Coherence scanning interferometry allows accurate characterization of micrometric spherical particles contained in complex media

Abstract

Characterizing very small particles, from a few dozen micrometers to the nanometric scale, is a very challenging application in a wide range of domains. In this work, we demonstrate, through the recovery of silica and polystyrene bead properties (i.e. their size and refractive index) that Coherence Scanning Interferometry (CSI), in addition of being contactless, non-destructive, label-free and very well spatially resolved, is a very interesting and promising tool for such complex characterization. The CSI system is used as an imaging Fourier transform spectrometer meaning that the characterizations are achieved by analyzing the interference signal in the spectral domain. Some simulations of the proposed technique are presented and show that the accuracy of such characterization, in particular the measurement of the refractive index, are closely related to the signal to noise ratio. This observation is thereafter confirmed by the experimental results of beads buried within the depth of a transparent sample. Finally, the method is theoretically tested in the case of a scattering medium in which the quality of the signal is highly degraded. In this context, a geometrical approach enabling the simulation of an interference signal from a scattering layer is first proposed and then validated by means of comparison with experimental data.