An optical measurement technique for studying residual surface charge distribution

Based on the electro-optic Pockels effect, a modified optical measurement technique for studying residual surface charge distribution is developed. A simple relationship between the total optical retardation distribution and the light intensity distribution of the difference of the detected images is deduced. The total effective non-uniform natural retardation distribution caused by residual mechanical stress distributions in optical components is measured and its influence is cancelled. To improve the signal-to-noise ratio, an equivalent system model is also proposed, which permits direct application of an image lock-in amplifier technique. Furthermore, to ensure the stability and reliability of the measurement system, a diagnosis criterion for defects in the system is given. Finally, as an example, residual surface charge distributions are deposited on BSO crystal and PET film by the application of an 8 kV HV impulse to the needle-plane electrode system.