The back focal plane contained the Fourier transform of the optical field transmitted by the sample upon illumination, i.e. the angular dispersion of the transmitted light. The image on the CCD contained 2D angular information for all the wavelengths illuminating the sample. Closing the slit that controlled the light entering the imaging spectrometer allowed selection of one angular component and its spectral decomposition into the CCD. To get accurate wavelength resolution, a grating of 150 g/mm was used. This allowed ±150 nm range to be imaged for a selected wavelength center. To image the full spectrum of the sample (400-1000 nm) we measured spectra at several wavelength centers (i.e. 470, 620, 770, and 900 nm, respectively). Using a polarizer before the illumination objective allowed us to select between TM and TE polarizations.