularly polarized microwave fields of frequencies in the vicinity of 10 GHz ionization of Na Rydberg atoms occurs at a field E=1/16n4, up to principal quantum number n=50. This field is equal to the classical field for ionization and the static field required to ionize a Na atom. On the other hand, this field is far below the linearly polarized 10 GHz field required to ionize Na atoms, E=1/3n5. If the problem is transformed to a frame rotating with the microwave field, the field becomes a static field. In this case it is straightforward to calculate the ionization field classically. However, it is far lower than the experimentally observed field, a discrepancy which may be due to an angular momentum barrier.

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Circularly and elliptically polarized microwave ionization of Na Rydberg atoms

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We have measured the 17.3 GHz circularly polarized microwave ionization (CPMI) threshold fields for Na Rydberg atoms and compared them to the previous 8.5 GHz measurements. In both cases the ionization fields are near for low n and fall below this value at high n. A small ellipticity in the polarization and a small static field in the plane of the rotating microwave field both lead to ionization at substantially lower fields, approaching . In addition, elliptically polarized microwave ionization (EPMI) of Rydberg atoms and CPMI in the presence of a small static field have much lower threshold fields for ionization and unexpected resonant peaks at microwave fields below the CPMI threshold fields are observed in both cases at 8, but not at 17, GHz. Sequences of resonant microwave transitions are proposed to explain these resonant structures.We have measured the 17.3 GHz circularly polarized microwave ionization (CPMI) threshold fields for Na Rydberg atoms and compared them to the previous 8.5 GHz measurements. In both cases the ionization fields are near for low n and fall below this value at high n. A small ellipticity in the polarization and a small static field in the plane of the rotating microwave field both lead to ionization at substantially lower fields, approaching . In addition, elliptically polarized microwave ionization (EPMI) of Rydberg atoms and CPMI in the presence of a small static field have much lower threshold fields for ionization and unexpected resonant peaks at microwave fields below the CPMI threshold fields are observed in both cases at 8, but not at 17, GHz. Sequences of resonant microwave transitions are proposed to explain these resonant structures.

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Ionization of Rydberg atoms by a precessing electric field of constant amplitude

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We have studied in detail the continuous evolution from static field ionization to ionization by a circularly polarized microwave field by combining a z-polarized static field with a circularly polarized microwave field in the x-y plane. We have measured the ionization threshold for Na states of $27<~n<~50$ in the precessing total field ${F}_{t},$ as a function of its angle \ensuremath{\theta} from the z axis. For low n, ${F}_{t}\ensuremath{\cong}{1/16n}^{4},$ independent of \ensuremath{\theta}. For $n>~45,$ ${F}_{t}$ decreases from ${1/16n}^{4}$ to ${0.8/16n}^{4}$ as \ensuremath{\theta} is increased from 0\ifmmode^\circ\else\textdegree\fi{} to 25\ifmmode^\circ\else\textdegree\fi{}, and it remains at this value until $\ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{}.$ We also observe ionization at quite low values of ${F}_{t},$ which we attribute to resonantly enhanced ionization, with the resonances driven by a stray static field in the x-y plane.We have studied in detail the continuous evolution from static field ionization to ionization by a circularly polarized microwave field by combining a z-polarized static field with a circularly polarized microwave field in the x-y plane. We have measured the ionization threshold for Na states of $27<~n<~50$ in the precessing total field ${F}_{t},$ as a function of its angle \ensuremath{\theta} from the z axis. For low n, ${F}_{t}\ensuremath{\cong}{1/16n}^{4},$ independent of \ensuremath{\theta}. For $n>~45,$ ${F}_{t}$ decreases from ${1/16n}^{4}$ to ${0.8/16n}^{4}$ as \ensuremath{\theta} is increased from 0\ifmmode^\circ\else\textdegree\fi{} to 25\ifmmode^\circ\else\textdegree\fi{}, and it remains at this value until $\ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{}.$ We also observe ionization at quite low values of ${F}_{t},$ which we attribute to resonantly enhanced ionization, with the resonances driven by a stray static field in the x-y plane.

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Ionization of Rydberg atoms by circularly and elliptically polarized microwave fields

Jennifer A. Griffiths, David Farrelly

A classical study of the dynamics of atomic Rydberg states interacting with both elliptically and circularly polarized microwave fields is presented. In recent experiments, enhanced ionization rates were observed in elliptically as opposed to circularly polarized fields. A classical phase-space simulation provides good qualitative agreement with experimental findings. These results are explained in terms of the breakdown of almost conserved quantities as the polarization of the field is changed from circular to elliptical.A classical study of the dynamics of atomic Rydberg states interacting with both elliptically and circularly polarized microwave fields is presented. In recent experiments, enhanced ionization rates were observed in elliptically as opposed to circularly polarized fields. A classical phase-space simulation provides good qualitative agreement with experimental findings. These results are explained in terms of the breakdown of almost conserved quantities as the polarization of the field is changed from circular to elliptical.

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Ionization of Li Rydberg atoms by 8.5- and 18-GHz circularly polarized microwave fields

C. H. Cheng, C. Y. Lee, Thomas F. Gallagher

We have measured separately the ionization threshold fields of the sets of Li states composed of l+m even and l+m odd zero field states. In spite of the fact that the states composed of l+m even states are, by one measure, more nonhydrogenic than those composed of the l+m odd states, we observe that both sets of states ionize at a microwave field well below the hydrogenic ionization field. The ionization of the states composed of l+m odd states shows that even small departures from hydrogen lead to completely nonhydrogenic ionization, as in a static field. In contrast, in a linearly polarized microwave field small departures from hydrogen do not lead to nonhydrogenic ionization. The excitation spectrum of the states composed of l+m odd states exhibits regular structure, while that of the states composed of l+m even states does not, a difference due to the differing energy shifts of m=0 and \ifmmode\pm\else\textpm\fi{}1 states on transformation between the laboratory and rotating frames. \textcopyright{} 1996 The American Physical Society.We have measured separately the ionization threshold fields of the sets of Li states composed of l+m even and l+m odd zero field states. In spite of the fact that the states composed of l+m even states are, by one measure, more nonhydrogenic than those composed of the l+m odd states, we observe that both sets of states ionize at a microwave field well below the hydrogenic ionization field. The ionization of the states composed of l+m odd states shows that even small departures from hydrogen lead to completely nonhydrogenic ionization, as in a static field. In contrast, in a linearly polarized microwave field small departures from hydrogen do not lead to nonhydrogenic ionization. The excitation spectrum of the states composed of l+m odd states exhibits regular structure, while that of the states composed of l+m even states does not, a difference due to the differing energy shifts of m=0 and \ifmmode\pm\else\textpm\fi{}1 states on transformation between the laboratory and rotating frames. \textcopyright{} 1996 The American Physical Society.

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Microwave ionization of Na Rydberg atoms

P. Pillet, H. B. van Linden van den Heuvell, W. W. Smith +3 more

Electric field ionization of excited Na atoms by microwave fields between 12 and 15 GHz exhibits several interesting phenomena. The $|m|=0 \mathrm{and} 1$ states may be ionized with a very low microwave field, $\ensuremath{\sim}\frac{1}{{3n}^{5}}$, corresponding to the point at which the $n$ and $n+1$ Stark manifolds of principal quantum numbers $n$ and $n+1$ intersect. The ionization occurs by an atom's making a succession of Landau-Zener transitions to higher-lying states, finally reaching the classical ionization limit. The $|m|=2$ states, on the other hand, ionize at a very high microwave field, $\ensuremath{\sim}\frac{1}{{9n}^{4}}$. Both these observations and the more familiar static or low-frequency result of ionization by a field of $\ensuremath{\sim}\frac{1}{{16n}^{4}}$ are all consistent with ionization in a completely classical fashion. The apparent differences are due to the dynamics of passing from zero field to a high ionizing field.Electric field ionization of excited Na atoms by microwave fields between 12 and 15 GHz exhibits several interesting phenomena. The $|m|=0 \mathrm{and} 1$ states may be ionized with a very low microwave field, $\ensuremath{\sim}\frac{1}{{3n}^{5}}$, corresponding to the point at which the $n$ and $n+1$ Stark manifolds of principal quantum numbers $n$ and $n+1$ intersect. The ionization occurs by an atom's making a succession of Landau-Zener transitions to higher-lying states, finally reaching the classical ionization limit. The $|m|=2$ states, on the other hand, ionize at a very high microwave field, $\ensuremath{\sim}\frac{1}{{9n}^{4}}$. Both these observations and the more familiar static or low-frequency result of ionization by a field of $\ensuremath{\sim}\frac{1}{{16n}^{4}}$ are all consistent with ionization in a completely classical fashion. The apparent differences are due to the dynamics of passing from zero field to a high ionizing field.

Physical Review AJul 1, 198481 citations

We report the first observation of the ionization of Rydberg atoms by a circularly polarized 8.5-GHz microwave field. The observed threshold field for ionization is E=1/16

{\mathrm{n}}^{4}

27<~n<~50

in the precessing total field

{F}_{t},

as a function of its angle \ensuremath{\theta} from the z axis. For low n, ${F}_{t}\ensuremath{\cong}{1/16n}^{4},$ independent of \ensuremath{\theta}. For

n>~45,

{F}_{t}

decreases from

{1/16n}^{4}

{0.8/16n}^{4}

as \ensuremath{\theta} is increased from 0\ifmmode^\circ\else\textdegree\fi{} to 25\ifmmode^\circ\else\textdegree\fi{}, and it remains at this value until $\ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{}.$ We also observe ionization at quite low values of

{F}_{t},

which we attribute to resonantly enhanced ionization, with the resonances driven by a stray static field in the x-y plane.

Electric field ionization of excited Na atoms by microwave fields between 12 and 15 GHz exhibits several interesting phenomena. The

|m|=0 \mathrm{and} 1

states may be ionized with a very low microwave field, $\ensuremath{\sim}\frac{1}{{3n}^{5}}$, corresponding to the point at which the

n

and

n+1

Stark manifolds of principal quantum numbers

n

and

n+1

intersect. The ionization occurs by an atom's making a succession of Landau-Zener transitions to higher-lying states, finally reaching the classical ionization limit. The

|m|=2

states, on the other hand, ionize at a very high microwave field, $\ensuremath{\sim}\frac{1}{{9n}^{4}}$. Both these observations and the more familiar static or low-frequency result of ionization by a field of $\ensuremath{\sim}\frac{1}{{16n}^{4}}$ are all consistent with ionization in a completely classical fashion. The apparent differences are due to the dynamics of passing from zero field to a high ionizing field.