Harnessing the Diamond-Air Interface as an Efficient Photon Antenna for Solid-State Emitters

Abstract: Extracting photons from defect centers is challenging due to the high refractive index of typical substrates. For nitrogen-vacancy centers in diamond, reaching saturation count rates above $2.5\times10^5\,\mathrm{counts}/\mathrm{s}$ so far requires nanofabricated optics like diamond waveguides or solid immersion lenses. Here we present an experimental and theoretical study of defect center emission at unmodified planar dielectric surfaces by quantitative back focal plane imaging and analytical modeling. Our results indicate that photon count rates approaching those of nanofabricated optics can also be achieved by oil-immersion optics. This is due to a dielectric antenna effect which directs the majority of the emission into the substrate within a narrow angle window suitable for back-side collection. By quantifying the collection efficiency of back-side detection, our work also enables a novel measurement method for the quantum efficiency of shallow defect centers. Its result challenges established values. Possible reasons for the discrepancy are discussed.