Physical Review A

Microwave forced autoionization of Na2 Rydberg states

Christopher R. Mahon, Chung Yi Lee, Thomas F. Gallagher

Published Sep 1, 1993• 1 citation

Abstract

We have examined the ionization of ${\mathrm{Na}}_{2}$ Rydberg states of principal quantum number n=11--16 converging to rotational-vibrational, v=3--6 and R10, states of ${\mathrm{Na}}_{2}^{+}$ by 8-GHz microwave fields. Rydberg states lying below the lowest, v=0, R=0 (v and R are the vibrational and rotational quantum numbers of the molecular ion), ion limit of ${\mathrm{Na}}_{2}^{+}$ are observed to ionize at approximately E=1/3${\mathit{n}}_{0}^{5}$, where ${\mathit{n}}_{0}$ is the effective quantum number relative to the v=R=0 limit. The agreement with this dependence is not nearly as good as in an atom, and the possible reasons for the deviations are discussed.

DOI: 10.1103/physreva.48.2270

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Physical Review A

Microwave forced autoionization of Na2 Rydberg states

Christopher R. Mahon, Chung Yi Lee, Thomas F. Gallagher

Published Sep 1, 1993• 1 citation

Publisher

Abstract

We have examined the ionization of

{\mathrm{Na}}_{2}

Rydberg states of principal quantum number n=11--16 converging to rotational-vibrational, v=3--6 and R10, states of

{\mathrm{Na}}_{2}^{+}

by 8-GHz microwave fields. Rydberg states lying below the lowest, v=0, R=0 (v and R are the vibrational and rotational quantum numbers of the molecular ion), ion limit of

{\mathrm{Na}}_{2}^{+}

are observed to ionize at approximately E=1/3

{\mathit{n}}_{0}^{5}

, where

{\mathit{n}}_{0}

is the effective quantum number relative to the v=R=0 limit. The agreement with this dependence is not nearly as good as in an atom, and the possible reasons for the deviations are discussed.

DOI: 10.1103/physreva.48.2270

Related papers

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.

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Bound ${\mathrm{Li}}_{2}$ states of principal quantum number n=12--14 converging to v=2 and 3 levels of the ground state of ${\mathrm{Li}}_{2}$ ${\mathrm{}}^{+}$ can be ionized by fields of \ensuremath{\sim}200 V/cm, 2 orders of magnitude less than expected for direct field ionization of these levels. The result is shown to be due to forced autoionization. The field depresses the ionization limit of the series converging to the lowest rotational-vibrational ${\mathrm{Li}}_{2}$ ${\mathrm{}}^{+}$ levels, and the n=12--14 levels in question autoionize to the Stark-induced continuum.Bound ${\mathrm{Li}}_{2}$ states of principal quantum number n=12--14 converging to v=2 and 3 levels of the ground state of ${\mathrm{Li}}_{2}$${\mathrm{}}^{+}$ can be ionized by fields of \ensuremath{\sim}200 V/cm, 2 orders of magnitude less than expected for direct field ionization of these levels. The result is shown to be due to forced autoionization. The field depresses the ionization limit of the series converging to the lowest rotational-vibrational ${\mathrm{Li}}_{2}$${\mathrm{}}^{+}$ levels, and the n=12--14 levels in question autoionize to the Stark-induced continuum.

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The authors have observed the ionization of Na Rydberg states by strong microwave fields and have found that the field required for ionization is $\frac{1}{(3.7{n}^{5})}$ (in atomic units) for $n=20\ensuremath{-}37$. This field is close to the field $\frac{1}{(3{n}^{5})}$ at which the Stark manifolds of principal quantum numbers $n$ and $n+1$ intersect. The ionization can be shown to arise from transitions occurring near these intersections.The authors have observed the ionization of Na Rydberg states by strong microwave fields and have found that the field required for ionization is $\frac{1}{(3.7{n}^{5})}$ (in atomic units) for $n=20\ensuremath{-}37$. This field is close to the field $\frac{1}{(3{n}^{5})}$ at which the Stark manifolds of principal quantum numbers $n$ and $n+1$ intersect. The ionization can be shown to arise from transitions occurring near these intersections.

Physical Review LettersApr 4, 198346 citations

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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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M. Seng, U. Eichmann, Volker Lange +2 more

\n \nWe have investigated the electric field ionization of highly excited (ns)\nand (nd) Rydberg states of the barium ion by microwave fields. For states\nwith a principal quantum number $n\\leq 40$ the observed microwave ionization\nthreshold fields show the $Z^3/3n^5$ dependence expected on the basis of\npreviously observed ionization of neutral Rydberg states with Z=1. We show\nthat for states in this n regime microwave ionization is a state selective\ndetection technique. Threshold fields for states with n> 40, however,\ndepart from the expected behaviour, the thresholds become broader and shift\nto higher fields. For a total of 58 states we present the field strengths\nwhere 90% , 50% and 10% ionization occur.\n\n\n\n \nWe have investigated the electric field ionization of highly excited (ns)\nand (nd) Rydberg states of the barium ion by microwave fields. For states\nwith a principal quantum number $n\\leq 40$ the observed microwave ionization\nthreshold fields show the $Z^3/3n^5$ dependence expected on the basis of\npreviously observed ionization of neutral Rydberg states with Z=1. We show\nthat for states in this n regime microwave ionization is a state selective\ndetection technique. Threshold fields for states with n> 40, however,\ndepart from the expected behaviour, the thresholds become broader and shift\nto higher fields. For a total of 58 states we present the field strengths\nwhere 90% , 50% and 10% ionization occur.\n\n\n

The European Physical Journal DJan 1, 19983 citations

Resonant production of high-lying states in the microwave ionization of Na

Alexandr Arakelyan, Thomas F. Gallagher

We report microwave ionization experiments with Rydberg states of Na using several microwave frequencies near 80 GHz. We observe substantial ionization of states as low as $n=26$ with microwave pulses of 170-V/cm amplitude. Unlike experiments at 38 and 17 GHz, microwave ionization is not always accompanied by the production of the extremely high-lying states just below the limit. It only occurs when the initial Rydberg state is in multiphoton resonance with the high-lying states. The resonance condition is apparent at 80 GHz because the ponderomotive energy shift of the limit, and of the high-lying states, is small compared to the microwave frequency, even at fields strong enough to produce ionization. At the lower microwave frequencies, the ponderomotive shift exceeds the microwave frequency, ensuring that the resonance condition is met and obscuring its importance. The same is true of many laser experiments.We report microwave ionization experiments with Rydberg states of Na using several microwave frequencies near 80 GHz. We observe substantial ionization of states as low as $n=26$ with microwave pulses of 170-V/cm amplitude. Unlike experiments at 38 and 17 GHz, microwave ionization is not always accompanied by the production of the extremely high-lying states just below the limit. It only occurs when the initial Rydberg state is in multiphoton resonance with the high-lying states. The resonance condition is apparent at 80 GHz because the ponderomotive energy shift of the limit, and of the high-lying states, is small compared to the microwave frequency, even at fields strong enough to produce ionization. At the lower microwave frequencies, the ponderomotive shift exceeds the microwave frequency, ensuring that the resonance condition is met and obscuring its importance. The same is true of many laser experiments.

Physical Review AJan 14, 20162 citations

We have examined the ionization of

{\mathrm{Na}}_{2}

Rydberg states of principal quantum number n=11--16 converging to rotational-vibrational, v=3--6 and R10, states of

{\mathrm{Na}}_{2}^{+}

by 8-GHz microwave fields. Rydberg states lying below the lowest, v=0, R=0 (v and R are the vibrational and rotational quantum numbers of the molecular ion), ion limit of

{\mathrm{Na}}_{2}^{+}

are observed to ionize at approximately E=1/3

{\mathit{n}}_{0}^{5}

, where

{\mathit{n}}_{0}

is the effective quantum number relative to the v=R=0 limit. The agreement with this dependence is not nearly as good as in an atom, and the possible reasons for the deviations are discussed.

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.

Bound

{\mathrm{Li}}_{2}

states of principal quantum number n=12--14 converging to v=2 and 3 levels of the ground state of

{\mathrm{Li}}_{2}

{\mathrm{}}^{+}

can be ionized by fields of \ensuremath{\sim}200 V/cm, 2 orders of magnitude less than expected for direct field ionization of these levels. The result is shown to be due to forced autoionization. The field depresses the ionization limit of the series converging to the lowest rotational-vibrational

{\mathrm{Li}}_{2}

{\mathrm{}}^{+}

levels, and the n=12--14 levels in question autoionize to the Stark-induced continuum.

The authors have observed the ionization of Na Rydberg states by strong microwave fields and have found that the field required for ionization is

\frac{1}{(3.7{n}^{5})}

(in atomic units) for $n=20\ensuremath{-}37$. This field is close to the field

\frac{1}{(3{n}^{5})}

at which the Stark manifolds of principal quantum numbers

n

and

n+1

intersect. The ionization can be shown to arise from transitions occurring near these intersections.

\n \nWe have investigated the electric field ionization of highly excited (ns)\nand (nd) Rydberg states of the barium ion by microwave fields. For states\nwith a principal quantum number

n\\leq 40

the observed microwave ionization\nthreshold fields show the

Z^3/3n^5

dependence expected on the basis of\npreviously observed ionization of neutral Rydberg states with Z=1. We show\nthat for states in this n regime microwave ionization is a state selective\ndetection technique. Threshold fields for states with n> 40, however,\ndepart from the expected behaviour, the thresholds become broader and shift\nto higher fields. For a total of 58 states we present the field strengths\nwhere 90% , 50% and 10% ionization occur.\n\n\n

We report microwave ionization experiments with Rydberg states of Na using several microwave frequencies near 80 GHz. We observe substantial ionization of states as low as

n=26

with microwave pulses of 170-V/cm amplitude. Unlike experiments at 38 and 17 GHz, microwave ionization is not always accompanied by the production of the extremely high-lying states just below the limit. It only occurs when the initial Rydberg state is in multiphoton resonance with the high-lying states. The resonance condition is apparent at 80 GHz because the ponderomotive energy shift of the limit, and of the high-lying states, is small compared to the microwave frequency, even at fields strong enough to produce ionization. At the lower microwave frequencies, the ponderomotive shift exceeds the microwave frequency, ensuring that the resonance condition is met and obscuring its importance. The same is true of many laser experiments.