Flow-cytometer for characterisation of nanoparticles

The present disclosure relates to an optical system for determining at least one parameter of at least one particle. The system comprises a first light beam and a second light beam, a modulator, a sample carrier, one or more light detectors, and a data processing means. The modulator is arranged along a path of the first light beam and configured to modulate the first light beam. The sample carrier containing the at least one particle to be analyzed and arranged so that at least part of the sample with the at least one particle is provided at an interrogation region. The modulated first light beam and the second light beam are arranged to intersect with each other at the interrogation region and to form an interference pattern thereto. The sample with particles and the interference pattern are configured to move with respect to each other. The one or more light detectors are configured to detect an output signal scattered and/or emitted from the at least one particle being transported by the sample carrier and also being configured to deliver an electrical signal to the data processing means based on this output signal. The data processing means being configured to determine said at least one parameter of the at least one particle from the received electrical signal.