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

Many fundamental processes of radiation-matter interaction, which take plac e 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 techn iques for generating such pulses: broad-band parametric amplification, whic h allows the generation of pulses in the visible range suitable for spectro scopy, and compression of high-energy light;pulses in a hollow fiber As an example of application in time-resolved spectroscopy we report results of p ump-probe experiments in a prototypical conjugated molecule, namely sexithi ophene. The new laser sources, due to their characteristics of peak power a nd coherence, also allow the exploration of new fields of experimental phys ics, such as extreme nonlinear optics. We focus on high-order harmonics, sh owing that a high-energy bunch of photons, up to the X-ray-energy region, w ith coherence typical of laser radiation and time duration comparable to or shorter than the exciting pulses, can be generated.