Abstract
Unlike conventional semiconductor platforms, 3D Dirac semimetals (DSMs) require relatively low input laser intensities for efficient terahertz (THz) high harmonic generation (HHG), making them promising materials for developing compact THz light sources. Here, we show that 3D DSMs’ high nonlinearity opens up a regime of nonlinear optics where extreme subwavelength current density features develop within nanoscale propagation distances of the driving field. Our results reveal orders-of-magnitude enhancement in HHG intensity with thicker 3D DSM films, and show that these subwavelength features fundamentally limit HHG enhancement beyond an optimal film thickness. This decrease in HHG intensity beyond the optimal thickness constitutes an effective propagation-induced dephasing. Our findings highlight the importance of propagation dynamics in nanofilms of extreme optical nonlinearity.
Highlights
Unlike conventional semiconductor platforms, 3D Dirac semimetals (DSMs) require relatively low input laser intensities for efficient terahertz (THz) high harmonic generation (HHG), making them promising materials for developing compact THz light sources
We show that highly nonlinear materials like 3D DSMs open up a regime of nonlinear optics in which an extremely subwavelength phase-flip in the induced current density appears over nanoscale propagation distances—an effect not seen in conventional nonlinear materials
This subwavelength phase-flip results in an optimal thickness for HHG in 3D DSM nanofilms, beyond which the output HHG intensity falls rapidly falls—an effect which can be understood as an effective propagation-induced dephasing mechanism
Summary
3D Dirac semimetals (DSMs) require relatively low input laser intensities for efficient terahertz (THz) high harmonic generation (HHG), making them promising materials for developing compact THz light sources. We show that highly nonlinear materials like 3D DSMs open up a regime of nonlinear optics in which an extremely subwavelength phase-flip in the induced current density appears over nanoscale propagation distances—an effect not seen in conventional nonlinear materials. This subwavelength phase-flip results in an optimal thickness for HHG in 3D DSM nanofilms, beyond which the output HHG intensity falls rapidly falls—an effect which can be understood as an effective propagation-induced dephasing mechanism. Our findings highlight the importance of accounting for light propagation dynamics in highly nonlinear nanofilms (even beyond 3D DSMs) and pave the way to the development of efficient, solidstate THz light sources and optoelectronics based on 3D DSMs
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