Abstract: The secondary electron detector unit for a scanning electron microscope is mounted in a head body (1). In the lower part of the head body (1), a lower throttling aperture (2) is placed. Above the lower throttling aperture (2), the microporous plate (3) is sealed in the head body (1) by a gasket (5) and fastened with the use of the frame plate (6) which has an opening that exposes the active input area (7) placed asymmetrically with respect to the axis of the scanning electron beam (WE). Above the microporous plate (3), the scintillator (11) and the light pipe (12) are fixed at the side of the head body (1).