Abstract: Cathodoluminescence is detected either in the transmitted or emitted mode in a scanning electron microscope by means of a photodiode mounted to the specimen base in the sample stage of the system, thereby permitting a broader spectral response. Preferably, the photodiode is mounted together with its feedback amplifier resistor and capacitor in a metallic housing secured to the sample base beneath the sample (in the transmitted mode) or above and to the side of the sample (in the emitted mode). The response signal is thus coupled from the vacuum chamber in electrical, not optical form.