Time-resolved investigation of transient charges in laser-produced nanoplasmas

We report on the observation of a transient C4+ ion charge state in nanoplasmas produced by the interaction of intense near-infrared (NIR) laser pulses with CH4 clusters. The underlying dynamics are studied by pump-probe spectroscopy, which reveals that the ion charge states are lowered by electron-ion recombination. Furthermore, we present direct evidence that autoionization of multiply-excited ions plays an important role in expanding nanoplasmas, in contrast to models that neglect quantum phenomena

Observation of correlated electronic decay in expanding clusters triggered by near-infrared fields

When an excited atom is embedded into an environment, novel relaxation pathways can emerge that are absent for isolated atoms. A well-known example is interatomic Coulombic decay, where an excited atom relaxes by transferring its excess energy to another atom in the environment, leading to its ionization. Such processes have been observed in clusters ionized by extreme-ultraviolet and X-ray lasers. Here, we report on a correlated electronic decay process that occurs following nanoplasma formation and Rydberg atom generation in the ionization of clusters by intense, non-resonant infrared laser fields. Relaxation of the Rydberg states and transfer of the available electronic energy to adjacent electrons in Rydberg states or quasifree electrons in the expanding nanoplasma leaves a distinct signature in the electron kinetic energy spectrum. These so far unobserved electron-correlation-driven energy transfer processes may play a significant role in the response of any nano-scale system to intense laser light

Impulsive orientation and alignment of quantum-state-selected NO molecules

Manipulation of the molecular-axis distribution is an important ingredient in experiments aimed at understanding and controlling molecular processes(1-6). Samples of aligned or oriented molecules can be obtained following the interaction with an intense laser field(7-9), enabling experiments in the molecular rather than the laboratory frame(10-12). However, the degree of impulsive molecular orientation and alignment that can be achieved using a single laser field is limited(13) and crucially depends on the initial states, which are thermally populated. Here we report the successful demonstration of a new technique for laser-field-free orientation and alignment of molecules that combines an electrostatic field, non-resonant femtosecond laser excitation(14) and the preparation of state-selected molecules using a hexapole(2). As a unique quantum-mechanical wavepacket is formed, a large degree of orientation and alignment is observed both during and after the femtosecond laser pulse, which is even further increased (to < cos theta > = -0.74 and < cos(2)theta > = 0.82, respectively) by tailoring the shape of the femtosecond laser pulse. This work should enable new applications such as the study of reaction dynamics or collision experiments in the molecular frame, and orbital tomography(11) of heteronuclear molecules.No Full Tex

Attosecond electron wave packet interferometry

International audienceAcomplete quantum-mechanical description of matter and its interaction with the environment requires detailed knowledge of a number of complex parameters. In particular, information about the phase of wavefunctions is important for predicting the behaviour of atoms, molecules or larger systems. In optics, information about the evolution of the phase of light in time and space is obtained by interferometry. To obtain similar information for atoms and molecules, it is vital to develop analogous techniques. Here we present an interferometric method for determining the phase variation of electronic wave packets in momentum space, and demonstrate its applicability to the fundamental process of single-photon ionization. We use a sequence of extreme-ultraviolet attosecond pulses to ionize argon atoms and an infrared laser field, which induces a momentum shear between consecutive electron wave packets. The interferograms that result from the interaction of these wave packets provide useful information about their phase. This technique opens a promising new avenue for reconstructing the wavefunctions of atoms and molecules and for following the ultrafast dynamics of electronic wave packets