First-principles simulations of high-order harmonics generation in thin films of wide bandgap materials [Invited]

High-order harmonics generation (HHG) is the only process that enables tabletop-sized sources of extreme ultraviolet (XUV) light. The HHG process typically involves light interactions with gases or plasma––material phases that hinder wider adoption of such sources. This motivates the research in HHG from nanostructured solids. Here, we employ the time-dependent density function theory (TDDFT) to investigate material platforms for HHG at the nanoscale using first-principles supercomputer simulations. We reveal that wide bandgap semiconductors, aluminum nitride (AlN) and silicon nitride (Si₃N₄), are highly promising for XUV light generation when compared to silicon, one of the most common nonlinear nanophotonic materials. In our calculations, we assume excitation with a 100 fs pulse duration, 1 × 10¹³ W/cm² peak power, and 800 nm central wavelength. We demonstrate that in AlN material the interplay between the crystal symmetry and the incident light direction and polarization can enable the generation of both even and odd harmonics. Our results should advance the development of high-harmonics generation of XUV light from nanostructured solids.