Measurement Sensitivity and Reliability Analysis of the Space Charge Ellipsometry Detection System

Space charge ellipsometry detection method provides an effective technical means to clarify the charge accumulation mechanism under transient stress, which can support the reliable assessment for the power electronic equipment insulation. In this article, the multisource signal transmission is constructed, which validates the feasibility of the measurement method from theoretical perspective. Meanwhile, the influencing factors of the measurement sensitivity are analyzed. The analysis and experiments show that there is a negative correlation between the measurement sensitivity with the substrate material elastic modulus and the sensor thickness. Then, the elastooptical sensor with micrometer thickness is designed. Although the structure influence of the millimeter-thickness sensor has been analyzed in the previous study, considering the large difference between micrometer and millimeter thicknesses, the micrometer-thickness sensor shape influence is further explored to avoid the influence of the size effect. It shows that as for the micrometer-thickness sensor, the refractive index variation of the hexagonal structure sensor shows a higher consistency with the applied elastic wave. Finally, the measurement reliability of the ellipsometry detection method is evaluated. The experiment finds that compared with the piezoelectric sensor, the ellipsometry detection method when using the sensor with micrometer-level thickness can achieve the tracking of the femtosecond pulsewidth elastic wave with less broadening of 1 ns and higher space charge measurement spatial resolution of
$2~\mu \text{m}$
.