Light-sample interaction in microsphere enhanced 2D superresolution imaging

摘要

We simulate the image generated by a microsphere residing in contact on top of an exposed Blu-ray disk surface, whenobserved by a conventional microscope objective. While microsphere lenses have been used to focus light beyond thediffraction limit and to produce super-resolution images, the nature of the light-sample interaction is still under debate.Simulations in related articles predict the characteristics of the photonic nanojet (PNJ) formed by the microsphere, but sofar, no data has been published on the image formation in the far-field. For our simulations, we use the open source packageAngora and the commercial software RSoft FullWave. Both packages implement the Finite Difference Time Domain(FDTD) approach. Angora permits us to accurately simulate microscope imaging at the diffraction limit. The RSoftFullWave is able to record the steady-state complex electrical and magnetic fields for multiple wavelengths inside thesimulation domain. A microsphere is simulated residing on top of a dielectric substrate featuring sub-wavelength surfacefeatures. The scattered light is recorded at the edges of the simulation domain and is then used in the near-field to far-fieldtransformation. The light in the far field is then refocused using an idealized objective model, to give us the simulatedmicroscope image. Comparisons between the simulated image and experimentally acquired microscope images verify theaccuracy of our model, whereas the simulation data predicts the interaction between the PNJ and the imaged sample. Thisallows us to isolate and quantify the near-field patterns of light that enable super-resolution imaging, which is importantwhen developing new micro-optical focusing structures.