This detector has been in use since 1977. Following Labeyrie (1977), it consists of a microchannel plate electrostatically focussed intensifier (TH 9304) coupled by fiber optics to an SIT camera (TH 9655), these parts being manufactured by THOMSON-CSF (FRANCE). The diameter of the S20 photocathode is 25mm but the silicon target is only 18mm wide. The scanning electronics are conventional. The detector is cooled to -5°C, the photocathode being in a dry nitrogen chamber. The system has been described by Boulesteix (1978).