# Sub-band picture of high-harmonic generation in solids

## TL;DR

This paper introduces a new perspective on high-harmonic generation in solids by considering temporally evolving band structures, explaining experimental observations and connecting to other high-field phenomena.

## Contribution

It presents a novel sub-band picture of HHG in solids, elucidating the origin of spectral features and non-monotonic intensity dependence.

## Key findings

- Identification of sub-bands around the band-gap energy influenced by THz light
- Explanation of the non-monotonic HSG intensity as a function of THz amplitude
- Connection of HHG spectral plateau to underlying band structure dynamics

## Abstract

We propose a novel picture of high-harmonic generation (HHG) in solids based on the concept of temporally changing band structures. To demonstrate the utility of this picture, we focus on the high-order sideband generation (HSG) caused by strong terahertz (THz) and weak near-infrared (NIR) light in the context of pump-probe spectroscopy. We find that the NIR frequency dependence of the HSG indicates the existence of new energy levels (sub-bands) around the band-gap energy, which have multiple frequencies of THz light. This sub-band picture explains why the HSG intensity becomes a non-monotonic function of the THz light amplitude. The present analysis not only reveals the origin of the plateau structure in HHG spectra, but also provides a connection to other high-field phenomena.