Optical flow cell detector comprising a sample inlet and outlet in fluidic communication through a flow cell channel of cross sectional area A, an input light guide with an light exit surface arranged adjacent and in optical alignment with a light entrance surface of an output light guide, wherein the input light guide and the output light guide protrudes into the flow cell channel and wherein the distance between the light exit surface and the light entrance surface is less than 1.0 mm, and wherein the cross sectional area of the protruding portions of the input light guide and the output light guide in the flow direction is less than A/2.