Coherence properties of high harmonics and their applications

We recall the main characteristics of high harmonic generation (HHG) by int ense laser pulses in gas, which proceed from the fact that HHG is a laser-d riven non linear process, We particularly outline the properties of intrins ic, spatial and temporal coherence which are investigated experimentally. W e show that they can be controlled through various phase-matching parameter s, on account of the particular form of the atomic dipole phase involved in HHG. Finally, we present two feasibility experiments demonstrating that th is XUV source can be effectively used in time-resolved interferometry measu rements, in particular in the diagnostic of laser-produced ultra-short dens e plasmas.