Spectral tuning of directional scattering for high precision position sensing

Summary form only given. High precision optical position sensing of a single nanoparticle or a biomolecule is of paramount importance in modern nanometrology, microscopy and medicine. In the context of resolution, the last decade has undergone a revolutionary development achieving localization precision down to few nanometers or even Ångströms, using different linear and nonlinear techniques. As a proof-of-concept experiment, we have demonstrated Ångström lateral localization precision utilizing strongly directional light emission of a single subwavelength dielectric scatterer placed in a tailored electromagnetic field distribution. Silicon nanoparticles, due to their high refractive index, support both electric and magnetic resonances in the visible regime. By taking advantage of simultaneous excitation of multiple particle modes and the interference of their emission, a strong directional scattering signal can be observed. When interacting with a selectively tailored inhomogeneous electromagnetic field distribution, different coupling scenarios can be achieved, resulting in strong position dependent lateral directional scattering. Based on this approach, relative particle positions can be resolved with Ångström precision. For further improvement, an even stronger position dependence of the directional emission is necessary. We now also explore the wavelength dependence of this effect. Furthermore, we study the influence of the spatially tailored focal fields by using different vectorial input beams focused tightly to create the field landscape the particle is interacting with.