Extreme ultraviolet interferometry measurements with high-order harmonics

We demonstrate that high-order harmonics generated by short, intense laser pulses in gases provide an interesting radiation source for extreme ultravi olet interferometry, since they are tunable, coherent, of short pulse durat ion, and simple to manipulate. Harmonics from the 9th to the 15th are used to measure the thickness of an aluminum layer. The 11th harmonic is used to determine the spatial distribution of the electron density of a plasma pro duced by a 300-ps laser. Electronic densities higher than 2-10(20) electron s/cm(3) are measured. (C) 2000 Optical Society of America. OCIS codes: 190. 0190, 190.4160, 190.7110, 120.3180, 140.7240, 350.4500.