Generation of high harmonics from silicon

TL;DR

This paper demonstrates high-harmonic generation in silicon via electron-hole recollision, extending high-harmonic spectroscopy to technologically relevant indirect bandgap materials and exploring their susceptibility to electric fields.

Contribution

It shows that silicon can generate high harmonics through electron-hole recollision, similar to direct bandgap materials, and investigates the effects of electric fields on this process.

Findings

High harmonics originate from electron-hole recollision in silicon.

Generation is affected by electric fields as low as 30 V/μm.

High-harmonic spectroscopy can be applied to silicon, a key technological material.

Abstract

We generate high-order harmonics of a mid-infrared laser from a silicon single crystal and find their origin in the recollision of coherently accelerated electrons with their holes, analogously to the atomic and molecular case, and to ZnO [Vampa et al., Nature 522, 462-464 (2015)], a direct bandgap material. Therefore indirect bandgap materials are shown to sustain the recollision process as well as direct bandgap materials. Furthermore, we find that the generation is perturbed with electric fields as low as 30 V/$\mu$m, equal to the DC damage threshold. Our results extend high-harmonic spectroscopy to the most technologically relevant material, and open the possibility to integrate high harmonics with conventional electronics.