Morphology of laser-produced carbon nanoparticle plasmas and high-order harmonic generation of ultrashort pulses in clustered media

We analyse the morphology of the laser plasmas produced on surfaces containing various carbon clusters (nanotubes, nanofibres, fullerenes, and nanoparticles). It is shown that the presence of C5-C25 nanoparticles in the laser plasmas coincides with the enhancement of harmonics in the spectral range of 40-80 nm. We suggest that these nanoparticles, rather than larger clusters, play a decisive role in the observed growth of harmonic yield.