Electron motion enhanced high harmonic generation in xenon clusters

TL;DR

This paper demonstrates that electron oscillations within xenon clusters significantly enhance high harmonic generation (HHG), leading to higher efficiency and providing insights into bulk material HHG mechanisms and potential X-ray sources.

Contribution

It reveals the role of collective electron motion in clusters to enhance HHG and distinguishes phase matching conditions between clusters and atoms, confirming theoretical predictions.

Findings

Enhanced harmonic dipole and quantum phase in clusters

Amplitude of HHG in clusters is 5 orders higher than in atoms

Conversion efficiency in clusters is 4 times higher

Abstract

Atomic clusters presents an isolated system that models the bulk materials whose mechanism of HHG remains uncertain, and a promising medium to produce HHG beyond the limited conversion efficiency for gaseous atoms. Here we reveal that the oscillation of collective electron motion within clusters develops after the interaction of intense laser fields, and it significantly enhances the harmonic dipole and increases the quantum phase of the harmonics. Experimentally, the phase matching conditions of HHG from nanometer xenon clusters and atoms are distinguished, which confirms the enhanced internal field that was proposed theoretically a decade ago. The separation of HHG from atoms and clusters allows the determination of the amplitude of the HHG for clusters to be 5 orders higher, corresponding to 4 times higher conversion efficiency for atomic response. The finding provides an insight on the HHG mechanism of bulk materials and a means by which an efficient coherent X-ray source can be developed.