ANALYSIS OF ELECTRON IMAGE DETECTION EFFICIENCY OF SLOW-SCAN CCD CAMERAS

We develop a stochastic model of electron image detection by slow-scan CCD cameras, and employ the model to investigate the performance of the cameras. The model takes full account of the channel mixing effect in multi-channel detectors. We demonstrate that channel mixing may result in an apparent detective quantum efficiency (DQE) greater than the theoretical limit of one, and that taking the channel mixing into account corrects this deficiency. We then determine the DQE of an actual slow-scan camera (Gatan model 679) from stochastic measurements, and show that its DQE closely approaches the ideal performance over a wide range of input intensities. The principal factors responsible for the good performance of the camera are shown to be: (i) high gain factor of the camera; (ii) low total system noise; and (iii) ability to correct gain variation of the camera by dividing by a gain reference image.