Aluminum nanoparticle plasma formation for high-order harmonics generation

We demonstrate the efficient high-order harmonic generation (HHG) of 35 fs pulses from the nanoparticle (NP)?containing plasmas produced during laser ablation of aluminum (Al) target using picosecond and nanosecond pulses. The role of NPs in the enhancement of harmonic yield is discussed. To achieve the maximal HHG yield, we use different experimental schemes, including two-color pump, HHG using extended and multi-jet laser-produced plasmas, ablation of rotating target and temporal variation between the heating and driving pulses. A fivefold increase of harmonic yield from Al NP-containing plasmas compared to the plasmas containing only Al atoms and ions is obtained. The harmonics up to the 35th order are generated from the Al NP-containing plasmas. HHG calculations show that this cutoff is attributed to Al neutral atoms rather than Al ions. To interpret the experimental results, we also study the fundamental mechanism of NP formation. The simulations are carried out for different Al NP-containing ablation plumes. Our calculations and plasma debris analysis show the presence of NPs in the plasmas exposed to the driving 35 fs pulses.