Comparison of Harmonic Generation from Crystalline and Amorphous Gallium Phosphide Nanofilms

摘要

Gallium phosphide (GaP) is a promising material for nanophotonics, given itslarge refractive index and a transparency over most of the visible spectrum.However, since easy phase-matching is not possible with bulk GaP, acomprehensive study of its nonlinear optical properties for harmonicgeneration, especially when grown as thin films, is still missing. Here, secondharmonic generation is studied from epitaxially grown GaP thin films,demonstrating that the absolute conversion efficiencies are comparable to abulk wafer over the pump wavelength range from 1060 to 1370 nm.Furthermore, the results are compared to nonlinear simulations, and thesecond order nonlinear susceptibility is extracted, showing a similardispersion and magnitude to that of the bulk material. Furthermore, the thirdorder nonlinear susceptibility of amorphous GaP thin films is extracted fromthird harmonic generation to be more than one order of magnitude largerthan that of the crystalline material, and generation of up to the fifth harmonicis reported. The results show the potential of crystalline and amorphous thinfilms for nonlinear optics with nanoantennas and metasurfaces, particularly inthe visible to near infrared part of the spectrum.