A parabolic reflector and an inclined planar light reflector in a cathodoluminescence detector are integrated with a set of photo-sensitive solid-state detector cells mounted in quadrature on a supporting plate, and supported by an electron microscope vacuum chamber specimen stage adaptor unit. Designed for CL emission operation in an electron microscope, the parabolic light reflector, the inclined planar light reflector and the photo-sensitive, solid-state detector cells are optically aligned and mechanically combined through the supporting plate of the detector cells. A readily exchangeable unit is thus obtained. The unit is further supported by the specimen stage adaptor unit so as to obtain a mechanical unit which can easily be mounted in and removed from any standard electron microscope vacuum chamber stage as a single integrated unit.