Quasi-Phase-Matched High-Harmonic Generation by Modulation of Metal Nanoparticle Density in a Noble Gas

Abstract

We theoretically investigate high harmonic generation (HHG) in a composite which consists of ellipsoidal silver nanoparticles in argon. Significant field enhancement in the vicinity of metal nanoparticles allows to use much lower incident intensities than in typical HHG experiments. Different materials for the NPS, such as silver, aluminum, and copper, are studied. A periodic modulation of the nanoparticle concentration provides quasi-phase-matching, which mitigates the negative effect of the significant phase-mismatch. We study the linear optical properties of such a composite and the field enhancement, and consider the technological possibilities to create such a composite. The generation of high harmonics is simulated using a propagation equation which includes field enhancement, phase mismatch, absorption of pump beam and harmonics, and other relevant effects. Generation of high harmonics with efficiency above 10 -7 is predicted.