Stochastic ionization through noble tori: Renormalization results

We find that chaos in the stochastic ionization problem develops through the break-up of a sequence of noble tori. In addition to being very accurate, our method of choice, the renormalization map, is ideally suited for analyzing properties at criticality. Our computations of chaos thresholds agree closely with the widely used empirical Chirikov criterion

Ionization via Chaos Assisted Tunneling

A simple example of quantum transport in a classically chaotic system is studied. It consists in a single state lying on a regular island (a stable primary resonance island) which may tunnel into a chaotic sea and further escape to infinity via chaotic diffusion. The specific system is realistic : it is the hydrogen atom exposed to either linearly or circularly polarized microwaves. We show that the combination of tunneling followed by chaotic diffusion leads to peculiar statistical fluctuation properties of the energy and the ionization rate, especially to enhanced fluctuations compared to the purely chaotic case. An appropriate random matrix model, whose predictions are analytically derived, describes accurately these statistical properties.Comment: 30 pages, 11 figures, RevTeX and postscript, Physical Review E in pres

Microwave "ionization" of excited hydrogen atoms: frequency dependence in a resonance zone

In the microwave "ionization" of excited 3d H atoms by a linearly polarized field, we observe experimentally for the first time a fine-scale frequency dependence that is suppressed when relatively weak broad-band noise is added to the driving field. We use 1d classical calculations, 1d quantal calculations and Husimi wave function distributions to give a semiclassical explanation for the delicate behavior

Decay of oriented Rydberg wave-packets excited with far-infrared radiation.

Transitions from bound atomic Rydberg Stark states in a static electric field to autoionizing Rydberg states above the electric-field-induced ionization threshold are studied using a broadband, tunable free-electron laser (photon energy 160-1400 cm(-1), pulse duration similar to 1 ps) and compared with multichannel quantum defect theory calculations. An atomic streak camera is used to record the time-resolved electron emission transients of the autoionizing atoms. For Stark states located on the downfield side of the potential, the far-infrared ionization spectrum is found to be smooth and the electron emission prompt (<2 ps), whereas for Stark states located on the upfield side, the far-infrared spectrum has sharp resonances, and the lifetime of the quasicontinuum states is considerably longer. The electron-emission transients from optical ionization of ground-state atoms are compared to transients from far-infrared ionization of Rydberg atoms, showing that the angular motion of the wave packet is responsible for the ionization dynamics for both cases, but different coherent superpositions of angular momentum states are excited depending on the initial state. Finally, we discuss the feasability of using Rydberg atoms as an ultrafast far-infrared detector, starting from a downfield state, or as a wavelength-selective detector, starting from an upheld state