Harmonic generation in laser-produced plasmas containing atoms, ions and clusters: a review

New Approaches in Frequency Conversion of Laser Radiation in Plasma Plumes

“…In the latter case, a 1 kHz repetition rate Ti:sapphire laser generating 4 mJ, 40 fs pulses was used. The HHG conversion efficiency for the 40 fs pulses at the beginning of plateau range in the case of the plasma plume containing fullerenes was estimated to be ~5 × 10 −6 using a comparison with the HHG conversion efficiency in a silver plasma, which has previously been reported at similar experimental conditions to be 1 × 10 −5 [43]. One can note that the cutoff in the case of longer pulses (25 th harmonic) was shorter with regard to the few-cycle pulses at similar intensities of these pulses in the plasma plume.…”

“…Previously, even at 10 Hz pulse repetition rate, the ablation of powdered targets that were not moved led to their rapid degradation and abrupt decrease of harmonic yield [43]. With this new technique, one can glue the powdered material onto the rotating rod to improve the stability of the harmonic emission.…”

“…It was shown in [45] that laser-irradiated cluster-contained plasmas can emit low-order harmonics efficiently. The advantages of highly efficient harmonic generation in laser-produced plasmas containing nanoparticles have been analyzed in [43]. In this connection small-sized clusters, such as fullerenes, could show the advanced nonlinear optical properties…”

“…Small sized nanostructures are an attractive approach, since they exhibit local-field-induced enhancement of the nonlinear optical response of the medium [41][42][43]. Another mechanism that can enhance harmonic efficiency of clusters is the increase of the recombination cross section of accelerated electron and parent particle in the final step of the three-step mechanism of HHG [44].…”

“…Previous HHG studies in fullerenes were performed using the multi-cycle pulses (30 fs, 48 fs, and 110 fs [43]). The stability of C 60 against fragmentation in multicycle laser fields leads to fast diffusion of the excitation energy.…”