By means of projecting a reference light and measuring the light on the photocathode of a streak camera, the minimum excited threshold in electron trapping materials can be measured. The infrared minimum excited threshold of CaS∶Eu, Sm is measured to be less than 4.8×10 -9 J/mm 2 by a visible streak camera. The minimum detectable energy density of the camera is less than 8.3×10 -10 J/mm 2 (532 nm). The phosphor investigated is efficiently stimulated with the 1.064 μm photons from a pulsed CPM Nd∶YAG laser. According to the result, it is shown that this kind of novel materials might be used in the ETM based infrared photocathodes and other fields.