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Subfemtosecond light pulses can be obtained by superposing several high harmonics of an intense laser pulse. Provided that the harmonics are emitted simultaneously, increasing their number should result in shorter pulses. However, we found that the high harmonics were not synchronized on an attosecond time scale, thus setting a lower limit to the achievable x-ray pulse duration. We showed that the synchronization could be improved considerably by controlling the underlying ultrafast electron dynamics, to provide pulses of 130 attosecands in duration. We discuss the possibility of achieving even shorter pulses, which would allow us to track fast electron processes in matter., The generation of soft x-ray, subfemtosecond light pulses is providing new opportunities for time-resolved spectroscopy (1). With the recent production of pulses as short as 650 attoseconds (as) (2) and [...]

When diatomic and triatomic molecules are exposed to subpicosecond laser pulses (focused intensities well in excess of [10.sup.14] W [cm.sup.-2]; wavelengths of the order 600 nm), they are highly ionized. The laser electric fields are so large that they compete with, and in some cases exceed, the internal fields binding the valence electrons. The result is that conventional perturbation theory is inapplicable and one has to resort to alternative approaches. A simple starting point is the field ionization, Coulomb explosion model. This model is partially successful in explaining the ionization and subsequent fragmentation of the heavy molecule, [I.sub.2], exposed to short (sub-100 fs) laser pulses, but even here the fine details are not understood. The dynamics of the fragmentation of the lighter molecules such as [N.sub.2] and CO are not understood at all: true complication is that the time scales of dissociation and stepwise ionization overlap. In the case of the simplest molecular ion, [H+.sub.2], there has been some progress, leading to the tentative conclusion that bond softening and laser-induced bound states will be important ingredients of a successful theory of multielectron dissociative ionization.

A new class of femtosecond, intense, short – wavelength lasers – the free-electron laser – has opened up new opportunities to investigate the structure and dynamics in many scientific areas. These new lasers, whose performance keeps increasing, enable the understanding of physical and chemical changes at an atomic spatial scale and on the time scale of atomic motion which is essential for a broad range of scientific fields. We describe here the interaction of fullerenes in the multiphoton regime with the Linac Coherent Light Source (LCLS) X-ray free-electron laser at SLAC National Laboratory. In particular, we report on new data regarding the ionization of Ho3N@C80molecules and compare the results with our prior C60investigation of radiation damage induced by the LCLS pulses. We also discuss briefly the potential impact of newly available instrumentation to physical and chemical sciences when they are coupled with FELs as well as theoretical calculations and modeling. [ABSTRACT FROM AUTHOR]

Covariance Mapping: A Correlation Method Applied to Multiphoton Multiple Ionization IN AN INTERESTING APPLICATION OF the covariance approach, Hanbury Brown and Twiss used intensity interferometry to determine the angular diameter […]

The molecular hydrogen ion in intense (>1015 W/cm2) laser fields is modelled assuming instant ionization followed by Coulomb explosion. The initial vibrational state is reconstructed from the final proton energy spectrum. A semi-classical iterative method based on the de Broglie–Bohm concept of quantum potential gives an improved reconstruction. [Copyright &y& Elsevier]