Strongly enhanced photon collection from diamond defect centers under microfabricated integrated solid immersion lenses

Abstract

The efficiency of collecting photons from optically active defect centres in bulk diamond is greatly reduced by refraction and reflection at the diamond-air interface. We report on the fabrication and measurement of a geometrical solution to the problem; integrated solid immersion lenses (SILs) etched directly into the surface of diamond. An increase of a factor of 10 was observed in the saturated count-rate from a single negatively charged nitrogen-vacancy (NV − ) within a 5 µm diameter SIL compared with NV − s under a planar surface in the same crystal. A factor of 3 reduction in background emission was also observed due to the reduced excitation volume with a SIL present. Such a system is potentially scalable and easily adaptable to other defect centres in bulk diamond.The ability to address single defect centres in diamond using confocal microscopy allows optical access to these single 'atom like' systems trapped within a macro-scale solid. The negatively charged nitrogenvacancy centre (NV − ) is of particular interest for applications such as single photon generation [1,2], nanoscale magnetometery [3], and fundamental investigations of spin interactions and entanglement at room temperature [4][5][6]. Other defect centres that exhibit single photon emission have also been identified (e.g. the nickel-related 'NE8' [7], the silicon-vacancy [8], and chromium related centres [9]), but the search continues for other defect centres with spin properties like those of the NV − centre [10]. The high refractive index of diamond causes refraction of the emitted light at the diamond-air interface, reducing the possible angular collection of a microscope objective. Thus the NV − photon collection efficiency is severely reduced. This is a problem regardless of the application, or of the particular defect centre of interest. Here we report on the fabrication and measurement of hemispherical integrated solid immersion lenses (SILs) etched directly into the surface of diamond. These structures eliminate surface refraction, thus increasing the numerical aperture (NA) of the microscope system. This allows a substantial increase in the resolution and background rejection of our system, along with a strong enhancement in NV − photon collection efficiency. Moreover, this geometrical solution can easily be applied to other defect centres in bulk diamond which emit at different wavelengths [11].The photon collection efficiency from NV − centres in diamond has previously been improved by using NV − centres located within nanocrystals small enough that the centres effectively emit into free space [2,12], or nanophotonic structures such as nanowires which guide emission towards collection [13]. Photon collection is increased by a factor of up to about 5 in the former case and 10 in the latter. However with the NV − centres positioned so close to the surface, local strain, impurities and other surface effects have been shown to degrade the stability, and spin coherence time of the NV − centre [14,15], so a solution which improves the p...

Efficient photon detection from color centers in a diamond optical waveguide

“…5 However, NVs in diamond nanostructures typically have much shorter spin coherence times 16 than those in bulk diamond. 3,17 One approach to increase η c for NVs in bulk diamond is to construct a solid-immersion lens (SIL) out of the diamond substrate, using either macroscopic 18 or microscopic 19 fabrication techniques. Light from NVs at the center of a hemispherical diamond SIL passes through the surface at normal incidence, allowing 20% < η c < 30%.…”

Highly Efficient Coupling of Photons from Nanoemitters into Single-Mode Optical Fibers

“…To enhance the fluorescence collection efficiency of photons from these nanoemitters, various photon collection optics have been investigated, including solid immersion lenses, 10,11 photonic crystal fibers, 12 and tapered fibers. [13][14][15] Tapered fibers are particularly promising in view of their high collection efficiencies and their ability to directly couple fluorescence photons into a singlemode fiber.…”

Polymer photonic microstructures for quantum applications and sensing

“…Both structures also enhance the excitation of the dipole because of their respective lensing effects leading to higher focal intensities (Serrels et al 2008b). In comparison, for NV À centres coupled to hemispheres (Hadden et al 2010) or bullseye gratings (Li et al 2015) in bulk diamond, coupling efficiencies into the collected mode of up to 30% have been found. For nanodiamonds placed on the flat surface of zirconium dioxide hemisphere coupling efficiencies up to 18.3% are reported (Schröder et al 2011).…”

“…Hadden et al (2010). Light can be more efficiently coupled and collected, for example to or from a solid state emitter like an NV À centre.…”