Abstract: The invention relates to a plasmon resonance sensor that comprises collimator optics (13) in the form of a cylindrical lens that is interposed between the laser diode (7) and the prism (1), said prism being provided with a reflective metal layer (5). This arrangement preserves the beam divergence in the plane of incidence that comprises all angles of incidence that are potentially possible for a resonance and that are detected by the detector (8). In a plane perpendicular to the plane of incidence the beam path is collimated, thereby allowing for a compact design and for the simultaneous arrangement of a plurality of measuring cells that are arranged perpendicular to the plane of incidence one behind the other.