Optical properties of microfabricated fully-metal-coated near-field probes in collection mode

A study of the optical properties of microfabricated, fully-metal-coated quartz probes collecting longitudinal and transverse optical fields is presented. The measurements are performed by raster scanning the focal plane of an objective, focusing azimuthally and radially polarized beams by use of two metal-coated quartz probes with different metal coatings. A quantitative estimation of the collection efficiencies and spatial resolutions in imaging both longitudinal and transverse fields is made. Longitudinally polarized fields are collected with a resolution approximately 1.5 times higher as compared with transversely polarized fields, and this behavior is almost independent of the roughness of the probe's metal coating. Moreover, the coating roughness is a critical parameter in the relative collection efficiency of the two field orientations. A dispersive compact Fourier transform spectrometer is realized which operates in the visible wavelength range. No moving parts, no imaging system and compactness are the characteristics of this spectrometer. It is based on a novel beam splitter design, which reduces the influence of the size of the light source and therefore the spatial coherence requirements. The effect of dispersion due to an asymmetric configuration is described. A mathematical correction to get rid of eventual mirror distortion is reported. Finally, some considerations on noise and a method to reduce its influence are presented. A resolution of 3nm was measured at 633nm.