Structure in low frequency microwave ionisation excited hydrogen atoms

Abstract

We present experimental results for the ionisation of excited hydrogen atoms, with initial principal quantum number no in the range 32 5 no 5 48, by low frequency microwaves in the scaled frequency range 0.05 < R < 0.2. We compare these with results of a classical Monte Carlo calculation showing that there is structure in the experimental ionisation curves of quantal origin. A further comparison with a simple one-dimensional quantal theory, using an adiabatic basis, shows that the observed structure can be explained in terms of resonances between a few adiabatic states. A very simple two-state model is shown to possess all the relevant features of the system. Further analysis of this onedimensional model shows that when the field frequency tends to zero the static field ionisation limit is approached through infinitely many such resonances. at R 2 I/p, of width O(e-P), p being a large integer.

Polarization Dependence of Microwave "ionization" of Excited Hydrogen Atoms

“…Comparisons of 9.91 GHz data for n0 = 24-32 with 3d quantal and theoretical calculations [94], reviewed in [1], show this behavior: as n0 decreases with fixed ω, the experimental onset of ionization falls systematically bełow the classical onset. A id theoretical model [43,95,96] reproduces and explains this behavior when the coupling constant Cn0 = 1.5n0(n30ω)(n40F) between adjacent quantal adiabatic basis states is sufficiently small. At 9.91 GHz, this occurs for n 0 < 28, or Ω0 < 0.03; see Fig.…”

“…For 0.05 < ,Ω0 < 0.3, some experimental microwave ionization and quench curves have shown structures such as non-monotonic bumps, steps, or changes in slope; see ionization curves in [1,96] for examples. These structures can be understood as the consequence of amplitude-tuned resonances between the adiabatic basis states mentioned above.…”

“…Note that the nonclassical stability near the upper branch of the separatrix occurs at (n0; ω/2π) = (96,97;9.904 GHz). This may be compared to previous LP data [33,87], where it occurred for (62;36.0 GHz), (66;30.36 GHz), and (69;26.4 GHz).…”

Classical aspects of quantum localization in microwave ionization of H atoms

“…By comparison, the simulations for the pure one-dimensional Coulomb problem, equivalent to the so called classical chaos border [5], fall well below and decrease with increasing co". Also, the classical three-dimensional simulations [20] significantly underestimate the threshold.…”

Multiphoton classification of prethreshold structures in measured microwave ionization curves of hydrogen Rydberg atoms

“…The central result of this experiment is the existence of sharp ionization thresholds as a function of field strength which were shown theoretically to coincide with chaos thresholds [2][3][4]. Detailed follow-up experiments performed by Koch and his group at Stony Brook [5][6][7] revealed additional structures in measured ionization curves which occur before the main rise of the ionization signal. We refer to these structures as prethreshold structures.…”