Dynamic process of femtosecond laser-induced damage formation in dielectric thin films is reconstructed from a series of time-resolved images. Ta2O5 single-layer coatings of four different thicknesses have been investigated in transmission mode by means of time-resolved off-axis digital holography. Different processes overlapped in time were found to occur; namely, the Kerr effect, free-electron generation, ultrafast lattice heating, and shockwave generation. The trends in contribution of these effects are qualitatively reproduced by numerical models based on electron-rate equations and Drude theory, which take into account transient changes in the films and interference effects of the pump and probe pulses.
Interaction dynamics of two copropagating femtosecond light filaments in sapphire crystal is studied by means of time-resolved off-axis digital holographic and shadowgraphic microscopy with 22 fs temporal and 1 μm spatial resolution. In particular, we demonstrate that filament interaction originates from instantaneous modification of the refractive index resulting from the Kerr effect. Fusion, splitting, and even suppression of the resulting plasma channels induced by interacting filaments was observed by varying time delay between the input pulses. Free electron channels were reconstructed in the form of the time-lapse movie with unprecedented spatial and temporal resolution.
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