Efficient extreme UV harmonics generated from picosecond laser pulse interactions with solid targets

Harmonic orders up to the 68th are demonstrated at 15.5nm in first-order diffraction, as well as indications of the 75th in second-order diffraction at 14.0nm. These are produced during the interaction of a 2.5ps, 1053nm laser pulse with a solid target for irradiances. The dependence of both the number of harmonics and their energy conversion efficiency with intensity is investigated. The results show that there is little difference in the harmonic spectra between both s and p polarizations of the laser beam and with the addition of a prepulse. The power into the high harmonics is comparable to the output power of saturated collisional XUV lasers at similar wavelengths.