Bulk dipole contribution to second harmonic generation in diamond lattices

TL;DR

This paper demonstrates that certain diamond crystal orientations can produce bulk dipole second harmonic generation (SHG) despite inversion symmetry, challenging previous assumptions and suggesting experimental ways to detect this effect.

Contribution

It analytically shows that specific diamond lattice orientations can generate bulk dipole SHG, contrary to the common belief that inversion symmetry suppresses such bulk effects.

Findings

Diamond orientations like Si(111) can produce bulk dipole SHG.

In fcc and bcc metals, SHG mainly arises from surface disturbances.

Proposes an experiment to distinguish bulk dipole SHG using dispersion differences.

Abstract

It is generally argued that material classes with inversion symmetry do not produce bulk dipole related second harmonic generation (SHG). So, SHG is then either ascribed to surface effects or bulk related electric quadrupole or magnetic dipole effects. Using symmetry and \emph{ab-initio} potentials we show analytically that due to the fact of the decaying harmonic electric field certain diamond crystal orientations, as e.g. Si(111), produce a bulk dipole SHG response. For fcc and bcc lattices with a single atom basis, i.e. for the most important metals, however, SHG can purely arise due to the disturbance induced by the surface. Finally we propose an experiment, exploiting the different dispersion for the fundamental as well as frequency doubled radiation to determine this effect.