Quasi-phase-matched high-harmonic generation in composites of metal nanoparticles and a noble gas

Abstract

We theoretically study high-harmonic generation (HHG) in a composite which consists of ellipsoidal silver nanoparticles in argon. The significant field enhancement in argon in the vicinity of metal nanoparticles allows us to use much lower incident intensities than in typical HHG experiments. A periodic modulation of the nanoparticle concentration provides quasi--phase matching, which mitigates the negative effect of the significant phase mismatch. First, we study the linear optical properties of such a composite and the field enhancement and consider the technological possibilities of creating such a composite. Then the generation of high harmonics is simulated using a propagation equation which includes field enhancement, phase mismatch, absorption of the pump beam and harmonics, and other relevant effects. Generation of harmonics with an efficiency above ${10}^{\ensuremath{-}7}$ is predicted.