Bulletin of the American Physical Society

Microwave ionization of highly excited hydrogen atoms

Benjamin Edward Sauer

Published May 1, 1993• 0 citations

Abstract

Excitation/ionization probabilities have been measured as a function of microwave electric amplitude F at three different microwave frequencies {omega}/2{pi} = 26.43, 30.36, 36.02 GHz for a wide range of initial no states of hydrogen Rydberg atoms. Using classically scaled variables n{sub 0}{sup 3}{omega}, n{sub 0}{sup 4}F, we discuss the scaling properties of these data. In particular, we note the scaling properties of nonclassical stability observed near n{sub 0}{sup 3}{omega} = 1.3. Our data support the assertion that this stability is due to the presence of a {open_quote}scarred{close_quote} wavefunction.

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Bulletin of the American Physical Society

Microwave ionization of highly excited hydrogen atoms

Benjamin Edward Sauer

Published May 1, 1993• 0 citations

OpenAlex

Abstract

Related papers

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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.

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.

We study experimentally and theoretically the detailed field-amplitude dependence of the multiphoton ionization and excitation probability of highly excited

{\mathit{n}}_{0}

^{3}

S helium atoms in a 9.924-GHz linearly polarized microwave electric field. For ionization, with principal quantum numbers in the range

{\mathit{n}}_{0}

=25--32, we use a quasistatic analysis that employs integration of the time-dependent Schr\"odinger equation using basis states of the static field Hamiltonian. The calculated results are used to interpret the observed ionization threshold structure. For excitation, the results of

{\mathit{n}}_{0}

^{3}

S\ensuremath{\rightarrow}

{\mathit{n}}_{0}

^{3}

L, L>2 excitation experiments are explained quantitatively and precisely using a theory of multiphoton resonances. We present maps of quasienergy levels that allow the study of the dynamics of the field-switching transients. These transient effects are analyzed along the lines of standard atomic collision theory and are shown to determine the shape of the observed resonances.