Despite their broad implications for phenomena such as molecular bonding or chemical reac tions, our knowledge of multi electron dynamics is limited and their theoretical modelling remains a most difficult task. From the experimental side, it is highly desirable to study the dynamical evolution and interaction of the electrons over the relevant timescales, which extend into the attosecond regime. Here we use near single cycle laser pulses with well defined electric field evolution to confine the double ionization of argon atoms to a single laser cycle. The measured two electron momentum spectra, which substantially differ from spectra recorded in all previous experiments using longer pulses, allow us to trace the correlated emission of the two electrons on sub femtosecond timescales. The experimental results, which are discussed in terms of a semiclassical model, provide strong constraints for the development of theories and lead us to revise common assumptions about the mechanism that governs double ionization.

The first hundred attoseconds of the electron dynamics during strong field tunneling ionization are investigated. We quantify theoretically how the electron's classical trajectories in the continuum emerge from the tunneling process and test the results with those achieved in parallel from attoclock measurements. An especially high sensitivity on the tunneling barrier is accomplished here by comparing the momentum distributions of two atomic species of slightly deviating atomic potentials (argon and krypton) being ionized under absolutely identical conditions with near-infrared laser pulses (1300 nm). The agreement between experiment and theory provides clear evidence for a nonzero tunneling time delay and a nonvanishing longitudinal momentum of the electron at the "tunnel exit."

Our findings suggest that some patients without major criteria for severe community-acquired pneumonia, according to the recent Infectious Diseases Society of America/American Thoracic Society consensus guideline, may benefit from direct transfer to the intensive care unit. Further studies are needed to prospectively identify patients who may benefit from direct intensive care unit admission despite a lack of major severity criteria for community-acquired pneumonia based on the current guidelines.