44 research outputs found
Double Ionization by Strong Elliptically Polarized Laser Pulses
We join the tribute to Professor N.B. Delone in this memorial issue by
presenting the results of new calculations on the effects of ellipticity on
double ionization by short and strong near-optical laser pulses.Comment: 3 pages, 4 figures, accepted in Professor N.B. Delone's memorial
issu
Attosecond electron thermalization by laser-driven electron recollision in atoms
Nonsequential multiple ionization of atoms in intense laser fields is
initiated by a recollision between an electron, freed by tunneling, and its
parent ion. Following recollision, the initial electron shares its energy with
several bound electrons. We use a classical model based on rapid electron
thermalization to interpret recent experiments. For neon, good agreement with
the available data is obtained with an upper bound of 460 attoseconds for the
thermalization time.Comment: 5 pages revtex and 4 figures (eps files
Single ionization of atoms in intense laser pulses: Evolution from multiphoton to tunnel ionization
We present results of high resolution fully differential measurements on single ionization of He, Ne, and Ar by 7-25 fs linearly polarized 800nm laser pulses at intensities of up to 2.1015 W/cm2. Using a 'Reaction-Microscope' we were able to trace signatures of multiphoton ionization deep into the tunnelling regime. Surprisingly, in the low-energy electron spectra we observed several features (absence of the ponderomotive shifts, splitting of the peaks, their degeneration for few-cycle laser pulses) typical for resonantly-enhanced ionization. Other remarkable features, as the sharp cusp-like momentum distributions in the direction perpendicular to the laser field or the observed minima at zero longitudinal momentum for He and Ne, can be reproduced by semiclassical models, where the electron motion in the combined laser and Coulomb field is treated classically after the tunnelling
Correlated multi-electron dynamics in ultrafast laser pulse - atom interactions
We present the results of the detailed experimental study of multiple
ionization of Ne and Ar by 25 and 7 fs laser pulses. For Ne the highly
correlated "instantaneous" emission of up to four electrons is triggered by a
recollisional electron impact, whereas in multiple ionization of Ar different
mechanisms, involving field ionization steps and recollision-induced
excitations, play a major role. Using few-cycle pulses we are able to suppress
those processes that occur on time scales longer than one laser cycle.Comment: 9 pages, 4 figure
Resonant Structures in the Low-Energy Electron Continuum for Single Ionization of Atoms in the Tunneling Regime
We present results of high-resolution experiments on single ionization of He,
Ne and Ar by ultra-short (25 fs, 6 fs) 795 nm laser pulses at intensities
0.15-2.0x10^15 W/cm^2. We show that the ATI-like pattern can survive deep in
the tunneling regime and that the atomic structure plays an important role in
the formation of the low-energy photoelectron spectra even at high intensities.
The absence of ponderomotive shifts, the splitting of the peaks and their
degeneration for few-cycle pulses indicate that the observed structures
originate from a resonant process.Comment: 11 pages, 3 figure
Sequential versus nonsequential two-photon double ionization of the D2 molecule at 38 eV
ABSTRACT: A simple theoretical model is used to interpret recent experimental results for two-photon double ionization (DI) of D2 at 38 eV. We show that the measured kinetic energy distribution associated with emission of two protons can be interpreted as a sum of two processes: a sequential and an instantaneous absorption of the two incident photons. These processes lead to peaks in di erent regions of the spaectrum
Sequential and direct two-photon double ionization of D2 at FLASH
ABSTRACT: Sequential and direct two-photon double ionization (DI) of D2 molecule is studied experimentally and theoretically at a photon energy of 38.8 eV. Experimental and theoretical kinetic energy releases of D++D+ fragments, consisting of the contributions of sequential DI via the D2+(1ssg) state and direct DI via a virtual state, agree well with each other
Ultrafast mapping of H<sub>2</sub><sup>+</sup> (D<sub>2</sub><sup>+</sup>) nuclear wave packets using time-resolved Coulomb explosion imaging
The time evolution of H2+ (D2+) nuclear wave packets is studied exploiting a combination of coincident Coulomb explosion imaging and femtosecond pumpâprobe techniques. Using two 25 fs laser pulses, we map the motion of the dissociating molecular ion, observe an enhanced ionization rate at an internuclear separation of ~11 au and resolve trajectories due to the one- and two-photon Floquet channels. With two 7 fs pulses, we are able to visualize the vibrational motion of the bound part of the wave packet, which exhibits counterintuitive quantum behaviour and dephases within about 100 fs, in agreement with recent numerical simulations