A simple theory of the Rydberg atoms ionisation by electromagnetic pulses and microwave field is presented. The analysis is based on the scale transformation which reduces the number of parameters and reveals the functional dependencies of the processes. It is shown that the observed ionisation of Rydberg atoms by subpicosecond electromagnetic pulses scale classically. The threshold electric field required to ionise a Rydberg state may be simply evaluated in the photonic basis approach for the quantum dynamics or from the multiphoton ionisation theory.
Theoretical analysis of the recently observed ionization of Rydberg atoms by ultra-short half-cycle single-polarity electromagnetic pulses is presented. It is shown that the observations are consistent with the general classical scaling for the hydrogen atom in a microwave field, but the quantitative explanation of the results is possible only within the framework of quantum mechanics. In other words, the photonic basis approach for quantum dynamics and the multiphoton ionization theory yield the measured threshold fields. This is an example of classical scaling of a non-classical effect. 1.
We have ionized Rydberg atoms using subpicosecond half-cycle electromagnetic pulses. The threshold electric field required to ionize a Rydberg state with effective quantum number
n∗ is found to scale as ${\mathit{n}}^{\mathrm{*}\mathrm{\ensuremath{-}}2}$ for states with
n∗>13 in contradistinction to the ${\mathit{n}}^{\mathrm{*}\mathrm{\ensuremath{-}}4}$ threshold scaling for static field ionization and high order multiphoton ionization. This novel result is explained using a classical model.
We study experimentally and theoretically the detailed field-amplitude dependence of the multiphoton ionization and excitation probability of highly excited
n0 3S helium atoms in a 9.924-GHz linearly polarized microwave electric field. For ionization, with principal quantum numbers in the range
n0=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
n0 3S\ensuremath{\rightarrow}
n0 3L, 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.
Here we present experimental results connecting field ionization to photoionization in Li Rydberg atoms obtained with 17- and 36-GHz microwave fields. At a low principal quantum number
n, where the microwave frequency $\ensuremath{\omega}$ is much lower than the classical, or Kepler frequency, ${\ensuremath{\omega}}_{K}=1/{n}^{3}$, microwave ionization occurs by field ionization, at
E=1/9n4. When the microwave frequency exceeds the Kepler frequency, $\ensuremath{\omega}>1/{n}^{3}$, the field required for ionization is independent of
n and given by $E=2.4{\ensuremath{\omega}}^{5/3}$, in agreement with dynamic localization models, which cross over to a Fermi's Golden Rule approach at the photoionization limit. A surprising aspect of our results is that when $\ensuremath{\omega}\ensuremath{\approx}1/2{n}^{2}$, the one- and multiphoton ionization rates are similar, and even at the lowest microwave powers, all are 10 times lower than the perturbation theory rate calculated for single-photon ionization. Further, we show that when the Rydberg atoms are excited in the presence of the microwave field, the probability of an atom's being bound at the end of the microwave pulse passes smoothly across the limit. This microwave stimulated recombination to bound Rydberg states can be well described by a simple classical model. More generally, these results suggest that the problem of a Rydberg atom coupled to a high-frequency microwave field is similar to the problem of interchannel internal coupling in multilimit atoms, a problem well described by quantum defect theory.
The outer electron of a Rydberg atom is so weakly bound to the atomic core that a relatively small electric field may cause the electron to be stripped from the atom. The field strength at which this ionization happens is strongly dependent on the state of the Rydberg atom. Pulsed electric field ionization serves, therefore, not only as a means by which a Rydberg atom may be efficiently detected, but also a means by which the state of the Rydberg atom may be analyzed.\nThe first observation of predominantly diabatic passage to field ionization of a non-hydrogenic Rydberg atom has resulted in an improved understanding of the adiabatic and diabatic ionization processes. The magnitudes of the various field ionization features have been measured and found to agree with theory, and by detailed analysis, it is now possible to label the various field ionization signal features with the appropriate (VBAR)m(,l)(VBAR) quantum numbers. A much better understanding of the laser excitation process, the Rydberg state production, and the response of the excited state to an increasing electric field has enabled measurement of some Rydberg fine-structure intervals, through observation of field ionization quantum beats.