The laser-driven coherent processes in atoms and molecules can lead to applications in two distinct ways. On the one hand, the EWP diffraction or radiative recombination can probe the system from which it is derived, in a "self-probing" scheme. On the other hand, the XUV pulses produced can subsequently be focused to excite/probe a separated target system. Of the latter type, Photoionization in the diluted phase and XUV pulse/solid interaction are two recent applications that we performed, which exploit the high XUV intensity on target. As a rule, applications to time-resolved dynamical studies (in a pump-probe scheme), non linear studies, or using coherence, requires that a high coherent flux is delivered by the source. In the perspective of developing high flux and coherent XUV source, we contribute to the research on the Seeding of a Free Electron Laser by an external seed, namely the harmonic source.