High-order harmonic generation from a solid surface plasma by using a picosecond laser

Investigations have been performed on harmonic generation from solid-vacuum interfaces using a prepulse-free 2.2-ps 1054-nm laser pulse at maximum intensities of /spl sim/1/spl times/10/sup 15/ W/spl middot/cm/sup -2/. The harmonic intensities were strongest for p-polarized pump and dropped to about 50% in the case of s-polarized pumps. The ratio I/sub 4w/I/sub 2w/ between the intensities of the fourth and second harmonics was 0.25 at I/spl lambda//sup 2/=6/spl times/10/sup 14/ W/spl middot/cm/sup -2//spl middot//spl mu/m/sup 2/, which is relatively large when compared with the value predicted by simulations. The harmonics are collimated in the specular direction, with a transverse mode and divergence comparable to that of the driving laser.