Electron images of vidicon cathodes

Excessive patchiness of the emission from the oxide-coated cathodes used in cathode-ray tubes, camera tubes and traveling-wave tubes can have adverse effects on their performance or useful life. There is a simple technique for forming an electron image of a CRT cathode directly on the view screen. This technique, which has been known for more than 30 years, may be used to show patchiness when it exists, but it has not been possible in the past to image the cathode of a camera tube because of the lack of a built-in display mechanism (phosphor-coated view screen) and because of the peculiar geometry of the electron guns. A technique has now been devised for displaying the electron images of vidicon cathodes. This technique comprises) 1) priming the optical image-sensing surface with uniform light, 2) projecting a "pinhole snapshot" electron image of the cathode on the image-sensing surface with an unscanned beam and storing it there, and 3) reading out the stored image with the normal scanning beam and displaying it on a CRT monitor. Photographs of electron images of vidicon cathodes obtained in this manner are shown in this paper.