Pencil lead plasma for generating multimicrojoule high-order harmonics with a broad spectrum

Using the plasma harmonic method, we show the generation of efficient and intense high-order harmonics from plasma of pencil lead. We demonstrate multimicrojoule energy in each harmonic order for the 11th to the 17th order of a Ti:sapphire laser. By analyzing the target morphology and the plasma composition, we conclude that these intense harmonics are generated from nanoparticles of graphitic carbon.