Second harmonic generation in monolithic gallium phosphide metasurfaces

Area of Science:

• Nonlinear optics
• Quantum nanophotonics
• Materials science

Background:

• Gallium phosphide (GaP) possesses a wide transparency range and high nonlinear susceptibility, ideal for nanophotonics.
• Limited availability of single crystalline GaP thin films on low-index substrates hinders nonlinear dielectric metasurface fabrication.
• Tailoring nonlinear responses requires specific crystal orientations, posing fabrication challenges.

Purpose of the Study:

• To design and experimentally realize monolithic GaP metasurfaces for enhanced and tailored second harmonic generation (SHG).
• To provide a simple and broadly accessible alternative to existing thin-film metasurface designs.
• To investigate the SHG performance and emission characteristics of monolithic GaP metasurfaces.

Main Methods:

• Fabrication of monolithic GaP metasurfaces from bulk (110) GaP wafers.
• Utilized electron-beam lithography and optimized inductively coupled plasma etching without a hard mask.
• Characterized nonlinear performance using SHG measurements and nonlinear back-focal plane imaging.

Main Results:

• Achieved high near-infrared-to-visible (NIR-to-visible) conversion efficiency up to 10^-5, comparable to III-V semiconductor thin-film metasurfaces.
• Demonstrated tailored SHG through control of crystal orientation and metasurface design.
• Observed significant emission of second harmonic light into the zeroth diffraction order along the optical axis.

Conclusions:

• Monolithic GaP metasurfaces present a viable and accessible alternative to thin-film designs for nonlinear nanophotonics.
• The developed fabrication process enables efficient and tailorable nonlinear optical responses.
• These findings open new avenues for GaP-based devices in quantum and nonlinear optical applications.