Local excitation of surface plasmon polaritons using nitrogen-vacancy centers

Abstract

Surface plasmon polaritons (SPPs) are locally excited at silver surfaces using (~100) nm-sized nanodiamonds (NDs) with multiple nitrogen-vacancy (NV) centers (~400). The fluorescence from an externally illuminated (at 532 nm) ND and from nearby NDs, which are not illuminated but produce out-of-plane scattering of SPPs excited by the illuminated ND, exhibit distinctly different wavelength spectra, showing short-wavelength filtering due to the SPP propagation loss. The results indicate that NDs with multiple NV centers can be used as efficient sub-wavelength SPP sources in planar integrated plasmonics for various applications.Nitrogen-vacancy (NV) centers in diamond are defects in the crystal structure consisting of a nitrogen atom and a lattice vacancy oriented along the [111] direction [1]. NV centers are of interest because they behave as artificial atoms and can be used as single photon sources [2]. Photostability is another important characteristic of NV centers [3]. In addition, NV centers can be created in desired locations in bulk or deterministically moved and positioned in nanodiamonds [4,5]. In spintronics, these color centers offer the possibility to measure the electronic spin optically at room temperatures [6], thus facilitating the research in quantum information processing [7]. Although many of the interesting characteristics of NV centers are interesting for single NV centers, the study and application of diamond nanoparticles with multiple NV centers is also significant. Nanodiamonds (NDs) with multiple NV centers can be used to measure magnetic fields with higher precision, and with plasmonic devices it can be improved further [8]. Surface plasmon polaritons (SPPs) manifest as evanescent electromagnetic fields at the interface between a metal and a dielectric and can be confined well below the diffraction limit, thus the use of a sub-wavelength, tightly localized optical source to excite SPPs is a natural need [9].In recent work, NDs with NV centers have been used as single photon sources to couple propagating SPPs in silver nanowires where a reduction of lifetime [5,10], and the wave-particle duality were observed [11]. Additionally, the leakage radiation of SPPs excited with fluorescence from a ND, mounted on a scanning near-field microscopy (SNOM) tip, was measured to show the preservation of coherence through the first and second order correlation experiments [12]. Even though the latter reference deals with more than one NV center (~5), the research is still in the frontier between classical and quantum optics. As commented before, most of the research related to SPPs and NV centers point towards quantum properties and have left the classical approximation unattended.In this Letter, we address the local excitation of SPPs with sub-wavelength optical sources using a single ND with multiple NV centers. The SPP propagation losses are estimated by comparing the fluorescence spectrum emitted at the source and the spectrum of the light dispersed by a scatterer. The main idea behind such an experi...

Excitation of surface plasmon polariton modes with multiple nitrogen vacancy centers in single nanodiamonds

“…The largest ratio observed is 1:2850 and the lowest is 1:4 (data not shown), where these two different pairs of NDs have the same separation of 7 µm. The decrease in signal strength when changing the detection from the source to scatterer ND is therefore not only related to the SPP propagation loss (as conjectured previously [40]) but also to the excitation polarization state, SPP coupling and scattering efficiencies, ND shape, and NV dipole-to-interface distance. We note that the ratio of scattered intensities pp:ps and sp:ss should, in principle, be the same (as observed for a distance 24 µm between source and scatterer [40]) .…”

“…The decrease in signal strength when changing the detection from the source to scatterer ND is therefore not only related to the SPP propagation loss (as conjectured previously [40]) but also to the excitation polarization state, SPP coupling and scattering efficiencies, ND shape, and NV dipole-to-interface distance. We note that the ratio of scattered intensities pp:ps and sp:ss should, in principle, be the same (as observed for a distance 24 μm between source and scatterer [40]). When the distance is smaller (7 and 9 μm), a small background due to the direct illumination of scatterer (by pump or fluorescence, which affect the ps and ss spectra the most) changes these ratios.…”

“…We use two different analytical models to fit the ratio of spectra measured from the source and the scatterer NDs. In the first model suggested previously [40], it is assumed that the ratio of spectra can be expressed as follows:…”

“…Subsequently, a 20 nm amorphous SiO 2 film is sputtered on top of the silver film while it remains in vacuum in order to minimize its reaction with atmospheric sulphur and oxygen. NDs are deposited on the sample using a technique that has been described in [40]. Briefly, spin coating of PMMA [Poly(methyl methacrylate)], electron-beam lithography and development is used to fabricate an array of holes in PMMA.…”

“…The same is observed when an analyzer is present: excitation by the p-polarized light consistently gives higher signals from the scatterer ND (the difference is small for the s-analyzed orientation). The dipoles excited by p polarization couple preferentially to the SPP propagating in the direction along the electric field of excitation [40]. A signal is still observed for the s polarization excitation, because many of the excited NV dipoles have a nonzero projection on the line connecting the source and scatterer NDs and can therefore couple to the SPPs propagating in that direction.…”