Polarisation characteristics of the harmonics and reflected radiation upon the interaction of 100-GW picosecond pulses with aluminium films

The generation of harmonics from a solid surface irradiated by 27-ps pulses (I≤1.5×1015 W cm-2) from a neodymium laser is studied. The conversion efficiency of p-polarised laser radiation was more than ten times greater than that of the s-polarised radiation for the second harmonic generation and more than one hundred times greater for the third harmonic generation. The optical rotation of the second harmonic generated by s- and p-polarised laser radiation is studied. The efficiencies of the second, third, and fourth harmonic generation were 2×10-8, 2×10-10, and 5×10-12, respectively. The intensities of the second, third, and fourth harmonics exhibit a power dependence on the laser radiation intensity with exponents equal to 1.5, 1.8, and 3.8, respectively.