We investigated molecular alignment wakes of femtosecond laser pulses. Evolution of nonadiabatic molecular alignment in nitrogen gas has been measured via its nonlinear interaction effects with a variably delayed probe pulse. The induced rotational wave packet was mapped as a function of the angular difference between polarization directions of femtosecond pump and probe pulses as well as their relative delay and the plot of the variations of the rotational wave packet, i.e. "quantum carpet", was found to be in good agreement with the calculated angular and temporal dependencies of molecular alignment parameter.

We investigate the formation of positively charged fragments of acetonitrile (CH 3 CN) in intense 800 nm, 50 fs pulses of radiation using a reflectron time-of-flight (TOF) ion mass spectrometer. Singly-charged ions of CH n CN + = -( ) n 0 3 , HCN + , CN + , + CH , 3 + CH , 2 CH + , C + and H + ; and the multiply charged ions of C 2+ , C 3+ , + CH , 2 2 and + CH 2 3 were observed in the mass spectra. Quantum chemical calculations with GAMESS (General Atomic and Molecular Electronic Structure System) of appearance energies for the parent molecule and daughter fragments have been carried out. Intensity dependent ion yields were measured for intensities between ´-4.4 10 W cm 13 2 and´-3.3 10 W cm . 14 2 Angular distributions of most fragment ions were found to peak when the laser radiation was polarized parallel to the TOF axis, while the carbon ions, C + and C 2+ , were found to have maxima for both polarizations parallel and perpendicular to this axis. Kinetic energies of H + fragments were experimentally measured and three different photo dissociation mechanisms were identified.

We experimentally studied the dependence of high harmonic generation in argon and molecular hydrogen on pressure changes in a gas jet that cause variations of the phase matching conditions and absorption. The study was performed at a peak laser intensity of ∼1.5 × 10(14) W/cm(2). To enable measurements over a wide range of pressures, we employed differential pumping with an additional cell (∼20 cm(3) volume) enclosing the gas jet. By increasing the pressure in the gas jet up to a maximum of 1.5 bars with argon or 0.5 bars with hydrogen, we observed an increase in the high harmonic (HH) yield until an optimum pressure of 0.2 bars was reached for Ar, beyond which the output began decreasing. For H2, we observed an increase of the HH output up to the maximum pressure of 0.5 bars. This pressure-dependence study allowed us to achieve a tenfold enhancement in the high harmonic yield at the optimum pressure.

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