Third Harmonic Generation at 223nm in the Metallic Regime of GaP

TL;DR

This paper demonstrates third harmonic generation at 223nm in GaP, showing that phase locking enables harmonic propagation in the metallic regime without absorption, even at resonant wavelengths.

Contribution

It reveals that phase locking allows harmonic generation and propagation in metallic regimes of GaP, expanding understanding of nonlinear optics in negative dielectric function materials.

Findings

Third harmonic generated at 223nm in GaP.

Harmonic fields propagate without absorption in metallic regime.

Phase locking mechanism maintains transparency at harmonic wavelengths.

Abstract

We demonstrate second and third harmonic generation from a GaP substrate 500{\mu}m thick. The second harmonic field is tuned at the absorption resonance at 335nm, and the third harmonic signal is tuned at 223nm, in a range where the dielectric function is negative. These results show that a phase locking mechanism that triggers transparency at the harmonic wavelengths persists regardless of the dispersive properties of the medium, and that the fields propagate hundreds of microns without being absorbed even when the harmonics are tuned to portions of the spectrum that display metallic behavior.