Strong field induced electron density tide in high harmonic generation from solids

TL;DR

This paper reveals a new electron density tide effect in solids under strong laser fields, demonstrating its role in high harmonic generation and showing experimental evidence with MgO, advancing understanding of ultrafast electron dynamics.

Contribution

It introduces a model for the strong field induced electron density tide and its impact on high harmonic generation in solids, beyond the single-active-electron approximation.

Findings

Electron density tide causes additional polarization current.

EDT effect increases with laser intensity.

Experimental observation of anisotropic structures in MgO.

Abstract

In strong laser fields, the electron density in solids can show up tidal motions caused by the laser ``pulling'' on the electrons, which forms an electron density tide (EDT). However, the strong field processes in solids are always explained by the single-active-electron (SAE) model and the fluctuation of background electrons is neglected previously. Here, we demonstrate the strong field induced EDT effect and propose a model for revealing its role in high harmoinc generation (HHG) from solids. We show that the EDT effect induces an additional polarization current beyond the SAE approximation. It gives a new mechanism for HHG and leads to new anisotropic structures, which are experimentally observed with MgO. Our experiment indicates that the EDT effect becomes more obvious with increasing the laser intensity. Our work establishes the bridge between the HHG and the microscopic EDT in solids induced by the strong laser field, which paves the way to probe the ultrafast electron dynamics.