Abstract: A method for measuring a property of radiation from different sources such as moving particles or different spatial locations on each particle includes providing a spatial modulator common to all of the sources having a sequence of configurations, each of which configurations causes the radiation flux to pass along paths to respective modulation ports and cycling the common spatial modulator past each of the modulation ports so that the sequence of configurations is applied to each modulation port. The sequence of configurations comprises an ordered array of optical elements on a substrate. In one embodiment, the modulator is arranged in a circle around an axis of rotation of a rotating singulation disk. At least one source is a reference source which has not interacted with the source to be analyzed and the sample and reference sources are compared.