High-order harmonics from backscattering of delocalized electrons

It is shown that electron backscattering can enhance high-order-harmonic generation in periodic systems with broken translational symmetry. Paradigmatically, we derive for a finite chain of atoms the harmonic cutoff due to electrons backscattered from the edges of the chain and demonstrate a maximum in the harmonic yield if twice the quiver amplitude of the driven electrons equals the chain length. For an intuitive understanding of our quantum results we develop a refined semiclassical trajectory model with finite electron-hole separation after tunneling. We demonstrate that the same tunnel exit also holds for interband harmonics in conventional periodic solid-state systems.

Automated summary

It is demonstrated that electron backscattering can enhance high-order-harmonic generation in periodic systems with broken translational symmetry. By deriving a finite chain of atoms as a paradigm, the harmonic cutoff caused by electrons backscattered from the edges of the chain is explored, and it is shown that there is a maximum in the harmonic yield when the quiver amplitude of the driven electrons is twice the chain length. To gain an intuitive understanding of the quantum results, a refined semiclassical trajectory model with finite electron-hole separation after tunneling is developed. It is also demonstrated that the same tunnel exit applies to interband harmonics in conventional periodic solid-state systems.