Frequency-domain interferometry in the XUV with high-order harmonics

We demonstrate that frequency-domain interferometry can be, performed in th e extreme ultraviolet; rang using high-order hai harmonics. We first show t hat two phase-locked harmonic sources delayed in time can be generated in t he same medium despite ionization, This gives insight into the dynamics of the generation and ionization processes. We then apply the technique to the study of the temporal evolution of an ultrashort laser-produced plasma at the femtosecond time scale.