New frontiers in attosecond science

We review recent advances in attosecond science; particular attention is devoted to the generation, temporal characterization and applications of isolated attosecond pulses. After a brief overview of the physical mechanisms at the basis of attosecond pulse generation, the experimental methods used for the production of isolated sub-femtosecond pulses are discussed, with particular emphasis on the polarization gating method, which is based on the use of driving pulses with a time-dependent polarization state. The recent emergence of attosecond metrology is described and various techniques for temporal characterization of extreme ultraviolet pulses in the sub-femtosecond regime are analyzed. The streak-camera approach turned out to be an extremely powerful method: all applications of isolated attosecond pulses reported so far are essentially based on such experimental approach. We furthermore discuss recently proposed applications of isolated attosecond pulses in various research fields. Particularly interesting will be the application of attosecond pulses to the investigation of multielectron systems. The collective electronic motion in complex systems and the electron correlation mechanisms represent fundamental problems in atomic and molecular physics, both from a theoretical and an experimental point of view: the application of attosecond pulses promises to offer a formidable tool for the experimental investigation of such fundamental physical processes. Moreover the possibility to directly measure and control the ultrafast charge migration process in complex molecules, which is at the basis of fundamental processes in nature, can open the way to the emergence of attochemistry, with important consequences both for fundamental research and technology.