# Corner Reflector Plasmonic Nanoantennas for Enhanced Single-Photon Emission
## 3 Results and Discussion  
An initial analysis was performed on the isolated dipole-NP feeder problem. This permitted the full evaluation of the impact on the emitter properties of the incorporation of the CR. To this end, a series of FDTD calculations were performed on the geometry displayed in Figure 1 in the absence of the metal sheets defining the CR. The resonances in the spectral responses of NPs are responsible for their characteristic colors, and their intensities and frequencies depend on the particle size, shape, and the dielectric properties of the surrounding medium. Figure 2 displays the resonances calculated from the emission spectrum of the corresponding NPs coupled to the dipole emitter. For gold NPs surrounded by air, the calculations show a negligible displacement of the plasmon resonance for the range of sizes considered, which is in accordance with previous calculations [35]. Furthermore, the spectral shift of the resonance with the particle size correlates well with the redshift of the resonance, as increased particle size was observed in measurements performed for colloidal suspensions of silver NPs of sizes varying between 60 and 80 nm in [36; 37]. To obtain the data in Figure 2, the smooth spectra from FDTD simulations were Nyquist interpolated to increase the spectral resolution without altering the information contained in the original data. Figure 3 displays the results obtained for the normalized factors \(f_{R}\) and \(f_{L}\) obtained from FDTD calculations for silver NPs of diameter \(d\) coupled to a dipole emitter at a distance \(s\) and perpendicular to a spherical NP. Particle sizes between \(d=30\) and 80 nm were considered, as well as dipole separations ranging from \(s=5\) nm to \(s=30\) nm. The plots display data collected at the resonance and at the target wavelength of \(\lambda_{Ag}=450\) nm. The corresponding results for gold NPs with their target wavelength at \(\lambda_{Au}=600\) nm are shown in Figure 4. In this case, the calculations were performed for the same range of parameters \(d\) and \(s\). Figure 2: Calculated resonance wavelengths of silver (**a**) and gold (**b**) NPs as a function of their diameters. Figure 4: Purcell, \(f_{R}\), and loss, \(f_{L}\), factors of gold NPs calculated for different spherical particle diameter values \(d\) and separation values \(s\) from the the dipole emitter. (**a**,**c**) plots are the values at resonance, and (**b**,**d**) are at the target wavelength of \(\lambda_{Au}=600\) nm. Figure 3: Purcell, \(f_{R}\), and loss, \(f_{L}\), factors of silver NPs calculated for different spherical particle diameter values \(d\) and separation values \(s\) from the the dipole emitter. (**a**,**c**) plots are the values at resonance and, (**b**,**d**) are at the target wavelength of \(\lambda_{Ag}=450\) nm. The calculated values of the radiative transition factor, \(f_{R}\), at the target wavelengths generally increased as the particle size grew and the distance between the emitter and the NP diminished, both for silver and gold NPs. However, the variation in terms of \(f_{R}\) with particle size \(d\) at resonance differed between silver and gold. For gold NPs, the trend for \(f_{R}\) at resonance was similar to that observed at \(\lambda_{Au}\), while for silver NPs, \(f_{R}\) exhibited a local maximum at a specific \(d\) when the separation \(s\) was small. In general, \(f_{R}\) reached higher values for silver NPs than for gold, both at resonance and at the target wavelength. Although the relative size of the NPs compared to the wavelength at which \(f_{R}\) was measured was larger for silver NPs, the ratio of the relative sizes was smaller than the observed ratios of \(f_{R}\) values. On the other hand, when the value of the wavelength was taken in consideration, the corresponding relative distances between the source and the NP were larger for silver NPs. Regarding photon loss due to absorption at the NP, the value of \(f_{L}\) increased significantly as the distance between the dipole emitter and the NP decreased.