Role of carbon clusters in high-order harmonic generation in graphite plasmas

Laser ablation is able to produce plasmas containing neutrals, ions, clusters, and nanoparticles, which can all act as emitters of harmonics from ultrashort laser pulses. Here the efficient low- and high-order harmonic generation (HHG) of femtosecond pulses from the carbon plasmas produced by nanosecond pulses is demonstrated. The efficiencies of harmonic generation from carbon clusters are analyzed using delayed ablation of graphite. We show that carbon clusters can be considered as the sources of efficient harmonics in the 40-100 nm spectral range. This approach of harmonic generation from the plasmas in double-pulse configuration of HHG can be applied for studying other clusters to determine the best conditions for HHG and the influence of multi-particle species on the nonlinear optical processes.