High-order harmonic generation in solid $\rm \bf C_{60}$

TL;DR

This paper investigates high harmonic generation in solid C60 using advanced computational methods, revealing the harmonic order, helicity dependence, and potential for band structure mapping through multi-photon excitation.

Contribution

First to study HHG in large C60 system with 240 valence electrons using density functional theory and time-dependent density matrix methods.

Findings

HHG signals reach 15th order under moderate laser pulses.

Weak helicity dependence due to high symmetry.

Potential to map band structure using long wavelength harmonics.

Abstract

High harmonic generation (HHG) has unleashed the power of strong laser physics in solids. Here we investigate HHG from a large system, solid C$_{60}$, with 240 valence electrons engaging harmonic generation at each crystal momentum, the first of this kind. We employ the density functional theory and the time-dependent Liouville equation of the density matrix to compute HHG signals. We find that under a moderately strong laser pulse, HHG signals reach 15th order, consistent with the experimental results from C$_{60}$ plasma. The helicity dependence in solid C$_{60}$ is weak, due to the high symmetry. In contrast to the general belief, HHG is unsuitable for band structure mapping in C$_{60}$. However, we find a window of opportunity using a long wavelength, where harmonics are generated through multiple-photon excitation. In particular, the 5th order harmonic energies closely follow the transition energy dispersion between the valence and conduction bands. This finding is expected to motivate future experimental investigations.