Ultra-fast spectroscopy and extreme nonlinear optics by few-optical-cycle laser pulses

Many fundamental processes of radiation-matter interaction, which take place on the ultra-short time scale, can now be directly investigated by using few-optical-cycles light pulses with duration < 10 fs. We discuss two techniques for generating such pulses: broad-band parametric amplification, which allows the generation of pulses in the visible range suitable for spectroscopy, and compression of high-energy light;pulses in a hollow fiber As an example of application in time-resolved spectroscopy we report results of pump-probe experiments in a prototypical conjugated molecule, namely sexithiophene. The new laser sources, due to their characteristics of peak power and coherence, also allow the exploration of new fields of experimental physics, such as extreme nonlinear optics. We focus on high-order harmonics, showing that a high-energy bunch of photons, up to the X-ray-energy region, with coherence typical of laser radiation and time duration comparable to or shorter than the exciting pulses, can be generated.