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 int ensities of similar to 1x10(15) W.cm(-2). The harmonic intensities were str ongest for p-polarized pump and dropped to about 50% in the case of s-polar ized pumps. The ratio I4 omegaI2 omega between the intensities of the fourt h and second harmonics was 0.25 at 1 lambda(2)=6x10(14) W.cm(-2).mu m(2), w hich is relatively large when compared with the value predicted by simulati ons. The harmonics are collimated in the specular direction, with a transve rse mode and divergence comparable to that of the driving laser.