Angular and spectrally resolved investigation of single particles by darkfield scattering microscopy

A darkfield scattering microscope has been constructed that enables both angular and spectrally resolved measurements of elastic scattering patterns. The comparison of the angular and spectral resolution modes is shown in detail. Angular patterns of the backscattered light by homogeneous polystyrene spheres were measured at 57 wavelengths and the diameters of the single spheres were determined by using Mie theory at each wavelength. The mean diameter values were estimated in the angular mode with a relative standard deviation of 0.25% or less. Spectral scattering patterns of the same beads were investigated and the diameters were determined and compared with the results of the angular measurements. The estimated diameter values in the angular and the spectral mode were in an excellent agreement with deviations of less than 0.20%.