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The fragmentation of deuterated benzene (C6D6) in ultrashort intense laser fields (9 fs, 1 × 1015W/cm2) is studied by the ion-coincidence momentum imaging technique. Five two-body and eight three-body Coulomb explosion pathways from the trication (C6D63+), associated with the deprotonation and ring-opening reactions, are identified. It is found from the fragment momentum correlation that all the observed three-body explosion processes proceed sequentially via the two-body Coulomb explosion forming molecular dications, CmDn2+, with (m,n) = (6,5), (5,5), (5,4), (4,4), (4,3), and (3,3), which further dissociate into pairs of monocations. The branching ratio of the fragmentation pathways estimated from the number of the observed coincidence events indicates that the fragmentation is nonstatistical. [ABSTRACT FROM AUTHOR]

Tunneling-ionization imaging of photoexcitation of NO has been demonstrated by using few-cycle near-infrared intense laser pulses (8 fs, 800 nm, 1.1?1014 W/cm²). The ion image of N+ fragment ions produced by dissociative ionization of NO in the ground state, NO (X2Π,2Π)→NO++e-→N++O+e-, exhibits a characteristic momentum distribution peaked at 45° with respect to the laser polarization direction. On the other hand, a broad distribution centered at ~0° appears when the A²Σ+ (3sσ) excited state is prepared as the initial state by deep-UV photoexcitation. The observed angular distributions are in good agreement with the corresponding theoretical tunneling ionization yields, showing that the fragment anisotropy reflects changes of the highest-occupied molecular orbital by photoexcitation. [ABSTRACT FROM AUTHOR]

We theoretically investigate the laser-assisted photoionization of He by an extreme ultra violet (XUV) pulse in the presence of a linearly chirped intense laser pulse by solving the time-dependent Schrödinger equation within the single-active-electron approximation. Analysis based on the time-dependent perturbation theory is also carried out to provide more physical insights. A new scheme is shown to be capable of extracting the arrival time of an XUV free-electron laser (FEL) pulse relative to an external laser pulse as well as the XUV pulse duration from the photoelectron sidebands resulting from XUV ionization in the presence of a chirped laser pulse. This scheme is independent of the energy fluctuation and the timing jittering of the FEL pulse. Therefore it can be implemented in a non-invasive way to characterize FEL pulses on a shot-by-shot basis in time-resolved spectroscopy. [ABSTRACT FROM AUTHOR]