High-harmonic generation in metallic titanium nitride

TL;DR

This paper demonstrates high-harmonic generation in metallic titanium nitride films, showing their potential for high-intensity laser applications and VUV frequency combs due to their high damage threshold and unique electronic properties.

Contribution

It is the first to report high-harmonic generation in a refractory plasmonic metal, titanium nitride, highlighting its advantages over traditional metals like gold.

Findings

TiN withstands laser pulses up to 13 TW/cm$^2$

Harmonics emitted up to 11 eV photon energy

Harmonic properties linked to TiN's anisotropic conduction band

Abstract

High-harmonic generation is the cornerstone of nonlinear optics. It has been demonstrated in a wide range of crystalline systems including dielectrics, semiconductors, and semi-metals, as well as in gases, leaving metals out due to their low damage threshold. Here, we report on the high-harmonic generation in metallic titanium nitride (TiN) films. TiN is a refractory plasmonic metal, known for its high melting temperature and laser damage threshold, with optical properties similar to those of gold. We show that TiN can withstand laser pulses with peak intensities as high as 13 TW/cm$^2$, one order of magnitude higher than gold, enabling the emission of intraband harmonics up to photon energies of 11 eV. These harmonics can pave the way for compact and efficient plasmonic devices producing vacuum ultraviolet (VUV) frequency combs. Through numerical calculations and experimental studies, we show that the intensity scaling and angular anisotropy of the emitted VUV radiation stem from the anisotropic conduction band structure of TiN, thus confirming its intraband origin.