Visualization and Quantification Technique of Latent Electric Charge Image using Pockels Effect

Abstract

A visualization and a quantification technique of a latent electric charge image on a dielectric material have been developed by using Pockels effect and a computer image processing technique. The Pockels cell of a BSO (Bi,2SiO20) single crystal was used as a transducer to transfer the surface charge density to retardation of transmitted light beam. In order to reduce a spatial noise of light beam, an optical phase modulation technique and a computer image lock-in amplifier processing were used. The measurement system has several improved performances ; the sensitivity of surface charge of 1 nC/cm2, the spatial resolution of 200 um and discrimination of the charge polarity. The basic principle of advanced electrooptic surface charge measurement is described and the typical surface charge distribution of positive discharge streamer produced by an impulse high voltage (5 kVpeak) is demonstrated. The measured surface charge images are shown on a color computer monitor as pseudo color in three-dimensional beautiful figures.