Polarization-Sensitive Optical Coherence Tomography for Characterization of Size and Shape of Nano-Particles

Measuring the size and shape of nanoparticles inside a solid or liquid medium is a challenging task. Light microscopy does not provide sufficient resolution. Scanning and transmission electron microscopy (SEM/TEM) enable nanometre imaging resolution, but are associated with high investment cost, require expensive sample preparation, and can only provide information from micrometre-scale areas on the sample surface. In this paper we demonstrate that OCT can be used to derive not only size, but also shape information of nanoscale scatterers. We use a polarization-sensitive OCT (PS-OCT) system to measure the scattering parameters of spherical and disk-shaped nano-particles. For spherical particles, the polarization states of the incident and scattered light are identical. Non-spherical shapes, in contrast, exhibit polarization-dependent scattering. This is confirmed by extracting polarization-dependent scattering parameters from OCT measurements and comparing them to simulations. Our experiments show that randomly oriented non-spherical scatterers can thus be distinguished from spherical particles in a PS-OCT measurement.