A device is presented with a multi-capillary array, a first source of first excitation light beams, a first polarizing plate, and a second source of second excitation light beams. The multi-capillary array includes a plurality of capillaries arranged in a row on a reference plane and filled with a separation medium. Each capillary of the plurality has a respective first portion for introducing a sample and a respective light-irradiatable portion capable of being irradiated with excitation light. The first source of first excitation light beams is disposed in a position to emit first excitation beams in a first direction along a beam path through the light irradiatable portions. The first polarizing plate is disposed along an excitation beam path between the first excitation light source and the multi-capillary array. The second source of second excitation light beams is disposed in a position to emit second excitation beams in a second direction that is substantially opposite to the first direction and through the light-irradiatable portions.
