Physical Review A

Spectroscopic study of nonresonant photon absorption by highly excited hydrogen atoms in a strong microwave field

J. E. Bayfield, L. D. Gardner, Y. Z. Gulkok, S. D. Sharma

Published Jul 1, 1981• 32 citations

Abstract

Hydrogen atoms with principal quantum number $n=10$ have been laser excited to states between $n=44 \mathrm{and} 67$ in the presence of a strong microwave field whose frequency $\ensuremath{\omega}$ was adjustable between 5.9 and 8.0 GHz. The excitation probability has been studied as a function of $n$, $\ensuremath{\omega}$, microwave field strength and the number of microwave photons absorbed.

DOI: 10.1103/physreva.24.138

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Two-frequency excitation of hydrogen atoms

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Physical Review A

Spectroscopic study of nonresonant photon absorption by highly excited hydrogen atoms in a strong microwave field

J. E. Bayfield, L. D. Gardner, Y. Z. Gulkok, S. D. Sharma

Published Jul 1, 1981• 32 citations

Publisher

Abstract

Hydrogen atoms with principal quantum number

n=10

have been laser excited to states between

n=44 \mathrm{and} 67

in the presence of a strong microwave field whose frequency

\ensuremath{\omega}

was adjustable between 5.9 and 8.0 GHz. The excitation probability has been studied as a function of

n

\ensuremath{\omega}

, microwave field strength and the number of microwave photons absorbed.

DOI: 10.1103/physreva.24.138

Related papers

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P. Stehle

When a hydrogen atom in a state with principal quantum number ${n}_{i}$ is irradiated simultaneously with light of frequency ${\ensuremath{\omega}}_{L}$, nearly that required to produce a transition to a higher state with principal quantum number ${n}_{f}$ and with microwave radiation of frequency $\ensuremath{\omega}$, the transition is very probable when the resonance condition ${\ensuremath{\omega}}_{L}+k\ensuremath{\omega}={E}_{f}\ensuremath{-}{E}_{i}$ is satisfied, the emission or absorption of the net number $k$ of microwave photons just compensating for the detuning of the light from the resonance. This process is analyzed with the use of a forward scattering method and the results are used to discuss the experiments of Bayfield et al. on the excitation of hydrogen.When a hydrogen atom in a state with principal quantum number ${n}_{i}$ is irradiated simultaneously with light of frequency ${\ensuremath{\omega}}_{L}$, nearly that required to produce a transition to a higher state with principal quantum number ${n}_{f}$ and with microwave radiation of frequency $\ensuremath{\omega}$, the transition is very probable when the resonance condition ${\ensuremath{\omega}}_{L}+k\ensuremath{\omega}={E}_{f}\ensuremath{-}{E}_{i}$ is satisfied, the emission or absorption of the net number $k$ of microwave photons just compensating for the detuning of the light from the resonance. This process is analyzed with the use of a forward scattering method and the results are used to discuss the experiments of Bayfield et al. on the excitation of hydrogen.

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The dynamics of hydrogen atom in the presence of a strong radiation field of the titanium-sapphire laser is studied for the Keldysh parameters γ ≥ 1 and γ ≤ 1. It is demonstrated that the ionization is supplemented with the effective population of the excited states with the principal quantum numbers n = 5–10 in the entire range of variation in the Keldysh parameter. The population of the excited Rydberg states can be interpreted as a consequence of the multiphoton resonance involving the initial 1 s state and a group of excited states in the vicinity of the continuum boundary with the simultaneous repopulation of these states by Λ-type Raman transitions under the action of the laser field. The resulting coherent Rydberg packet appears to be stable with respect to ionization, so that the ionization of the atomic system in the presence of strong electromagnetic field is suppressed. Physical reasons for the stabilization are discussed. An interpretation of the effective population of the Rydberg states in the recent experiments on the ionization of atomic helium by the titanium-sapphire laser is proposed.The dynamics of hydrogen atom in the presence of a strong radiation field of the titanium-sapphire laser is studied for the Keldysh parameters γ ≥ 1 and γ ≤ 1. It is demonstrated that the ionization is supplemented with the effective population of the excited states with the principal quantum numbers n = 5–10 in the entire range of variation in the Keldysh parameter. The population of the excited Rydberg states can be interpreted as a consequence of the multiphoton resonance involving the initial 1 s state and a group of excited states in the vicinity of the continuum boundary with the simultaneous repopulation of these states by Λ-type Raman transitions under the action of the laser field. The resulting coherent Rydberg packet appears to be stable with respect to ionization, so that the ionization of the atomic system in the presence of strong electromagnetic field is suppressed. Physical reasons for the stabilization are discussed. An interpretation of the effective population of the Rydberg states in the recent experiments on the ionization of atomic helium by the titanium-sapphire laser is proposed.

Laser PhysicsMay 1, 201023 citations

Hydrogen atoms with principal quantum number

n=10

have been laser excited to states between

n=44 \mathrm{and} 67

in the presence of a strong microwave field whose frequency

\ensuremath{\omega}

was adjustable between 5.9 and 8.0 GHz. The excitation probability has been studied as a function of

n

\ensuremath{\omega}

, microwave field strength and the number of microwave photons absorbed.

When a hydrogen atom in a state with principal quantum number

{n}_{i}

is irradiated simultaneously with light of frequency ${\ensuremath{\omega}}_{L}$, nearly that required to produce a transition to a higher state with principal quantum number

{n}_{f}

and with microwave radiation of frequency $\ensuremath{\omega}$, the transition is very probable when the resonance condition ${\ensuremath{\omega}}_{L}+k\ensuremath{\omega}={E}_{f}\ensuremath{-}{E}_{i}$ is satisfied, the emission or absorption of the net number

k

of microwave photons just compensating for the detuning of the light from the resonance. This process is analyzed with the use of a forward scattering method and the results are used to discuss the experiments of Bayfield et al. on the excitation of hydrogen.

We report on an experimental study of the frequency dependence of the microwave ``ionization'' probability for laser-excited Rb(np

{)}^{2}

{\mathit{P}}_{3/2}

(\ensuremath{\Vert}

{\mathit{M}}_{\mathit{J}}

\ensuremath{\Vert}=1/2) Rydberg atoms. Most data are for n=84. The microwave field was produced by a low-noise frequency synthesizer, and the laser-excited atoms subsequently driven by microwaves were kept in an environment cooled to 77 K in order to minimize the perturbing effects of the thermal, blackbody-radiation field. The driving frequency covered 4--14-MHz intervals around three frequencies between 8.87 and 16.14 GHz. Data are shown for 1- and 5-\ensuremath{\mu}s interaction times, which correspond to the driving frequency being resolved by the atoms to about 1 and 0.2 MHz, respectively. The turnon and turnoff parts of the microwave pulse shape were slow, lasting about 6 ns (circa 70 field oscillations). For the narrow frequency intervals used, the microwave field amplitude was calibrated in situ with use of two-photon Rabi-nutation measurements, which also directly demonstrated the spatial uniformity of the driving field amplitude and its coherence over at least a 1-\ensuremath{\mu}s time scale. Within the frequency intervals studied experimentally, we have observed no sharp, frequency-dependent structure outside of that expected from experimental counting statistics. We give physical arguments based on experimental data and previous experimental and theoretical work on microwave ``ionization'' that show that the present experiments have been in the range of the scaled frequency above 1. Thus, these experimental data examine in a continuous fashion the frequency dependence of microwave ``ionization'' in the high-scaled-frequency regime. Finally, we discuss our results in the light of published theoretical discussions of what might be expected to be the frequency dependence of the microwave ``ionization'' probability for various quantal models for the one-dimensional hydrogen atom in this high-frequency regime.