Phase-dispersion light scattering for quantitative size-imaging of spherical scatterers

Using phase-dispersion spectra measured with optical coherence tomography (OCT) in the frequency domain, we demonstrated the quantitative sizing of multiple spherical scatterers on a surface. We modeled the light scattering as a slab-mode resonance and determined the size of the scatterers from a Fourier transform of the measured phase-dispersion spectra. Using a swept-source OCT system, we mapped the detected size of the scatters to the intensity of a two-dimensional surface image. The image was formed by raster-scanning a collimated beam of 200 mu m diameter across a sample with distinct size domains. The image shows a clear distinction between deposited polystyrene microspheres of 26 and 15 mu m average sizes. In a separate experiment, we demonstrated tissue-relevant sizing of scatters as small as 5 mu m with a Fourier domain OCT system that utilized 280 mu m of bandwidth from a super-continuum source. Our previous studies have demonstrated that the light scattered from a single sphere is, in general, non-minimum-phase; therefore, phase spectra can provide unique information about scattered light not available from intensity spectra alone. Also, measurements of phase spectra do not require background normalization to correct for the spectral shape of light sources or the spectral absorption of specimens. The results we report here continue our efforts towards combining intensity and phase spectra to enable improved quantitative analysis of complex tissue structures.