Space Charge Measurement Validation and Evaluation of a Novel Ellipsometry Detection Method Based on Nanosecond Pulse Laser Excitation

The space charge measurement and evaluation can provide a dielectric performance analysis for the insulating materials, while the existing measurement methods cannot realize the charge measurement by the noncontact methods and be used in complex transient electrical voltage conditions. The charge measurement under pulsed voltage excitation with optical ellipsometry detection has been realized in previous studies, while they haven’t achieved the charge measurement based on all-optical and noncontact modes. This article designs a novel space charge measurement system under optical excitation and detection methods by introducing high-power pulse laser and ellipsometry techniques. The feasibility of this all-optical method in charge measurement is further verified by experimentally optimizing the excitation and detection modules. First, the pressure wave excitation parameters at the excitation module are evaluated experimentally, which indicates that the signal-to-noise ratio of the system can be improved to 38.02 dB at the laser energy of 340 mJ and the target electrode material of aluminum-sprayed graphene. Then, the main parameters affecting the measurement sensitivity are evaluated based on the established transmission model of the ellipsometry detection system. The further parameter optimization experiments show that the system has good measurement sensitivity at He–Ne laser incidence angle of 60° with a $10.2~\mu $ m thickness elastooptical sensor. Finally, Kapton-type polyimide samples are tested under different voltage conditions based on the optimized system. The compared results with the traditional pulsed electro-acoustic (PEA) method show that the proposed method can achieve noncontact space charge measurement with a spatial resolution of $14~\mu $ m based on all-optical modules.