Third and fourth harmonics generation in laser-induced periodic plasmas

We present the studies of low (third and fourth) order harmonic generation of picosecond laser radiation in the perforated plasma plumes. The periodic plasma structures were produced on the perforated aluminium targets, the copper strips, and the bunch of pencil leads. We analysed the influence of the distance between plasma jets and the low-order harmonic intensity using single-colour and two-colour pumps of the extended periodic plasmas produced on various surfaces. We also studied the influence of heating pulse energy on the variation of the harmonic yield from extended periodic plasmas. While the shortening of the length of extended homogeneous plasmas led to a considerable decrease of plasma harmonic intensity, the application of perforated plasmas led to the enhancement of the harmonics at the smallest used sizes of plasma jets. We obtained the 8× enhancement of third harmonic yield from the set of 0.15-mm-long plasma jets compared with the plain aluminium plasma.