Calibration Algorithm of Surface Charge Density on Insulating Materials Measured by Pockels Technique

Surface charges greatly affect the discharge/flashover development process across an insulator. The relationship between surface charge distribution on insulating materials and measurement data based on Pockels technique is discussed, and an improved algorithm is built to calculate the real surface charge density from original data. In this algorithm, two-dimensional Fourier transform technique and Wiener filter are employed to reduce the amount of numerical calculation and improve the stability of computation, Moreover, this algorithm considers not only the influence of sample＇s thickness and permittivity, but also the impact of charges at different positions. The achievement of this calibration algorithm is demonstrated in details. Compared with traditional algorithms, the improved one supplies a better solution in the calibration of surface charge distribution on different samples with different thickness.

Twin boundary dominated electric field distribution in CdZnTe detectors

The performance of CdZnTe X/γ-ray detectors is strongly affected by the electric field distribution in terms of charge transport and charge collection.Factors which determine the electric field distribution are not only electric contact,but also intrinsic defects,especially grown-in twin boundaries.Here,the electric field distribution around twin boundaries is investigated in a CdZnTe bicrystal detector with a{111}–{111}twin plane using the Pockels electro-optic effect.The results of laser beam induced current pulses are also obtained by the transient current technique,and we discuss the influence of the twin boundary on the electric field evolution.These studies reveal a significant distortion of the electric field,which is attributed to the buildup of space charges at twin boundaries.Also,the position of these space charge regions depends on the polarity of the detector bias.An energy band model based on the formation of an n–n+–n junction across the twin boundary has been established to explain the observed results.

Optical Analog-to-digital Conversion Scheme Based on Tunable Fabry-Perot Resonator

Proposed is an interference type of optical analog-to-digital conversion(ADC). The refractive index of Fabry-Perot cavity changes with different voltages. The Fabry-Perot resonator converts electronic intensity into light wavelength through selecting lights of different wavelengthes. The parameters of the scheme are acquired with the transmission matrix of optical element and the time of steady-state light field. The maximum sampling speedes of 4-bit, 6-bit, 7-bit, 8-bit and 9-bit(ADC) are 1.695×1010 count/s, 4.33×109 count/s, 2.38×109 count/s, 1.24×109 count/s and 5.9×108 count/s, respectively.