Visualization of surface charge distribution on insulating films using spatial optical phase modulation system

Abstract

A visualization and a quantification technique of a latent electric charge image on a dielectric material has been developed by using Pockels effect and a computer image processing. An optical phase modulation technique and computer image lock-in amplifier processing were used to improve the signal to noise ratio. The measurement system has several improved performances: a sensitivity of surface charge of 1 nC cm/sup -2/; a spatial resolution of 200 /spl mu/m; and discrimination of the charge polarity. The basic principle of advanced electrooptic surface charge measurement is described and the typical surface charge distribution of a positive discharge streamer produced by an impulse high voltage (5 kV/sub peak/) is demonstrated. A comparison is also made between the modulation method and the nonmodulation method.<>