Loss mechanisms of surface plasmon polaritons on gold probed by cathodoluminescence imaging spectroscopy

We use cathodoluminescence imaging spectroscopy to excite surface plasmon polaritons and measure their decay length on single crystal and polycrystalline gold surfaces. The surface plasmon polaritons are excited on the gold surface by a nanoscale focused electron beam and are coupled into free space radiation by gratings fabricated into the surface. By scanning the electron beam on a line perpendicular to the gratings, the propagation length is determined. Data for single-crystal gold are in agreement with calculations based on dielectric constants. For polycrystalline films, grain boundary scattering is identified as additional loss mechanism, with a scattering coefficient SG=0.2%

Local density of states, spectrum, and far-field interference of surface plasmon polaritons probed by cathodoluminescence

The surface plasmon polariton (SPP) field intensity in the vicinity of gratings patterned in an otherwise planar gold surface is spatially resolved using cathodoluminescence (CL). A detailed theoretical analysis is presented that successfully explains the measured CL signal based upon interference of transition radiation directly generated by electron impact and SPPs launched by the electron and outcoupled by the grating. The measured spectral dependence of the SPP yield per incoming electron is in excellent agreement with rigorous electromagnetic calculations. The CL emission is shown to be similar to that of a dipole oriented perpendicular to the surface and situated at the point of electron impact, which allows us to establish a solid connection between the CL signal and the photonic local density of states associated to the SPPs

Surface plasmon polariton modes in a single-crystal Au nanoresonator fabricated using focused-ion-beam milling

We use focused-ion-beam milling of a single-crystal Au surface to fabricate a 590-nm-long linear ridge that acts as a surface plasmon nanoresonator. Cathodoluminescence imaging spectroscopy is then used to excite and image surface plasmons on the ridge. Principal component analysis reveals distinct plasmonic modes, which proves confinement of surface-plasmon oscillations to the ridge. Boundary-element-method calculations confirm that a linear ridge is able to support highly-localized surface-plasmon modes (mode diameter < 100 nm). The results demonstrate that focused-ion-beam milling can be used in rapid prototyping of nanoscale single-crystal plasmonic components.Comment: 4 pages, 4 figure

Atomic-scale confinement of optical fields

In the presence of matter there is no fundamental limit preventing confinement of visible light even down to atomic scales. Achieving such confinement and the corresponding intensity enhancement inevitably requires simultaneous control over atomic-scale details of material structures and over the optical modes that such structures support. By means of self-assembly we have obtained side-by-side aligned gold nanorod dimers with robust atomically-defined gaps reaching below 0.5 nm. The existence of atomically-confined light fields in these gaps is demonstrated by observing extreme Coulomb splitting of corresponding symmetric and anti-symmetric dimer eigenmodes of more than 800 meV in white-light scattering experiments. Our results open new perspectives for atomically-resolved spectroscopic imaging, deeply nonlinear optics, ultra-sensing, cavity optomechanics as well as for the realization of novel quantum-optical devices

Angle-resolved cathodoluminescence spectroscopy

We present a novel cathodoluminescence spectroscopy technique which combines a deep subwavelength excitation resolution with angle-resolved detection capabilities. The cathodoluminescence emission is collected by a paraboloid mirror (effective NA=0.96) and is projected onto a 2D CCD array. The azimuthal and polar emission pattern is directly deduced from the image. As proof of principle we use the technique to measure the angular distribution of transition radiation from a single crystalline gold surface under 30 keV electron irradiation. We find that the experiment matches very well with theory, illustrating the potential of this new technique for the characterization of photonic structures with deep subwavelength dimensions.Comment: This paper has been withdrawn because of additional experiment