The future development of attosecond science will largely depend on the availability of better attosecond pulsesources. In particular, the current generation of laser-based attosecond sources suffers from a low photon-flux,especially in the soft X-ray region, and a limited tunability of attosecond pulse parameters, such as its centralenergy, bandwidth and consequently pulse duration, from a single source. The latter is of particular interestin order to selectively excite electronic transitions and to concentrate the photon flux in the spectral region ofinterest. Moreover, the possibility of controlling the pulse duration can elucidate its impact on the decoherencemechanisms that follow ionization[1].In our group we use tailored IR waveforms, obtained via coherent synthesis of the output pulses from differentOPA sources, to drive the generation of attosecond pulses via HHG. Due to the optical bandwidth of almost2 octaves, these IR waveforms can have FWHM durations down to a fraction of the central optical cycle,allowing to directly generate isolated attosecond pulses (IAPs) without additional gating[2]. Moreover bycontrolling two synthesis parameters, the relative phase among the two combined pulses and the overall CEP,we demonstrated the possibility to tune the central energy and the bandwidth of the IAPs as well as theirduration, in the XUV spectral region[3]. Recently we started investigating the generation of IAPs in the softX-ray region. Preliminary observations, shown in Fig.1, suggests the possibility to obtain IAPs with photonenergies up to ~450 eV. At present, measurements to explore the possibility of increasing IAP generationefficiency in the soft X-ray region by means of non-sinusoidal optical waveforms are underway.We believe that the possibility of tuning the IAP parameters over a wide range offered by waveform synthesiscould be a great stimulus for the development of increasingly sophisticated attosecond experiments
