In situ study of two interacting femtosecond filaments in sapphire.

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.

Direct holographic imaging of ultrafast laser damage process in thin films.

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.

Holographic study of ultrafast optical excitation in GaN film induced by nonlinear propagation of light.

The dynamics of pulse transformation and free-carrier generation associated with the nonlinear propagation of 1030 nm and 300 fs light pulses in Gallium nitride film has been studied by use of pulsed digital holography with 25 fs temporal resolution. Domination of the Kerr effect at the leading part and electron plasma at the trailing part of the pulse has been identified from the reconstructed spatiotemporal phase-contrast images. Experimental results have been supported by the simplified numerical model capable to reproduce the main features of a dynamic process.