We investigate various aspects of light-matter interaction by using ultrafast (femtoseconds) intense laser pulses, with particular emphasis on spatially structured systems. The processes that are nonlinear in the optical field add new potentialities to standard optical spectroscopy, which has always been an invaluable experimental tool for elucidating fundamental mechanisms in soft and condensed matter physics. For instance, by exploiting second-order processes we investigate surface and interface properties with sub-nanometer resolution (second harmonic generation – SHG). Another example is given by two colors Four-Wave-Mixing in air, which we exploit to coherently generate broad-band single-cycle THz pulses, so to expand our spectroscopic capability to the very-far infrared region. The THz pulses generated in this way are extremely intense, thus enabling the observation of nonlinear optical effects until now investigated only in the visible range of the electromagnetic spectrum. This is the case of the coherent THz Hyper-Raman (THYR) effect, which we have very recently discovered (see figure).
We apply our spectroscopic tools to a large variety of materials with a special focus in recent years on the hetero-structures of strongly correlated transition-metal oxides, ultrathin ferroelectric films, laser-treated diamond for THz applications and ionic liquids. We are also interested in developing spatially structured ultrafast pulses and studying their interaction with matter.