Abstract
Negatively charged nitrogen vacancy centers (NV−) in diamond serve as highly sensitive, optically readable sensors for magnetic fields. Improved sensing approaches rely on NV− centers embedded in diamond nanopillar waveguides, which enable scanning probe imaging and use multi-color laser schemes for efficient spin readout. In this work, we investigate the free-beam coupling of the most relevant laser wavelengths to diamond nanopillars with different geometries. We focus on cylindrical pillars, conical pillars, and conical pillars with an added parabolic dome. We study the effects of the pillar geometry, NV− position, laser wavelength, position of laser focus, and excitation geometry (excitation from the top facet or from the substrate side). We find a pronounced impact of the laser wavelength that should be considered in multi-color excitation of NV−. Within the pillars, exciting laser fields can be enhanced up to a factor of 11.12 compared to bulk. When focusing the laser to the interface between the substrate and the nanopillar, even up to 29.78-fold enhancement is possible. Our results are in accordance with the experimental findings for green laser excitation of NV− in different pillar geometries.
Highlights
Active point defects in diamond, termed color centers, are atom-like quantum systems
For some color centers, the PL’s brightness is directly linked to the color center’s electronic spin state [spindependent PL, optically detected magnetic resonance (ODMR4)]. The latter is especially prominent for negatively charged nitrogen vacancy (NV−) centers in diamond: ODMR enables using even individual NV− centers, e.g., as highly sensitive magnetic sensors under ambient conditions
For the cylindrical and domed cone geometry, the evanescent fields that propagate into the side surface of the waveguides can cause a high local enhancement for any NV center located at these fringes
Summary
Active point defects in diamond, termed color centers, are atom-like quantum systems They are applied in various fields ranging from life science, where they serve as non-bleaching fluorescent labels, to quantum technologies, where their use spans from quantum sensing (e.g., Ref. 2) to quantum communication and computing.. For some color centers, the PL’s brightness is directly linked to the color center’s electronic spin state [spindependent PL, optically detected magnetic resonance (ODMR4)] The latter is especially prominent for negatively charged nitrogen vacancy (NV−) centers in diamond: ODMR enables using even individual NV− centers, e.g., as highly sensitive magnetic sensors under ambient conditions.. The latter is especially prominent for negatively charged nitrogen vacancy (NV−) centers in diamond: ODMR enables using even individual NV− centers, e.g., as highly sensitive magnetic sensors under ambient conditions.5 For this purpose, typically green laser light (532, 510 nm) excites NV centers non-resonantly. We investigate the influence of the NP geometry and laser wavelength and compare our results to the experimental findings
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