Optical dispersion measurements. An unpolarized broadband light source was used to illuminate the samples and investigate their optical dispersion. The light was focused onto the sample and collected with a Nikon L Plan 20x/0.45NA and a Nikon S Plan Fluor 40x/0.6NA objectives, respectively. Using a dedicated lens system, the back focal plane of the objective was imaged with an imaging spectrometer connected to a multiplying CCD camera (ProEM: 512B).