The spatial resolution and fluorescence signal amplitude in stimulated emission depletion (STED) microscopy is limited by the photostability of available fluorophores. Here, we show that negativelycharged silicon vacancy (SiV) centers in diamond are promising fluorophores for STED microscopy, owing to their photostable, near-infrared emission and favorable photophysical properties. A homebuilt pulsed STED microscope was used to image shallow implanted SiV centers in bulk diamond at room temperature. The SiV stimulated emission cross section for 765-800 nm light is found to be (4.0 ± 0.3)×10 −17 cm 2 , which is approximately 2-4 times larger than that of the negatively-charged diamond nitrogen vacancy center and approaches that of commonly-used organic dye molecules. We performed STED microscopy on isolated SiV centers and observed a lateral full-width-at-halfmaximum spot size of 89 ± 2 nm, limited by the low available STED laser pulse energy (0.4 nJ). For a pulse energy of 5 nJ, the resolution is expected to be ∼20 nm. We show that the present microscope can resolve SiV centers separated by 150 nm that cannot be resolved by confocal microscopy.

Classical analogues of the well-known effect of electromagnetically induced transparency (EIT) in quantum optics have been the subject of considerable research in recent years from microwave to optical frequencies, because of their potential applications in slow light devices, studying nonlinear effects in low-loss nanostructures, and development of low-loss metamaterials. A large variety of plasmonic structures has been proposed for producing classical EIT-like effects in different spectral ranges. The current approach for producing plasmon-induced transparency is usually based on precise design of plasmonic "molecules," which can provide specific interacting dark and bright plasmonic modes with Fano-type resonance couplings. In this paper, we show that classical interactions of coupled plasmonic and excitonic spherical nanoparticles (NPs) can result in much more effective transparency and slow light effects in metamaterials composed of such coupled NPs. To reveal more details of the wave-particle and particle-particle interactions, the electric field distribution and field lines of Poynting vector inside and around the NPs are calculated using the finite element method. Finally, using extended Maxwell Garnett theory, we study the coupled-NP-induced transparency and slow light effects in a metamaterial comprising random mixture of silver and copper chloride (CuCl) NPs, and more effectively in a metamaterial consisting of random distribution of coated NPs with CuCl cores and aluminum shells in the UV region.

Metal-assisted chemical etching is applied to fabricate deep, high aspect ratio nanopores in silicon. The authors’ simple and cost-effective fabrication process has proven capable of generating nanopores with diameters as small as 30 nm, over the whole wafer surface (50.8 mm in diameter). The process uses a thin layer of DC-sputtered gold and H2O2/H2O/HF treatment to generate Au nanoislands. The formation of these nanoislands is confirmed by scanning electron microscopy. In this paper, the authors study the effect of Au-layer thickness on the diameter and morphology of the fabricated nanopores. The resulting structures have wide applications in optical sensing and filtering.

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Radio frequency (RF) magnetometers based on nitrogen vacancy centers in diamond are predicted to offer femtotesla sensitivity, but previous experiments were limited to the picotesla level. We demonstrate a femtotesla RF magnetometer using a diamond membrane inserted between ferrite flux concentrators. The device provides ~300-fold amplitude enhancement for RF magnetic fields from 70 kHz to 3.6 MHz, and the sensitivity reaches ~70 fT√s at 0.35 MHz. The sensor detected the 3.6-MHz nuclear quadrupole resonance (NQR) of room-temperature sodium nitrite powder. The sensor’s recovery time after an RF pulse is ~35 μs, limited by the excitation coil’s ring-down time. The sodium-nitrite NQR frequency shifts with temperature as −1.00±0.02 kHz/K, the magnetization dephasing time is T 2 *=887±51 μs, and multipulse sequences extend the signal lifetime to 332±23 ms, all consistent with coil-based studies. Our results expand the sensitivity frontier of diamond magnetometers to the femtotesla range, with potential applications in security, medical imaging, and materials science.