A novel method that enables the measurement of an electrostatic latent image on a photoconductor is proposed. An electrostatic latent image is formed through electric charging and laser exposure of a photoconductor within a vacuum chamber. The significant feature of this method is that the charging, exposure, and detection devices are all incorporated in the same system, making real-time measurement possible. The electrostatic latent image is measured by detecting secondary electrons generated

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... y the scanning of an electron beam probe. When a primary electron beam hits the photoconductor, secondary electrons are generated. Secondary electrons generated in a charged area travel to an electron detector. In contrast, secondary electrons generated in an exposed area are pulled back to the photoconductor, thereby decreasing the number of secondary electrons that reach the detector. This method has good performance with high-resolution measurement on the order of microns.