The spatial distribution of high-order harmonics from solid surface plasmas

Investigations have been performed on harmonic generation from solid-vacuum interfaces using a 2,2-ps 1054-nm laser pulse at maximum intensities of si milar to 2x10(17) W . cm(-2). It is found that the divergence of the harmon ics gradually increases at intensities between I lambda(2) = 2 x 10(15) and 2 x 10(16) W cm(-2) . mu m(2). We experimentally observe that the divergen ce of cm the harmonics decreases as the order of the harmonic increases. We also found that the divergence of the third harmonics emission is smaller for 2,2-ps pulsewidth for the driving lasers as compared with those for 100 -ps pulsewidth lasers.