Hyperspectral Nonlinear Optical Light Generation from a Monolithic GaN Microcavity

Localized spatial excitation of a single hexagonal GaN micropyramid with () facets formed by selective area growth is optimized for nonlinear optical light (NLO) generation due to second harmonic generation (SHG) and multiphoton luminescence (MPL). Multiphoton transition induced ultraviolet and yellow luminescence is observed for excitations above and below half bandgap energy. SHG and MPL observed for excitations below half the bandgap energy are superimposed to realize broadband emission in the UV–visible range. The light generation is optimized by controlling the cavity modes formed by the hexagonal facets and the tip enhanced effects from the pyramid. The MPL is optimum at the apex of the pyramid. The SHG is most efficient within the pyramid (≈4 µm above the base) due to the formation of spatially stable cavity modes within the cavity. The NLO interactions within the pyramid are optimized to realize microphotonic white light sources and coherent tunable UV–visible sources using spatially controlled excitation without any change in material parameters. At the bandgap of GaN, the resonant two‐photon emission dominates the nonlinear light generation process compared to the coherent SHG light generated within the cavity.