Nanoscale mapping of refractive index by using scattering-type scanning near-field optical microscopy

We present a novel method for nanoscale reconstruction of complex refractive index by using scattering-type Scanning Near-field Optical Microscopy (s-SNOM). Our method relies on correlating s-SNOM experimental image data with computational data obtained through simulation of the classical oscillating point-dipole model. This results in assigning a certain dielectric function for every pixel of the s-SNOM images, which further results in nanoscale mapping of the refractive index. This method is employed on human erythrocytes to demonstrate the approach in a biologically relevant manner. The presented results advance the current knowledge on the capabilities of s-SNOM to extract quantitative information with nanoscale resolution from optical data sets with biological application. The experimental s-SNOM results (Amplitude and Phase images) are correlated to the theoretical model of oscillating point-dipole. Together they lead to a 4D visual representation with nanoscale resolution of the sample (red blood cells). The topography is represented in three spatial dimensions, while the refractive index is coded using a colormap. [Display omitted]